Psychology child development reading log

The journal writing is based on the readings of the chapter , reading chapters for this week are (chapter 9 and 10 book is attached). You can pick a topic from chapter 9 or 10 and expand your thoughts based on questions asked below. On your papers include the typed questions before your response.  Answers must be typed and double-spaced with 1” margins on all four sides and 12 pt font. Make sure to use in text citation.  Answer all the questions below. 

  1. Identify one important concept, research finding, theory, or idea in the current module and briefly describe it.
  2. Describe why you think this is an important concept.
  3. What possible research could be added to your concept?
  4. Describe how this relates to your life.

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How Children
Robert Siegler Judy DeLoache Nancy Eisenberg Jenny Saffran
F o u r t h E d i t i o n
This is an exciting time in the field of child development. The past decade has brought new theories, new ways
of thinking, new areas of research, and innumerable new findings to the field. We originally wrote How Children
Develop to describe this ever improving body of knowledge of children and their development and to convey our
excitement about the progress that is being made in understanding the developmental process. We are pleased to
continue this endeavor with the publication of the Fourth Edition of How Children Develop.
—From the Preface
As new research expands the field’s understanding of child and adolescent development, the authors of How Chil-
dren Develop continue their commitment to bringing the story of today’s developmental science to the classroom in
a clear and memorable way. Joined in this Fourth Edition by Jenny Saffran of the University of Wisconsin–Madison,
they maintain their signature emphasis on the “Seven Classic Themes” of development, which facilitates students’
understanding by highlighting the fundamental questions posed by investigators past and present. The new and ex-
panded coverage in the Fourth Edition spans a wide range of topics—from broad areas like the epigenetic aspects
of development, the links between brain function and behavior, and the pervasive influence of culture to specific
subjects such as the mechanisms of infants’ learning, the effects of math anxiety, and the rapidly growing influence
of social media in children’s and adolescents’ lives. This edition also features the highly anticipated debut of Launch-
Pad, an online learning system that features Worth Publishers’ celebrated video collection; the full e-Book of How
Children Develop; and the LearningCurve quizzing system, which offers students instant feedback on their learning.
Learn more about and request access at
Order How Children Develop, Fourth Edition, with LaunchPad at no additional cost by using
ISBN 10: 1-4641-8284-1 / ISBN-13: 978-1-4641-8284-6.
Coverage of contemporary developmental science is very important to me. I prefer a text that describes the relevant
research and is updated regularly. I find How Children Develop to be very good in this area, as all of the authors are
primarily researchers.
—Jeffery Gagne, University of Texas at Arlington
I highly recommend this textbook. The main strengths are up-to-date research with clear descriptions of study
methods and findings as well as excellent real-world examples that get students interested in a topic so that they are
excited enough to read about the research and evidence that support real-world developmental phenomenon. I do
not think the text has a major weakness.
—Katherine O’Doherty, Bowdoin College
Since its inception, I think that How Children Develop is the best child development textbook available. I would not
hesitate to use it again in my classes.
—Richard Lanthier, George Washington University
Cover art: Football, Bentota, Sri Lanka, 1998 (oil on canvas)
©Andrew Macara / Private Collection / The Bridgeman Art Library
F o u r t h
E d i t i o n

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How Children

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How Children
F o u r t h E d i t i o n
Robert Siegler
Carnegie Mellon University
Judy DeLoache
University of Virginia
Nancy Eisenberg
Arizona State University
Jenny Saffran
University of Wisconsin–Madison
And Campbell Leaper,
University of California–Santa Cruz, reviser of Chapter 15: Gender Development

This is dedicated to the ones we love
Senior Vice President, Editorial and Production: Catherine Woods
Publisher: Kevin Feyen
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Printing and Binding: Quad/Graphics, Versailles
Library of Congress Control Number: 2013952245
ISBN-10: 1-4292-4231-0
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© 2014, 2011, 2006, 2003 by Worth Publishers
All rights reserved.
Printed in the United States of America
First printing
Worth Publishers
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New York, NY 10010

about the authors:
Robert Siegler is the Teresa Heinz Professor of Cognitive Psychology at Carnegie
Mellon University. He is author of the cognitive development textbook Children’s
Thinking and has written or edited several additional books on child development. His
books have been translated into Japanese, Chinese, Korean, Spanish, French, Greek,
Hebrew, and Portuguese. In the past few years, he has presented keynote addresses at
the conventions of the Cognitive Development Society, the International Society for the
Study of Behavioral Development, the Japanese Psychological Association, the Eastern
Psychological Association, the American Psychological Society, and the Conference on
Human Development. He also has served as Associate Editor of the journal Developmental
Psychology, co-edited the cognitive development volume of the 2006 Handbook of Child
Psychology, and served on the National Mathematics Advisory Panel from 2006 to 2008.
Dr. Siegler received the American Psychological Association’s Distinguished Scientific
Contribution Award in 2005, was elected to the National Academy of Education in 2010,
and was named Director of the Siegler Center for Innovative Learning at Beijing Normal
University in 2012.
Judy DeLoache is the William R. Kenan Jr. Professor of Psychology at the University
of Virginia. She has published extensively on aspects of cognitive development in infants
and young children. Dr. DeLoache has served as President of the Developmental Division
of the American Psychological Association, as President of the Cognitive Development
Society, and as a member of the executive board of the International Society for the Study of
Infancy. She has presented major invited addresses at professional meetings, including the
Association for Psychological Science and the Society for Research in Child Development.
Dr. DeLoache is the holder of a Scientific MERIT Award from the National Institutes
of Health, and her research is also funded by the National Science Foundation. She has
been a visiting fellow at the Center for Advanced Study in the Behavioral Sciences in
Palo Alto, California, and at the Rockefeller Foundation Study Center in Bellagio, Italy.
She is a Fellow of the National Academy of Arts and Sciences. In 2013, she received
the Distinguished Research Contributions Award from the Society for Research in Child
Development and the William James Award for Distinguished Contributions to Research
from the Association for Psychological Science.
Nancy Eisenberg is Regents’ Professor of Psychology at Arizona State University.
Her research interests include social, emotional, and moral development, as well as so-
cialization influences, especially in the areas of self-regulation and adjustment. She has
published numerous empirical studies, as well as books and chapters on these topics.
She has also been editor of Psychological Bulletin and the Handbook of Child Psychology
and was the founding editor of the Society for Research in Child Development journal
Child Development Perspectives. Dr. Eisenberg has been a recipient of Research Scientist
Development Awards and a Research Scientist Award from the National Institutes of
Health (NICHD and NIMH). She has served as President of the Western Psychological
Association and of Division 7 of the American Psychological Association and is president-
elect of the Association for Psychological Science. She is the 2007 recipient of the Ernest
R. Hilgard Award for a Career Contribution to General Psychology, Division 1, American
Psychological Association; the 2008 recipient of the International Society for the Study
of Behavioral Development Distinguished Scientific Contribution Award; the 2009 re-
cipient of the G. Stanley Hall Award for Distinguished Contribution to Developmental
Psychology, Division 7, American Psychological Association; and the 2011 William James

Fellow Award for Career Contributions in the Basic Science of Psychology from the
Association for Psychological Science.
Jenny R. Saffran is the College of Letters & Science Distinguished Professor of
Psychology at the University of Wisconsin–Madison, and an investigator at the Waisman
Center. Her research is focused on learning in infancy and early childhood, with a particular
focus on language. Dr. Saffran currently holds a MERIT award from the Eunice Kennedy
Shriver National Institute of Child Health and Human Development. She has been the
recipient of numerous awards for her scientific research, including the Boyd McCandless
Award from the American Psychological Association for early career contributions to
developmental psychology, and the Presidential Early Career Award for Scientists and
Engineers from the National Science Foundation.

Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xx
1 An Introduction to Child Development . . . . . . . . . . . . . . . . . . 1
2 Prenatal Development and the Newborn Period . . . . . . . . . . . 39
3 Biology and Behavior . . . . . . . . . . . . . . . . . . . . . . . . . . 85
4 Theories of Cognitive Development . . . . . . . . . . . . . . . . . 129
5 Seeing, Thinking, and Doing in Infancy . . . . . . . . . . . . . . . . 171
6 Development of Language and Symbol Use . . . . . . . . . . . . . 215
7 Conceptual Development . . . . . . . . . . . . . . . . . . . . . . . 259
8 Intelligence and Academic Achievement . . . . . . . . . . . . . . . 297
9 Theories of Social Development . . . . . . . . . . . . . . . . . . . 339
10 Emotional Development . . . . . . . . . . . . . . . . . . . . . . . . 383
11 Attachment to Others and Development of Self . . . . . . . . . . 425
12 The Family . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 467
13 Peer Relationships . . . . . . . . . . . . . . . . . . . . . . . . . . . . 509
14 Moral Development . . . . . . . . . . . . . . . . . . . . . . . . . . . 553
15 Gender Development . . . . . . . . . . . . . . . . . . . . . . . . . . 593
16 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 637
Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G-1
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . R-1
Name Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . NI-1
Subject Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SI-1
brief contents:

Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xx
Chapter 1 An Introduction to Child Development . . . . . . 1
Reasons to Learn About Child Development . . . . . . . . . . . . . . . . 3
Raising Children 3
Choosing Social Policies 4
Understanding Human Nature 6
Review 7
Historical Foundations of the Study of Child Development . . . . . . . . 7
Early Philosophers’ Views of Children’s Development 8
Social Reform Movements 9
Darwin’s Theory of Evolution 9
The Beginnings of Research-Based Theories of Child Development 10
Review 10
Enduring Themes in Child Development . . . . . . . . . . . . . . . . . . . 10
1 . Nature and Nurture: How Do Nature and Nurture Together Shape
Development? 10
2 . The Active Child: How Do Children Shape Their Own
Development? 12
3 . Continuity/Discontinuity: In What Ways Is Development Continuous,
and in What Ways Is It Discontinuous? 13
4 . Mechanisms of Development: How Does Change Occur? 16
5 . The Sociocultural Context: How Does the Sociocultural Context
Influence Development? 17
6 . Individual Differences: How Do Children Become So Different
from One Another? 20
7 . Research and Children’s Welfare: How Can Research Promote
Children’s Well-Being? 21
Review 22
Methods for Studying Child Development . . . . . . . . . . . . . . . . . 22
The Scientific Method 23
Contexts for Gathering Data About Children 25
Correlation and Causation 28
Designs for Examining Development 32
Ethical Issues in Child-Development Research 35
Review 36

Chapter 2 Prenatal Development and
the Newborn Period . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Prenatal Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Box 2.1: A Closer look Beng Beginnings 41
Conception 42
Box 2.2: Individual differences The First—and Last—Sex Differences 44
Developmental Processes 45
Box 2.3: A Closer look Phylogenetic Continuity 46
Early Development 47
An Illustrated Summary of Prenatal Development 48
Fetal Behavior 51
Fetal Experience 52
Fetal Learning 54
Hazards to Prenatal Development 56
Box 2.4: Applications Face Up to Wake Up 61
Review 66
The Birth Experience . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
Diversity of Childbirth Practices 68
Review 69
The Newborn Infant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
State of Arousal 70
Negative Outcomes at Birth 74
Box 2.5: Applications Parenting a Low-Birth-Weight Baby 78
Review 81
Chapter 3 Biology and Behavior . . . . . . . . . . . . . . . . . 85
Nature and Nurture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
Genetic and Environmental Forces 88
Box 3.1: Applications Genetic Transmission of Disorders 94
Behavior Genetics 99
Box 3.2: Individual differences Identical Twins Reared Apart 101
Review 105
Brain Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
Structures of the Brain 106
Developmental Processes 109
Box 3.3: A Closer look Mapping the Mind 110
The Importance of Experience 114
Brain Damage and Recovery 117
Review 118
The Body: Physical Growth and Development . . . . . . . . . . . . . . . 119
Growth and Maturation 119

Nutritional Behavior 121
Review 126
Chapter 4 Theories of Cognitive Development . . . . . . . 129
Piaget’s Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
View of Children’s Nature 132
Central Developmental Issues 133
The Sensorimotor Stage (Birth to Age 2 Years) 135
The Preoperational Stage (Ages 2 to 7) 138
The Concrete Operational Stage (Ages 7 to 12) 141
The Formal Operational Stage (Age 12 and Beyond) 141
Piaget’s Legacy 142
Box 4.1: Applications Educational Applications of Piaget’s Theory 143
Review 144
Information-Processing Theories . . . . . . . . . . . . . . . . . . . . . . 145
View of Children’s Nature 146
Central Developmental Issues 147
Box 4.2: Applications Educational Applications of Information-Processing
Theories 154
Review 155
Sociocultural Theories . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
View of Children’s Nature 156
Central Developmental Issues 158
Review 160
Box 4.3: Applications Educational Applications of Sociocultural Theories 161
Dynamic-Systems Theories . . . . . . . . . . . . . . . . . . . . . . . . . 161
View of Children’s Nature 163
Central Development Issues 165
Box 4.4: Applications Educational Applications of Dynamic-Systems
Theories 166
Review 167
Chapter 5 Seeing, Thinking, and Doing in Infancy . . . . . 171
Perception . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173
Vision 173
Box 5.1: A Closer look Infants’ Face Perception 176
Box 5.2: A Closer look Picture Perception 183
Auditory Perception 182
Taste and Smell 186
Touch 186
Intermodal Perception 186
Review 188

Motor Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188
Reflexes 189
Motor Milestones 190
Current Views of Motor Development 191
Box 5.3: A Closer look “The Case of the Disappearing Reflex” 192
The Expanding World of the Infant 192
Box 5.4: Applications A Recent Secular Change in Motor Development 195
Box 5.5: A Closer look “Gangway—I’m Coming Down” 196
Review 198
Learning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198
Habituation 199
Perceptual Learning 199
Statistical Learning 200
Classical Conditioning 201
Instrumental Conditioning 201
Observational Learning/Imitation 202
Rational Learning 204
Review 205
Cognition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205
Object Knowledge 206
Physical Knowledge 207
Social Knowledge 208
Looking Ahead 211
Review 211
Chapter 6 Development of Language and
Symbol Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215
Language Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216
The Components of Language 217
What Is Required for Language? 218
Box 6.1: Applications Two Languages Are Better Than One 222
The Process of Language Acquisition 224
Box 6.2: Individual differences The Role of Family and School Context
in Early Language Development 235
Box 6.3: Applications: iBabies: Technology and Language Learning 240
Theoretical Issues in Language Development 246
Box 6.4: A Closer look: “I Just Can’t Talk Without My Hands” What Gestures
Tell Us About Language 248
Box 6.5: Individual differences Developmental Language Disorders 251
Review 252
Nonlinguistic Symbols and Development . . . . . . . . . . . . . . . . . 252
Using Symbols as Information 253
Drawing 254
Review 256

Chapter 7 Conceptual Development . . . . . . . . . . . . . 259
Understanding Who or What . . . . . . . . . . . . . . . . . . . . . . . . 261
Dividing Objects into Categories 261
Knowledge of Other People and Oneself 266
Box 7.1: Individual differences Children with Autism Spectrum
Disorders (ASD) 270
Box 7.2: Individual differences Imaginary Companions 273
Knowledge of Living Things 273
Review 278
Understanding Why, Where, When, and How Many . . . . . . . . . . . 278
Causality 279
Box 7.3: A Closer look Magical Thinking and Fantasy 282
Space 283
Time 286
Number 288
Relations Among Understanding of Space, Time, and Number 292
Review 293
Chapter 8 Intelligence and Academic Achievement . . . 297
What Is Intelligence? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 299
Intelligence as a Single Trait 299
Intelligence as a Few Basic Abilities 299
Intelligence as Numerous Processes 300
A Proposed Resolution 300
Review 301
Measuring Intelligence . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301
The Contents of Intelligence Tests 302
The Intelligence Quotient (IQ) 304
Continuity of IQ Scores 305
Box 8.1: Individual differences Gifted Children 306
Review 306
IQ Scores as Predictors of Important Outcomes . . . . . . . . . . . . . 307
Review 308
Genes, Environment, and the Development of Intelligence . . . . . . . 308
Qualities of the Child 309
Influence of the Immediate Environment 310
Influence of Society 313
Box 8.2: Applications: A Highly Successful Early Intervention: The Carolina
Abecedarian Project 318
Review 320
Alternative Perspectives on Intelligence . . . . . . . . . . . . . . . . . . 320
Review 322

Acquisition of Academic Skills: Reading, Writing,
and Mathematics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 322
Reading 322
Box 8.3: Individual differences Dyslexia 326
Writing 328
Mathematics 330
Mathematics Anxiety 334
Box 8.4: Applications Mathematics Disabilities 335
Review 335
Chapter 9 Theories of Social Development . . . . . . . . . 339
Psychoanalytic Theories . . . . . . . . . . . . . . . . . . . . . . . . . . . 341
View of Children’s Nature 342
Central Developmental Issues 342
Freud’s Theory of Psychosexual Development 342
Erikson’s Theory of Psychosocial Development 345
Current Perspectives 347
Review 348
Learning Theories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 348
View of Children’s Nature 349
Central Developmental Issues 349
Watson’s Behaviorism 349
Skinner’s Operant Conditioning 350
Social Learning Theory 352
Box 9.1: A Closer look Bandura and Bobo 352
Current Perspectives 355
Review 356
Theories of Social Cognition . . . . . . . . . . . . . . . . . . . . . . . . . 356
View of Children’s Nature 356
Central Developmental Issues 356
Selman’s Stage Theory of Role Taking 357
Dodge’s Information-Processing Theory of Social Problem Solving 357
Dweck’s Theory of Self-Attributions and Achievement Motivation 359
Current Perspectives 361
Review 361
Ecological Theories of Development . . . . . . . . . . . . . . . . . . . . 362
View of Children’s Nature 362
Central Developmental Issues 362
Ethological and Evolutionary Theories 362
The Bioecological Model 366
Box 9.2: Individual differences Attention-Deficit Hyperactivity Disorder 370
Box 9.3: Applications Preventing Child Abuse 373
Current Perspectives 378
Review 379

Chapter 10 Emotional Development . . . . . . . . . . . . . 383
The Development of Emotions in Childhood . . . . . . . . . . . . . . . 385
Theories on the Nature and Emergence of Emotion 386
The Emergence of Emotion in the Early Years and Childhood 387
Box 10.1: Individual differences Gender Differences in Adolescent
Depression 396
Review 398
Regulation of Emotion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 398
The Development of Emotional Regulation 399
The Relation of Emotional Self-Regulation to Social Competence and
Adjustment 401
Review 402
Individual Differences in Emotion and Its Regulation . . . . . . . . . . . 402
Temperament 403
Box 10.2: A Closer look Measurement of Temperament 406
Review 410
Children’s Emotional Development in the Family . . . . . . . . . . . . . 410
Quality of the Child’s Relationships with Parents 410
Parental Socialization of Children’s Emotional Responding 411
Review 414
Culture and Children’s Emotional Development . . . . . . . . . . . . . . 414
Review 416
Children’s Understanding of Emotion . . . . . . . . . . . . . . . . . . . . 416
Identifying the Emotions of Others 416
Understanding the Causes and Dynamics of Emotion 418
Children’s Understanding of Real and False Emotions 419
Review 421
Chapter 11 Attachment to Others and
Development of Self . . . . . . . . . . . . . . . . . . . . . . . . . . 425
The Caregiver–Child Attachment Relationship . . . . . . . . . . . . . . 427
Attachment Theory 428
Measurement of Attachment Security in Infancy 430
Box 11.1: Individual differences Parental Attachment Status 432
Cultural Variations in Attachment 434
Factors Associated with the Security of Children’s Attachment 435
Box 11.2: Applications Interventions and Attachment 436
Does Security of Attachment Have Long-Term Effects? 437
Review 439
Conceptions of the Self . . . . . . . . . . . . . . . . . . . . . . . . . . . 439
The Development of Conceptions of Self 440

Identity in Adolescence 446
Review 449
Ethnic Identity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 449
Ethnic Identity in Childhood 450
Ethnic Identity in Adolescence 451
Review 453
Sexual Identity or Orientation . . . . . . . . . . . . . . . . . . . . . . . . 453
The Origins of Youths’ Sexual Identity 453
Sexual Identity in Sexual-Minority Youth 454
Review 458
Self-Esteem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 458
Sources of Self-Esteem 459
Self-Esteem in Minority Children 462
Culture and Self-Esteem 463
Review 464
Chapter 12 The Family . . . . . . . . . . . . . . . . . . . . . . . 467
Family Dynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 470
Box 12.1: A Closer look Parent–Child Relationships
in Adolescence 471
Review 472
The Role of Parental Socialization . . . . . . . . . . . . . . . . . . . . . . 472
Parenting Styles and Practices 472
The Child as an Influence on Parenting 477
Socioeconomic Influences on Parenting 479
Box 12.2: A Closer look Homelessness 481
Review 482
Mothers, Fathers, and Siblings . . . . . . . . . . . . . . . . . . . . . . . . 482
Differences in Mothers’ and Fathers’ Interactions with Their
Children 482
Sibling Relationships 483
Review 485
Changes in Families in the United States . . . . . . . . . . . . . . . . . . 485
Box 12.3: Individual differences Adolescents as Parents 486
Older Parents 488
Divorce 489
Stepparenting 494
Lesbian and Gay Parents 496
Review 497
Maternal Employment and Child Care . . . . . . . . . . . . . . . . . . . 498
The Effects of Maternal Employment 498
The Effects of Child Care 500
Review 506

Chapter 13 Peer Relationships . . . . . . . . . . . . . . . . . . 509
What Is Special About Peer Relationships? . . . . . . . . . . . . . . . . 512
Friendships . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 513
Early Peer Interactions and Friendships 513
Developmental Changes in Friendship 515
The Functions of Friendships 517
Effects of Friendships on Psychological Functioning and Behavior
over Time 520
Box 13.1: Individual differences Culture and Children’s Peer
Experience 522
Children’s Choice of Friends 523
Review 525
Peers in Groups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 525
The Nature of Young Children’s Groups 525
Cliques and Social Networks in Middle Childhood and Early
Adolescence 526
Cliques and Social Networks in Adolescence 526
Negative Influences of Cliques and Social Networks 528
Box 13.2: A Closer look Cyberspace and Children’s Peer Experience 529
Romantic Relationships with Peers 531
Review 532
Status in the Peer Group . . . . . . . . . . . . . . . . . . . . . . . . . . . 532
Measurement of Peer Status 533
Characteristics Associated with Sociometric Status 533
Box 13.3: Applications Fostering Children’s Peer Acceptance 538
Stability of Sociometric Status 539
Cross-Cultural Similarities and Differences in Factors Related to
Peer Status 539
Peer Status as a Predictor of Risk 540
Review 543
The Role of Parents in Children’s Peer Relationships . . . . . . . . . . . 544
Relations Between Attachment and Competence with Peers 544
Quality of Ongoing Parent–Child Interactions and
Peer Relationships 545
Parental Beliefs 546
Gatekeeping and Coaching 546
Family Stress and Children’s Social Competence 548
Review 548
Chapter 14 Moral Development . . . . . . . . . . . . . . . . 553
Moral Judgment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 555
Piaget’s Theory of Moral Judgment 555
Kohlberg’s Theory of Moral Judgment 558

Prosocial Moral Judgment 562
Domains of Social Judgment 563
Review 566
The Early Development of Conscience . . . . . . . . . . . . . . . . . . . 566
Factors Affecting the Development of Conscience 567
Review 568
Prosocial Behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 568
The Development of Prosocial Behavior 569
The Origins of Individual Differences in Prosocial Behavior 571
Box 14.1: A Closer look Cultural Contributions to Children’s Prosocial
and Antisocial Tendencies 573
Box 14.2: Applications School-Based Interventions for Promoting
Prosocial Behavior 576
Review 577
Antisocial Behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 577
The Development of Aggression and Other Antisocial Behaviors 577
Consistency of Aggressive and Antisocial Behavior 579
Box 14.3: A Closer look Oppositional Defiant Disorder and
Conduct Disorder 580
Characteristics of Aggressive-Antisocial Children and Adolescents 581
The Origins of Aggression 582
Biology and Socialization: Their Joint Influence on Children’s Antisocial
Behavior 587
Box 14.4: Applications The Fast Track Intervention 588
Review 589
Chapter 15 Gender Development . . . . . . . . . . . . . . . 593
Theoretical Approaches to Gender Development . . . . . . . . . . . . 595
Biological Influences 596
Box 15.1: A Closer look: Gender Identity: More than Socialization? 598
Cognitive and Motivational Influences 599
Box 15.2: A Closer look Gender Typing at Home 604
Box 15.3: Applications Where Are SpongeSally SquarePants and
Curious Jane? 605
Cultural Influences 606
Review 607
Milestones in Gender Development . . . . . . . . . . . . . . . . . . . . 607
Infancy and Toddlerhood 608
Preschool Years 608
Middle Childhood 610
Adolescence 612
Box 15.4: A Closer look Gender Flexibility and Asymmetry 613
Review 614

Comparing Girls and Boys . . . . . . . . . . . . . . . . . . . . . . . . . . 614
Physical Growth: Prenatal Development Through Adolescence 617
Cognitive Abilities and Academic Achievement 619
Personality Traits 625
Interpersonal Goals and Communication 626
Box 15.5: A Closer look Gender and Children’s Communication Styles 627
Aggressive Behavior 628
Box 15.6: Applications Sexual Harassment and Dating Violence 631
Review 633
Chapter 16 Conclusions . . . . . . . . . . . . . . . . . . . . . . . 637
Theme 1: Nature and Nurture: All Interactions, All the Time . . . . . . . 638
Nature and Nurture Begin Interacting Before Birth 638
Infants’ Nature Elicits Nurture 639
Timing Matters 639
Nature Does Not Reveal Itself All at Once 640
Everything Influences Everything 641
Theme 2: Children Play Active Roles in Their Own Development . . . . 641
Self-Initiated Activity 642
Active Interpretation of Experience 643
Self-Regulation 643
Eliciting Reactions from Other People 644
Theme 3: Development Is Both Continuous and Discontinuous . . . . . 645
Continuity/Discontinuity of Individual Differences 645
Continuity/Discontinuity of Overall Development: The Question
of Stages 646
Theme 4: Mechanisms of Developmental Change . . . . . . . . . . . . 648
Biological Change Mechanisms 648
Behavioral Change Mechanisms 649
Cognitive Change Mechanisms 651
Change Mechanisms Work Together 653
Theme 5: The Sociocultural Context Shapes Development . . . . . . . 653
Growing Up in Societies with Different Practices and Values 653
Growing Up in Different Times and Places 655
Growing Up in Different Circumstances Within a Society 655
Theme 6: Individual Differences . . . . . . . . . . . . . . . . . . . . . . . 656
Breadth of Individual Differences at a Given Time 657
Stability Over Time 658
Predicting Future Individual Differences on Other Dimensions 658
Determinants of Individual Differences 659
Theme 7: Child-Development Research Can Improve
Children’s Lives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 660

Implications for Parenting 660
Implications for Education 662
Implications for Helping Children at Risk 662
Improving Social Policy 664
Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G-1
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . R-1
Name Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . NI-1
Subject Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SI-1

This is an exciting time in the field of child development. The past decade has
brought new theories, new ways of thinking, new areas of research, and innumera-
ble new findings to the field. We originally wrote How Children Develop to describe
this ever-improving body of knowledge of children and their development and to
convey our excitement about the progress that is being made in understanding the
developmental process. We are pleased to continue this endeavor with the publica-
tion of the fourth edition of How Children Develop.
As teachers of child development courses, we appreciate the challenge that in-
structors face in trying to present these advances and discoveries—as well as the
major older ideas and findings—in a one-semester course. Therefore, rather than
aim at encyclopedic coverage, we have focused on identifying the most important
developmental phenomena and describing them in sufficient depth to make them
meaningful and memorable to students. In short, our goal has been to write a text-
book that makes the child development course coherent and enjoyable for students
and teachers alike.
Classic Themes
The basic premise of the book is that all areas of child development are unified by a
small set of enduring themes. These themes can be stated in the form of questions
that child development research tries to answer:
1. How do nature and nurture together shape development?
2. How do children shape their own development?
3. In what ways is development continuous and in what ways is it
4. How does change occur?
5. How does the sociocultural context influence development?
6. How do children become so different from one another?
7. How can research promote children’s well-being?
These seven themes provide the core structure of the book. They are introduced
and illustrated in Chapter 1, highlighted repeatedly, where relevant, in the subse-
quent fourteen content chapters, and utilized in the final chapter as a framework
for integrating findings relevant to each theme from all areas of development. The
continuing coverage of these themes allows us to tell a story that has a beginning
(the introduction of the themes), a middle (discussion of specific findings relevant
to them), and an ending (the overview of what students have learned about the
themes). We believe that this thematic emphasis and structure will not only help
students to understand enduring questions about child development but will also
leave them with a greater sense of satisfaction and completion at the end of the

Contemporary Perspective
The goal of providing a thoroughly contemporary perspective on how children
develop has influenced the organization of our book as well as its contents. Whole
new areas and perspectives have emerged that barely existed when most of today’s
child development textbooks were originally written. The organization of How
Children Develop is designed to present these new topics and approaches in the
context of the field as it currently stands, rather than trying to shoehorn them into
organizations that once fit the field but no longer do.
Consider the case of Piaget’s theory and current research relevant to it. Piaget’s
theory often is presented in its own chapter, most of which describes the theory
in full detail and the rest of which offers contemporary research that demonstrates
problems with the theory. This approach often leaves students wondering why so
much time was spent on Piaget’s theory if modern research shows it to be wrong
in so many ways.
The fact is that the line of research that began over 40 years ago as an effort to
challenge Piaget’s theory has emerged since then as a vital area in its own right—
the area of conceptual development. Research in conceptual development provides
extensive information on such fascinating topics as children’s understanding of
human beings, plants and animals, and the physical universe. As with other re-
search areas, most studies in this field are aimed primarily at uncovering evidence
relevant to current claims, not those of Piaget.
We adapted to this changing intellectual landscape in two ways. First, our chap-
ter “Theories of Cognitive Development” (Chapter 4) describes the fundamental
aspects of Piaget’s theory in depth and honors his legacy by focusing on the aspects
of his work that have proven to be the most enduring. Second, a first-of-its-kind
chapter called “Conceptual Development” (Chapter 7) addresses the types of issues
that inspired Piaget’s theory but concentrates on modern perspectives and findings
regarding those issues. This approach allows us to tell students about the numerous
intriguing proposals and observations that are being made in this field, without the
artificiality of classifying the findings as “pro-Piagetian” or “anti-Piagetian.”
The opportunity to create a textbook based on current understanding also led
us to assign prominent positions to such rapidly emerging areas as epigenetics,
behavioral genetics, brain development, prenatal learning, infant cognition, acquisi-
tion of academic skills, emotional development, prosocial behavior, and friendship
patterns. All these areas have seen major breakthroughs in recent years, and their
growing prominence has led to even greater emphasis on them in this edition.
Getting Right to the Point
Our desire to offer a contemporary, streamlined approach led to other departures
from the traditional organization. It is our experience that today’s students take
child development courses for a variety of practical reasons and are eager to learn
about children. Traditionally, however, they have had to wait two or three or even
four chapters—on the history of the field, on major theories, on research methods,
on genetics—before actually getting to the study of children. We wanted to build
on their initial motivation from the start.
Rather than beginning the book, then, with an extensive examination of the his-
tory of the field, we include in Chapter 1 a brief overview of the social and intel-
lectual context in which the scientific study of children arose and provide historical

background wherever it is pertinent in subsequent chapters. Rather than have an
early “blockbuster” theories chapter that covers all the major cognitive and social
theories at once (at a point far removed from the content chapters to which the
theories apply), we present a chapter on cognitive developmental theories just before
the chapters that focus on specific aspects of cognitive development, and we simi-
larly present a chapter on social developmental theories just before the chapters that
focus on specific aspects of social development. Rather than have a separate chapter
on genetics, we include basic aspects of genetics as part of Chapter 3, “Biology and
Behavior,” and then discuss the contributions of genetics to some of the differences
among individuals throughout the book. When we originally chose this organization,
we hoped that it would allow us, from the first weeks of the course, to kindle students’
enthusiasm for finding out how children develop. Judging by the overwhelmingly
positive response we have received from students and instructors alike, it has.
The most important feature of this book is the exposition, which we have tried to
make as clear, compelling, and interesting as possible. As in previous editions, we
have given extra attention to making it accessible to a broad range of students.
To further enhance the appeal and accessibility of the text, we have re-
tained three types of discussion boxes that explore topics of special interest.
“Applications” boxes focus on how child development research can be used to
promote children’s well-being. Among the applications that are summed up in
these boxes are board-game procedures for improving preschoolers’ understand-
ing of numbers; the Carolina Abecedarian Project; interventions to reduce child
abuse; programs, such as PATHS, for helping rejected children gain acceptance
from their peers; and Fast Track interventions, which help aggressive children
learn how to manage their anger and antisocial behavior. “Individual Differences”
boxes focus on populations that differ from the norm with regard to the specific
topic under consideration, or on variations among children in the general popu-
lation. Some of these boxes highlight developmental problems such as autism,
ADHD, dyslexia, specific language impairment, and conduct disorder, while oth-
ers focus on differences in the development of children that center on attachment
status, gender, and cultural differences. “A Closer Look” boxes examine important
and interesting research in greater depth than would otherwise be possible: the
areas examined range from brain imaging techniques to discrepant gender iden-
tity to the developmental impact of homelessness.
We have also retained a number of other features intended to improve students’
learning. These features include boldfacing key terms and supplying definitions
both within the immediate text and in marginal glossaries; providing summaries at
the end of each major section, as well as summaries for the overall chapter; and,
at the end of each chapter, posing critical thinking questions intended to promote
deeper consideration of essential topics.
New to the Fourth Edition
We have expanded our coverage of a number of research areas that have become
increasingly important in recent years for both the students of child development
and the instructors who teach it. In the following paragraphs, we outline some of

the highlights of the fourth edition. Thank you for taking the time to look through
this new edition of How Children Develop. We hope that you find it to be useful
and appealing.
New and Expanded Coverage
In selecting what to cover from among the many new discoveries about child de-
velopment, we have emphasized the studies that strike us as the most interesting
and important. While retaining and thoroughly updating its essential coverage, the
fourth edition of How Children Develop continues to explore a number of fascinat-
ing areas in which there has been great progress in the past few years. Following is
a very brief sampling of the many areas of new and expanded coverage:
n Epigenetics
n Gene–environment relations, including methylation
n The role of specific gene variants in certain behaviors
n Differential susceptibility to the environment
n Brain development and functioning
n Mechanisms of infants’ learning
n Infants’ understanding of other people
n Executive functioning
n Cultural influences on development
n Relations among understanding of time, space, and number
n Mathematics anxiety
n Applications of research to education
n The growing role and impact of social media in children’s and adolescents’ lives
n Interventions to foster children’s social adjustment
How Children Develop, Fourth Edition, features a wide array of multimedia tools
designed for the individual needs of students and teachers. For more information
about any of the items below, visit Worth Publishers’ online catalog at www. worth
LaunchPad with LearningCurve Quizzing
A comprehensive Web resource for teaching and learning psychology
LaunchPad combines Worth Publishers’ awarding-winning media with an in-
novative platform for easy navigation. For students, it is the ultimate online study
guide with rich interactive tutorials, videos, e-Book, and the LearningCurve
adaptive quizzing system. For instructors, LaunchPad is a full course space where
class documents can be posted, quizzes are easily assigned and graded, and students’
progress can be assessed and recorded. Whether you are looking for the most effec-
tive study tools or a robust platform for an online course, LaunchPad is a powerful
way to enhance your class.

LaunchPad for How Children Develop, Fourth
Edition, can be previewed and purchased at http://
How Children Develop, Fourth Edition, and
LaunchPad can be ordered together with ISBN 10:
1-4641-8284-1 / ISBN-13: 978-1-4641-8284-6.
LaunchPad for How Children Develop, Fourth Edition,
includes the following resources:
n The LearningCurve quizzing system was designed
based on the latest findings from learning and memory
research. It combines adaptive question selection,
immediate and valuable feedback, and a game-like
interface to engage students in a learning experience that
is unique to them. Each LearningCurve quiz is fully
integrated with other resources in LaunchPad through
the Personalized Study Plan, so students will be able
to review with Worth’s extensive library of videos and
activities. And state-of-the-art question analysis reports
allow instructors to track the progress of individual
students as well as their class as a whole.
n An interactive e-Book allows students to highlight,
bookmark, and make their own notes, just as they
would with a printed textbook. Digital enhancements
include full-text search and in-text glossary definitions.
n Student Video Activities include more than 100
engaging video modules that instructors can easily assign
for student assessment. Videos cover classic experiments,
current news footage, and cutting-edge research, all of
which are sure to spark discussion and encourage critical thinking.
n The Scientific American Newsfeed delivers weekly articles, podcasts, and news
briefs on the very latest developments in psychology from the first name in
popular science journalism.
Additional Student Supplements
CourseSmart e-Book
The CourseSmart e-Book offers the complete text of How Children Develop,
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table media player, such as a smart phone or iPad. The CourseSmart e-Book for
How Children Develop, Fourth Edition, can be previewed and purchased at www
Scientific American Reader to Accompany How Children Develop
The authors have compiled fifteen Scientif ic American articles relevant to key top-
ics in the text. The selections range from classics such as Harry Harlow’s “Love in
Infant Monkeys” and Eleanor Gibson and Richard Walk’s “The ‘Visual Cliff ’” to

contemporary articles on such topics as the interaction of games and environment
in the development of intelligence (Robert Plomin and John DeFries), the effects
of child abuse on the developing brain (Martin Teicher), balancing work and family
(Robert Pleck), and moral development (William Damon). These articles should
enrich students’ learning and help them to appreciate the process by which devel-
opmental scientists gain new understanding. This premium item can be packaged
with the text at no additional cost.
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Presentation slides are available in three formats that can be used as they are or
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second set consists of lecture slides that focus on key themes and terms in the book
and include text illustrations and tables. A third set of PowerPoint slides provides
an easy way to integrate the supplementary video clips into classroom lectures. All
these prebuilt PowerPoint presentations are available through http://www.worth
Presentation Videos
Worth’s video clips for development psychology span the full range of topics for
the child development course. With hundreds of clips to choose from, this pre-
mium collection includes research and news footage on topics ranging from pre-
natal development to the experience of child soldiers to empathy in adolescence.
These clips are made available to instructors for lecturing in the classroom and
also through LaunchPad.
Instructor’s Resource Manual
Written by Lynne Baker-Ward, North Carolina State University, this innovative
Instructor’s Resource Manual includes handouts for student projects, reading lists of
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The Instructor’s Resource Manual can be downloaded at
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Test Bank
The Test Bank for How Children Develop by Jill L. Saxon
features 80 multiple-choice and 20 essay questions for each chapter. Each question
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Test Bank on CD-ROM
The Diploma Test Bank CD-ROM, on a dual platform for Windows and Macintosh,
guides instructors through the process of creating a test and allows them to add,
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tions, and media links. The CD-ROM is also the access point for Diploma Online
Testing, which allows creating and administering examinations on paper, over a
network, or over the Internet.
The iClicker Classroom Response System is a versatile polling system developed
by educators for educators that makes class time more efficient and interactive.
iClicker allows you to ask questions and instantly record your students’ responses,
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So many people have contributed (directly and indirectly) to this textbook that
it is impossible to know where to start or where to stop in thanking them. All
of us have been given exceptional support by our spouses and significant oth-

ers—Jerry Clore, Jerry Harris, Xiaodong Lin, and Seth Pollak—and by our chil-
dren—Benjamin Clore; Michael Harris; Todd, Beth, and Aaron Siegler; Avianna
McGhee; and Eli and Nell Pollak—as well as by our parents, relatives, friends, and
other loved ones. Our advisors in college and graduate school, Richard Aslin, Ann
Brown, Les Cohen, Harry Hake, Robert Liebert, Jim Morgan, Paul Mussen, Ellisa
Newport, and Jim Pate, helped to launch our careers and taught us how to recog-
nize and appreciate good research. We also have all benefited from collaborators
who shared our quest for understanding child development and from a great many
exceptionally helpful and generous colleagues, including Karen Adolph, Martha
Alibali, Renee Baillargeon, Sharon Carver, Zhe Chen, Richard Fabes, Cindy Fisher,
Melanie Jones, David Klahr, Patrick Lemaire, Angeline Lillard, John Opfer, Kristin
Shutts, Tracy Spinrad, David Uttal, and Carlos Valiente. We owe special thanks to
our assistants, Sheri Towe and Theresa Treasure, who helped in innumerable ways
in preparing the book.
We would also like to thank the many reviewers who contributed to this and
previous editions: Daisuke Akiba, Queens College, City University of New York;
Kimberly Alkins, Queens College, City University of New York; Lynne Baker-
Ward, North Carolina State University; Hilary Barth, Wesleyan University;
Christopher Beevers, Texas University; Martha Bell, Virginia Tech; Cynthia
Berg, University of Utah; Rebecca Bigler, Texas University; Margaret Borkowski,
Saginaw Valley State University; Eric Buhs, University of Nebraska–Lincoln; G.
Leonard Burns, Washington State University; Wendy Carlson, Shenandoah
University; Kristi Cordell-McNulty, Angelo State University; Myra Cox, Harold
Washington College; Emily Davidson, Texas A&M University–Main Campus; Ed
de St. Aubin, Marquette University; Marissa Diener, University of Utah; Sharon
Eaves, Shawnee State University; Urminda Firlan, Grand Rapids Community
College; Dorothy Fragaszy, University of Georgia; Jeffery Gagne, University of
Texas–Austin; Jennifer Ganger, University of Pittsburgh; Alice Ganzel, Cornell
College; Janet Gebelt, Westfield State University; Melissa Ghera, St. John Fisher
College; Susan Graham, University of Calgary; Andrea Greenhoot, University
of Kansas; Frederick Grote, Western Washington University; John Gruszkos,
Reynolds University; Hanna Gustafsson, University of North Carolina; Alma
Guyse, Midland College; Lauren Harris, Michigan State University; Karen
Hartlep, California State University–Bakersfield; Patricia Hawley, University of
Kansas–Main; Susan Hespos, Northwestern University; Doris Hiatt, Monmouth
University; Susan Holt, Central Connecticut State University; Lisa Huffman,
Ball State University; Kathryn Kipp, University of Georgia; Rosemary Krawczyk,
Minnesota State University; Raymond Krukovsky, Union County College;
Tara Kuther, Western Connecticut State University; Richard Lanthier, George
Washington University; Elida Laski, Boston College; Kathryn Lemery, Arizona
State University; Barbara Licht, Florida State University; Angeline Lillard,
University of Virginia; Wayne McMillin, Northwestern State University; Martha
Mendez-Baldwin, Manhattan College; Scott Miller, University of Florida; Keith
Nelson, Pennsylvania State University–Main Campus; Paul Nicodemus, Austin
Peay State University; Katherine O’Doherty, Vanderbilt University; John Opfer,
The Ohio State University; Ann Repp, Texas University; Leigh Shaw, Weber
State University; Jennifer Simonds, Westminster College; Rebekah Smith,
University of Texas–San Antonio; Mark Strauss, University of Pittsburgh–Main;
Spencer Thompson, University of Texas–Permian Basin; Lisa Travis, University
of Illinois Urbana–Champaign; Roger Webb, University of Arkansas–Little Rock;
Keri Weed, University of South Carolina–Aiken; Sherri Widen, Boston College.

We would especially like to thank Campbell Leaper, University of California–
Santa Cruz, for his major contributions to the revision of our chapter on gender
development (Chapter 15). We are indebted to Campbell for bringing to the fourth
edition his expertise and keen insight in this important area.
Thanks are particularly due to our friends and collaborators at Worth Publishers.
As acquisitions editor and publisher, respectively, Daniel DeBonis and Kevin Feyen
provided exceptional support and any number of excellent suggestions. We would
also like to thank Marge Byers, who nurtured our first edition from its incep-
tion and helped us to realize our vision. Peter Deane, our development editor, is
in a class by himself in both skill and dedication. Peter’s creative thinking and
firm understanding of the field enhanced the content of the book in innumerable
ways. We are deeply grateful to him. Our thanks go also to assistant editor Nadina
Persaud, senior project editor Vivien Weiss, director of development (print and
digital) Tracey Kuehn, art director Barbara Reingold, cover and text designer Kevin
Kall, photo editor Bianca Moscatelli, photo researcher Elyse Rieder, production
manager Sarah Segal, and compositor Northeastern Graphic for their excellent
work. They have helped to create a book that we hope you will find a pleasure to
look at as well as to read. Marketing manager Katherine Nurre provided outstand-
ing promotional materials to inform professors about the book. Anthony Casciano
and Stacey Alexander managed the superb package of ancillary material.
Finally, we want to thank our “book team” of sales representatives and man-
agers. Tom Kling, Julie Hirshman, Kari Ewalt, Greg David, Tom Scotty, Cindy
Rabinowitz, Glenn Russell, and Matt Dunning provided a sales perspective, valu-
able suggestions, and unflagging enthusiasm throughout this project.

How Children

DOROTHEA SHARP (1874-1955), Young Explorers (oil on canvas)

An Introduction
to Child Development
n Reasons to Learn About Child Development
Raising Children
Choosing Social Policies
Understanding Human Nature
n Historical Foundations of the Study
of Child Development
Early Philosophers’ Views of Children’s
Social Reform Movements
Darwin’s Theory of Evolution
The Beginnings of Research-Based Theories
of Child Development
n Enduring Themes in Child Development
1. Nature and Nurture: How Do Nature and Nurture
Together Shape Development?
2. The Active Child: How Do Children Shape Their
Own Development?
3. Continuity/Discontinuity: In What Ways Is
Development Continuous, and in What Ways Is It
4. Mechanisms of Development: How Does
Change Occur?
5. The Sociocultural Context: How Does the
Sociocultural Context Influence Development?
6. Individual Differences: How Do Children Become
So Different from One Another?
7. Research and Children’s Welfare: How Can
Research Promote Children’s Well-Being?
n Methods for Studying Child Development
The Scientific Method
Contexts for Gathering Data About Children
Correlation and Causation
Designs for Examining Development
Ethical Issues in Child-Development Research
n Chapter Summary
chapter 1:

In 1955, a group of child-development researchers began a unique study. Their goal, like that of many developmental researchers, was to find out how bio-logical and environmental factors influence children’s intellectual, social, and emotional growth. What made their study unique was that they examined these diverse aspects of development for all 698 children born that year on the
Hawaiian island of Kauai and continued studying the children’s development for
more than 30 years.
With the parents’ consent, the research team, headed by Emmy Werner, col-
lected many types of data about the children. To learn about possible complica-
tions during the prenatal period and birth, they examined physicians’ records. To
learn about family interactions and the children’s behavior at home, they arranged
for nurses and social workers to observe the families and to interview the children’s
mothers when the children were 1 year old and again when they were 10 years old.
The researchers also interviewed teachers about the children’s academic perfor-
mance and classroom behavior during the elementary school years and examined
police, family court, and social service records that involved the children, either as
victims or perpetrators. Finally, the researchers administered standardized intelli-
gence and personality tests to the participants when they were 10 and 18 years old
and interviewed them at age 18 and again in their early 30s to find out how they
saw their own development.
Results from this study illustrated some of the many ways in which biological
and environmental factors combine to produce child development. For example,
children who experienced prenatal or birth complications were more likely than
others to develop physical handicaps, mental illness, and learning difficulties. But
whether they developed such problems—and if so, to what degree—depended a
great deal on their home environment. Parents’ income, education, and mental
health, together with the quality of the relationship between the parents, especially
influenced children’s development. By age 2, toddlers who had experienced severe
prenatal or birth problems but who lived in harmonious middle-income families
were nearly as advanced in language and motor skills as were children who had not
experienced such problems. By the time the children were 10-year-olds, prenatal
and birth problems were consistently related to psychological difficulties only if the
children also grew up in poor rearing conditions.
What of children who faced both biological and environmental challenges—
prenatal or birth complications and adverse family circumstances? The majority of
these children developed serious learning or behavior problems by age 10. By age
18, most had acquired a police record, had experienced mental health problems,
or had become an unmarried parent. However, one-third of such at-risk children
showed impressive resilience, growing up into young adults who, in the words of
Werner (1989, p. 108D), “loved well, worked well, and played well.”
Michael was one such resilient child. Born prematurely, with low birth weight,
to teenage parents, he spent the first 3 weeks of his life in a hospital, separated
from his mother. By his 8th birthday, Michael’s parents were divorced, his mother
had deserted the family, and he and his three brothers and sisters were being
raised by their father, with the help of their elderly grandparents. Yet by age 18,
Michael was successful in school, had high self-esteem, was popular with his
peers, and was a caring young man with a positive attitude toward life. The fact
that there are many children like Michael—children who show great resilience
in the face of adversity—is among the most heartening findings of research on
n Nature and Nurture
n The Active Child
n Continuity/Discontinuity
n Mechanisms of Change
n The Sociocultural Context
n Individual Differences
n Research and Children’s

child development. Learning about the Michaels of the world inspires child de-
velopment researchers to conduct further investigations aimed at answering such
questions as why individual children differ so much in their response to similar
environments, and how to apply research findings to help more children overcome
the challenges they face.
Reading this chapter will increase your understanding of these and other basic
questions about child development. It also will introduce you to some historical
perspectives on these fundamental questions and to the perspectives and methods
that modern researchers use to address them. But first, we would like you to con-
sider perhaps the most basic question of all: Why study child development?
Reasons to Learn About Child Development
For us, as both parents and researchers, the sheer enjoyment of watching children
and trying to understand them is reason enough for studying child development.
What could be more fascinating than the development
of a child? But there are also practical and intellectual
reasons for studying child development. Understand-
ing how children develop can improve child-rearing,
promote the adoption of wiser social policies regard-
ing children’s welfare, and answer intriguing questions
about human nature. We examine each of these reasons
in the following sections.
Raising Children
Being a good parent is not easy. Among its many chal-
lenges are the endless questions it raises over the years.
Is it okay to take my infant outside in the cold weather?
Should my baby stay at home, or would going to day
care be better for his social development? If my daughter
starts walking and talking early, should I consider plac-
ing her in a school for gifted children? Should I try to teach my 3-year-old to read
early? My son seems so lonely at preschool; how can I help him make friends? How
can I help my kindergartner deal with her anger?
Child-development research can help answer such questions. For example, one
problem that confronts almost all parents is how to help their children control
their anger and other negative emotions. One tempting, and frequent, reaction
is to spank children who express anger in inappropriate ways, such as fighting,
name-calling, and talking back. In a study involving a representative U.S. sam-
ple, 80% of parents of kindergarten children reported having spanked their child
on occasion, and 27% reported having spanked their child the previous week
( Gershoff et al., 2012). In fact, spanking made the problem worse. The more
often parents spanked their kindergartners, the more often the same children
argued, fought, and acted inappropriately at school when they were 3rd-graders.
This relation held true for Blacks, Whites, Hispanics, and Asians alike, and it
held true above and beyond the effects of other relevant factors, such as parents’
income and education.
Fortunately, research suggests several effective alternatives to spanking
(Denham, 1998, 2006). One is expressing sympathy: when parents respond to their
Will these children be resilient enough to
overcome their disadvantaged environment?
The answer will depend in large part on how
many risk factors they face and on their per-
sonal characteristics.

children’s distress with sympathy, the children are better able
to cope with the situation causing the distress. Another ef-
fective approach is helping angry children find positive alter-
natives to expressing anger. For example, encouraging them
to do something they enjoy helps them cope with the hostile
These strategies and similar ones, such as time-outs, can
also be used effectively by others who contribute to raising
children, such as day-care personnel and teachers. One dem-
onstration of this was provided by a special curriculum that
was devised for helping preschoolers (3- and 4-year-olds) who
were angry and out of control (Denham & Burton, 1996).
With this curriculum, preschool teachers helped children rec-
ognize their own and other children’s emotions, taught them
techniques for controlling their anger, and guided them in
resolving conflicts with other children. One approach that
children were taught for coping with anger was the “turtle
technique.” When children felt themselves becoming angry,
they were to move away from other children and retreat into
their “turtle shell,” where they could think through the situation until they were
ready to emerge from the shell. Posters were placed around the classroom to remind
children of what to do when they became angry.
The curriculum was quite successful. Children who participated in it became
more skillful in recognizing and regulating anger when they experienced it and
were generally less negative. For example, one boy, who had regularly gotten into
fights when angry, told the teacher after a dispute with another child, “See, I used
my words, not my hands” (Denham, 1998, p. 219). The benefits of this program can
be long-term. In one test conducted with children in special education classrooms,
positive effects were still evident 2 years after children completed the curricu-
lum (Greenberg & Kusché, 2006). As this example suggests, knowledge of child-
development research can be helpful to everyone involved in the care of children.
Choosing Social Policies
Another reason to learn about child development is to be able to make informed de-
cisions not just about one’s own children but also about a wide variety of social-policy
questions that affect children in general. For example, how much trust should judges
and juries place in preschoolers’ testimony in child-abuse cases? Should children
who do poorly in school be held back, or should they be promoted to the next
grade so that they can be with children of the same age? How effective are health-
education courses aimed at reducing teenage smoking, drinking, and pregnancy?
Child-development research can inform discussion of all of these policy decisions
and many others.
Consider the issue of how much trust to put in preschoolers’ courtroom tes-
timony. At present, more than 100,000 children testify in legal cases each year
(Bruck, Ceci, & Principe, 2006). Many of these children are very young: more than
40% of children who testify in sexual-abuse trials, for example, are younger than 5
years, and almost 40% of substantiated sexual-abuse cases involve children younger
than age 7 (Bruck et al., 2006; Gray, 1993). The stakes are extremely high in such
cases. If juries believe children who falsely testify that they were abused, innocent
people may spend years in jail. If juries do not believe children who accurately
posters like this are used in the turtle tech-
nique to remind children of ways to control

report abuse, the perpetrators will go free and probably abuse other children. So
what can be done to promote reliable testimony from young children and to avoid
leading them to report experiences that never occurred?
Psychological research has helped answer such questions. In one experiment, re-
searchers tested whether biased questioning affects the accuracy of young children’s
memory for events involving touching one’s own and other people’s bodies. The re-
searchers began by having 3- to 6-year-olds play a game, similar to “Simon Says,”
in which the children were told to touch various parts of their body and those of
other children. A month later, the researchers had a social worker interview the
children about their experiences during the game (Ceci & Bruck, 1998). Before
the social worker conducted the interviews, she was given a description of each
child’s experiences. Unknown to her, the description included inaccurate as well as
accurate information. For example, she might have been told that a particular child
had touched her own stomach and another child’s nose, when in fact the child had
touched her own stomach and the other child’s foot. After receiving the descrip-
tion, the social worker was given instructions much like those in a court case: “Find
out what the child remembers.”
As it turned out, the version of events that the social worker had heard often in-
fluenced her questions. If, for example, a child’s account of an event was contrary
to what the social worker believed to be the case, she
tended to question the child repeatedly about the event
(“Are you sure you touched his foot? Is it possible you
touched some other part of his body?”). Faced with such
repeated questioning, children fairly often changed their
responses, with 34% of 3- and 4-year-olds eventually
corroborating at least one of the social worker’s incorrect
beliefs. Children were led to “remember” not only plau-
sible events that never happened but also unlikely ones
that the social worker had been told about. For example,
some children “recalled” their knee being licked and a
marble being inserted in their ear.
Studies such as this have yielded a number of con-
clusions regarding children’s testimony in legal pro-
ceedings. One important finding is that when 3- to
5-year-olds are not asked leading questions, their testi-
mony is usually accurate, as far as it goes (Bruck et al.,
2006; Howe & Courage, 1997). However, when prompted by leading questions,
young children’s testimony is often inaccurate, especially when the leading ques-
tions are asked repeatedly. The younger children are, the more susceptible they are
to being led, and the more their recall reflects the biases of the interviewer’s ques-
tions. In addition, realistic props, such as anatomically correct dolls and drawings,
that are often used in judicial cases in the hopes of improving recall of sexual abuse,
do not improve recall of events that occurred; they actually increase the number
of inaccurate claims, perhaps by blurring the line between fantasy play and reality
(Lamb et al., 2008; Poole, Bruck, & Pipe, 2011). Research on child eyewitness tes-
timony has had a large practical impact, leading many judicial and police agencies
to revise their procedures for interviewing child witnesses to incorporate the les-
sons of this research (e.g., State of Michigan, Governor’s Task Force, 2005). In ad-
dition to helping courts obtain more accurate testimony from young children, such
research-based conclusions illustrate how, at a broader level, knowledge of child
development can inform social policies.
In courtrooms such as this one, asking ques-
tions that will help children to testify accu-
rately is of the utmost importance.
. P
/ T

Understanding Human Nature
A third reason to study child development is to better understand human nature.
Many of the most intriguing questions regarding human nature concern children.
For example, does learning start only after children are born, or can it occur in the
womb? Can later upbringing in a loving home overcome the detrimental effects of
early rearing in a loveless institutional setting? Do children vary in personality and
intellect from the day they are born, or are they similar at birth, with differences
arising only because they have different experiences? Until recently, people could
only speculate about the answers to such questions. Now, however, developmental
scientists have methods that enable them to observe, describe, and
explain the process of development.
A particularly poignant illustration of the way in which scien-
tific research can increase understanding of human nature comes
from studies of how children’s ability to overcome the effects of
early maltreatment is affected by its timing, that is, the age at which
the maltreatment occurs. One such research program has examined
children whose early life was spent in horribly inadequate orphan-
ages in Romania in the late 1980s and early 1990s (McCall et al.,
2011; Nelson et al., 2007; Rutter et al., 2004). Children in these
orphanages had almost no contact with any caregiver. For reasons
that remain unknown, the brutal Communist dictatorship of that
era instructed staff workers not to interact with the children, even
when giving them their bottles. Staff members provided the infants
with so little physical contact that the crown of many infants’ heads
became flattened from the babies’ lying on their backs for 18 to 20
hours per day.
Shortly after the collapse of Communist rule in Romania, a number of these
children were adopted by families in Great Britain. When these children arrived in
Britain, most were severely malnourished, with more than half being in the low-
est 3% of children their age in terms of height, weight, and head circumference.
Most also showed varying degrees of mental retardation and were socially imma-
ture. The parents who adopted them knew of their deprived backgrounds and were
highly motivated to provide loving homes that would help the children overcome
the damaging effects of their early mistreatment.
To evaluate the long-term effects of their early deprivation, the physical, intel-
lectual, and social development of about 150 of the Romanian-born children was
examined at age 6 years. To provide a basis of comparison, the researchers also fol-
lowed the development of a group of British-born children who had been adopted
into British families before they were 6 months of age. Simply put, the question
was whether human nature is sufficiently flexible that the Romanian-born children
could overcome the extreme deprivation of their early experience, and if so, would
that flexibility decrease with the children’s age and the length of the deprivation.
By age 6, the physical development of the Romanian-born children had im-
proved considerably, both in absolute terms and in relation to the British-born
comparison group. However, the Romanian children’s early experience of depriva-
tion continued to influence their development, with the extent of negative effects
depending on how long the children had been institutionalized. Romanian-born
children who were adopted by British families before age 6 months, and who had
therefore spent the smallest portion of their early lives in the orphanages, weighed
about the same as British-born children when both were 6-year-olds. Romanian-
born children adopted between the ages of 6 and 24 months, and who therefore had
This infant is one of the children adopted
from a romanian orphanage in the 1990s.
how successfully he develops will depend
not only on the quality of caregiving he
receives in his adoptive home but also
on the amount of time he spent in the
orphanage and the age at which he was
/ C

spent more of their early lives in the orphanages, weighed less; and those adopted
between the ages of 24 and 42 months weighed even less (Rutter et al., 2004).
Intellectual development at age 6 years showed a similar pattern. The Romanian-
born children who had been adopted before age 6 months demonstrated levels of in-
tellectual competence comparable with those of the British-born group. Those who
had been adopted between ages 6 and 24 months did somewhat less well, and those
adopted between ages 24 and 42 months did even more poorly (Rutter et al., 2004).
The intellectual deficits of the Romanian children adopted after age 6 months were
just as great when the children were retested at age 11, indicating that the negative
effects of the early deprivation persisted over time (Beckett et al., 2006; Kreppner
et al., 2007).
The early experience in the orphanages had similar damaging effects on the
children’s social development (Kreppner et al., 2007; O’Connor, Rutter, & English
and Romanian Adoptees Study Team, 2000). Almost 20% of the Romanian-born
children who were adopted after age 6 months showed extremely abnormal social
behavior at age 6 years, not looking at their parents in anxiety-provoking situations
and willingly going off with strangers (versus 3% of the British-born comparison
group who did so). This atypical social development was accompanied by abnormal
brain activity. Brain scans obtained when the children were 8 years old showed that
those adopted after living for a substantial period in the orphanages had unusu-
ally low levels of neural activity in the amygdala, a brain area involved in emotional
reactions (Chugani et al., 2001). Subsequent studies have identified similar brain
abnormalities among children who spent their early lives in poor-quality orphan-
ages in Russia and East Asia as well (Nelson et al., 2011; Tottenham et al., 2010).
These findings reflect a basic principle of child development that is relevant to
many aspects of human nature: The timing of experiences influences their effects. In the
present case, children were sufficiently flexible to overcome the effects of living in the
loveless, unstimulating institutions if the deprivation ended relatively early; living in
the institutions until older ages, however, had effects that were rarely overcome, even
when children spent subsequent years in loving and stimulating environments. The
adoptive families clearly made a huge positive difference in their children’s lives, but
the later the age of adoption, the greater the long-term effects of early deprivation.
There are at least three good reasons to learn about child development: to improve one’s own
child-rearing, to help society promote the well-being of children in general, and to better un-
derstand human nature.
Historical Foundations of the Study
of Child Development
From ancient Greece to the early years of the twentieth century, a number of pro-
found thinkers observed and wrote about children. Their goals were like those
of contemporary researchers: to help people become better parents, to improve
children’s well-being, and to understand human nature. Unlike contemporary
researchers, they usually based their conclusions on general philosophical beliefs
and informal observations of a few children. Still, the issues they raised are suf-
ficiently important, and their insights sufficiently deep, that their views continue
to be of interest.

Early Philosophers’ Views of Children’s Development
Some of the earliest recorded ideas about children’s development were those of
Plato and Aristotle. These classic Greek philosophers, who lived in the fourth cen-
tury b.c.e., were particularly interested in how children’s development is influenced
by their nature and by the nurture they receive.
Both Plato and Aristotle believed that the long-term welfare of society de-
pended on the proper raising of children. Careful upbringing was essential because
children’s basic nature would otherwise lead to their becoming rebellious and un-
ruly. Plato viewed the rearing of boys as a particularly demanding challenge for
parents and teachers:
Now of all wild things, a boy is the most difficult to handle. Just because he more
than any other has a fount of intelligence in him which has not yet “run clear,” he is
the craftiest, most mischievous, and unruliest of brutes.
(Laws, bk. 7, p. 808)
Consistent with this view, Plato emphasized self-control and discipline as the most
important goals of education (Borstelmann, 1983).
Aristotle agreed with Plato that discipline was necessary, but he was more
concerned with fitting child-rearing to the needs of the individual child. In his
It would seem . . . that a study of individual character is the best way of making edu-
cation perfect, for then each [child] has a better chance of receiving the treatment
that suits him.
(Nicomachean Ethics, bk. 10, chap. 9, p. 1180)
Plato and Aristotle differed more profoundly in their views of how children acquire
knowledge. Plato believed that children have innate knowledge. For example, he
believed that children are born with a concept of “animal” that, from birth onward,
automatically allows them to recognize that the dogs, cats, and other creatures they
encounter are animals. In contrast, Aristotle believed that all knowledge comes
from experience and that the mind of an infant is like a blackboard on which noth-
ing has yet been written.
Roughly 2000 years later, the English philosopher John Locke (1632–1704) and
the French philosopher Jean-Jacques Rousseau (1712–1778) refocused attention
on the question of how parents and society in general can best promote children’s
development. Locke, like Aristotle, viewed the child as a tabula rasa, or blank slate,
whose development largely reflects the nurture provided by the child’s parents and
the broader society. He believed that the most important goal of child-rearing is
the growth of character. To build children’s character, parents need to set good ex-
amples of honesty, stability, and gentleness. They also need to avoid indulging the
child, especially early in life. However, once discipline and reason have been in-
stilled, Locke believed,
authority should be relaxed as fast as their age, discretion, and good behavior could
allow it. . . . The sooner you treat him as a man, the sooner he will begin to be one.
(Cited in Borstelmann, 1983, p. 20)
In contrast to Locke’s advocating discipline before freedom, Rousseau believed
that parents and society should give children maximum freedom from the begin-
ning. Rousseau claimed that children learn primarily from their own spontaneous
interactions with objects and other people, rather than through instruction by par-
ents or teachers. He even argued that children should not receive any formal edu-
cation until about age 12, when they reach “the age of reason” and can judge for

themselves the worth of what they are told. Before then, they should be allowed the
freedom to explore whatever interests them.
Although formulated long ago, these and other philosophical positions continue
to underlie many contemporary debates, including whether children should receive
direct instruction in desired skills and knowledge or be given maximum freedom
to discover the skills and knowledge for themselves, and whether parents should
build their children’s character through explicit instruction or through the implicit
guidance provided by the parents’ own behavior.
Social Reform Movements
Another precursor of the contemporary field of child psychology was early social
reform movements that were devoted to improving children’s lives by changing the
conditions in which they lived. During the Industrial Revolution of the eighteenth
and nineteenth centuries, a great many children in Europe and the United States
worked as poorly paid laborers with no legal protections. Some were as young as 5
and 6 years; many worked up to 12 hours a day in factories or mines, often in ex-
tremely hazardous circumstances. These harsh conditions worried a number of so-
cial reformers, who began to study how such circumstances affected the children’s
development. For example, in a speech before the British House of Commons in
1843, the Earl of Shaftesbury noted that the narrow tunnels where children dug
out coal had
very insufficient drainage [and] are so low that only little
boys can work in them, which they do naked, and often
in mud and water, dragging sledge-tubs by the girdle and
chain. . . . Children of amiable temper and conduct, at 7
years of age, often return next season from the collieries
greatly corrupted . . . with most hellish dispositions.
(Quoted in Kessen, 1965, pp. 46–50)
The Earl of Shaftesbury’s effort at social reform
brought partial success—a law forbidding employment
of girls and of boys younger than 10. In addition to bring-
ing about the first child labor laws, this and other early
social reform movements established a legacy of research
conducted for the benefit of children and provided some
of the earliest recorded descriptions of the adverse effects
that harsh environments can have on children.
Darwin’s Theory of Evolution
Later in the nineteenth century, Charles Darwin’s work on evolution inspired a
number of scientists to propose that intensive study of children’s development
might lead to important insights into human nature. Darwin himself was in-
terested in child development and in 1877 published an article entitled “A Bio-
graphical Sketch of an Infant,” which presented his careful observations of the
motor, sensory, and emotional growth of his infant son, William. Darwin’s “baby
biography”—a systematic description of William’s day-to-day development—
represented one of the first methods for studying children.
Such intensive studies of individual children’s growth continue to be a distinc-
tive feature of the modern field of child development. Darwin’s evolutionary theory
also continues to influence the thinking of modern developmentalists on a wide
During the eighteenth, nineteenth, and early
twentieth centuries, many young children
worked in coal mines and factories. Their
hours were long, and the work was often
unhealthy and dangerous. concern over the
well-being of such children led to some of
the earliest research on child development.

range of topics: infants’ attachment to their mothers (Bowlby, 1969), innate fear of
natural dangers such as spiders and snakes (Rakison & Derringer, 2008), sex differ-
ences (Geary, 2009), aggression and altruism (Tooby & Cosmides, 2005), and the
mechanisms underlying learning (Siegler, 1996).
The Beginnings of Research-Based Theories
of Child Development
At the end of the nineteenth century and the beginning of the twentieth, the first
theories of child development that incorporated research findings were formulated.
One prominent theory, that of the Austrian psychiatrist Sigmund Freud, was based
in large part on his patients’ recollections of their dreams and childhood experi-
ences. Freud’s psychoanalytic theory proposed that biological drives, especially sexual
ones, are a crucial influence on development.
Another prominent theory of the same era, that of American psychologist John
Watson, was based primarily on the results of experiments that examined learning
in animals and children. Watson’s behaviorist theory argued that children’s develop-
ment is determined by environmental factors, especially the rewards and punish-
ments that follow the children’s actions.
By current standards, the research methods on which these theories were based
were crude. Nonetheless, these early scientific theories were better grounded in re-
search evidence than were their predecessors, and, as you will see later in the chap-
ter, they inspired more sophisticated ideas about the processes of development and
more rigorous research methods for studying how development occurs.
Philosophers such as Plato, Aristotle, Locke, and Rousseau, as well as early scientific theorists
such as Darwin, Freud, and Watson, raised many of the deepest issues about child develop-
ment. These issues included how nature and nurture influence development, how best to raise
children, and how knowledge of children’s development can be used to advance their welfare.
Enduring Themes in Child Development
The modern study of child development begins with a set of fundamental ques-
tions. Everything else—theories, concepts, research methods, data, and so on—is
part of the effort to answer these questions. Although experts in the field might
choose different particular questions as the most important, there is widespread
agreement that the seven questions in Table 1.1 are among the most important.
These questions form a set of themes that we will highlight throughout the book
as we examine specific aspects of child development. In this section, we introduce
and briefly discuss each question and the theme that corresponds to it.
1 Nature and Nurture: How Do Nature and Nurture
Together Shape Development?
The most basic question about child development is how nature and nurture in-
teract to shape the developmental process. Nature refers to our biological endow-
ment, in particular, the genes we receive from our parents. This genetic inheritance
Basic Questions about
child Development
1. How do nature and nurture together
shape development? (Nature and nurture)
2. How do children shape their own
development? (The active child)
3. In what ways is development continuous,
and in what ways is it discontinuous?
4. How does change occur? (Mechanisms of
5. How does the sociocultural context
influence development? (The
sociocultural context)
6. How do children become so different
from one another? (Individual
7. How can research promote children’s
well-being? (Research and children’s
nature n our biological endowment; the
genes we receive from our parents

influences every aspect of our make-up, from broad characteristics such as physical
appearance, personality, intellect, and mental health to specific preferences, such
as political attitudes and propensity for thrill-seeking (Plomin, 2004; Rothbart &
Bates, 2006). Nurture refers to the wide range of environments, both physical and
social, that influence our development, including the womb in which we spend the
prenatal period, the homes in which we grow up, the schools that we attend, the
broader communities in which we live, and the many people with whom we interact.
Popular depictions often present the nature–nurture question as an either/or
proposition: “What determines how a person develops, heredity or environment?”
However, this either/or phrasing is deeply misleading. All human characteristics—
our intellect, our personality, our physical appearance, our emotions—are created
through the joint workings of nature and nurture, that is, through the constant
interaction of our genes and our environment. Accordingly, rather than asking
whether nature or nurture is more important, developmentalists ask how nature and
nurture work together to shape development.
That this is the right question to ask is vividly illustrated by findings on the
development of schizophrenia. Schizophrenia is a serious mental illness, often
characterized by hallucinations, delusions, confusion, and irrational behavior.
There is obviously a genetic component to this disease. Children who have a
schizophrenic parent have a much higher probability than other children of de-
veloping the illness later in life, even when they are adopted as infants and there-
fore are not exposed to their parents’ schizophrenic behavior (Kety et al., 1994).
Among identical twins—that is, twins whose genes are identical—if one twin has
schizophrenia, the other has a roughly 50% chance of also having schizophrenia,
as opposed to the roughly 1% probability for the general population (Gottesman,
1991; Cardno & Gottesman, 2000; see Figure 1.1). At the same time, the envi-
ronment is also clearly influential, since roughly 50% of children who have an
identical twin with schizophrenia do not become schizophrenic themselves, and
children who grow up in troubled homes are more likely to become schizophrenic
than are children raised in a normal household. Most important, however, is
the interaction of genes and environment. A study of adopted children, some of
whose biological parents were schizophrenic, indicated that the only children
who had any substantial likelihood of becoming schizophrenic were those who
had a schizophrenic parent and who also were adopted into a troubled family
(Tienari, Wahlberg, & Wynne, 2006).
A remarkable recent series of studies has revealed
some of the biological mechanisms through which na-
ture and nurture interact. These studies show that just
as the genome—each person’s complete set of hered-
itary information—influences behaviors and experi-
ences, behaviors and experiences influence the genome
(Cole, 2009; Meaney, 2010). This might seem im-
possible, given the well-known fact that each person’s
DNA is constant throughout life. However, the ge-
nome includes not only DNA but also proteins that
regulate gene expression by turning gene activity on
and off. These proteins change in response to experi-
ence and, without structurally altering DNA, can re-
sult in enduring changes in cognition, emotion, and
behavior. This discovery has given rise to a new field
called epigenetics, the study of stable changes in gene
could appropriate nurture have allowed
the Three Stooges to become upper-class
e o
g o
t o
Relation to schizophrenic patient
FIGURE 1.1 Genetic relatedness and
schizophrenia The closer the biological
relation, the stronger the probability that
relatives of a person with schizophrenia
will have the same mental illness. (after
Gottes man, 1991)
nurture n the environments, both
physical and social, that influence our
genome n each person’s complete set of
hereditary information
epigenetics n the study of stable
changes in gene expression that are medi-
ated by the environment

expression that are mediated by the environment. Stated simply, epigenetics exam-
ines how experience gets under the skin.
Evidence for the enduring epigenetic impact of early experiences and behav-
iors comes from research on methylation, a biochemical process that reduces ex-
pression of a variety of genes and that is involved in regulating reactions to stress
(Champagne & Curley, 2009; Meaney, 2001). One recent study showed that the
amount of stress that mothers reported experiencing during their children’s infancy
was related to the amount of methylation in the children’s genomes 15 years later
(Essex et al., 2013). Other studies showed increased methylation in the cord-blood
DNA of newborns of depressed mothers (Oberlander et al., 2008) and in adults who
were abused as children (McGowan et al., 2009), leading researchers to speculate that
such children are at heightened risk for depression as adults (Rutten & Mill, 2009).
As these examples illustrate, developmental outcomes emerge from the constant
bidirectional interaction of nature and nurture. To say that one is more important
than the other, or even that the two are equally important, drastically oversimplifies
the developmental process.
2 The Active Child: How Do Children Shape
Their Own Development?
With all the attention that is paid to heredity and environment, many people over-
look the ways in which children’s own actions contribute to their development.
Even in infancy and early childhood, this contribution can be seen in a multitude
of areas, including attention, language use, and play.
Children first begin to shape their own development through their selection of
what to pay attention to. Even newborns prefer to look at things that move and
make sounds. This preference helps them learn about important parts of the world,
such as people, other animals, and inanimate moving objects. When looking at peo-
ple, infants’ attention is particularly drawn to faces, especially their mother’s face:
Given a choice of looking at a stranger’s face or their mother’s, even 1-month-olds
choose to look at Mom (Bartrip, Morton, & de Schonen, 2001). At first, infants’
attention to their mother’s face is not accompanied by any visible emotion, but by
the end of the 2nd month, infants smile and coo more when focusing intently on
their mother’s face than at other times. This smiling and cooing by the infant elic-
its smiling and talking by the mother, which elicits further cooing and smiling by
the infant, and so on (Lavelli & Fogel, 2005). In this way, infants’ preference for
attending to their mother’s face leads to social interactions that can strengthen the
mother–infant bond.
Once children begin to speak, usually between 9 and 15 months of age, their
contribution to their own development becomes more evident. For example, tod-
dlers (1- and 2-year-olds) often talk when they are alone in a room. Only if chil-
dren were internally motivated to learn language would they practice talking when
no one was present to react to what they are saying. Many parents are startled when
they hear this “crib speech” and wonder if something is wrong with a baby who
would engage in such odd-seeming behavior. However, the activity is entirely nor-
mal, and the practice probably helps toddlers improve their speech.
Young children’s play provides many other examples of how their internally mo-
tivated activity contributes to their development. Children play by themselves for
the sheer joy of doing so, but they also learn a great deal in the process. Anyone
who has seen a baby bang a spoon against the tray of a high chair or intentionally
drop food on the floor would agree that, for the baby, the activity is its own reward.
One of the earliest ways children shape their
own development is through their choice of
where to look. From the first month of life,
seeing Mom is a high priority.
play contributes to children’s development
in many ways, including the spatial under-
standing and attention to detail required to
complete puzzles.
methylation n A biochemical process
that influences behavior by suppressing
gene activity and expression

At the same time, the baby is learning about the
noises made by colliding objects, about the speed
at which objects fall, and about the limits of his or
her parents’ patience.
Young children’s fantasy play seems to make an
especially large contribution to their knowledge of
themselves and other people. Starting at around
age 2 years, children sometimes pretend to be dif-
ferent people in make-believe dramas. For ex-
ample, they may pretend to be superheroes doing
battle with monsters or play the role of parents
taking care of babies. In addition to being inher-
ently enjoyable, such play appears to teach chil-
dren valuable lessons, including how to cope with
fears and how to interact with others (Howes &
Matheson, 1992; Smith, 2003). Older children’s
play, which typically is more organized and rule-
bound, teaches them additional valuable lessons,
such as the self-control needed for turn-taking, adhering to rules, and controlling
one’s emotions in the face of setbacks (Hirsch-Pasek et al., 2008). As we discuss
later in the chapter, children’s contributions to their own development strengthen
and broaden as they grow older and become increasingly able to choose and shape
their environments.
3 Continuity/Discontinuity: In What Ways Is
Development Continuous, and in What Ways
Is It Discontinuous?
Some scientists envision children’s development as a continuous process of small
changes, like that of a pine tree growing taller and taller. Others see the process as
a series of sudden, discontinuous changes, like the transition from caterpillar to
cocoon to butterfly (Figure 1.2). The debate over which of these views is more ac-
curate has continued for decades.
/ T
adolescents who participate in sports and
other extracurricular activities are more
likely to complete high school, and less
likely to get into trouble, than peers who
are not engaged in these activities. This is
another example of how children contribute
to their own development.
l o
(in cocoon)
l o
Pine tree: Developmental continuity Butterfly: Developmental discontinuity
(a) (b)
FIGURE 1.2 continuous and discon-
tinuous development Some researchers
see development as a continuous, gradual
process, akin to a tree’s growing taller with
each passing year. Others see it as a discon-
tinuous process, involving sudden dramatic
changes, such as the transition from cater-
pillar to cocoon to butterfly. each view fits
some aspects of child development.
continuous development n the idea
that changes with age occur gradually, in
small increments, like that of a pine tree
growing taller and taller
discontinuous development n the
idea that changes with age include occa-
sional large shifts, like the transition from
caterpillar to cocoon to butterfly

Researchers who view development as discontinuous start from a common ob-
servation: children of different ages seem qualitatively different. A 4-year-old and
a 6-year-old, for example, seem to differ not only in how much they know but in
the whole way they think about the world. To appreciate these differences, consider
two conversations between Beth, the daughter of one of the authors, and Beth’s
mother. The first conversation took place when Beth was 4 years old, the second,
when she was 6. Both conversations occurred after Beth had watched her mother
pour all the water from a typical drinking glass into a taller, narrower glass. Here is
the conversation that occurred when Beth was 4:
Mother: Is there still the same amount of water?
Beth: No.
Mother: Was there more water before, or is there more now?
Beth: There’s more now.
Mother: What makes you think so?
Beth: The water is higher; you can see it’s more.
Mother: Now I’ll pour the water back into the regular glass. Is there the same
amount of water as when the water was in the same glass before?
Beth: Yes.
Mother: Now I’ll pour all the water again into the tall thin glass. Does the
amount of water stay the same?
Beth: No, I already told you, there’s more water when it’s in the tall glass.
Two years later, Beth responded to the same problem quite differently:
Mother: Is there still the same amount of water?
Beth: Of course!
What accounts for this change in Beth’s thinking? Her everyday observations
of liquids being poured cannot have been the reason for it; Beth had seen liquids
poured on a great number of occasions before she was 4, yet failed to develop the
understanding that the volume remains constant. Experience with the specific
task could not explain the change either, because Beth had no further exposure
to the task between the first and second conversation. Then why, as a 4-year-old,
would Beth be so confident that pouring the water into the taller, narrower glass
increased the amount and, as a 6-year-old, be so confident that it did not?
This conservation-of-liquid-quantity problem is actually a classic technique de-
signed to test children’s level of thinking. It has been used with thousands of chil-
dren around the world, and virtually all the children studied, no matter what their
culture, have shown the same type of change in reasoning as Beth did (though
usually at somewhat older ages). Furthermore, such age-related differences in
: B
children’s behavior on piaget’s conser-
vation-of-liquid-quanity problem is often
used to exemplify the idea that develop-
ment is discontinuous. The child first sees
equal amounts of liquid in similarly shaped
glasses and an empty, differently shaped
glass. Then, the child sees the liquid from
one glass poured into the differently shaped
glass. Finally, the child is asked whether
the amount of liquid remains the same or
whether one glass has more. Young children,
like this girl, are unshakable in their belief
that the glass with the taller liquid column
has more liquid. a year or two later, they are
equally unshakable in their belief that the
amount of liquid in each glass is the same.

understanding pervade children’s thinking. Consider two letters to Mr. Rogers,
one sent by a 4-year-old and one by a 5-year-old (Rogers, 1996, pp. 10–11):
Dear Mr. Rogers,
I would like to know how you get in the TV.
(Robby, age 4)
Dear Mr. Rogers,
I wish you accidentally stepped out of the TV into my house so I could play with you.
( Josiah, age 5)
Clearly, these are not ideas that an older child would entertain. As with Beth’s
case, we have to ask, “What is it about 4- and 5-year-olds that leads them to form
such improbable beliefs, and what changes occur that makes such notions laugh-
able to 6- and 7-year-olds?”
One common approach to answering these questions comes from stage
theories, which propose that development occurs in a progression of distinct age-
related stages, much like the butterfly example in Figure 1.2b. According to these
theories, a child’s entry into a new stage involves relatively sudden, qualitative
changes that affect the child’s thinking or behavior in broadly unified ways and
move the child from one coherent way of experiencing the world to a different co-
herent way of experiencing it.
Among the best-known stage theories is Jean Piaget’s theory of cognitive
development, the development of thinking and reasoning. This theory holds that
between birth and adolescence, children go through four stages of cognitive growth,
each characterized by distinct intellectual abilities and ways of understanding the
world. For example, according to Piaget’s theory, 2- to 5-year-olds are in a stage of
development in which they can focus on only one aspect of an event, or one type
of information, at a time. By age 7, children enter a different stage, in which they
can simultaneously focus on and coordinate two or more aspects of an event and
can do so on many different tasks. According to this view, when confronted with a
problem like the one that Beth’s mother presented to her, most 4- and 5-year-olds
focus on the single dimension of height, and therefore perceive the taller, narrower
glass as having more water. In contrast, most 7- and 8-year-olds consider both rel-
evant dimensions of the problem simultaneously. This allows them to realize that
although the column of water in the taller glass is higher, the column also is nar-
rower, and the two differences offset each other.
In the course of reading this book, you will encounter a number of other stage
theories, including Sigmund Freud’s theory of psychosexual development, Erik
Erikson’s theory of psychosocial development, and Lawrence Kohlberg’s theory of
moral development. Each of these stage theories proposes that children of a given
age show broad similarities across many situations and that children of different
ages tend to behave very differently.
Such stage theories have been very influential. In the past 20 years, however,
many researchers have concluded that most developmental changes are gradual
rather than sudden, and that development occurs skill by skill, task by task, rather
than in a broadly unified way (Courage & Howe, 2002; Elman et al., 1996; Thelen
& Smith, 2006). This view of development is less dramatic than that of stage theo-
ries, but a great deal of evidence supports it. One such piece of evidence is the fact
that a child often will behave in accord with one proposed stage on some tasks but
in accord with a different proposed stage on other tasks (Fischer & Bidell, 2006).
This variable level of reasoning makes it difficult to view the child as being “in”
either stage.
stage theories n approaches that pro-
pose that development involves a series of
discontinuous, age-related phases
cognitive development n the develop-
ment of thinking and reasoning

Much of the difficulty in deciding whether de-
velopment is continuous or discontinuous is that the
same facts can look very different, depending on one’s
perspective. Consider the seemingly simple question
of whether children’s height increases continuously
or discontinuously. Figure 1.3a shows a boy’s height,
measured yearly from birth to age 18 (Tanner, 1961).
When one looks at the boy’s height at each age, devel-
opment seems smooth and continuous, with growth
occurring rapidly early in life and then slowing down.
However, when you look at Figure 1.3b, a different
picture emerges. This graph illustrates the same boy’s
growth, but it depicts the amount of growth from one
year to the next. The boy grew every year, but he grew
most during two periods: from birth to age 2½, and
from ages 13 to 15. These are the kinds of data that
lead people to talk about discontinuous growth and
about a separate stage of adolescence that includes a
physical growth spurt.
So, is development fundamentally continuous or
fundamentally discontinuous? The most reasonable
answer seems to be, “It depends on how you look at it
and how often you look.” Imagine the difference be-
tween the perspective of an uncle who sees his niece
every 2 or 3 years and that of the niece’s parents, who
see her every day. The uncle will almost always be
struck with the huge changes in his niece since he last
saw her. The niece will be so different that it will seem
that she has progressed to a higher stage of develop-
ment. In contrast, the parents will most often be struck
by the continuity of her development; to them, she usually will just seem to grow up
a bit each day. Throughout this book, we will be considering the changes, large and
small, sudden and gradual, that have led some researchers to emphasize the conti-
nuities in development and others to emphasize the discontinuities.
4 Mechanisms of Development: How Does
Change Occur?
Perhaps the deepest mystery about children’s development is expressed by the ques-
tion “How does change occur?” In other words, what are the mechanisms that
produce the remarkable changes that children undergo with age and experience?
A very general answer was implicit in the earlier discussion of the theme of nature
and nurture. The interaction of genome and environment determines both what
changes occur and when those changes occur. The challenge comes in specifying
more precisely how any given change occurs.
One particularly interesting analysis of the mechanisms of developmental change
involves the roles of brain activity, genes, and learning experiences in the development
of effortful attention (e.g., Rothbart, Sheese, & Posner, 2007). Effortful attention in-
volves voluntary control of one’s emotions and thoughts. It includes processes such as
inhibiting impulses (e.g., obeying requests to put all of one’s toys away, as opposed to
putting some away but then getting distracted and playing with the remaining ones);
B 2
Age (years)
4 6 8 10 12 14 16 18
B 2
Age (years)
4 6 8 10 12 14 16 18
FIGURE 1.3 continuous and discon-
tinuous growth Depending on how it is
viewed, changes in height can be viewed
as either continuous or discontinuous. (a)
examining a boy’s height in absolute terms
from birth to 18 years makes the growth
look gradual and continuous (from Tanner,
1961). (b) examining the increases in the
same boy’s height from one year to the next
over the same period shows rapid growth
during the first 2½ years, then slower
growth, then a growth spurt in adolescence,
then a rapid decrease in growth; viewed this
way, growth seems discontinuous.

controlling emotions (e.g., not crying when failing to get one’s way); and focus-
ing attention (e.g., concentrating on one’s homework despite the inviting sounds of
other children playing outside). Difficulty in exerting effortful attention is associated
with behavioral problems, weak math and reading skills, and mental illness (Blair &
Razza, 2007; Diamond & Lee, 2011; Rothbart & Bates, 2006).
Studies of the brain activity of people performing tasks that require control of
thoughts and emotions show that connections are especially active between the
anterior cingulate, a brain structure involved in setting and attending to goals, and
the limbic area, a part of the brain that plays a large role in emotional reactions
(Etkin et al., 2006). Connections between brain areas such as the anterior cingulate
and the limbic area develop considerably during childhood, and their development
appears to be one mechanism that underlies improving effortful attention during
childhood (Rothbart et al., 2007).
What role do genes and learning experiences play in influencing this mech-
anism of effortful attention? Specific genes influence the production of key
neuro transmitters—chemicals involved in communication among brain cells.
Variations among children in these genes are associated with variations in the
quality of performance on tasks that require effortful attention (Canli et al., 2005;
Diamond et al., 2004; Rueda et al., 2005). These genetic influences do not occur
in a vacuum, however. As noted in the discussion of epigenetics, the environment
plays a crucial role in the expression of genes. Infants with a particular form of
one of the genes in question show differences in effortful attention related to the
quality of parenting they receive, with lower-quality parenting being associated
with lower ability to regulate attention (Sheese et al., 2007). Among children
who do not have that form of the gene, quality of parenting has less effect on ef-
fortful attention.
Children’s experiences also can change the wiring of the brain system that pro-
duces effortful attention. Rueda and colleagues (2005) presented 6-year-olds with
a 5-day training program that used computerized exercises to improve capacity
for effortful attention. Examination of electrical activity in the anterior cingulate
indicated that those 6-year-olds who had completed the computerized exercises
showed improved effortful attention. These children also showed improved perfor-
mance on intelligence tests, which makes sense given the sustained effortful atten-
tion required by such tests. Thus, the experiences that children encounter influence
their brain processes and gene expression, just as brain processes and genes influ-
ence children’s reactions to experiences. More generally, a full understanding of the
mechanisms that produce developmental change requires specifying how genes,
brain structures and processes, and experiences interact.
5 The Sociocultural Context: How Does the
Sociocultural Context Influence Development?
Children grow up in a particular set of physical and social environments, in a par-
ticular culture, under particular economic circumstances, at a particular time in
history. Together, these physical, social, cultural, economic, and historical circum-
stances interact to constitute the sociocultural context of a child’s life. This socio-
cultural context influences every aspect of children’s development.
A classic depiction of the components of the sociocultural context is Urie
Bronfenbrenner’s (1979) bioecological model (discussed in depth in Chapter 9).
The most obviously important component of children’s sociocultural contexts is the
people with whom they interact—parents, grandparents, brothers, sisters, day-care
neurotransmitters n chemicals
involved in communication among brain
sociocultural context n the physical,
social, cultural, economic, and historical
circumstances that make up any child’s

providers, teachers, friends, classmates, and so on—and the physical environment
in which they live—their house, day-care center, school, neighborhood, and so on.
Another important but less tangible component of the sociocultural context is the
institutions that influence children’s lives: educational systems, religious institu-
tions, sports leagues, social organizations (such as boys’ and girls’ clubs), and so on.
Yet another important set of influences are the general characteristics of the
child’s society: its economic and technological advancement; its values, attitudes,
beliefs, and traditions; its laws and political structure; and so on. For example, the
simple fact that most toddlers and preschoolers growing up in the United States
today go to child care outside their homes reflects a number of these less tangible
sociocultural factors, including:
1. The historical era (50 years ago, far fewer children in the United States
attended child-care centers)
2. The economic structure (there are far more opportunities today for women
with young children to work outside the home)
3. Cultural beliefs (for example, that receiving child care outside the home does
not harm children)
4. Cultural values (for example, the value that mothers of young children should
be able to work outside the home if they wish).
Attendance at child-care centers, in turn, partly determines the people children
meet and the activities in which they engage.
One method that developmentalists use to understand the influence of the so-
ciocultural context is to compare the lives of children who grow up in different
cultures. Such cross-cultural comparisons often reveal that practices that are rare or
nonexistent in one’s own culture are common in other cultures. The following com-
parison of young children’s sleeping arrangements in different societies illustrates
the value of such cross-cultural research.
In most families in the United States, newborn infants sleep in their parents’
bedroom, either in a crib or in the same bed. However, when infants are 2 to 6
months old, parents usually move them to another bedroom where they sleep alone
(Greenfield, Suzuki, & Rothstein-Fisch, 2006). This seems natural to most people
raised in the United States, because it is how we and others whom we know were
raised. From a worldwide perspective, however, such sleep-
ing arrangements are highly unusual. In most other societies,
including economically advanced nations such as Italy, Japan,
and South Korea, babies almost always sleep in the same bed as
their mother for the first few years, and somewhat older chil-
dren also sleep in the same room as their mother, sometimes in
the same bed (e.g., Nelson, Schiefenhoevel, & Haimerl, 2000;
Whiting & Edwards, 1988). Where does this leave the fa-
ther? In some cultures, the father sleeps in the same bed with
mother and baby; in others, he sleeps in a separate bed or in a
different room.
How do these differences in sleeping arrangements af-
fect children? To find out, researchers interviewed mothers in
middle-class U.S. families in Salt Lake City, Utah, and in rural
Mayan families in Guatemala (Morelli et al., 1992). These in-
terviews revealed that by age 6 months, the large majority of
the U.S. children had begun sleeping in their own bedroom. As
the children grew out of infancy, the nightly separation of child OW
In many countries, including Denmark,
the country in which this mother and child
live, mothers and children sleep together
for the first several years of the child’s life.
This sociocultural pattern is in sharp con-
trast to the U.S. practice of having infants
sleep separately from their parents soon
after birth.

and parents became a complex ritual, surrounded by activities intended to comfort
the child, such as telling stories, reading children’s books, singing songs, and so on.
About half the children were reported as taking a comfort object, such as a blanket
or teddy bear, to bed with them.
In contrast, interviews with the Mayan mothers indicated that their children
typically slept in the same bed with them until the age of 2 or 3 years and continued
to sleep in the same room with them for years thereafter. The children usually went
to sleep at the same time as their parents. None of the Mayan parents reported bed-
time rituals, and almost none reported their children taking comfort objects, such
as dolls or stuffed animals, to bed with them.
Why do sleeping arrangements differ across cultures? Interviews with the Mayan
and U.S. parents indicated that the crucial consideration for them in determining
sleeping arrangements was cultural values. Mayan culture prizes interdependence
among people. The Mayan parents expressed the belief that having a young child
sleep with the mother is important for developing a good parent–child relationship,
for avoiding the child’s becoming distressed at being alone, and for helping parents
spot any problems the child is having. They often expressed shock and pity when
told that infants in the United States typically sleep separately from their parents
(Greenfield et al., 2006). In contrast, U.S. culture prizes independence and self-
reliance, and the U.S. mothers expressed the belief that having babies and young
children sleep alone promotes these values, as well as allowing intimacy between
husbands and wives (Morelli et al., 1992). These differences illustrate both how
practices that strike us as natural may differ greatly across cultures and how the
simple conventions of everyday life often reflect deeper values.
Contexts of development differ not just between cultures but also within them.
In modern multicultural societies, many contextual differences are related to eth-
nicity, race, and socioeconomic status (SES)—a measure of social class that is
based on income and education. Virtually all aspects of children’s lives—from the
food they eat to the parental discipline they receive to the games they play—vary
with ethnicity, race, and SES.
The socioeconomic context exerts a particularly large influence on children’s
lives. In economically advanced societies, including the United States, most chil-
dren grow up in comfortable circumstances, but millions of other children do not.
In 2011, about 19% of U.S. families with children had incomes below the poverty
line (in that year, $18,530 for a family of three with one adult and two children). In
absolute numbers, that translates into about 16 million children growing up in pov-
erty (U.S. Census Bureau, 2012). As shown in Table 1.2, poverty rates are especially
high in Black and Hispanic families and in families of all races that are headed by
single mothers. Poverty rates are also very high among the roughly 25% of children
in the United States who are either immigrants or the children of immigrants—
roughly twice as high as among children of native-born parents (Hernandez,
Denton, & Macartney, 2008; Smeeding, 2008).
Children from poor families tend to do less well than other children in many ways
(G. W. Evans et al., 2005; Morales & Guerra, 2006). In infancy, they are more likely
to have serious health problems. In childhood, they are more likely to have social/
emotional and behavioral problems. Throughout childhood and adolescence, they
tend to have smaller vocabularies, lower IQs, and lower math and reading scores on
standardized achievement tests. In adolescence, they are more likely to have a baby
or drop out of school (G. W. Evans et al., 2005; Luthar, 1999; McLoyd, 1998).
These negative outcomes are not surprising when we consider the huge array
of disadvantages that poor children face. Compared with children who grow up in
percentages of U.S. Families with
children Younger than 18 Living
Below poverty Line in 2011
Group % in
Overall U.S. Population 19
White, non-Hispanic 12
Black 33
Hispanic 29
Asian 12
Married Couples 9
White, non-Hispanic 5
Black 12
Hispanic 20
Asian 9
Single Parent: Female Head of
White, non-Hispanic 33
Black 47
Hispanic 49
Asian 26
Source: U.S. Census Bureau, 2012
socioeconomic status (SES) n a mea-
sure of social class based on income and

more affluent circumstances, they are more likely to live in dangerous neighbor-
hoods, to attend inferior day-care centers and schools, and to be exposed to high
levels of air and water pollution (Dilworth-Bart & Moore, 2006; G. W. Evans,
2004). In addition, their parents read to them less, talk to them less, provide fewer
books in the home, and are less involved in their schooling. Poor children also are
more likely than affluent children to grow up in single-parent homes or to be raised
by neither biological parent. The accumulation of these disadvantages, rather than
any single one of them, seems to be the greatest obstacle to poor children’s success-
ful development (Luthar, 2006; Morales & Guerra, 2006).
And yet as we saw in Werner’s study of the children of Kauai, described at the
beginning of the chapter, many children do overcome the obstacles that poverty
presents. Such resilient children tend to have three characteristics: (1) positive per-
sonal qualities, such as high intelligence, an easygoing personality, and an optimis-
tic outlook on the future; (2) a close relationship with at least one parent; and (3) a
close relationship with at least one adult other than their parents, such as a grand-
parent, teacher, coach, or family friend (Chen & Miller, 2012; Masten, 2007). Thus,
although poverty poses serious obstacles to successful development, many children
do surmount the challenges—usually with the help of adults in their lives.
6 Individual Differences: How Do Children Become So
Different from One Another?
Anyone who has experience with children is struck by their uniqueness—their dif-
ferences not only in physical appearance but in everything from activity level and
temperament to intelligence, persistence, and emotionality. These differences among
children emerge quickly. Some infants in their first year are shy, others outgoing.
Some infants play with or look at objects for prolonged periods; others rapidly shift
from activity to activity. Even children in the same family often differ substantially,
as you probably already know if you have siblings.
Scarr (1992) identified four factors that can lead children from a single family (as
well as children from different families) to turn out very different from one another:
1. Genetic differences
2. Differences in treatment by parents and others
3. Differences in reactions to similar experiences
4. Different choices of environments
The most obvious reason for differences among children is that, except for
identical twins, every individual is genetically unique. All other siblings (includ-
ing fraternal twins) share 50% of their genes and differ in the
other 50%.
A second major source of variation among children is dif-
ferences in the treatment they receive from parents and other
people. This differential treatment is often associated with
preexisting differences in the children’s characteristics. For
example, parents tend to provide more sensitive care to easy-
going infants than to difficult ones; by the second year, parents
of difficult children are often angry with them even when the
children have done nothing wrong in the immediate situation
(van den Boom & Hoeksma, 1994). Teachers, likewise, tend
to provide positive attention and encouragement to pupils
who are learning well and are well behaved, but with pupils FOT
Different children, even ones within the
same family, often react to the same experi-
ence in completely different ways.

who are doing poorly and are disruptive, they tend to be openly critical and to deny
the pupils’ requests for special help (Good & Brophy, 1996).
In addition to being shaped by objective differences in the treatment they re-
ceive, children also are influenced by their subjective interpretations of the treat-
ment. A classic example occurs when each of a pair of siblings feels that their
parents favor the other. Siblings also often react differently to events that affect the
whole family. In one study, 69% of negative events, such as parents’ being laid off or
fired, elicited fundamentally different reactions from siblings (Beardsall & Dunn,
1992). Some children were very concerned at a parent’s loss of a job; others were
sure that everything would be okay.
A fourth major source of differences among children relates to the previously
discussed theme of the active child: As children grow older, they increasingly choose
activities and friends for themselves and thus influence their own subsequent de-
velopment. They may also accept or choose niches for themselves: within a family,
one child may become “the smart one,” another “the popular one,” another “the bad
one,” and so on (Scarr & McCartney, 1983). A child labeled by family members
as “the smart one” may strive to live up to the label; so, unfortunately, may a child
labeled “the troublemaker.”
As discussed in the section on nature and nurture and in the section on mech-
anisms of development, differences in biology and experience interact in com-
plex ways to create the infinite diversity of human beings. Thus, a study of 11- to
17-year-olds found that the grades of children who were highly engaged with
school changed in more positive directions than would have been predicted by their
genetic background or family environments alone ( Johnson, McGue, & Iacono,
2006). The same study revealed that children of high intelligence were less nega-
tively affected by adverse family environments than were other children. Thus,
children’s genes, their treatment by other people, their subjective reactions to their
experiences, and their choice of environments interact in ways that contribute to
differences among children, even ones in the same family.
7 Research and Children’s Welfare: How Can Research
Promote Children’s Well-Being?
Improved understanding of child development often leads to practical benefits.
Several examples have already been described, including the program for helping
children deal with their anger and the recommendations for fostering valid eyewit-
ness testimony from young children.
Another type of practical benefit arising from child-development research in-
volves educational innovations. One fascinating example comes from studies of
how children’s beliefs about intelligence influence their learning. Carol Dweck and
her colleagues (Dweck, 2006; Dweck & Leggett, 1988) have found that some chil-
dren (and adults) believe that intelligence is a fixed entity. They see each person as
having a certain amount of intelligence that is set at birth and cannot be changed
by experience. Other children (and adults) believe that intelligence is a changeable
characteristic that increases with learning and that the time and effort people put
into learning is the key determinant of their intelligence.
People who believe that intelligence increases with learning tend to react to
failure in more effective ways (Dweck, 2006). When they fail to solve a problem,
they more often persist on the task and try harder. Such persistence in the face
of failure is an important quality. As the great British Prime Minister Winston
Churchill once said, “Success is the ability to go from one failure to another with

no loss of enthusiasm.” In contrast, people who be-
lieve that intelligence is a fixed entity tend to give
up when they fail, because they think the problem
is too hard for them.
Building on this research regarding the relation
between beliefs about intelligence and persistence
in the face of difficulty, Blackwell, Trzesniewski,
and Dweck (2007) devised an effective educational
program for middle school students from low-
income backgrounds. They presented randomly se-
lected students with research findings about how
learning alters the brain in ways that improve sub-
sequent learning and thus “makes you smarter.”
Other randomly selected students from the same classrooms were presented with
research findings about how memory works. The investigators predicted that the
students who were told about the effects that learning has on the brain would
change their beliefs about intelligence in ways that would help them persevere in
the face of failure. In particular, the changed beliefs were expected to improve stu-
dents’ learning of mathematics, an area in which children often experience initial
This prediction was borne out. Children who were presented information about
how learning changes the brain and enhances intelligence subsequently improved
their math grades, whereas the other children did not. Children who initially be-
lieved that intelligence was an inborn, unchanging quality but who came to believe
that intelligence reflected learning showed especially large improvements. Perhaps
most striking, when the children’s teachers, who did not know which type of in-
formation each child had received, were asked if any of their students had shown
unusual improvement in motivation or performance, the teachers cited more than
three times as many students who had been given information about how learning
builds intelligence.
In subsequent chapters, we review many additional examples of how child de-
velopment research is being used to promote children’s welfare.
The modern field of child development is in large part an attempt to answer a small set of
fundamental questions about children. These include:
1. How do nature and nurture jointly contribute to development?
2. How do children contribute to their own development?
3. Is development best viewed as continuous or discontinuous?
4. What mechanisms produce development?
5. How does the sociocultural context influence development?
6. Why are children so different from one another?
7. How can we use research to improve children’s welfare?
Methods for Studying Child Development
As illustrated in the preceding section, modern scientific research has advanced
the understanding of fundamental questions about child development well beyond
that of the historical figures who first raised the questions. This progress reflects the
/ W
Screenshot from Brainology, a commer-
cially available educational program based
on the findings of Blackwell, Trzesniewski,
and Dweck (2007). The software, like the
research study, emphasizes that learning
makes children smarter by building new
connections within the brain.


successful application of the scientific method to the study of child development.
In this section, we describe the scientific method and examine how its use has ad-
vanced understanding of child development.
The Scientific Method
The basic assumption of the scientific method is that all beliefs, no matter how
probable they seem and no matter how many people share them, may be wrong.
Therefore, until beliefs have been tested, they must be viewed as hypotheses, that
is, as educated guesses, rather than as truth. If a hypothesis is tested, and the evi-
dence repeatedly does not support it, the hypothesis must be abandoned no matter
how reasonable it seems.
Use of the scientific method involves four basic steps:
1. Choosing a question to be answered
2. Formulating a hypothesis regarding the question
3. Developing a method for testing the hypothesis
4. Using the data yielded by the method to draw a conclusion regarding the
To illustrate these steps, let’s make the question to be answered “What abilities
predict which children will become good readers?” A reasonable hypothesis might
be “Kindergartners who can identify the separate sounds within words will become
better readers than those who cannot.” A straightforward method for testing this
hypothesis would be to select a group of preschoolers, test their ability to identify
the separate sounds within words, and then, several years later, test the reading
skills of the same children. Research has, in fact, shown that kindergartners who are
aware of the component sounds within words later tend to read more skillfully than
their peers who lacked this ability as kindergartners. This pattern holds true regard-
less of whether the children live in the United States, Australia, Norway, or Sweden
(Furnes & Samuelsson, 2011). These results support the conclusion that kindergart-
ners’ ability to identify sounds within words predicts their later reading skill.
The first, second, and fourth of these steps are not unique to the scientific
method. As we have seen, great thinkers of the past also asked questions, formu-
lated hypotheses, and drew conclusions that were reasonable given the evidence
available to them. What distinguishes scientific research from nonscientific ap-
proaches is the third step: the methods used to test the hypotheses. When rigor-
ously employed, these research methods yield high-quality evidence that allows
investigators to progress beyond their initial hypotheses to draw firmly grounded
The Importance of Appropriate Measurement
For the scientific method to work, researchers must use measures that are directly
relevant to the hypotheses being tested. Even measures that initially seem reason-
able sometimes turn out to be less informative than originally thought. For ex-
ample, a researcher who hypothesized that a supplemental food program would
help children suffering from malnutrition might evaluate the program on the basis
of weight gain from just before the program to just after it. However, weight is an
inadequate measure of nutrition: Providing unlimited supplies of Cheetos would
probably produce weight gain but not improve nutrition, and many people are
obese yet malnourished (Sawaya et al., 1995). Better measures of nutrition would
scientific method n an approach to
testing beliefs that involves choosing
a question, formulating a hypothesis,
testing the hypothesis, and drawing a
hypotheses n educated guesses

include whether more adequate levels of essential nutrients were present in the
children’s bloodstreams at the end of the study (Shetty, 2006).
Regardless of the particular measure used, many of the same criteria determine
whether a measure is a good one. One key criterion has already been noted—the
measure must be directly relevant to the hypothesis. Two other qualities that good
measures must possess are reliability and validity.
reliability The degree to which independent measurements of a behavior under
study are consistent is referred to as reliability. One important type of consistency,
interrater reliability, indicates how much agreement there is in the observations
of different raters who witness the same behavior. Sometimes the observations are
qualitative, as when raters classify a baby’s attachment to her mother as “secure” or
“insecure.” Other times the observations are quantitative, as when raters score on
a scale of 1 to 10 how upset babies become when they are presented with an un-
familiar noisy toy or a boisterous stranger. In both cases, interrater reliability is at-
tained when the raters’ observations are in close agreement—as when, for example,
Baby A in a group being observed for a particular behavior gets a 6 or 7 from all the
raters, Baby B gets a 3 or 4, Baby C gets an 8 or 9, and so on. Without such close
agreement, one cannot have confidence in the research findings, because there is no
way to tell which (if any) rating was accurate.
A second important type of consistency is test–retest reliability. This type of
reliability is attained when measures of a child’s performance on the same test,
administered under the same conditions, are similar on two or more occasions.
Suppose, for example, that researchers presented a vocabulary test to a group of
children on two occasions one week apart. If the test is reliable, those children who
scored highest on the first testing should also score highest on the second, because
none of the children’s vocabularies would have changed much over such a short
period. As in the example of interrater reliability, a lack of test–retest reliability
would make it impossible to know which result (if either) accurately reflected each
child’s status.
Validity The validity of a test or experiment refers to the degree to which it mea-
sures what it is intended to measure. Researchers strive for two types of validity:
internal and external. Internal validity refers to whether effects observed within
experiments can be attributed with confidence to the factor that the researcher is
testing. For example, suppose that a researcher tests the effectiveness of a type of
psychotherapy for depression by administering it to a number of depressed adoles-
cents. If three months later many of the adolescents are no longer depressed, can it
be concluded that this type of psychotherapy caused the improvement? No, because
the students’ recovery may have been due to the mere passage of time. Moods fluc-
tuate, and many adolescents who are depressed at any given time will be happier at
a later date even without psychotherapy. In this example, the passage of time is a
source of internal invalidity, because the factor believed to cause the improvement
(the psychotherapy) may have had no effect.
External validity, in contrast, refers to the ability to generalize research findings
beyond the particulars of the research in question. Studies of child development are
almost never intended to apply only to the particular children and research meth-
ods involved in a given study. Rather, the goal is to draw conclusions that apply
to children more generally. Thus, the findings of a single experiment are only the
first step in determining the external validity of the results. Additional studies with
participants from different backgrounds and with different research methods are
reliability n the degree to which inde-
pendent measurements of a given
behavior are consistent
interrater reliability n the amount of
agreement in the observations of different
raters who witness the same behavior
test–retest reliability n the degree of
similarity of a child’s performance on two
or more occasions
validity n the degree to which a test
measures what it is intended to measure
internal validity n the degree to which
effects observed within experiments
can be attributed to the factor that the
researcher is testing
external validity n the degree to which
results can be generalized beyond the
particulars of the research

invariably needed to establish the external validity of the findings. (Table 1.3 sum-
marizes the key properties of behavioral measures.)
Contexts for Gathering Data About Children
Researchers obtain data about children in three main contexts: interviews, natu-
ralistic observation, and structured observation. In the following sections, we con-
sider how gathering data in each context can help answer different questions
about children.
The most obvious way to collect data about children is to go straight to the source
and ask the children themselves about their lives. One type of interview, the struc­
tured interview, is especially useful when the goal is to collect self-reports on the
same topics from everyone being studied. For example, Valeski and Stipek (2001)
asked kindergartners and 1st-graders questions regarding their feelings about
school (How much does your teacher care about you? How do you feel when you’re
at school?) and also questions about their beliefs about their academic competence
(How much do you know about numbers? How
good are you at reading?). The children’s general
attitude toward school and their feelings about
their relationship with their teacher proved to be
positively related to their beliefs about their com-
petence in math and reading. Asking large num-
bers of children identical questions about their
feelings and beliefs provides a quick and straight-
forward way for researchers to learn about chil-
dren’s beliefs and attitudes.
A second type of interview, the clinical inter­
view, is especially useful for obtaining in-depth
information about an individual child. In this ap-
proach, the interviewer begins with a set of pre-
pared questions, but if the child says something
intriguing, the interviewer can depart from the
script to follow up on the child’s lead.
Key properties of Behavioral Measures
Property Question of Interest
Relevance to hypotheses Do the hypotheses predict in a straightforward way what should happen on
these measures?
Interrater reliability Do different raters who observe the same behavior classify or score it the
same way?
Test–retest reliability Do children who score higher on a measure at one time also score higher
on the measure at other times?
Internal validity Can effects within the experiment be attributed to the variables that the
researcher intentionally manipulated?
External validity How widely can the findings be generalized to different children in
different places at different times?
One-on-one clinical interviews like this one
can elicit unique in-depth information about
a child.
structured interview n a research pro-
cedure in which all participants are asked
to answer the same questions
clinical interview n a procedure in
which questions are adjusted in accord
with the answers the interviewee provides

The usefulness of clinical interviews can be seen in the case of Bobby, a 10-year-
old child who was assessed for symptoms of depression (Schwartz & Johnson,
1985). When the interviewer asked him about school, Bobby said that he did not
like it because the other children disliked him and he was bad at sports. As he put
it, “I’m not really very good at anything” (p. 214). To explore the source of this
sad self-description, the interviewer asked Bobby what he would wish for if three
wishes could be granted. Bobby replied, “I would wish that I was the type of boy my
mother and father want, I would wish that I could have friends, and I would wish
that I wouldn’t feel sad so much” (p. 214). Such heartrending comments provide a
sense of the painful subjective experience of this depressed child, one that would be
impossible to obtain from methods that were not tailored to the individual.
As with all contexts for collecting data, interviews have both strengths and weak-
nesses. On the positive side, they yield a great deal of data quickly and can provide
in-depth information about individual children. On the negative side, answers to
interview questions often are biased. Children (like adults) often avoid disclosing
facts that show them in a bad light, distort the way that events happened, and fail
to understand their own motivations (Wilson & Dunn, 2004). These limitations
have led many researchers to use observational methods that allow them to witness
the behavior of interest for themselves.
Naturalistic Observation
When the primary research goal is to describe how children behave in their usual
environments—homes, schools, playgrounds, and so on—naturalistic observation
is the method of choice for gathering data. In this approach, observers try to remain
unobtrusively in the background in the chosen setting, allowing them to see the
relevant behaviors while minimizing the chances that their presence will influence
those behaviors.
A classic example of naturalistic observation is Gerald Patterson’s (1982) com-
parative study of family dynamics in “troubled” and “typical” families. The troubled
families were defined by the presence of at least one child who had been labeled
“out of control” and referred for treatment by a school, court, or mental health pro-
fessional. The typical families were defined by the fact that none of the children in
them showed signs of serious behavioral difficulties. Income levels and children’s
ages were the same for the troubled and typical families.
To observe the frequency with which children and parents engaged in nega-
tive behaviors—teasing, yelling, whining, criticizing, and so on—research assis-
tants repeatedly observed dinnertime interactions in both
troubled and typical homes. To accustom family mem-
bers to his or her presence, the research assistant for each
family made several home visits before beginning to col-
lect data.
The researchers found that the behaviors and attitudes
of both parents and children in the troubled families dif-
fered strikingly from those of their counterparts in the
typical families. Parents in the troubled families were
more self-absorbed and less responsive to their children
than were parents in the typical households. Children in
the troubled families responded to parental punishment
by becoming more aggressive, whereas children in the
typical households responded to punishment by becoming MO
/ D
psychologists sometimes observe family
interactions around the dinner table,
because mealtime comments can evoke
strong emotions.
naturalistic observation n examina-
tion of ongoing behavior in an environ-
ment not controlled by the researcher

less aggressive. In the troubled families, interactions often fell into a vicious cycle
in which:
n The child acted in a hostile or aggressive manner, for example, by defying a
parent’s request to clean up his or her room.
n The parent reacted angrily, for example, by shouting at the child to obey.
n The child escalated the level of hostility, for example, by yelling back.
n The parent ratcheted up the aggression even further, perhaps by spanking the
As Patterson’s study suggests, naturalistic observations are particularly useful for
illuminating everyday social interactions, such as those between children and
Although naturalistic observation can yield detailed information about certain
aspects of children’s everyday lives, it also has important limitations. One is that
naturally occurring contexts vary on many dimensions, so it is often hard to know
which ones influenced the behavior of interest. For example, it was clear in the
Patterson study that the interactions of troubled families differed from those of the
more harmonious families, but the interactions and family histories differed in so
many ways that it was impossible to specify their contributions to the current situ-
ation. A second limitation of naturalistic studies is that many behaviors of interest
occur only occasionally in the everyday environment, which reduces researchers’
opportunities to learn about them. A means for overcoming both limitations is the
method known as structured observation.
Structured Observation
When using structured observation, researchers design a situation that will elicit
behavior that is relevant to a hypothesis and then observe how different children
behave in that situation. The researchers then relate the observed behaviors to char-
acteristics of the child, such as age, sex, or personality, and to the child’s behavior in
other situations that are also observed.
In one such study, Kochanska, Coy, and Murray (2001) investigated the links
between 2- and 3-year-olds’ compliance with their mother’s requests to forego ap-
pealing activities and their compliance with her requests that they participate in
unappealing ones. Mothers brought their toddlers to a laboratory room that had
a number of especially attractive toys sitting on a shelf and a great many less at-
tractive toys scattered around the room. The experimenter asked each mother to
tell her child that he or she could play with any of the toys except the ones on the
shelf. Raters observed the children through a one-way mirror over the next few
minutes and classified them as complying with their mother’s request wholeheart-
edly, grudgingly, or not at all. Then the experimenter asked the mother to leave
the room and observed whether the child played with the “forbidden” toys in the
mother’s absence.
The researchers found that children who had complied wholeheartedly in the
first instance tended to avoid playing with the forbidden toys for a longer time in
the second. Moreover, these children were also more likely to comply with their
mother’s request that they put away the many toys on the floor after she left the
room. When retested near their 4th birthday, most children showed the same type
of compliance as they had as toddlers. Overall, the results indicated that the quality
of young children’s compliance with their mother’s requests is a somewhat stable,
general property of the mother–child relationship.
structured observation n a method
that involves presenting an identical situ-
ation to each child and recording the
child’s behavior
Temptation is everywhere, but children who
are generally compliant with their moth-
er’s requests when she is present are also
more likely to resist temptation when she is
absent (like this boy, the nephew of one of
the authors, whose reach, despite appear-
ances, stopped just short of the cake).

This type of structured observation offers an important advantage over natural-
istic observation: it ensures that all the children being studied encounter identical
situations. This allows direct comparisons of different children’s behavior in a given
situation and, as in the research just discussed, also makes it possible to establish
the generality of each child’s behavior across different tasks. On the other hand,
structured observation does not provide as extensive information about individual
children’s subjective experience as do interviews, nor can it provide the open-ended,
everyday kind of data that naturalistic observation can yield.
As these examples suggest, which data-gathering approach is best depends on
the goals of the research. (Table 1.4 summarizes the advantages and disadvantages
of interviews, naturalistic observation, and structured observation as contexts for
gathering data.)
Correlation and Causation
People differ along an infinite number of variables, that is, attributes that vary
across individuals and situations, such as age, sex, activity level, socioeconomic sta-
tus, particular experiences, and so on. A major goal of child-development research
is to determine how these and other major variables are related to one another,
both in terms of associations and in terms of cause–effect relations. In the follow-
ing sections, we consider the research designs that are used to examine each type
of relation.
Correlational Designs
The primary goal of studies that use correlational designs is to determine whether
children who differ in one variable also differ in predictable ways in other variables.
For example, a researcher might examine whether toddlers’ aggressiveness is related
to the number of hours they spend in day care or whether adolescents’ popularity
is related to their self-control.
advantages and Disadvantages of Three contexts for Gathering Data
Features Advantages Disadvantages
Interview Children answer questions asked
either in person or on a questionnaire.
Can reveal children’s subjective experience.
Structured interviews are inexpensive
means for collecting in-depth data about
Clinical interviews allow flexibility for
following up unexpected comments.
Reports are often biased to reflect favorably on
Memories of interviewees are often inaccurate
and incomplete.
Prediction of future behaviors often is
Activities of children in everyday
settings are observed.
Useful for describing behavior in everyday
Helps illuminate social interaction processes.
Difficult to know which aspects of situation are
most influential.
Limited value for studying infrequent behaviors.
Children are brought to laboratory and
presented prearranged tasks.
Insures that all children’s behaviors are
observed in same context.
Allows controlled comparison of children’s
behavior in different situations.
Context is less natural than in naturalistic
Reveals less about subjective experience than
variables n attributes that vary across
individuals and situations, such as age,
sex, and popularity
correlational designs n studies
intended to indicate how two variables are
related to each other

The association between two variables is known as their correlation. When
variables are strongly correlated, knowing a child’s score on either variable allows
accurate prediction of the child’s score on the other. For example, the fact that
the number of hours per week that children spend reading correlates highly with
their reading-test scores (Guthrie et al., 1999) means that a child’s reading-test
score can be accurately predicted if one knows how much time the child spends
reading. It also means that the number of hours the child spends reading can be
predicted if one knows the child’s reading-test score.
Correlations range from 1.00, the strongest positive correlation, to 21.00, the
strongest negative correlation. The direction is positive when high values of one
variable are associated with high values of the other and low values of one are as-
sociated with low values of the other; the direction is negative when high values of
one are associated with low values of the other. Thus, the correlation between time
spent reading and reading-test scores is positive, because children who spend high
amounts of time reading also have high reading-test scores; the correlation between
obesity and running speed is negative, because the more obese the child, the slower
his or her running speed. (For a more in-depth discussion of how correlations work,
see the Appendix.)
Correlation Does Not Equal Causation
When two variables are strongly correlated and there is a plausible cause–effect
relation between them, it often is tempting to infer that one causes the other.
However, this inference is not justified, for two reasons. The first is the direction­
of­causation problem: a correlation does not indicate which variable is the cause
and which variable is the effect. In the above example of the correlation between
time spent reading and reading achievement, greater time spent reading might
cause increased reading achievement. On the other hand, the cause–effect relation
could run in the opposite direction: greater reading skill might cause children to
spend more time reading, because reading faster and with greater comprehension
makes reading more enjoyable.
The second reason that correlation does not imply causation is the third­
variable problem: the correlation between two variables may actually be the result
of some third, unspecified variable. In the reading example, for instance, rather than
greater reading achievement being caused by greater reading time, or vice versa,
both of these aspects of reading could be caused by growing up in a family that val-
ues knowledge and intelligence.
Recognizing that correlation does not imply causation is crucial for interpret-
ing accounts of research. Even findings published in prestigious research journals
can easily be misinterpreted. For example, based on a correlation between children
younger than 2 years sleeping with a night-light and their later becoming near-
sighted, an article in the prestigious journal Nature concluded that the light was
harmful to visual development (Quinn et al., 1999). Not surprisingly, the claim
received considerable publicity in the popular media (e.g., Torassa, 2000). Sub-
sequent research, however, showed that the inference about causation was wrong.
What actually seems to have happened is that the nearsighted infants generally
had nearsighted parents, and the nearsighted parents, for unknown reasons, more
often placed nightlights in their infants’ rooms (Gwiazda et al., 2000; Zadnik et
al., 2000). As the example illustrates, even seemingly straightforward inferences of
causation, based on correlational evidence, frequently prove to be wrong.
correlation n the association between
two variables
direction-of-causation problem n
the concept that a correlation between
two variables does not indicate which, if
either, variable is the cause of the other
third-variable problem n the concept
that a correlation between two variables
may stem from both being influenced by
some third variable

If correlation does not imply causation, why do researchers often use correla-
tional designs? One major reason is that the influence of many variables of great
interest—age, sex, race, and social class among them—cannot be studied experi-
mentally (see the next section) because researchers cannot manipulate them; that
is, they cannot assign participants to one sex or another, to one SES or another,
and so on. Consequently, these variables can only be studied through correlational
methods. Correlational designs are also of great use when the goal is to describe re-
lations among variables rather than to identify cause–effect relations among them.
If, for example, the research goal is to discover how moral reasoning, empathy, anxi-
ety, and popularity are related to one another, correlational designs would almost
certainly be employed.
Experimental Designs
If correlational designs are insufficient to indicate cause–effect relations, what type
of approach is sufficient? The answer is experimental designs. The logic of ex-
perimental designs can be summarized quite simply: If children in one group are
exposed to a particular experience and subsequently behave differently from a com-
parable group of children who were not exposed to the experience or were exposed
to a different experience, then the subsequent differences in behavior must have
resulted from the differences in experience.
Two techniques are crucial to experimental designs: random assignment of par-
ticipants to groups, and experimental control. Random assignment involves assign-
ing the participants to one experimental group or another according to chance so
that the groups are comparable at the outset. This comparability is crucial for being
able to infer that it was the varying experiences to which the groups were exposed
in the experiment that caused the later differences between them. Otherwise, those
differences might have arisen from some preexisting difference between the people
in the groups.
Say, for example, that researchers wanted to compare the effectiveness of two
interventions for helping depressed mothers improve their relationship with their
infant—providing the mothers with home visits from trained therapists versus
providing them with supportive phone calls from such therapists. If the research-
ers provided the home visits to families in one neighborhood and the supportive
phone calls to families in another neighborhood, it would be unclear whether any
differences in mother–infant relationships following the experiment were
caused by differences between the effectiveness of the two types of support
or by differences between the families in the two areas. Depressed mothers
in one neighborhood might suffer from less severe forms of depression than
mothers in the other, or they might have greater access to other support, such
as close families, mental health centers, or parenting programs.
In contrast, when groups are created through random assignment and
include a reasonably large number of participants (typically 20 or more
per group), initial differences between the groups tend to be minimal. For
example, if 40 families with mothers who suffer from depression are di-
vided randomly into two experimental groups, each group is likely to have
roughly equal numbers of families from each neighborhood. Similarly, each
group is likely to include a few mothers who are extremely depressed, a few
with mild forms of depression, and many in between, as well as a few in-
fants who have been severely affected by their mother’s depression, a few RO
Depressed mothers often have difficulty pro-
viding sensitive parenting; home visits from
trained therapists can help alleviate this
experimental designs n a group of
approaches that allow inferences about
causes and effects to be drawn
random assignment n a procedure in
which each child has an equal chance of
being assigned to each group within an

who have been minimally affected, and many in be-
tween. The logic implies that groups created through
random assignment should be comparable on all vari-
ables except the different treatment that people in the
experimental groups encounter during the experi-
ment. Such an experiment was in fact conducted, and
it showed that home visits helped depressed mothers
more than supportive phone calls did (Van Doesum
et al., 2008).
The second essential characteristic of an experi-
mental design, experimental control, refers to the
ability of the researcher to determine the specific ex-
periences that children in each group encounter dur-
ing the study. In the simplest experimental design, one
with two conditions, the groups are often referred to
as the “experimental group” and the “control group.”
Children in the experimental group are presented
with the experience of interest; children in the control
group are treated identically except that they are not
presented with the experience of interest or are pre-
sented with a different experience that is expected to
have less effect on the variables being tested.
The experience that children in the experimental
group receive, and that children in the control group do not receive, is referred to as
the independent variable. The behavior that is hypothesized to be affected by ex-
posure to the independent variable is referred to as the dependent variable. Thus, if
a researcher hypothesized that showing schoolchildren an anti-bullying film would
reduce school bullying, the researcher might randomly assign some children in a
school to view the film and other children in the same school to view a film about
a different topic. In this case, the anti-bullying film would be the independent vari-
able, and the amount of bullying after the children watched it would be the depen-
dent variable. If the independent variable had the predicted effect, children who saw
the anti-bullying film would show less bullying after watching it than children who
saw the other film.
One illustration of how experimental designs allow researchers to draw con-
clusions about causes and effects is a study that tested the hypothesis that televi-
sion shows running in the background lower the quality of infants’ and toddlers’
play (Schmidt et al., 2008). The independent variable was whether or not a televi-
sion program was on in the room where the participants were playing; the depen-
dent variables were a variety of measures of children’s attention to the television
program and of the quality of their play. The television program that was playing
was Jeopardy!, which presumably would have been of little interest to the 1- and
2-year-olds in the study; indeed, they looked at it an average of only once per
minute and only for a few seconds at a time. Nonetheless, the television show
disrupted the children’s play, reducing the length of play episodes and the chil-
dren’s focus on their play. These findings indicate that there is a causal, and nega-
tive, relation between background exposure to television shows and the quality of
young children’s play.
Experimental designs are the method of choice for establishing causal rela-
tions, a central goal of scientific research. However, as noted earlier, experimental
The quality of infants’ and toddlers’ play
is adversely affected by a television being
on in the same room. This is true for even
the most precocious children, such as
this 1-year-old, the grandson of one of the
experimental control n the ability of
researchers to determine the specific
experiences that children have during the
course of an experiment
experimental group n a group of chil-
dren in an experimental design who are
presented the experience of interest
control group n the group of children
in an experimental design who are not
presented the experience of interest but
in other ways are treated similarly
independent variable n the experience
that children in the experimental group
receive and that children in the control
group do not receive
dependent variable n a behavior that
is measured to determine whether it is
affected by exposure to the independent

designs cannot be applied to all issues of interest. For example, hypotheses about
why boys tend to be more physically aggressive than girls cannot be tested experi-
mentally because gender cannot be randomly assigned to children. In addition,
many experimental studies are conducted in laboratory settings; this improves
experimental control but can raise doubts about the external validity of the find-
ings, that is, whether the findings from the lab apply to the outside world. (The
advantages and disadvantages of correlational and experimental designs are sum-
marized in Table 1.5.)
Designs for Examining Development
A great deal of research on child development focuses on the ways in which chil-
dren change or remain the same as they grow older and gain experience. To study
development over time, investigators use three types of research designs: cross-
sectional, longitudinal, and microgenetic.
Cross-Sectional Designs
The most common and easiest way to study changes and continuities with age
is to use the cross­ sectional approach. This method compares children of dif-
ferent ages on a given behavior, ability, or characteristic, with all the children
being studied at roughly the same time—for example, within the same month.
In one cross-sectional study, Evans, Xu, and Lee (2011) examined the develop-
ment of lying in Chinese 3-, 4-, and 5-year-olds. The children played a game
in which, to win a prize, they needed to guess the type of object hidden under
an upside-down paper cup. However, before the child could guess, the experi-
menter left the room after telling the child not to peek while she was gone.
The cup was so fully packed with candies that if the child peeked, some would
spill out and it would be virtually impossible for the child to put them all back
under the cup.
At all ages, many children peeked and then denied doing so. However, 5-year-
olds lied more often, and their lies were cleverer. For example, many 5-year-olds
explained away the presence of candies on the table by saying that they accidentally
knocked over the cup with their elbow; other 5-year-olds destroyed the evidence
by eating it. Three-year-olds were the least-skilled fibbers, generating implausible
advantages and Disadvantages of correlational and experimental Designs
Type of Design Features Advantages Disadvantages
Correlational Comparison of existing groups of children
or examination of relations among each
child’s scores on different variables.
Only way to compare many groups of interest
(boys–girls, rich–poor, etc.).
Only way to establish relations among many
variables of interest (IQ and achievement,
popularity and happiness, etc.).
Third-variable problem.
Direction-of-causation problem.
Experimental Random assignment of children to groups
and experimental control of procedures
presented to each group.
Allows causal inferences because design rules
out direction-of-causation and third-variable
Allows experimental control over the exact
experiences that children encounter.
Need for experimental control often leads
to artificial experimental situations.
Cannot be used to study many differences
and variables of interest, such as age, sex,
and temperament.
cross-sectional design n a research
method in which children of different
ages are compared on a given behavior or
characteristic over a short period

excuses such as that some other child entered the room and knocked over the cup
or that the candies came out by themselves.
Cross-sectional designs are useful for revealing similarities and differences
between older and younger children. However, they do not yield information
about the stability of behavior over time or about the patterns of change shown
by individual children. This is where longitudinal approaches are especially
Longitudinal Designs
The longitudinal approach involves following a group of children over a sub-
stantial period (usually at least a year) and observing changes and continuities in
these children’s development at regular intervals during that time. In one lon-
gitudinal study, Brendgen and colleagues (2001) examined children’s popularity
with classmates each year from the time they were
7-year-olds to the time they were 12-year-olds. The
popularity of most children proved to be quite sta-
ble over this period; a substantial number of chil-
dren were popular in the large majority of years,
and quite a few others were unpopular throughout.
At the same time, some individuals showed idio-
syncratic patterns of change from year to year; the
same child might be popular at age 8, unpopular at
age 10, and of average popularity at age 12. Such
findings about the stability of individual differences
over time and about individual children’s patterns of
change could only have been obtained in a longitu-
dinal design.
If longitudinal designs are so useful for reveal-
ing stability and change over time, why are cross-
sectional designs more common? The reasons are
mainly practical. Studying the same children over
long periods involves the difficult task of locating the children for each re-exami-
nation. Inevitably, some of the children move away or stop participating for other
reasons. Such loss of participants may call into question the validity of the find-
ings, because the children who do not continue may differ from those who par-
ticipate throughout. Another threat to the validity of longitudinal designs is the
possible effects of the repeated testing. For example, repeatedly taking IQ tests
could familiarize children with the type of items on the tests, thus improving the
children’s scores. For these reasons, longitudinal designs are used primarily when
the main issues are stability and change in individual children over time—issues
that can be studied only longitudinally. When the central developmental issue
involves age-related changes in typical performance, cross-sectional studies are
more commonly used.
Microgenetic Designs
An important limitation of both cross-sectional and longitudinal designs is that
they provide only a broad outline of the process of change. Microgenetic designs,
in contrast, are specifically designed to provide an in-depth depiction of the pro-
cesses that produce change (Miller & Coyle, 1999; Siegler, 2006). The basic idea
Being excluded is no fun for anyone. Longi-
tudinal research has been used to determine
whether the same children are unpopular
year after year or whether popularity changes
over time.
longitudinal design n a method of
study in which the same children are
studied twice or more over a substantial
length of time
microgenetic design n a method of
study in which the same children are
studied repeatedly over a short period

of this approach is to recruit children who are thought to be on the verge of an
important developmental change, heighten their exposure to the type of experi-
ence that is believed to produce the change, and then intensively study the change
as it is occurring. Microgenetic designs are like longitudinal ones in repeatedly test-
ing the same children over time. They differ in that microgenetic studies typically
include a greater number of sessions presented over a shorter time than in a
longitudinal study.
Siegler and Jenkins (1989) used a microgenetic design to study how young
children discover the counting­on strategy for adding two small numbers.
This strategy involves counting up from the larger addend the number of
times indicated by the smaller addend; for example, when asked the answer
to 3 1 5, a child who was counting-on would start from the addend 5 and
say or think “6, 7, 8” before answering “8.” Prior to discovering this strategy,
children usually solve addition problems by counting from 1. Counting from
the larger addend rather than from 1 reduces the amount of counting, pro-
ducing faster and more accurate solutions.
To observe the discovery process, the researchers selected 4- and 5-year-
olds who did not yet use counting-on but who knew how to add by count-
ing from 1. Over an 11-week period, these children received many addition
problems—far more than they would normally encounter before entering
school—and each child’s behavior was videotaped for every problem. This
approach allowed the researchers to identify exactly when each child discov-
ered the counting-on strategy.
Examination of the problems immediately preceding the discovery re-
vealed a surprising fact: necessity is not always the mother of invention.
Quite a few children discovered the counting-on strategy while working on
easy problems that they previously had solved correctly by counting from 1.
The microgenetic method also revealed that children’s very first use of the new
strategy often was accompanied by insight and excitement, like that shown by
Experimenter: How much is 6 1 3?
Lauren: (long pause) 9.
E: OK, how did you know that?
L: I think I said . . . I think I said . . . oops, um . . . 7 was 1, 8 was 2, 9 was 3.
E: How did you know to do that? Why didn’t you count 1, 2, 3, 4, 5, 6, 7, 8, 9?
L: (with excitement) ’Cause then you have to count all those numbers.
(Siegler & Jenkins, 1989, p. 66)
Despite her insightful explanation of counting-on and her excitement over
discovering it, Lauren, and most other children, only gradually increased their
use of the new strategy on subsequent problems. Many other microgenetic stud-
ies have also shown that generalization of new strategies tends to be slow (Kuhn
& Franklin, 2006).
As this example illustrates, microgenetic methods provide insight into the pro-
cess of change over brief periods. However, unlike standard longitudinal methods,
microgenetic designs do not yield information about stability and change over long
periods. They therefore are typically used when the basic pattern of age-related
change has already been established and the goal becomes to understand how the
changes occur. (Table 1.6 outlines the strengths and weaknesses of the three ap-
proaches to studying changes with age and experience: cross-sectional, longitudi-
nal, and microgenetic designs.)
. /
Discovering how to solve problems is an
inherently rewarding experience. Micro-
genetic designs can provide insight into both
the process of discovery and children’s emo-
tional response to it.
counting-on strategy n counting up
from the larger addend the number of
times indicated by the smaller addend

Ethical Issues in Child-Development Research
All research with human beings raises ethical issues, and this is especially the case
when the research involves children. Researchers have a vital responsibility to antici-
pate potential risks that the children in their studies may encounter, to minimize such
risks, and to make sure that the benefits of the research outweigh any potential harm.
The Society for Research on Child Development, an organization devoted to
research on children, has formulated a code of ethical conduct for investigators to
follow (SRCD Governing Council, 2007). Some of the most important ethical
principles in the code are:
n Be sure that the research does not harm children physically or psychologically.
n Obtain informed consent for participating in the research, preferably in
writing, from parents or other responsible adults and also from children if
they are old enough that the research can be explained to them. The experi-
menter should inform children and relevant adults of all aspects of the research
that might influence their willingness to participate and should explain that
refusing to participate will not result in any adverse consequences to them.
n Preserve individual participants’ anonymity, and do not use information for
purposes other than that for which permission was given.
n Discuss with parents or guardians any information yielded by the investigation
that is important for the child’s welfare.
n Try to counteract any unforeseen negative consequences that arise during the
n Correct any inaccurate impressions that the child may develop in the course of
the study. When the research has been completed, explain the main findings to
participants at a level they can understand.
Recognizing the importance of such ethical issues, universities and governmental
agencies have established institutional review boards made up of independent scien-
tists and sometimes others from the community. These boards evaluate the proposed
research to ensure that it does not violate ethics guidelines. However, the individual
investigator is in the best position to anticipate potential problems and bears the
ultimate responsibility for seeing that his or her study meets high ethical standards.
advantages and Disadvantages of Designs for Studying Development
Design Features Advantages Disadvantages
Cross-sectional Children of different ages are
studied at a single time.
Yields useful data about differences among
age groups.
Quick and easy to administer.
Uninformative about stability of individual
differences over time.
Uninformative about similarities and differences
in individual children’s patterns of change.
Longitudinal Children are examined repeatedly
over a prolonged period.
Indicates the degree of stability of individual
differences over long periods.
Reveals individual children’s patterns of
change over long periods.
Difficult to keep all participants in study.
Repeatedly testing children can threaten
external validity of study.
Microgenetic Children are observed intensively
over a relatively short period while
a change is occurring.
Intensive observation of changes while they are
occurring can clarify process of change.
Reveals individual change patterns over short
periods in considerable detail.
Does not provide information about typical
patterns of change over long periods.
Does not yield data regarding change patterns
over long periods.

The scientific method, in which all hypotheses are treated as potentially incorrect, has al-
lowed contemporary understanding of child development to progress well beyond the under-
standing of even the greatest thinkers of the past. This progress has been built on a base of
four types of innovations:
1. Measures that are directly relevant to the main hypotheses of the study
2. Data-gathering situations that yield useful information about children’s behavior, such as
interviews, naturalistic observations, and structured observations
3. Designs that allow identification of associations and cause–effect relations among vari-
ables, notably correlational and experimental designs
4. Designs that allow analysis of the continuities and changes that occur with age and expe-
rience, notably cross-sectional, longitudinal, and microgenetic designs
Conducting scientific experiments also requires meeting high ethical standards, includ-
ing not in any way harming the children who participate; obtaining informed consent for their
participation in the research; preserving anonymity of all participants; and, after the study, ex-
plaining the findings to parents and, when possible, to children, at a level they can understand.
chapter summary:
Why Study Child Development?
n Learning about child development is valuable for many rea-
sons: it can help us become better parents, inform our views
about social issues that affect children, and improve our under-
standing of human nature.
Historical Foundations of the Study of Child
n Great thinkers such as Plato, Aristotle, Locke, and
Rousseau raised basic questions about child development
and proposed interesting hypotheses about them, but they
lacked the scientific methods to answer them. Early scientific
approaches, such as those of Freud and Watson, began the
movement toward modern research-based theories of child
Enduring Themes in Child Development
n The field of child development is an attempt to answer a set of
fundamental questions:
1. How do nature and nurture together shape development?
2. How do children shape their own development?
3. In what ways is development continuous, and in what ways
is it discontinuous?
4. How does change occur?
5. How does the sociocultural context influence development?
6. How do children become so different from one another?
7. How can research promote children’s well-being?
n Every aspect of development, from the most specific behavior
to the most general trait, reflects both people’s biological
endowment (their nature) and the experiences that they have
had (their nurture).
n Even infants and young children actively contribute to their
own development through their attentional patterns, use of
language, and choices of activities.
n Many developments can appear either continuous or discontin-
uous, depending on how often and how closely we look at them.
n The mechanisms that produce developmental changes involve
a complex interplay among experiences, genes, and brain struc-
tures and activities.
n The contexts that shape development include the people with
whom children interact directly, such as family and friends;
the institutions in which they participate, such as schools and
religious organizations; and societal beliefs and values, such as
those related to race, ethnicity, and social class.
n Individual differences, even among siblings, reflect differences
in children’s genes, in their treatment by other people, in their
interpretations of their own experiences, and in their choices of
n Principles, findings, and methods from child-development
research are being applied to improve the quality of children’s
Methods for Studying Child Development
n The scientific method has made possible great advances in
understanding children. It involves choosing a question, for-
mulating a hypothesis relevant to the question, developing
a method to test the hypothesis, and using data to decide
whether the hypothesis is correct.

n For a measure to be useful, it must be directly relevant to the
hypotheses being tested, reliable, and valid. Reliability means
that independent observations of a given behavior are consis-
tent. Validity means that a measure assesses what it is intended
to measure.
n Among the main situations used to gather data about children
are interviews, naturalistic observation, and structured obser-
vation. Interviews are especially useful for revealing children’s
subjective experience. Naturalistic observation is particu-
larly useful when the primary goal is to describe how children
behave in their everyday environments. Structured observation
is most useful when the main goal is to describe how different
children react to the identical situation.
n Correlation does not imply causation. The two differ in that
correlations indicate the degree to which two variables are
associated, whereas causation indicates that changing the value
of one variable will change the value of the other.
n Correlational designs are especially useful when the goal is to
describe relations among variables or when the variables of
interest cannot be manipulated because of technical or prac-
tical considerations.
n Experimental designs are especially valuable for revealing the
causes of children’s behavior.
n Data about development can be obtained through cross-
sectional designs (examining different children of different
ages), through longitudinal designs (examining the same chil-
dren at different ages), or through microgenetic designs (pre-
senting the same children repeated relevant experiences over
a relatively short period and analyzing the change process in
n It is vital for researchers to adhere to high ethical standards.
Among the most important ethical principles are striving to
ensure that the research does not harm children physically or
psychologically; obtaining informed consent from parents and,
where possible, from children; preserving participants’ ano-
nymity; and correcting any inaccurate impressions that chil-
dren form during the study.
Critical Thinking Questions
1. Do children have different natures, or are differences among
children purely due to differences in their experiences? What
personal observations, research findings, and reasoning lead
to your conclusion?
2. Why do you think that the children who spent less than 6
months in orphanages in Romania were able to catch up
physically, intellectually, and socially, whereas those who
spent more time there have not been able to catch up? Do
you think that they will catch up in the future?
3. In what ways is it fortunate and in what ways unfortunate that
children shape their own development to a substantial extent?
4. Did reading about sleeping arrangements in the United
States and in other cultures influence what you would like to
do if you have children? Explain why or why not.
5. Given what you learned in this chapter about child-
development research, can you think of practical applications
of the research (other than the ones described) that seem
both feasible and important to you?
Key Terms
clinical interview, p. 25
cognitive development, p. 15
continuous development, p. 13
control group, p. 31
correlation, p. 29
correlational designs, p. 28
counting-on strategy, p. 34
cross-sectional design, p. 32
dependent variable, p. 31
direction-of-causation problem, p. 29
discontinuous development, p. 13
epigenetics, p. 11
experimental control, p. 31
experimental designs, p. 30
experimental group, p. 31
external validity, p. 24
genome, p. 11
hypotheses, p. 23
independent variable, p. 31
internal validity, p. 24
interrater reliability, p. 24
longitudinal design, p. 33
methylation, p. 12
microgenetic design, p. 33
naturalistic observation, p. 26
nature, p. 10
neurotransmitters, p. 17
nurture, p. 11
random assignment, p. 30
reliability, p. 24
scientific method, p. 23
sociocultural context, p. 17
socioeconomic status (SES), p. 19
stage theories, p. 15
structured interview, p. 25
structured observation, p. 27
test–retest reliability, p. 24
third-variable problem, p. 29
validity, p. 24
variables, p. 28

Mother and Child

Prenatal Development
and the Newborn Period
n Prenatal Development
Box 2.1: A Closer Look Beng Beginnings
Box 2.2: Individual Differences The First—and Last—
Sex Differences
Developmental Processes
Box 2.3: A Closer Look Phylogenetic Continuity
Early Development
An Illustrated Summary of Prenatal Development
Fetal Behavior
Fetal Experience
Fetal Learning
Hazards to Prenatal Development
Box 2.4: Applications Face Up to Wake Up
n The Birth Experience
Diversity of Childbirth Practices
n The Newborn Infant
State of Arousal
Negative Outcomes at Birth
Box 2.5: Applications Parenting a Low-Birth-Weight
n Chapter Summary
chapter 2:

Picture the following scenario: a developmental psychologist is investigat­ing a very young research participant’s perceptual capacities and ability to learn from experience. First, she plays a loud sound near the participant’s ear. She notes that the participant moves vigorously in response and con­cludes that the participant can hear the sound. Now she continues to play
the same tone, over and over. As everyone else in the lab gets tired of repeatedly
hearing the same sound, so, apparently, does the participant, who responds less and
less to the repetitions of the sound and eventually does not react to it at all. Has
the participant learned to recognize the sound, or just gone to sleep? To find out,
the researcher next presents a different sound, to which the participant responds
vigorously. The participant seems to have recognized a difference between the new
sound and the old one, suggesting that the participant has experienced some simple
learning. Wanting to see if the participant can learn something more complex, and
in a natural setting, the researcher sends the participant home, asking the partici­
pant’s mother to read aloud from a Dr. Seuss book for several minutes each day for
six weeks. The idea is to see whether the participant later shows any recognition of
the passages that were read. But before the researcher can test the participant again,
something quite important happens: the participant is born!
This scenario is not at all fanciful. Indeed, as you will discover later in this chap­
ter, it is an accurate description of a fascinating and informative study that helped
to revolutionize the scientific understanding of prenatal development (DeCasper
& Spence, 1986). As you will also discover in this chapter, researchers have been
asking many questions about the sensory and learning capabilities of fetuses. They
have been finding that while in the womb, fetuses can detect a range of stimuli
coming from the outside world, and that they can learn from these experiences and
be affected by them after birth.
In this chapter, we will examine the extraordinary course of prenatal develop­
ment—a time of astonishingly rapid and dramatic change. In addition to discussing
the normal processes involved in prenatal development, including fetal learning, we
will consider some of the ways in which these processes can be disrupted by en­
vironmental hazards. We will also examine the birth process and what the infant
experiences during this dramatic turning point, as well as some of the most salient
aspects of neonatal behavior. Finally, we will outline issues associated with prema­
ture birth.
In our discussion of the earliest periods of development, most of the themes
we described in Chapter 1 will play prominent roles. The most notable will be
nature and nurture, as we emphasize how every aspect of development before
birth results from the continual interplay of biological and environmental fac­
tors. The active child theme will also be featured, because the activity of the fetus
contributes in numerous vital ways to its development. In fact, as you will see,
normal prenatal development depends on certain fetal behaviors. Another theme
we will highlight is the sociocultural context of prenatal development and birth.
There is substantial cultural variation in how people think about the beginning
of life and how they handle the birth process. The theme of individual differences
comes into play at many points, starting with sex differences in survival rates
from conception on. The continuity/discontinuity theme is also prominent: despite
the dramatic contrast between prenatal and postnatal life, the behavior of new­
borns shows clear connections to their behavior and experience inside the womb.
Finally, the theme of research and children’s welfare is central to our discussion of
n Nature and Nurture
n The Active Child
n The Sociocultural Context
n Individual Differences
n Continuity/Discontinuity
n Research and Children’s

PREnAtAl DEvElOPMEnt n 41
how poverty can affect prenatal development and birth outcomes, as well as to
our description of intervention programs designed to foster healthy development
for preterm infants.
Prenatal Development
Hidden from view, the process of prenatal development has always been mysteri­
ous and fascinating, and beliefs about the origins of human life and development
before birth have been an important part of the lore and traditions of all societies.
(Box 2.1 describes one set of cultural beliefs about the beginning of life that is quite
unlike those of Western societies.)
When we look back in history, we see great differences in how people have
thought about prenatal development. In the fourth century b.c.e., Aristotle posed
the fundamental question about prenatal development that was to underlie West­
ern thought about it for the next 15 centuries: Does prenatal life start with the
new individual already preformed, composed of a full set of tiny parts, or do the
many parts of the human body develop in succession? Aristotle rejected the idea
Few topics have generated more intense
debate and dispute in the United States
in recent years than the issue of when life
begins—at the moment of conception, the
moment of birth, or sometime in between.
The irony is that few who engage in this
debate recognize how complex the issue is
or the degree to which societies throughout
the world have different views on it.
Consider, for example, the perspective
of the Beng, a people in the Ivory Coast of
West Africa, who believe that every newborn
is a reincarnation of an ancestor (Gottlieb,
2004). According to the Beng, in the first
weeks after birth, the ancestor’s spirit, its
wru, is not fully committed to an earthly life
and therefore maintains a double existence,
traveling back and forth between the every-
day world and wrugbe, or “spirit village.”
(The term can be roughly translated as “af-
terlife,” but “before-life” might be just as
appropriate.) It is only after the umbilical
stump has dropped off that the newborn is
considered to have emerged from wrugbe
and to be a person. If the newborn dies be-
fore this point, there is no funeral, for the
infant’s passing is perceived as a return to
the wrugbe.
These beliefs underlie many aspects of
Beng infant-care practices. One is the fre-
quent application of an herbal mixture to the
newborn’s umbilical stump to hasten its dry-
ing out and dropping off. In addition, there is
the constant danger that the infant will be-
come homesick for its life in wrugbe and de-
cide to leave its earthly existence. To prevent
this, parents try to make their babies com-
fortable and happy so they will want to stay in
this life. Among the many recommended pro-
cedures is elaborately decorating the infant’s
face and body to elicit positive attention from
others. Sometimes diviners are consulted,
especially if the baby seems to be unhappy;
a common diagnosis for prolonged crying is
that the baby wants a different name—the
one from its previous life in wrugbe.
So when does life begin for the Beng? In
one sense, a Beng individual’s life begins
well before birth, since he or she is a rein-
carnation of an ancestor. In another sense,
however, life begins sometime after birth,
when the individual is considered to have
become a person.
BOX 2.1: a closer look
The mother of this Beng baby has spent con-
siderable time painting the baby’s face in an
elaborate pattern. She does this every day in
an effort to make the baby attractive so other
people will help keep the baby happy in this

42 n chapTer 2 PREnAtAl DEvElOPMEnt AnD thE nEwBORn PERIOD
of preformation in favor of what he termed epigenesis—the emergence of new
structures and functions during development (we will revisit this idea in Chapter
3 in its more modern form, epigenetics). Seeking support for his idea, he took what
was then a very unorthodox step: he opened fertile chicken eggs to observe chick
organs in various stages of development. Nevertheless, the idea of preformation
persisted long after Aristotle, degenerating into a dispute about whether the mini­
ature, preformed human was lodged inside the mother’s egg or the father’s sperm
(see Figure 2.1).
The notion of preformation may strike you as simpleminded. Remember, how­
ever, that our ancient forebears had no way of knowing about the existence of cells
and genes or about behavioral development in the womb. Many of the mysteries
that perplexed our ancestors have now been solved, but as is always true in science,
new mysteries have replaced them.
Each of us originated as a single cell that resulted from the union of two highly
specialized cells—a sperm from our father and an egg from our mother. These
gametes, or germ cells, are unique not only in their function but also in the fact
that each one contains only half the genetic material found in other cells. Gametes
are produced through meiosis, a special type of cell division in which the eggs and
sperm receive only one member from each of the 23 chromosome pairs contained
in all other cells of the body. This reduction to 23 chromosomes in each gamete is
necessary for reproduction, because the union of egg and sperm must contain the
normal amount of genetic material (23 pairs of chromosomes). A major difference
in the formation of these two types of gametes is the fact that almost all the eggs
a woman will ever have are formed during her own prenatal development, whereas
men produce vast numbers of new sperm continuously.
The process of reproduction starts with the launching of an egg (the largest cell
in the human body) from one of the woman’s ovaries into the adjoining fallopian
tube (see Figure 2.2). As the egg moves through the tube toward the uterus, it emits
a chemical substance that acts as a sort of beacon, a “come­hither” signal that at­
tracts sperm toward it. If an act of sexual intercourse takes place near the time the
egg is released, conception, the union of sperm and egg, will be possible. In every
ejaculation, as many as 500 million sperm are pumped into the woman’s vagina.
Each sperm, a streamlined vehicle for delivering the man’s genes to the woman’s
egg, consists of little more than a pointed head packed full of genetic material (the
23 chromosomes) and a long tail that whips around to propel the sperm through
the woman’s reproductive system.
To be a candidate for initiating conception, a sperm must travel for about
6 hours, journeying 6 to 7 inches from the vagina up through the uterus to the
egg­bearing fallopian tube. The rate of attrition on this journey is enormous: of
FIGURE 2.1 preformationism a seventeenth-century drawing of a preformed being
inside a sperm. This drawing was based on the claim of committed preformationists that
when they looked at samples of semen under the newly invented microscope, they could
actually see a tiny figure curled up inside the head of the sperm. They believed that the
miniature person would enlarge after entering an egg. as this drawing illustrates, we must
always take care not to let our cherished preconceptions so dominate our thinking that we
see what we want to see—not what is really there. (From Moore & persaud, 1993, p. 7)
epigenesis n the emergence of new
structures and functions in the course of
gametes (germ cells) n reproductive
cells—egg and sperm—that contain only
half the genetic material of all the other
cells in the body
meiosis n cell division that produces
conception n the union of an egg from
the mother and a sperm from the father
/ A

PREnAtAl DEvElOPMEnt n 43
Siegler, How Children Develop, 1e
Figure 2.3
Permanent #203
File name = 6101_Fig2.03! (Adobe Illustrator v8)
Placed eps file 6101_Fig2.03placed.eps (Adobe Photoshop v6)
Illustration by Todd Buck
Umbilical cord
Amniotic fluid
Fallopian tube
Ovary Fetus
FIGURE 2.2 Female reproductive system a simplified
illustration of the female reproductive system, with a fetus
developing in the uterus (womb). The umbilical cord runs from
the fetus to the placenta, which is burrowed deeply into the
wall of the uterus. The fetus is floating in amniotic fluid inside
the amniotic sac.
FIGURE 2.3 (a) Sperm nearing the egg
Of the millions of sperm that started out
together, only a few ever get near the egg.
The egg is the largest human cell (the only
one visible to the naked eye), but sperm are
among the smallest. (b) Sperm penetrating
the egg This sperm is whipping its tail
around furiously to drill itself through the
outer covering of the egg.
the millions of sperm that enter the vagina, only about 200 ever get near the egg
(see Figure 2.3). There are many causes for this high failure rate. Some failures are
due to chance: many of the sperm get tangled up with other sperm milling about
in the vagina; others wind up in the fallopian tube that does not currently harbor
an egg. Other failures have to do with the fact that a substantial portion of the
sperm have serious genetic or other defects that prevent them from propelling
themselves vigorously enough to reach and fertilize the egg. Thus, any sperm that
do get to the egg are relatively likely to be healthy and structurally sound, revealing
a Darwinian­type “survival of the fittest” process operating during fertilization.
(Box 2.2 describes the consequences of this selection process for the conception
of males and females.)

44 n chapTer 2 PREnAtAl DEvElOPMEnt AnD thE nEwBORn PERIOD
As soon as one sperm’s head penetrates the outer membrane of the egg, a chemi­
cal reaction seals the membrane, preventing other sperm from entering. The tail
of the sperm falls off, the contents of its head gush into the egg, and the nuclei of
the two cells merge within hours. The fertilized egg, known as a zygote, now has
a full complement of human genetic material, half from the mother and half from
the father. The first of the three periods of prenatal development (see Table 2.1)
has begun and, if everything proceeds normally, that development will continue for
approximately 9 months (on average, 38 weeks or 266 days).
The proverbial competition between the
sexes might be said to begin with millions of
sperm racing to fertilize the egg. Sperm that
carry a Y chromosome (the genetic basis for
maleness) are lighter and swim faster than
those bearing an X chromosome, so the race
to the egg is won much more often by the
“boys.” As a result, approximately 120 to
150 males are conceived for every 100
The girls win the next big competition—
survival. The ratio at birth is only 106
males to 100 females. Where are the miss-
ing males? Obviously, they are miscarried at
a much greater rate than females. Birth is
also more challenging for boys, who, usually
because of possible birth complications, are
50% more likely to need to be surgically re-
moved from the womb by means of a cesar-
ean delivery. This heightened vulnerability is
not limited to surviving the prenatal period.
Boys also suffer disproportionately from most
developmental disorders, including language
and learning disorders, dyslexia, attention-
deficit disorder, intellectual disabilities, and
autism. The greater fragility of males contin-
ues throughout life, as reflected in the graph.
Adolescent boys are more impulsive and take
more risks than girls, and they are more likely
to commit suicide or die violently.
Differential survival is not always left in
the hands of nature. In many societies, both
historically and currently, male offspring
are more highly valued than females, and
parents resort to infanticide to avoid hav-
ing daughters. For example, Inuit families
in Alaska traditionally depended on male
children to help in the hunt for food, and
in former times, Inuit girls were often killed
at birth. Over the past several decades,
the Chinese government strictly enforced a
“one-child” policy, a measure designed to
reduce population growth by forbidding cou-
ples to have more than one child. This policy
resulted in many parents killing or abandon-
ing their female babies (or giving them up
for adoption to Western families) in order to
make room for a male child. A more tech-
nological approach is currently practiced
in some countries that place a premium on
male offspring: prenatal tests are used to de-
termine the gender of the fetus, and female
fetuses are selectively aborted. These cases
dramatically illustrate the socio cultural
model of development described in Chapter
1 (pages 17–18), showing how cultural val-
ues, government policy, and available tech-
nology all affect developmental outcomes.
BOX 2.2: individual differences
Beginning at birth, the U.S. male-to-female
mortality ratio exceeds 1 across the life
span. The spike that occurs in adolescence
and early adulthood—peaking at 3 male
deaths for every female death—is largely the
result of external causes, such as accidents,
homicide, and suicide.
zygote n a fertilized egg cell
20 30 40 50 60 70 80
15 754535 6555250501
All Causes
External Causes
Internal Causes

PREnAtAl DEvElOPMEnt n 45
Developmental Processes
Before describing the course of prenatal development, we need to briefly out­
line four major developmental processes that underlie the transformation of a zy­
gote into an embryo and then a fetus. The first is cell division, known as mitosis.
Within 12 hours or so after fertilization, the zygote divides into two equal parts,
each containing a full complement of genetic material. These two cells then divide
into four, those four into eight, those eight into sixteen, and so on. Through con­
tinued cell division over the course of 38 weeks, the barely visible zygote becomes
a newborn consisting of trillions of cells.
A second major process, which occurs during the embryonic period, is cell migra-
tion, the movement of newly formed cells away from their point of origin. Among
the many cells that migrate are the neurons that originate deep inside the embry­
onic brain and then, like pioneers settling new territory, travel to the outer reaches
of the developing brain.
The third process in prenatal development is cell differentiation. Initially, all of
the embryo’s cells, referred to as embryonic stem cells, are equivalent and in­
terchangeable: none has any fixed fate or function. After several cell divisions,
however, these cells start to specialize in terms of both structure and function. In
humans, embryonic stem cells develop into roughly 350 different types of cells,
which perform particular functions on behalf of the organism. (Because of their de­
velopmental flexibility, embryonic stem cells are currently the focus of a great deal
of research in regenerative medicine. The hope is that when injected into a person
suffering from illness or injury, embryonic stem cells will develop into healthy cells
to replace the diseased or damaged ones.)
The process of differentiation is one of the major mysteries of prenatal develop­
ment. Since all cells in the body have the identical set of genes, what factors deter­
mine which type of cell a given stem cell will become? One key determinant is which
genes in the cell are “switched on” or expressed (see Box 2.3). Another is the cell’s
location, because its future development is influenced by what is going on in neigh­
boring cells.
The initial flexibility and subsequent inflexibility of cells, as well as the importance
of location, is vividly illustrated by classic research with frog embryos. If the region
of a frog embryo that would normally become an eye is grafted onto its belly area
early in fetal development, the transplanted region will develop as a normal part of
the belly. Thus, although the cells were initially in the right place to become an eye,
they had not yet become specialized. If the transplant is performed later in fetal de­
velopment, the same operation results in an eye—alone and unseeing—lodged in the
frog’s belly (Wolpert, 1991).
periods of prenatal Development
to 2 weeks
Germinal Begins with conception and lasts until the zygote becomes
implanted in the uterine wall. Rapid cell division takes place.
3rd to 8th week Embryonic Following implantation, major development occurs in all the organs
and systems of the body. Development takes place through the
processes of cell division, cell migration, cell differentiation, and
cell death, as well as hormonal influences.
9th week to birth Fetal Continued development of physical structures and rapid growth of the
body. Increasing levels of behavior, sensory experience, and learning.
embryo n the name given to the devel-
oping organism from the 3rd to 8th week
of prenatal development
fetus n the name given to the developing
organism from the 9th week to birth
mitosis n cell division that results in two
identical daughter cells
embryonic stem cells n embryonic
cells, which can develop into any type of
body cell

46 n chapTer 2 PREnAtAl DEvElOPMEnt AnD thE nEwBORn PERIOD
BOX 2.3: a closer look
Throughout this book, we will use research
with nonhuman animals to make points
about human development. In doing so, we
subscribe to the principle of phylogenetic
continuity—the idea that because of our
common evolutionary history, humans share
many characteristics and developmental
processes with other living things. Indeed,
you share most of your genes with your dog,
cat, or hamster.
The assumption that animal models of
behavior and development can be useful
and informative for human development
underlies a great deal of research. For ex-
ample, much of our knowledge about the
dangers of alcohol consumption by pregnant
women comes from research with nonhu-
man animals. Because scientists suspected
that drinking alcohol while pregnant caused
the constellation of defects now known as
fetal alcohol spectrum disorder (page 62),
they experimentally exposed fetal mice to
alcohol. At birth, these mice had atypical
facial features, remarkably similar to the
facial anomalies of human children heav-
ily exposed to alcohol in the womb by their
mother. This fact increased researchers’
confidence that the problems commonly as-
sociated with fetal alcohol syndrome are, in
fact, caused by alcohol rather than by some
other factor.
One of the most fascinating discoveries
in recent years, discussed later in this chap-
ter, is the existence of fetal learning. This
phenomenon was first documented in one
of comparative psychologists’ favorite crea-
tures—the rat. To survive after birth, new-
borns must find a milk-producing maternal
nipple. How do they know where to go? The
answer is that they search for something fa-
miliar to them. During the birth process, the
nipples on the underside of the mother rat’s
belly get smeared with amniotic fluid. The
scent of the amniotic fluid is familiar to the
rat pups from their time in the womb, and it
lures the babies to where they need to be—
with their noses, and hence their mouths,
near a nipple (Blass, 1990).
How was it determined that newborn rats
find their mother’s nipple by recognizing the
scent of amniotic fluid? For one thing, when
researchers washed the mother’s belly clean
of amniotic fluid, her pups failed to find her
nipples, and if half her nipples were washed,
the pups were attracted to the unwashed
ones with amniotic fluid still on them (Blass
& Teicher, 1980). Even more impressive,
when researchers introduced odors or flavors
into the amniotic fluid, either by directly in-
jecting them or by adding them to the moth-
er’s diet, her pups preferred those odors and
tastes after birth (Hepper, 1988; Pedersen
& Blass, 1982; Smotherman & Robinson,
1987). These and other demonstrations of
fetal learning in rodents inspired develop-
mental psychologists to look for similar pro-
cesses in human fetuses. As you will see
later, they found them.
Scientists interested in human development have learned a great deal by
studying maternal behavior in rats.
FIGURE 2.4 embryonic
hand plate Fingers will
emerge from the hand plate
of this 7-week-old embryo.
The fingers are formed as a
result of the death of the cells
between the ridges you can
see in the plate. If these cells
did not expire, the baby would
be born with webbed rather
than independent fingers.
The fourth developmental process is something
you would not normally think of as developmental
at all—death. However, the selective death of certain
cells is the “almost constant companion” to the other
developmental processes we have described (Wolpert,
1991). The role of this genetically programmed “cell
suicide,” known as apoptosis, is readily apparent in
hand development (see Figure 2.4): the formation of
fingers depends on the death of the cells in between lEn

PREnAtAl DEvElOPMEnt n 47
the ridges in the hand plate. In other words, death is preprogrammed for the cells
that disappear from the hand plates.
In addition to these four developmental processes, we need to call attention to
the influence of hormones on prenatal development. For example, hormones play
a crucial role in sexual differentiation. All human fetuses, regardless of the genes
they carry, can develop either male or female genitalia. The presence or absence of
androgens, a class of hormones that includes testosterone, causes development to
proceed one way or the other. If androgens are present, male sex organs develop;
if they are absent, female genitalia develop. The source of androgens is the male
fetus itself. Around the 8th week after conception, the testes begin to produce these
hormones, changing the developing organism forever. This is just one of the many
ways in which the fetus influences its own development.
We now turn our attention to the general course of prenatal development that
results from all the preceding influences, as well as other developmental processes.
Early Development
On its journey through the fallopian tube to the womb, the zygote doubles its
number of cells roughly twice a day. By the 4th day after conception, the cells ar­
range themselves into a hollow sphere with a bulge of cells, called the inner cell
mass, on one side.
This is the stage at which identical twins most often originate. They result
from a splitting in half of the inner cell mass, and thus they both have exactly
the same genetic makeup. In contrast, fraternal twins result when two eggs hap­
pen to be released from the ovary into the fallopian tube and both are fertilized.
Because they originate from two different eggs and two different sperm, fra­
ternal twins are no more alike genetically than nontwin siblings with the same
By the end of the 1st week following fertilization, if all goes well (which it does
for less than half the zygotes that are conceived), a momentous event occurs—
implantation, in which the zygote embeds itself in the uterine lining and becomes
dependent on the mother for sustenance. Well before the end of the 2nd week, it
will be completely embedded within the uterine wall.
After implantation, the embedded ball of cells starts to differenti­
ate. The inner cell mass becomes the embryo, and the rest of the cells
become an elaborate support system—including the amniotic sac and
placenta—that enables the embryo to develop. The inner cell mass is
initially a single layer thick, but during the 2nd week, it folds itself into
three layers, each with a different developmental destiny. The top layer
becomes the nervous system, the nails, teeth, inner ear, lens of the eyes,
and the outer surface of the skin. The middle layer eventually becomes
muscles, bones, the circulatory system, the inner layers of the skin, and
other internal organs. The bottom layer develops into the digestive sys­
tem, lungs, urinary tract, and glands. A few days after the embryo has
differentiated into these three layers, a U­shaped groove forms down the
center of the top layer. The folds at the top of the groove move together
and fuse, creating the neural tube (Figure 2.5). One end of the neural
tube will swell and develop into the brain, and the rest will become the
spinal cord.
The support system that is emerging along with the embryo is elabo­
rate and essential to the embryo’s development. One key element of this
phylogenetic continuity n the idea
that because of our common evolutionary
history, humans share many characteris-
tics, behaviors, and developmental pro-
cesses with other animals, especially
apoptosis n genetically programmed cell
identical twins n twins that result
from the splitting in half of the zygote,
resulting in each of the two resulting
zygotes having exactly the same set of
fraternal twins n twins that result
when two eggs happen to be released into
the fallopian tube at the same time and
are fertilized by two different sperm; fra-
ternal twins have only half their genes in
neural tube n a groove formed in the
top layer of differentiated cells in the
embryo that eventually becomes the brain
and spinal cord
FIGURE 2.5 Neural tube In the 4th
week, the neural tube begins to develop into
the brain and spinal cord. In this photo, the
neural groove, which fuses together first at
the center and then outward in both direc-
tions as if two zippers were being closed,
has been “zipped shut” except for one part
still open at the top. Spina bifida, a con-
genital disorder in which the skin over the
spinal cord is not fully closed, can originate
at this point. after closing, the top of the
neural tube will develop into the brain.

48 n chapTer 2 PREnAtAl DEvElOPMEnt AnD thE nEwBORn PERIOD
support system is the amniotic sac, a membrane filled with a clear, watery fluid
in which the fetus floats. The amniotic fluid operates as a protective buffer for the
developing fetus, providing it with a relatively even temperature and cushioning it
against jolting. As you will see shortly, because the amniotic fluid keeps the fetus
afloat, the fetus can exercise its tiny, weak muscles relatively unhampered by the
effects of gravity.
The second key element of the support system, the placenta, is a unique organ
that permits the exchange of materials carried in the bloodstreams of the fetus and
its mother. It is an extraordinarily rich network of blood vessels, including minute
ones extending into the tissues of the mother’s uterus, with a total surface area of
about 10 square yards—approximately the amount of driveway covered by the fam­
ily car (Vaughan, 1996). Blood vessels running from the placenta to the embryo
and back again are contained in the umbilical cord.
At the placenta, the blood systems of the mother and fetus come extremely close
to each other, but the placenta prevents their blood from actually mixing. However,
the placental membrane is semipermeable, meaning that some elements can pass
through it but others cannot. Oxygen, nutrients, minerals, and some antibodies—
all of which are just as vital to the fetus as they are to you—are transported to the
placenta by the mother’s circulating blood. They then cross the placenta and enter
the fetal blood system. Waste products (e.g., carbon dioxide, urea) from the fetus
cross the placenta in the opposite direction and are removed from the mother’s
bloodstream by her normal excretory processes.
The placental membrane also serves as a defensive barrier against a host of dan­
gerous toxins and infectious agents that can inhabit the mother’s body and could be
harmful or even fatal to the fetus. Unfortunately, being semipermeable, the placenta
is not a perfect barrier, and, as you will see later, a variety of harmful elements can
cross it and attack the fetus. One other function of the placenta is the production
of hormones, including estrogen, which increases the flow of maternal blood to the
uterus, and progesterone, which suppresses uterine contractions that could lead to
premature birth (Nathanielsz, 1994).
An Illustrated Summary of Prenatal Development
The course of prenatal development from the 4th week on is illustrated in Figures
2.6 through 2.13, and significant milestones are highlighted in the accompanying
text. (The fetal behaviors that are mentioned will be discussed in detail in the fol­
lowing section.) Notice that earlier development takes place at a more rapid pace
than later development, and that the areas nearer the head develop earlier than
those farther away (e.g., head before body, hands before feet)—a general tendency
known as cephalocaudal development.
Figure 2.6: At 4 weeks after conception, the embryo is curved so tightly that
the head and the tail­like structure at the other end are almost touching. Several
facial features have their origin in the set of four folds in the front of the embryo’s
head; the face gradually emerges as a result of these tissues moving and stretching,
as parts of them fuse and others separate. The round area near the top of the head
is where the eye will form, and the round gray area near the back of the “neck” is
the primordial inner ear. A primitive heart is visible; it is already beating and cir­
culating blood. An arm bud can be seen in the side of the embryo; a leg bud is also
present but less distinct.
Figure 2.7: (a) In this 5½­week­old fetus, the nose, mouth, and palate are be­
ginning to differentiate into separate structures. (b) Just 3 weeks later, the nose
amniotic sac n a transparent, fluid-
filled membrane that surrounds and pro-
tects the fetus
placenta n a support organ for the
fetus; it keeps the circulatory systems
of the fetus and mother separate, but
as a semipermeable membrane permits
the exchange of some materials between
them (oxygen and nutrients from mother
to fetus and carbon dioxide and waste
products from fetus to mother)
umbilical cord n a tube containing the
blood vessels connecting the fetus and
cephalocaudal development n the
pattern of growth in which areas near the
head develop earlier than areas farther
from the head
FIGURE 2.6 embryo at 4 weeks

PREnAtAl DEvElOPMEnt n 49
and mouth are almost fully formed. Cleft pal­
ate, one of the most common birth defects
worldwide, involves malformations (some­
times minor, sometimes major) of this area.
This condition originates sometime between
5½ and 8 weeks prenatally— precisely when
these structures are developing.
Figure 2.8: The head of this 9­week­
old fetus overwhelms the rest of its body.
The bulging forehead reflects the extremely
rapid brain growth that has been going on
for weeks. Rudimentary eyes and ears are
forming. All the internal organs are pres­
ent, although most must undergo further
development. Sexual differentiation has
started. Ribs are visible, fingers and toes have
emerged, and nails are growing. You can see
the umbilical cord connecting the fetus to the placenta. The fetus makes sponta­
neous movements, but because it is so small and is floating in amniotic fluid, the
mother cannot feel them.
Figure 2.9: This image of an 11­week­old fetus clearly shows the heart, which
has achieved its basic adult structure. You can also see the developing spine and
ribs, as well as the major divisions of the brain.
Figure 2.10: During the last 5 months of prenatal development, the growth
of the lower part of the body accelerates. The fetus’s movements have increased
dramatically: its chest makes breathing movements, and some reflexes—grasping,
FIGURE 2.7 Face development from 5½
to 8½ weeks
FIGURE 2.8 Fetus at 9 weeks
FIGURE 2.9 Fetus at 11 weeks
/ P

50 n chapTer 2 PREnAtAl DEvElOPMEnt AnD thE nEwBORn PERIOD
swallowing, sucking—are present. By 16 weeks,
the fetus is capable of intense kicks, although the
mother feels them only as a mild “flutter.” At this
age, the external genitalia are substantially devel­
oped, and a different camera angle would have re­
vealed whether this fetus is male or female.
Figure 2.11: This 18­week­old fetus is clearly
sucking its thumb, in much the same way it will as
a newborn. The fetus is covered with very fine hair,
and a greasy coating protects its skin from its long
immersion in liquid.
Figure 2.12: By the 20th week, the fetus spends
increasingly more time in a head­down position. The
components of facial expressions are present—the
fetus can raise its eyebrows, wrinkle its forehead, and
move its mouth. As the fetus rapidly puts on weight,
the amniotic sac becomes more cramped, leading to
a decrease in fetal movements.
Figure 2.13: The 28th week marks the point at
which the brain and lungs are sufficiently developed
that a fetus born at this time would have a chance of
surviving on its own, without medical intervention.
The eyes can open, and they move, especially during
periods of rapid eye movement (REM) sleep. The
auditory system is now functioning, and the fetus
hears and reacts to a variety of sounds. At this stage
of development, the neural activity of the fetus is
very similar to that of a newborn. During the last 3
FIGURE 2.10 Fetus at 16 weeks
FIGURE 2.12 Fetus at 20 weeks
FIGURE 2.11 Fetus at 18 weeks

PREnAtAl DEvElOPMEnt n 51
months of prenatal development, the fetus grows dramatically in size, essentially
tripling its weight.
The typical result of this 9­month period of rapid and remarkable development
is a healthy newborn.
Fetal Behavior
As we have noted, the fetus is an active participant in, and contributor to, its own
physical and behavioral development. Indeed, the normal formation of organs and
muscles depends on fetal activity, and the fetus rehearses the behavioral repertoire
it will need at birth.
Few mothers realize how early their child started moving in the womb. From 5 or
6 weeks after conception, the fetus moves spontaneously, starting with a simple
bending of the head and spine that is followed by the onset of increasingly complex
movements over the next weeks (De Vries, Visser, & Prechtl, 1982). One of the
earliest distinct patterns of movement to emerge (at around 7 weeks) is, remark­
ably enough, hiccups. Although the reasons for prenatal hiccups are unknown, one
recent theory posits that they are essentially a burping reflex, preparing the fetus
for eventual nursing by removing air from the stomach and making more room for
milk (Howes, 2012).
The fetus also moves its limbs, wiggles its fingers, grasps the umbilical cord,
moves its head and eyes, and yawns. Complete changes of position are achieved
by a kind of backward somersault. These various movements are initially jerky and
uncoordinated but gradually become more integrated. By 12 weeks, most of the
movements that will be present at birth have appeared (De Vries et al., 1982),
although the mother is still unaware of them.
Later on, when mothers can readily feel the movement of their fetuses, their re­
ports reveal that how much a fetus moves is quite consistent over time: some fetuses
are usually very active, whereas others are more sedentary (Eaton & Saudino, 1992).
This prenatal continuity extends into the postnatal period: more active fetuses turn
FIGURE 2.13 Fetus at 28 weeks
/ S
/ P

52 n chapTer 2 PREnAtAl DEvElOPMEnt AnD thE nEwBORn PERIOD
out to be more active infants (DiPietro et al., 1998). Further­
more, fetuses that have regular periods of sleep and waking are
more likely to have regular sleep times as newborns (DiPietro,
Bornstein et al., 2002).
A particularly important form of fetal movement is swallow-
ing. The fetus drinks amniotic fluid, which passes through its
gastrointestinal system. Most of the fluid is then excreted back
out into the amniotic sac. One benefit of this activity is that the
tongue movements associated with drinking and swallowing pro­
mote the normal development of the palate (Walker & Quarles,
1976). In addition, the passage of amniotic fluid through the
digestive system helps it to mature properly. Thus, swallowing
amniotic fluid prepares the fetus for survival outside the womb.
A second form of fetal movement anticipates the fact that at
birth the newborn must start breathing. For that to happen, the
lungs and the rest of the respiratory system, including the muscles that move the
diaphragm in and out, must be mature and functional. Beginning as early as 10
weeks after conception, the fetus promotes its respiratory readiness by exercising
its lungs through “fetal breathing,” moving its chest wall in and out (Nathanielsz,
1994). No air is taken in, of course; rather, small amounts of amniotic fluid are
pulled into the lungs and then expelled. Unlike real breathing, which involves an
ongoing and consistent pattern of lung activity, fetal breathing is initially infrequent
and irregular, but it increases in rate and stability, especially over the third trimester
(Govindan et al., 2007).
Behavioral Cycles
Once the fetus begins to move at 5 to 6 weeks, it is in almost constant motion for
the next month or so. Then periods of inactivity gradually begin to occur. Rest–
activity cycles—bursts of high activity alternating with little or no activity for a few
minutes at a time—emerge as early as 10 weeks and become very stable during the
second half of pregnancy (Robertson, 1990). In the latter half of the prenatal pe­
riod, the fetus moves only about 10% to 30% of the time (DiPietro et al., 1998).
Longer­term patterns, including daily (circadian) rhythms, also become appar­
ent, with less activity in the early morning and more activity in the late evening
(Arduini, Rizzo, & Romanini, 1995). This confirms the impression of most preg­
nant women that their fetuses wake up and start doing acrobatics just as they them­
selves are trying to go to sleep.
Near the end of pregnancy, the fetus spends more than three­fourths of its time
in quiet and active sleep states like those of the newborn ( James et al., 1995) (see
page 70). The active sleep state is characterized by REM, just as it is in infants
and adults.
Fetal Experience
There is a popular idea—promoted by everyone from scholars to cartoonists—that
we spend our lives longing for the tranquil sanctuary we experienced in our moth­
er’s womb. But is the womb a haven of peace and quiet? Although the uterus and
the amniotic fluid buffer the fetus from much of the stimulation impinging on the
mother, research has made it clear that the fetus experiences an abundance of sen­
sory stimulation.
“It’s a baby. Federal regulations prohibit our
mentioning its race, age, or gender.”
Developmental psychologist Janet Dipietro
is using ultrasound to study the movement
patterns of this woman’s fetus.

PREnAtAl DEvElOPMEnt n 53
Sight and Touch
Although it is not totally dark inside the womb, the visual experience of the fetus
is minimal. The fetus does, however, experience tactile stimulation as a result of
its own activity. In the course of moving around, its hands come into contact with
other parts of its body: fetuses have been observed not only grasping their umbilical
cords but also rubbing their face and sucking their thumbs (Figure 2.11). Indeed,
the majority of fetal arm movements during the second half of pregnancy result in
contact between their hand and mouth (Myowa­Yamakoshi & Takeshita, 2006). As
the fetus grows larger, it bumps against the walls of the uterus increasingly often.
By full term, fetuses respond to maternal movements (repeated rocking and sway­
ing), suggesting that their vestibular systems—the sensory apparatus in the inner
ear that provides information about movement and balance—is also functioning
before birth (Lecanuet & Jacquet, 2002).
The amniotic fluid contains a variety of flavors (Maurer & Maurer, 1988). The
fetus can detect these flavors, and likes some better than others. Indeed, the fetus
has a sweet tooth. The first evidence of fetal taste preferences came from a medi­
cal study performed more than 60 years ago (described by Gandelman, 1992). A
physician named DeSnoo devised an ingenious treatment for women with exces­
sive amounts of amniotic fluid. He injected saccharin into their amniotic fluid,
hoping that the fetus would help the mother out by ingesting increased amounts
of the sweetened fluid, thereby diminishing the excess. And, in fact, tests of the
mothers’ urine showed that the fetuses ingested more amniotic fluid when it had
been sweetened, demonstrating that taste sensitivity and flavor preferences exist
before birth.
Amniotic fluid takes on odors from what the mother has eaten (Mennella, Johnson,
& Beauchamp, 1995). Obstetricians have long reported that during birth they
can smell scents like curry and coffee in the amniotic fluid of women who had re­
cently consumed them. Indeed, human amniotic fluid has been shown to be rich in
odorants (although many do not sound very appealing—including those described
as being pungently rancid, goaty, or having a “strong fecal note”; Schaal, Orgeur,
& Rognon, 1995). Smells can be transmitted through liquid, and amniotic fluid
comes into contact with the fetus’s odor receptors through fetal breathing, provid­
ing fetuses with the opportunity for olfactory experience. Indeed, as discussed in
Box 2.3, rat pups use the familiar scent of their mother’s amniotic fluid to find their
mother’s nipples after birth.
Picture serious scientists hovering over a pregnant woman’s bulging abdomen,
ringing bells, striking a gong, clapping blocks of wood together, and even sound­
ing an automobile horn—all to see if her fetus reacts to auditory stimulation.
(Remind you of the opening to this chapter?) Such research has demonstrated
that external sounds that are audible to the fetus include the voices of people
talking to the woman. In addition, the prenatal environment includes many
maternal sounds—the mother’s heartbeat, blood pumping through her vascu­
lar system, her breathing, her swallowing, and various rude noises made by her

54 n chapTer 2 PREnAtAl DEvElOPMEnt AnD thE nEwBORn PERIOD
digestive system. A particularly prominent and frequent source
of sound stimulation is the mother’s voice as she talks, with the
clearest aspects being the general rhythm and pitch patterns of
her speech.
The fetus responds to these various sounds from at least the 6th
month of pregnancy on. During the last trimester, external noises
elicit changes in fetal movements and heart rate (Kisilevsky, Fearon,
& Muir, 1998; Lecanuet et al., 1995; Zimmer et al., 1993). By the
time fetuses are at term, changes in heart rate patterns suggest that
they can distinguish between music and speech played near the
mother’s abdomen (Granier­Deferre et al., 2011). The fetus’s heart
rate also decelerates briefly when the mother starts speaking (Fifer
& Moon, 1995). (Transitory heart­rate deceleration is a sign of in­
terest.) The fetus’s extensive auditory experience with human voices
has some lasting effects, as we discuss in the next section.
Fetal Learning
To this point, we have emphasized the impressive behavioral and sensory capabilities
of the fetus in the early stages of development. Even more impressive is the extent
to which the fetus learns from many of its experiences in the
last 3 months of pregnancy, after the central nervous system is
adequately developed to support learning.
Direct evidence for human fetal learning comes from
studies of habituation, one of the simplest forms of learning
(Thompson & Spencer, 1966). Habituation involves a de­
crease in response to repeated or continued stimulation (see
Figure 2.14). If you shake a rattle beside an infant’s head, the
baby will likely turn toward it. At the same time, the infant’s
heart rate may slow momentarily, indicating interest. If you re­
peatedly shake the rattle, however, the head­turning and heart­
rate changes will decrease and eventually stop. This decreased
response is evidence of learning and memory: the stimulus loses
its novelty (and becomes boring) only if the infant remembers
the stimulus from one presentation to the next. When a new
stimulus occurs, the habituated response recovers (increases).
Shaking a bell, for example, may reinstate the head­turning
and heart­rate responses. (Developmental psychologists have
exploited habituation to study a great variety of topics that you will read about in
later chapters.) The earliest time at which fetal habituation has been observed is 30
weeks, indicating that the central nervous system is sufficiently developed at this
point for learning and short­term memory to occur (Dirix et al., 2009).
The mother’s voice is probably the most interesting sound frequently available
to fetuses. If fetuses can learn something about their mother’s voice prenatally, this
could provide them with a running start for learning about other aspects of speech
after birth. To test this idea, Kisilevsky and colleagues (2003) tested term fetuses in
one of two conditions. Half of the fetuses listened to a recording of their mother
reading a poem, played through speakers placed on their mother’s abdomen. The
other half listened to recordings of the same poem read by another woman. The
researchers found that fetal heart rate increased in response to the mother’s voice,
and decreased in response to the other woman’s voice. These findings suggest that
The fetus of this pregnant woman may be
“eavesdropping” on her conversation with
her friends.
. /
Habituation to
a repeated
to a novel
FIGURE 2.14 habituation habituation
occurs in response to the repeated presen-
tation of a stimulus. as the first stimulus is
repeated and becomes familiar, the response
to it gradually decreases. When a novel
stimulus occurs, the response recovers. The
decreased response to the repeated stimulus
indicates the formation of memory for it;
the increased response to the novel stim-
ulus indicates discrimination of it from the
familiar one, as well as a general preference
for novelty.
habituation n a simple form of learning
that involves a decrease in response to
repeated or continued stimulation

PREnAtAl DEvElOPMEnt n 55
the fetuses recognized (and were aroused by) the sound of their own mother’s voice
relative to a stranger’s voice. For this to be the case, fetuses must be learning and
remembering the sound of their mother’s voice.
After birth, do newborns remember anything about their fetal experience? The
answer is a resounding yes! Like the rat pups discussed in Box 2.3, newborn hu­
mans remember the scent of the amniotic fluid in which they lived prenatally. In
one set of studies, newborns were presented with two pads, one saturated with their
own amniotic fluid and the other saturated with the amniotic fluid of a different
baby. With the two pads located on either side of their head, the infants revealed a
preference for the scent of their own amniotic fluid by keeping their head oriented
longer toward that scent (Marlier, Schaal, & Soussignan, 1998; Varendi, Porter, &
Winberg, 2002). These findings extend to specific flavors ingested by the mother.
For example, infants whose mothers ate anise (licorice flavor) while they were preg­
nant preferred the scent of anise at birth, while infants whose mothers did not eat
anise showed either a neutral or negative response to its scent (Schaal, Marlier, &
Soussignan, 2000).
Experiences in the womb can lead to long­lasting taste preferences. In one study,
pregnant women were asked to drink carrot juice four days a week for three weeks
near the end of their pregnancy (Mennella, Jagnow, & Beauchamp, 2001). When
tested at around 5½ months of age, their babies reacted more positively to cereal
prepared with carrot juice than to the same cereal prepared with water. Thus, the
flavor preferences of these babies reflected the influence of their experience in the
womb several months earlier. This finding reveals a persistent effect of prenatal
learning. Furthermore, it may shed light on the origins and strength of cultural
food preferences. A child whose mother ate a lot of chili peppers, ginger, and cumin
during pregnancy, for example, might be more favorably disposed to Indian food
than would a child whose mother’s diet lacked those flavors.
Along with taste, newborns also remember sounds they heard in the womb. In
a classic study, DeCasper and Spence (1986) asked pregnant women to read aloud
twice a day from The Cat in the Hat (or another Dr. Seuss book) during the last 6
weeks of their pregnancy. Thus, the women’s fetuses were repeatedly exposed to the
same highly rhythmical pattern of speech sounds. The question was whether they
would recognize the familiar story after birth. To find out, the researchers tested
them as newborns. The infants were fitted with miniature headphones and given a
special pacifier to suck on (see Figure 2.15). When the infants sucked in one partic­
ular pattern, they heard the familiar story through the headphones, but when they
sucked in a different pattern, they heard an unfamiliar story. The babies quickly
increased their sucking in the pattern that enabled them to hear the familiar story.
Thus, these newborns apparently recognized and preferred the rhythmic patterns
from the story they had heard in the womb.
Newborns exhibit numerous additional auditory preferences based on prenatal
experience. To begin with, they prefer to listen to their own mother’s voice rather
than to the voice of another woman (DeCasper & Fifer, 1980). But how do re­
searchers know that this isn’t due to experience in the hours or days after birth? It
turns out that newborns prefer to listen to a version of their mother’s voice that has
been filtered to sound the way it did in the womb (Moon & Fifer, 1990; Spence
& Freeman, 1996). Finally, newborns would rather listen to the language they
heard in the womb than to another language (Mehler et al., 1988; Moon, Cooper,
& Fifer, 1993). Newborns whose mothers speak French prefer listening to French
over Russian, for example, and this preference is maintained when the speech is fil­
tered to sound the way it sounded in the womb.
FIGURE 2.15 prenatal learning This
newborn can control what he gets to listen
to. his pacifier is hooked up to a computer,
which is in turn connected to an audio
player. If the baby sucks in one pattern
(predetermined by the researchers), he will
hear one recording. If he sucks in a different
pattern, he will hear a different recording.
researchers have used this technique to
investigate many questions about infant
abilities, including the influence of fetal
experience on newborn preferences.

56 n chapTer 2 PREnAtAl DEvElOPMEnt AnD thE nEwBORn PERIOD
There can be little question that the human fetus is listening and learning. Does
this mean that parents­to­be should sign up for programs that promise to “educate
your unborn child”? Such programs exhort the mother­to­be to talk to her fetus,
read books to it, play music through speakers attached to her abdomen, and so on.
Some also urge the father­to­be to speak through a megaphone aimed at his wife’s
bulging belly in the hope that the newborn will recognize his voice as well as the
mother’s. Is there any point in such exercises?
Probably not. Although it seems possible that hearing Dad’s voice more clearly
and more frequently might lead the newborn to prefer it over unfamiliar voices,
such a preference develops very quickly after birth anyway. And it is quite clear
that some of the advertised advantages of prenatal training would not occur. In
the first place, the fetal brain is unlikely to be sufficiently developed to be able to
process much about language meaning (after all, even newborn infants can’t learn
words). In addition, the liquid environment in the womb—provided by the am­
niotic fluid—filters out detailed speech sounds, leaving only pitch contours and
rhythmic patterns. Brain development aside, this acoustic environment, along with
the fetus’s lack of visual access to the external world, would make it impossible for
a fetus to learn the meaning of words or any kind of factual knowledge, no mat­
ter how much the mother­to­be might read aloud. In short, what the fetus learns
about is the mother’s voice and the general patterns of her language—not any spe­
cific content. We suspect that the current craze for “prenatal education” will go the
way of other ill­conceived attempts to shape early development to adult desires.
Hazards to Prenatal Development
Thus far, our focus has been on the normal course of development before birth.
Unfortunately, prenatal development is not always free of error or misfortune. The
most dire, and by far the most common, misfortune is spontaneous abortion—
commonly referred to as miscarriage. Most miscarriages occur before the woman
even knows that she is pregnant. For example, in a Chinese sample, Wang and col­
leagues (2003) found that approximately one­third of the fetuses did not survive to
birth, and that two­thirds of those miscarriages occurred before the pregnancy was
clinically detectable. The majority of embryos that are miscarried very early have
severe defects, such as a missing chromosome or an extra one, that make further
development impossible. In the United States, about 15% of clinically recognized
pregnancies end in miscarriage (Rai & Regan, 2006). Across their childbearing
years, at least 25% of women—and possibly as many as 50%—experience at least
one miscarriage. Few couples realize how common this experience is, making it all
the more painful if it happens to them. Yet more agonizing is the experience of the
approximately 1% of couples who experience recurrent miscarriages, or the loss of
three or more consecutive pregnancies (Rai & Regan, 2006).
For fetuses that survive the danger of miscarriage, there is still a range of fac­
tors that can lead to unforeseen negative consequences. Genetic factors, which are
the most common, will be discussed in the next chapter. Here, we consider some
of the many environmental influences that can have harmful effects on prenatal
Environmental Influences
In the spring of 1956, two sisters were brought to a Japanese hospital, delirious and
unable to walk. Their parents and doctors were mystified by the sudden deteriora­
tion in the girls, described as having been “the brightest, most vibrant, cutest kids

PREnAtAl DEvElOPMEnt n 57
you could imagine.” The mystery intensified as more children and adults developed
nearly identical symptoms. The discovery that all the patients were from the small
coastal town of Minamata suggested a common cause for what was referred to as
the “strange disease” (Newland & Rasmussen, 2003; Smith & Smith, 1975).
That cause was eventually traced to the tons of mercury that had been dumped
into Minamata Bay by a local petrochemical and plastics factory. For years, the
residents of Minamata had been catching and consuming fish that had absorbed
mercury from the polluted waters of the bay. By 1993, more than 2000 children
and adults had been diagnosed with what had come to be known as “Minamata
disease”—methylmercury poisoning (Harada, 1995). At least 40 children had been
poisoned prenatally by mercury in the fish eaten by their pregnant mothers and
were born with cerebral palsy, intellectual disabilities, and a host of other neuro­
logical disorders.
The tragedy of Minamata Bay provided some of the first clear evidence of the
seriously detrimental impact that environmental factors can have on prenatal de­
velopment. As you will see, a vast array of environmental agents, called teratogens,
have the potential to harm the fetus. The resulting damage ranges from relatively
mild and easily corrected problems to fetal death.
A crucial factor in the severity of the effects of potential teratogens is timing
(one of the basic developmental principles discussed in Chapter 1). Many terato­
gens cause damage only if they are present during a sensitive period in prena­
tal development. The major organ systems are most vulnerable to damage at the
time when their basic structures are being formed. Because the timing is different
for each system, the sensitive periods are different for each system, as shown in
Figure 2.16.
There is no more dramatic or straightforward illustration of the importance of
timing than the birth outcomes related to the drug thalidomide in the early 1960s.
Thalidomide was prescribed to treat morning sickness (among other things), and
was considered to be so safe that it was sold over the counter. At the time, it was be­
lieved that such medications would not cross the placental barrier. However, many
Victims of “Minamata disease” include indi-
viduals who were exposed to methylmercury
. Y
teratogen n an external agent that can
cause damage or death during prenatal
sensitive period n the period of time
during which a developing organism is
most sensitive to the effects of external
factors; prenatally, the sensitive period is
when the fetus is maximally sensitive to
the harmful effects of teratogens

58 n chapTer 2 PREnAtAl DEvElOPMEnt AnD thE nEwBORn PERIOD
pregnant women who took this new, presumably safe sedative gave birth to babies
with major limb deformities; some babies were born with no arms and with flip­
perlike hands growing out of their shoulders. In a striking illustration of sensitive
period effects, serious defects occurred only if the pregnant woman took the drug
between the 4th and 6th week after conception, the time when her fetus’s limbs
were emerging and developing (look again at Figures 2.6 to 2.13). Taking thalido­
mide either before the limbs started to develop or after they were basically formed
had no harmful effect.
As you can see in Figure 2.16, the sensitive periods for many organ systems—
and hence the time when the most significant teratogenic damage can result from
something the mother does or experiences—occur before the woman might real­
ize she is pregnant. Because a substantial number of pregnancies are unplanned,
Central nervous system (CNS)
External genitalia
Physiological defects and
minor structural abnormalitiesMajor structural abnormalities
Heart Heart
Eye Eye Ear Ear Ear
Period of
the ovum
Period of the embryo Period of the fetus
Most common
site of birth
Most likely
Severity of
Dark shading
4 5 6 7 8 12 16 20–36 38
Teeth External genitalia
FIGURE 2.16 Sensitive periods of prenatal development The most sensitive or critical period
of prenatal development is the embryonic period. During the first 2 weeks, before implantation in the
uterus, the zygote is generally not susceptible to environmental factors. every major organ system
of the body undergoes all or a major part of its development between the 3rd and the 9th week. The
dark green portions of the bars in the figure denote the times of most rapid development when major
defects originate. The light green portions indicate periods of continued but less rapid development
when minor defects may occur. (adapted from Moore & persaud, 1993)

PREnAtAl DEvElOPMEnt n 59
sexually active people of childbearing age need to be aware of be­
haviors that could compromise the health of a child they might
Another crucial factor influencing the severity of teratogenic
effects is the amount and length of exposure. Most teratogens
show a dose–response relation: the greater the fetus’s exposure to
a potential teratogen, the more likely it is that the fetus will suffer
damage and the more severe any damage is likely to be.
Avoiding environmental agents that have teratogenic effects
is complicated by the fact that they often cannot be readily iden­
tified. One reason is that environmental risk factors frequently
occur in combination, making it difficult to separate out their ef­
fects. For families living in urban poverty, for example, it is hard to
tease apart the effects of poor maternal diet, exposure to airborne
pollution, inadequate prenatal care, and psychological stress re­
sulting from underemployment, single parenthood, and living in
crime­ridden neighborhoods.
Furthermore, the presence of multiple risk factors can have a
cumulative impact. For example, in the case of marginal prena­
tal nutrition, the fetus’s metabolism adjusts to the level of nutritional deficiency
experienced in the womb and does not reset itself after birth. In a postnatal envi­
ronment with abundant opportunities for caloric intake, this sets the stage for the
development of overweight and obesity. Such belated emergence of effects of pre­
natal experience is referred to as fetal programming, because experiences during the
prenatal period “program the physiological set points that will govern physiology
in adulthood” (Coe & Lubach, 2008).
The effects of teratogens can also vary according to in-
dividual differences in genetic susceptibility (probably in
both the mother and the fetus). Thus, a substance that is
harmless to most people may trigger problems in a minor­
ity of individuals, whose genes predispose them to be af­
fected by it.
Finally, identifying teratogens is further complicated
by the existence of sleeper effects, in which the impact of
a given agent may not be apparent for many years. For
example, between the 1940s and 1960s, the hormone di­
ethylstilbestrol (DES) was commonly used to prevent mis­
carriage and had no apparent ill effects on babies born to
women who had taken it. However, in adolescence and
adulthood, these offspring turned out to have elevated
rates of cervical and testicular cancers.
An enormous number of potential teratogens have been
identified, but we will focus only on some of the most
common ones, emphasizing in particular those that are re­
lated to the behavior of the pregnant woman. Table 2.2
includes the agents discussed in the text as well as several additional ones, but you
should be aware that there are numerous other agents known to be, or suspected of
being, hazardous to prenatal development.
Legal drugs Although many prescription and over­the­counter drugs are per­
fectly safe for pregnant women, some are not. Pregnant women (and women
/ G
This young artist was damaged while in the
womb because his mother took the drug tha-
lidomide. She must have taken the drug in
the second month of her pregnancy, the time
when the arm buds develop—an unfortunate
example providing clear evidence of the
importance of timing in how environmental
agents can affect the developing fetus.
Some environmental hazards to Fetus or Newborn
Drugs Maternal Disease
Alcohol AIDS
Accutane Chicken pox
Birth control pills (sex hormones) Chlamydia
Cocaine Cytomegalovirus
Heroin Gonorrhea
Marijuana Herpes simplex (genital herpes)
Methadone Influenza
Tobacco Mumps
Environmental Pollutants Rubella (3-day measles)
Lead Syphilis
Mercury Toxoplasmosis
Note: This list of dangerous elements is not comprehensive; there are many other agents in the environ-
ment that can have a negative impact on developing fetuses or on newborns during the birth process.
dose–response relation n a rela-
tion in which the effect of exposure to
an element increases with the extent of
exposure (prenatally, the more exposure
a fetus has to a potential teratogen, the
more severe its effect is likely to be)

60 n chapTer 2 PREnAtAl DEvElOPMEnt AnD thE nEwBORn PERIOD
who have reason to think they might soon become pregnant) should take drugs
only under the supervision of a physician. This issue can become particularly
acute in the face of public health emergencies like the 2009 H1N1 (swine flu)
pandemic, during which even some physicians were confused about the appro­
priateness of common medications for pregnant women, including the influenza
vaccine and acetaminophen (Tylenol) (Rasmussen, 2012). Other prescription
drugs that are in common use by women of childbearing age, such the acne med­
ication isotretinoin (Accutane), are known human teratogens that cause severe
birth defects or fetal death. Indeed, because of the unambiguous relationship
between Accutane and birth defects, physicians require women to comply with
multiple contraceptive measures and ongoing pregnancy tests before prescribing
the drug.
The two legal “drugs” that wreak the most havoc on fetal development are ciga­
rettes (nicotine) and alcohol. Because the use of these substances represents a life­
style choice rather than a medical remedy for a specific condition (like flu shots,
antiseizure medications, or Accutane), their effects are particularly widespread.
CIGARETTE SMOKING We all know that smoking is unhealthy for the smoker, and
there is abundant evidence that it is not good for the smoker’s fetus, either. When
a pregnant woman smokes a cigarette, she gets less oxygen, and so does her fetus.
Indeed, the fetus makes fewer breathing movements while its mother is smoking.
In addition, the fetuses of smokers metabolize some of the cancer­causing agents
contained in tobacco. And because the mother­to­be inhales cigarette gases when
someone else is smoking nearby, secondhand smoke has an indirect effect on fetal
The main developmental consequences of maternal smoking are slowed fetal
growth and low birth weight, both of which compromise the health of the new­
born. In addition, evidence suggests that smoking may be linked to increased risk
of sudden infant death syndrome (SIDS) (discussed in Box 2.4) and a variety
of other problems, including lower IQ , hearing deficits, and cancer.
In spite of the well­documented negative effects of maternal smoking
on fetal development, it is estimated that approximately 1 in 10 women in
the United States smokes during pregnancy (Centers for Disease Control,
2009; Child Trends, 2012). For women who manage to quit smoking during
pregnancy, the relapse rate is high after they give birth; roughly half begin
smoking again within the first 6 months after their baby is born. Taken to­
gether, these data show that many infants are exposed to a known terato­
gen before birth, and numerous additional infants are exposed to a known
health hazard after birth. Given that the negative effects of maternal smok­
ing on fetal development are well publicized, you may not find it surprising
that mothers who nevertheless smoke during pregnancy are less sensitive
and less warm in interactions with their young infants (Schuetze, Eiden, &
Dombkowski, 2006).
ALCOHOL Alcohol is currently “the most common human teratogen”
(Ramadoss et al., 2008). Maternal alcohol use is the leading cause of fetal
brain injury and is generally considered to be the most preventable cause.
According to data collected between 2005 and 2010, approximately 7.6% of
women used alcohol during their pregnancies (Centers for Disease Control,
2012). Surprisingly, women who are White, older than 35 years, and em­
ployed are more likely to drink during pregnancy than are women who are
non­White, younger than 24 years, and unemployed. This statistic reverses
This woman is endangering the health
of her fetus.

PREnAtAl DEvElOPMEnt n 61
BOX 2.4: applications
For parents, nothing is more terrifying to
contemplate than the death of their child.
New parents are especially frightened by
the specter of sudden infant death syndrome
(SIDS). SIDS refers to the sudden, unex-
pected, and unexplained death of an infant
younger than 1 year. The most common
SIDS scenario is that an apparently healthy
baby, usually between 2 and 5 months of
age, is put to bed for the night and found
dead in the morning. In the United States,
the incidence of SIDS is 56 per 10,000
live births, making it the leading cause of
infant mortality between 28 days and 1
year of age (Task Force on Sudden Infant
Death Syndrome, 2011). African American
and Native American infants are most likely
to die from SIDS, whereas Hispanic Ameri-
can and Asian American infants are least
likely to die from SIDS. These patterns sug-
gest cultural differences in parenting that
might protect some infants from SIDS.
The causes of SIDS are still not well un-
derstood. One hypothesis is that SIDS may
involve an inadequate reflexive response
to respiratory occlusion—that is, an in-
ability to remove or move away from some-
thing covering the nose and mouth (Lipsitt,
2003). Infants may be particularly vulner-
able to SIDS between 2 and 5 months of
age because that is when they are making
a transition from neonatal reflexes under
the control of lower parts of the brain (the
brainstem) to deliberate, learned behaviors
mediated by higher brain areas (cerebral
cortex). A waning respiratory occlusion re-
flex during this transition period may make
infants less able to effectively pull their
head away from a smothering pillow or to
push a blanket away from their face.
In spite of the lack of certainty about the
causes of SIDS, researchers have identi-
fied several steps that parents can take to
decrease the risk to their baby. The most
important one is putting infants to sleep
on their back, reducing the possibility
of anything obstructing their breathing.
Sleeping on the stomach increases the risk
of SIDS more than any other single factor
(e.g., Willinger, 1995). (With respect to
the cultural differences in the incidence of
SIDS mentioned above, it is significant that
Hispanic American parents are the most
likely to put their infants to sleep on their
back [73%], and African Americans the
least likely to do so [53%].) A campaign
encouraging parents to put their infants to
sleep on their back—the “back to sleep”
movement—has contributed to a dramatic
reduction in the number of SIDS victims.
Second, to lower the risk of SIDS, par-
ents should not smoke. If they do smoke,
they should not smoke around the baby.
Infants whose mothers smoke during preg-
nancy and/or after the baby’s birth are more
than 3½ times more likely to succumb
to SIDS than are babies who are not ex-
posed to smokers in their home (Anderson,
Johnson, & Batal, 2005).
Third, babies should sleep on a firm mat-
tress with no pillow or crib bumpers. Soft
bedding can trap air around the infant’s
face, causing the baby to breathe in his or
her own carbon dioxide instead of oxygen.
Fourth, infants should not be wrapped
in lots of blankets or clothes. Being overly
warm is associated with SIDS.
Fifth, infants who are breastfed are less
likely to succumb to SIDS (e.g., Hauck
et al., 2011). Why would breastfeeding
protect infants from SIDS? One possible
reason is that breastfed infants are more
easily aroused from sleep than formula-fed
infants, and thus may more easily detect
when their airflow is interrupted (Horne et
al., 2004).
One unanticipated consequence of the
“back to sleep” movement has been that
North American infants are now beginning
to crawl slightly later than those in previ-
ous generations, presumably because of
reduced opportunity to strengthen their
muscles by pushing up off their mattress.
Parents are encouraged to give their babies
supervised “tummy time” to exercise their
muscles during the day.
“Face Up to Wake Up.” The parents of this infant are following the good advice of the
foundation dedicated to lowering the incidence of SIDS worldwide. Since the inaugu-
ration of this campaign, SIDS in the United States has declined to half its previous
rate (Task Force on Sudden Infant Death Syndrome, 2011).
sudden infant death syndrome
(SIDS) n the sudden, unexpected death
of an infant less than 1 year of age that
has no identifiable cause

62 n chapTer 2 PREnAtAl DEvElOPMEnt AnD thE nEwBORn PERIOD
the more typical pattern of maternal teratogen exposure, which tends to predomi­
nate among expectant mothers with fewer economic and social resources.
Women who use alcohol before becoming pregnant (about half of women of
childbearing age) are most likely to continue using alcohol during pregnancy. In
part, this is due to the fact that in the United States, 40% of women do not real­
ize that they are pregnant until after the fourth week of gestation, when they have
missed a menstruation cycle. As we have seen, those early weeks are a crucial period
in fetal development.
When a pregnant woman drinks, the alcohol in her blood crosses the placenta
into both the fetus’s bloodstream and the amniotic fluid. Thus, the fetus gets alco­
hol directly in its bloodstream, and indirectly by drinking an amniotic­fluid cock­
tail. Concentrations of alcohol in the blood of mother and fetus quickly equalize,
but the fetus has less ability to metabolize and remove alcohol from its blood,
so it remains in the fetus’s system longer. Immediate behavioral effects on the
fetus include altered activity levels and abnormal startle reflexes (Little, Hepper, &
Dornan, 2002).
In the long run, maternal drinking can result in fetal alcohol spectrum disorder
(FASD) (Sokol et al., 2003), which comprises a continuum of alcohol­related
birth defects. Babies born to alcoholic women often exhibit a condition known
as fetal alcohol syndrome (FAS) ( Jacobson & Jacobson, 2002; Jones & Smith, 1973;
Streissguth, 2001; Streissguth et al., 1993). The most obvious symptoms of FAS
are facial deformities like those shown in Figure 2.17. Other forms of FAS can in­
clude varying degrees of intellectual disability, attention problems, and hyperactiv­
ity. Many children who were prenatally exposed to alcohol and show similar but
fewer symptoms are diagnosed with fetal alcohol effects (FAE) (Mattson et al., 1998).
Even moderate drinking during pregnancy (i.e., less than one drink per day) can
have both short­ and long­term negative effects on development. So can occasional
drinking if it involves binge drinking (more than five drinks per episode) (e.g.,
Hunt et al., 1995; Sokol et al., 2003). And according to an analysis of self­report
FIGURE 2.17 Facial Features of FaS These two children display the three primary diagnostic
facial features of fetal alcohol syndrome: small eyes (as measured across); the absence of, or flattening
of, the vertical groove between the nose and the upper lip (smooth philtrum); and a thin upper lip. It
appears that the more pronounced these features are in an affected child, the greater the likelihood
that the child experienced prenatal brain damage. roughly 1 in 1000 infants born in the United States
has FaS.
fetal alcohol spectrum disorder
(FASD) n the harmful effects of maternal
alcohol consumption on a developing
fetus. Fetal alcohol syndrome (FAS)
involves a range of effects, including
facial deformities, mental retardation,
attention problems, hyperactivity, and
other defects. Fetal alcohol effects (FAE)
is a term used for individuals who show
some, but not all, of the standard effects
of FAS.
, U
/ S

PREnAtAl DEvElOPMEnt n 63
data from 2006 through 2010, 1.4% of pregnant women in the United States
engage in at least one incident of binge drinking during their pregnancy (Centers
for Disease Control, 2012).
Given the potential outcomes and the fact that no one knows whether there is
a safe level of alcohol consumption for a pregnant woman, the best approach for
expectant mothers is to avoid alcohol altogether.
Illegal drugs In the United States, the use of illegal drugs during pregnancy
ranges from a low of 3.1% among Hispanic women to a high of 7.7% among non­
Hispanic Black women (National Survey on Drug Use and Health, 2012). Almost
all commonly abused illegal drugs have been shown to be, or are suspected of being,
dangerous for prenatal development. It has proved difficult to pin down exactly
how dangerous particular drugs are, however, because pregnant women who use
one illegal substance often use others, along with smoking cigarettes and drinking
alcohol (Frank et al., 2001; Lester, 1998; Smith et al., 2006).
Prenatal exposure to marijuana, the illegal substance most commonly used
by women of reproductive age in the United States, is suspected of affecting
memory, learning, and visual skills after birth (Fried & Smith, 2001; Mereu
et al., 2003). Cocaine in its various forms is the second most common illegal
drug abused by young American women (Substance Abuse and Mental Health
Services Administration, 2011). Although some early reports of devastating ef­
fects from cocaine use during pregnancy turned out to be exaggerated, such use
has been associated with fetal growth retardation and premature birth (Hawley
& Disney, 1992; Singer et al., 2002). In addition, infants who endured prena­
tal exposure to cocaine have impaired ability to regulate arousal and attention
(e.g., DiPietro et al., 1995; Lewkowicz, Karmel, & Gardner, 1998). Especially
distressing is the case of newborns born to coke­ addicted mothers, because they
have to go through withdrawal just like a reforming addict (Kuschel, 2007).
Longitudinal studies of the development of cocaine­exposed children have re­
vealed persistent, although sometimes subtle, cognitive and social deficits (Lester,
1998). These deficits can be ameliorated to some degree, as suggested by improved
outcomes among affected children who were adopted into supportive middle­class
families (Koren et al., 1998).
environmental pollutants The bodies and bloodstreams of most Americans (in­
cluding women of childbearing age) contain a noxious mix of toxic metals, syn­
thetic hormones, and various ingredients of plastics, pesticides, and herbicides that
can be teratogenic (Moore, 2003). Echoing the story of Minamata disease, evi­
dence has accumulated that mothers whose diet was high in Lake Michigan fish
with high levels of polychlorinated biphenyls (PCBs) had newborns with small
heads. The children with the highest prenatal exposure to PCBs had slightly lower
IQ scores as long as 11 years later ( Jacobson & Jacobson, 1996; Jacobson et al.,
1992). In China, the rapid modernization that has led to economic success has also
taken a toll on health in general, and has led to a dramatic increase in pollution­
related birth defects due to the unregulated burning of coal, water pollution, and
pesticide use (e.g., Ren et al., 2011).
Occupational hazards Many women have jobs that bring them into contact with
a variety of environmental elements that are potentially hazardous to prenatal de­
velopment. Tollbooth collectors, for example, are exposed to high levels of auto­
mobile exhaust; farmers, to pesticides; and factory workers, to numerous chemicals.

64 n chapTer 2 PREnAtAl DEvElOPMEnt AnD thE nEwBORn PERIOD
As Figure 2.18 shows, even noise pollution can negatively affect fetal de­
velopment. Employers and employees alike are grappling with how best to
protect pregnant women from potential teratogens without subjecting them
to job discrimination.
Maternal Factors
Because the mother­to­be provides the most immediate environment for
her fetus, some of her characteristics can affect prenatal development. These
characteristics include age, nutritional status, health, and stress level.
age A pregnant woman’s age is related to the outcome of her pregnancy.
Infants born to girls 15 years or younger are three to four times more likely
to die before their first birthday than are those born to mothers who are
between 23 and 29 (Phipps, Blume, & DeMonner, 2002). However, the
rate of teenage pregnancy has declined substantially in recent years, and
in 2010, the birth rate for teenagers fell to the lowest recorded level in the
United States (34 births per 1000 females younger than 20; Hamilton,
Martin, & Ventura, 2011).
A different age­related cause for concern has to do with the increasing
age of first­time mothers. In recent decades, many women have chosen to wait
until their 30s or 40s to have children. At the same time, techniques to treat infer­
tility have continued to improve, increasing the likelihood of conception for older
parents. Older mothers are at greater risk for many negative outcomes for them­
selves and their fetus, including fetal chromosomal abnormalities (see Chapter 3)
and birth complications.
Nutrition The fetus depends on its mother for all its nutritional requirements. If
a pregnant woman has an inadequate diet, her unborn child may also be nutrition­
ally deprived (Pollitt et al., 1996). An inadequate supply of specific nutrients or
65–75 dB
Noise exposure during pregnancy
75–85 dB 85–95 dB
FIGURE 2.18 hearing loss in children
whose mothers worked in a noisy factory
while pregnant The greater the noise expo-
sure a pregnant woman experienced, the
greater the hearing impairment of her child.
SOURCE: lAlAnDE, hÉtU, & lAMBERt, 1986
These poor parents in Bolivia are wor-
rying about how they are going to feed
their children—a situation all too common
throughout the world.

PREnAtAl DEvElOPMEnt n 65
vitamins can have dramatic consequences. For example, women who get too little
folic acid (a form of B vitamin) are at high risk for having an infant with a neural­
tube defect such as spina bifida (see Figure 2.5). General malnutrition affects the
growth of the fetal brain: newborns who received inadequate nutrients while in
the womb tend to have smaller brains containing fewer brain cells than do well­
nourished newborns.
Because malnutrition is more common in impoverished families, it often coin­
cides with the host of other risk factors associated with poverty, making it difficult
to isolate its effects on prenatal development (Lozoff, 1989; Sigman, 1995). How­
ever, one unique study of development in very extreme circumstances made it possi­
ble to assess certain effects of malnutrition independent of socioeconomic status (Stein
et al., 1975). In parts of Holland during World War II, people of all income and
education levels suffered severe famine. Later, the health records of those Dutch
women who had been pregnant during this time of general malnourishment were
examined. Their babies were, on average, underweight at birth, but the severity of
effects depended on how early in their pregnancy the women had become malnour­
ished. Those who became malnourished only in the last few months of pregnancy
tended to have slightly underweight babies with relatively small heads. However,
those whose malnutrition started early in their pregnancy often had very small
babies with serious physical defects.
Disease Although most maternal illnesses that occur during a pregnancy have no
impact on the fetus, some do. For example, if contracted early in pregnancy, rubella
(also called the 3­day measles) can have devastating developmental effects, in­
cluding major malformations, deafness, blindness, and intellectual disabilities. Any
woman of childbearing age who does not have immunities against rubella should
be vaccinated before becoming pregnant.
Sexually transmitted diseases (STDs) that have become increasingly common
throughout the world are also quite hazardous to the fetus. Cytomegalovirus, a
type of herpes virus that is present in 50% to 80% of the adult population in the
United States, is currently the most common cause of congenital infection (1 of
every 150 infants). It can damage the fetus’s central nervous system and cause a
variety of other serious defects. Genital herpes can also be very dangerous: if the
infant comes into contact with active herpes lesions in the birth canal, blindness or
even death can result. HIV infection is sometimes passed to the fetus in the womb
or during birth, but the majority of infants born to women who are HIV­positive
or have AIDS do not become infected themselves. HIV can also be transmitted
through breast milk after birth, but recent research suggests that breast milk con­
tains a carbohydrate that may actually protect infants from HIV infection (Bode
et al., 2012).
Evidence has been accumulating for effects of maternal illness on the develop­
ment of psychopathology later in life. For example, the incidence of schizophrenia is
higher for individuals whose mothers had influenza (flu) during the first trimester
of pregnancy (Brown et al., 2004). Maternal flu may interact with genetic or other
factors to lead to mental illness.
Maternal emotional state For centuries, people have believed that a woman’s
emotions can affect her fetus. This view is now supported by research suggesting
that maternal stress can have negative consequences for development (DiPietro,
2012). For example, the fetuses of women who reported higher levels of stress

66 n chapTer 2 PREnAtAl DEvElOPMEnt AnD thE nEwBORn PERIOD
during pregnancy were more physically active throughout their
gestation than were the fetuses of women who felt less stressed
(DiPietro, Hilton et al., 2002). This increased activity is likely
related to hormones, including adrenaline and cortisol, that the
mother secretes in response to stress (Relier, 2001). Such effects
can continue after birth. In a study that involved more than 7000
pregnant women and their infants, maternal anxiety and depres­
sion during pregnancy were assessed. The higher the level of dis­
tress the pregnant women reported, the higher the incidence of
behavior problems in their children at 4 years of age—including
hyperactivity and inattention in boys, conduct problems in girls,
and emotional problems in both boys and girls (O’Connor et al.,
2002). Findings such as these, linking prenatal maternal stress
to postnatal behavior problems, are likely to also be mediated by
increased levels of maternal hormones, such as cortisol, that are
elicited by stress (Susman et al., 2001; Susman, 2006).
Like other types of teratogens, it is difficult to tease apart the
specific effects of maternal stress from other factors that often
co­occur with stress; for example, expectant mothers who are
stressed during pregnancy are likely to still be stressed after giv­
ing birth. That said, the increased popularity of prenatal yoga
and meditation classes may point to ways in which pregnancy­
related stress may be reduced, with potential benefits for both
mother and fetus.
The most rapid period of development starts at conception, with the union of egg and sperm,
and continues for roughly 9 months, divided into three developmental periods: germinal, em-
bryonic, and fetal. The processes through which prenatal development occurs include cell
division, cell migration, cell differentiation, and cell death. Every major organ system un-
dergoes all or a substantial part of its development between the 3rd and 8th week following
conception, making this a sensitive period for potential damage from environmental hazards.
Scientists have learned an enormous amount about the behavior and experience of the
developing organism, which begins to move at 5 to 6 weeks after conception. Some behav-
iors of the fetus contribute to its development, including swallowing amniotic fluid and mak-
ing breathing motions. The fetus has relatively rich sensory experience from stimulation both
within and outside the womb, and this experience is the basis for fetal learning. Some effects
of fetal learning after birth have been shown to be persistent.
Many environmental agents can have a negative impact on prenatal development. The
most common teratogens in the United States are cigarette smoking, alcohol consumption,
and environmental pollution. Maternal factors (malnutrition, illness, stress, and so forth) can
also cause problems for the developing fetus and child. Timing is crucial for exposure to many
teratogens; the severity of effects is also related to the amount and length of exposure, as well
as to the number of different negative factors with which a fetus has to contend.
The Birth Experience
Approximately 38 weeks after conception, contractions of the muscles of the uterus
begin, initiating the birth of the baby. Typically, the baby has already contributed
to the process by rotating itself into the normal head­down position. In addition,
/ A
prenatal exercise classes, as well as yoga
or meditation classes, may help reduce
pregnancy-related stress.

the maturing lungs of the fetus may release a protein that triggers the onset of
labor. Uterine contractions, as well as the baby’s progress through the birth canal,
are painful for the mother, so women in labor are often given pain­relieving drugs.
Women who self­report a great deal of fear about childbirth earlier in their preg­
nancies are more likely to choose pain medications, such as epidurals, during the
birth process (Haines et al., 2012). Although these drugs can help the mother get
through childbirth more comfortably, they do not help her baby. Indeed, many ob­
stetric medications slow labor, and prolonged labor increases the chance of fetal
oxygen deprivation, which can result in brain damage.
Is birth as painful for the newborn as for the mother? Actually, there is good rea­
son to believe that birth is not particularly painful for the baby. Compare how much
pain you feel when you pinch and pull on a piece of skin on your forearm versus
when you wrap your hand around your forearm and squeeze as tightly as you can.
The stretching is painful, but the squeezing is not. The mother’s pain comes from
her tissues being greatly stretched, but the baby experiences squeezing. Hence, the
experiences of the two participants are not really comparable (Maurer & Maurer,
1988). Childbirth programs designed to prevent birth from being painful and trau­
matic for newborns are probably based on faulty premises.
Furthermore, the squeezing that the fetus experiences during birth serves sev­
eral important functions. First, it temporarily reduces the overall size of the fetus’s
disproportionately large head, allowing it to pass safely through the mother’s pel­
vic bones. This is possible because the skull is composed of separate plates that can
overlap one another slightly during birth (see Figure 2.19). The squeezing of the
fetus’s head during birth also stimulates the production of hormones that help the
fetus withstand mild oxygen deprivation during birth and to regulate breathing
after birth. The squeezing of the fetus’s body also forces amniotic fluid out of
the lungs, in preparation for the newborn’s first, crucial gasp of air (Lagercrantz
& Slotkin, 1986; Nathanielsz, 1994). This first breath usually comes by way of
the birth cry, which is a very efficient mechanism for jump­starting respiration: a
strong cry not only obtains some essential oxygen but also forces open the small air
sacs in the lungs, making subsequent breaths easier. (An important disadvantage of
cesarean deliveries is that surgical removal from the womb deprives the fetus of the
squeezing action of a normal delivery, increasing the likelihood of its experiencing
respiratory problems as a newborn.)
FIGURE 2.19 head plates pres-
sure on the head during birth can
cause the separate plates of the
skull to overlap, resulting in a tem-
porarily misshapen head. Fortu-
nately, the condition rapidly corrects
itself after birth. The “soft spot,” or
fontanel, is simply the temporary
space between separate skull plates
in the top of the baby’s head.

68 n chapTer 2 PREnAtAl DEvElOPMEnt AnD thE nEwBORn PERIOD
Diversity of Childbirth Practices
Although the biological aspects of birth are pretty much the same everywhere,
childbirth practices vary enormously. As with many human behaviors, what is con­
sidered a normal and desirable birth custom in one society may seem strange or
deviant—or even dangerous—in another.
All cultures pursue the dual goals of safeguarding the survival and health of both
the mother and the baby and ensuring the social integration of the new person.
Groups differ, however, regarding the relative importance they give to these goals.
An expectant mother on the South Pacific island of Bali assumes that her husband
and other kin, along with any children she may already have, will all want to be
present at the joyous occasion of the birth of a new child. Her female relatives, as
well as a midwife, actively help her throughout the birth, which occurs in her home.
Having already been present at many births, the Balinese woman knows what to
expect from childbirth, even when it is her first child (Diener, 2000).
A very different scenario has been the tradition in the United States, where the
woman in labor usually withdraws almost totally from her everyday life. In most
cases, she enters a hospital to give birth, typically attended by a small group of fam­
ily or close friends. The birth is supervised by a variety of medical personnel, most
of whom are strangers. Unlike her Balinese counterpart, the first­time U.S. mother
has probably never witnessed a birth, so she may not have very realistic expectations
about the birth process. Also, unlike her counterparts in most societies, a U.S.
woman in labor has a 33% chance of having a surgical delivery by cesarean—a rate
that has steadily increased in the United States over the past 2 decades (Martin et
al., 2012). There are a number of reasons for the ever higher rate of surgical deliver­
ies, including a vastly increased rate of multiple births (discussed below), schedul­
ing convenience for the physician and/or the parents, and physicians’ attempts to
decrease risk of lawsuits concerning medical malpractice should problems arise
from a vaginal birth (e.g., Yang et al., 2009).
Underlying the Balinese approach to childbirth is great emphasis on the social
goal of immediately integrating the newborn into the family and community—
hence the presence of many kin and friends to support mother and baby. In con­
trast, modern Western groups have elevated the physical health of the mother and
newborn above all other concerns. The belief that childbirth is safer in a hospital
setting outweighs the resulting social isolation of mother and baby.
The practices of both societies have changed to some degree. In the United
States, the social dimensions of birth are increasingly recognized by doctors and
hospitals, which often now employ certified nurse­midwives as alternative practi­
tioners for expectant parents who prefer a less medicalized birth plan. As in Bali,
various family members—sometimes even including the parents’ other children—
are encouraged to be present to support the laboring mother and to share a family
experience. Another increasingly common practice in the United States is the use
of doulas, individuals trained to assist women in terms of both emotional and physi­
cal comfort during labor and delivery. This shift has been accompanied by more
moderate use of delivery drugs, thereby enhancing the woman’s participation in
childbirth and her ability to interact with her newborn. In addition, many expect­
ant parents attend childbirth education classes, where they learn some of what their
Balinese counterparts pick up through routine attendance at births. Social support
is a key component of these programs; the pregnant woman’s husband or partner, or
some other supportive person, is trained to assist her during the birth. Such child­
birth programs are generally beneficial (Lindell, 1988), and obstetricians routinely

advise expectant couples to enroll in them. At the same time that these changes are
occurring in the United States, Western medical practices are increasingly adopted
in traditional, nonindustrialized societies like Bali, in an effort to improve newborn
survival rates.
Research on the birth process has revealed that many aspects of the experience of being
born, including squeezing in the birth canal, have adaptive value and increase the likelihood
of survival for the newborn. Although cultural groups differ in their beliefs and practices re-
lated to childbirth, these differences are decreasing as expectant mothers gain access to
more diverse birthing options.
This childbirth in Brazil is quite different
from the norm in the United States. The
baby was born at home, welcomed by his
father, older brother, and grandmother. also
present are an obstetrician and midwife who
assisted with the birth.
The medical model of childbirth prevails in
the United States.

70 n chapTer 2 PREnAtAl DEvElOPMEnt AnD thE nEwBORn PERIOD
The Newborn Infant
A healthy newborn is ready and able to continue the developmental saga in a new
environment. The baby begins interacting with that environment right away, ex­
ploring and learning about newfound physical and social entities. Newborns’ explo­
ration of this uncharted territory is very much influenced by their state of arousal.
State of Arousal
State refers to a continuum of arousal, ranging from deep sleep to intense activ­
ity. As you well know, your state dramatically affects your interaction with the
environment—with what you notice, do, learn, and think about. It also affects
the ability of others to interact with you. State strongly mediates how young in­
fants experience the world around them.
Figure 2.20 depicts the average amount of time in a 24­hour period that
Western newborns typically spend in each of six states, ranging from quiet
sleep to crying. Within this general pattern, however, there is a great deal of
individual variation. Some infants cry relatively rarely, whereas others cry for
hours every day; some babies sleep much more, and others much less, than the
16­hour average shown in the figure. Some infants spend more than the aver­
age of 2½ hours in the awake­alert state, in which they are fairly inactive but
attentive to the environment. To appreciate how these differences might affect
parent–infant interactions, imagine yourself as the parent of a newborn who
cries more than the average, sleeps little, and spends less time in the awake­
alert state. Now imagine yourself with a baby who cries relatively little, sleeps
well, and spends an above­average amount of time quietly attending to you
and the rest of his or her environment (see Figure 2.21). Clearly, you would have
many more opportunities for pleasurable interactions with the second newborn.
The two newborn states that are of particular concern to parents—sleeping and
crying—have both been studied extensively.
Figure 2.22 summarizes several important facts about sleep and its development,
two of which are of particular importance. First, “sleeping like a baby” means, in
part, sleeping a lot; on average, newborns sleep twice as much as young adults do.
Total sleep time declines regularly during childhood and continues to decrease,
although more slowly, throughout life.
Second, the pattern of two different sleep states—REM sleep and
non-REM sleep—changes dramatically with age. Rapid eye move-
ment (REM) sleep is an active sleep state that is associated with
dreaming in adults and is characterized by quick, jerky eye move­
ments under closed lids; a distinctive pattern of brain activity; body
movements; and irregular heart rate and breathing. Non-REM
sleep, in contrast, is a quiet sleep state characterized by the absence
of motor activity or eye movements and more regular, slow brain
waves, breathing, and heart rate. As you can see in Figure 2.22,
REM sleep constitutes fully 50% of a newborn’s total sleep time.
The proportion of REM sleep declines quite rapidly to only 20% by
3 or 4 years of age and remains low for the rest of life.
Why do infants spend so much time in REM sleep? Some re­
searchers believe that it helps develop the infant’s visual system.
1 hr.
2.5 hrs.
2.5 hrs.
2 hrs.
8 hrs.
8 hrs.
Quiet sleep
Active sleep
FIGURE 2.20 Newborn states This
figure shows the average proportion of time,
in a 24-hour day, that Western newborns
spend in each of the six states of arousal.
There are substantial individual and cultural
differences in how much time babies spend
in the different states.
FIGURE 2.21 Quiet-alert state The par-
ents of this quiet-alert newborn have a good
chance of having a pleasurable interaction
with the baby.
state n level of arousal and engagement
in the environment, ranging from deep
sleep to intense activity
rapid eye movement (REM) sleep n
an active sleep state characterized by
quick, jerky eye movements under closed
lids and associated with dreaming in
non-REM sleep n a quiet or deep
sleep state characterized by the absence
of motor activity or eye movements and
more regular, slow brain waves, breathing,
and heart rate

thE nEwBORn InFAnt n 71
The normal development of the human visual system, including the visual area of
the brain, depends on visual stimulation, but relatively little visual stimulation is ex­
perienced in the womb (particularly in contrast to fetal auditory stimulation, which,
as you will see in the next section, is extensive). In addition, the fact that newborns
spend so much time asleep means that they do not have much opportunity to amass
waking visual experience. The high level of internally generated brain activity that
occurs during REM sleep may help to make up for the natural deprivation of visual
stimulation, facilitating the early development of the visual system in both fetus
and newborn (Roffwarg, Muzio, & Dement, 1966). This theory is supported by a
study showing that newborns who had been given a high level of extra visual stimu­
lation during the day spent less of their subsequent sleep time in REM sleep than
did infants exposed to lower levels of visual stimulation (Boismier, 1977).
Another distinctive feature of sleep in the newborn period is that napping new­
borns may actually be learning while asleep. In one study that investigated this
possibility, infants were exposed to recordings of Finnish vowel sounds while they
slumbered in the newborn nursery. When tested in the morning, their brain activity
revealed that they recognized the sounds they had heard while asleep (Cheour et
al., 2002). In a recent study, researchers trained sleeping neonates to make an eye­
movement response to a puff of air toward their closed eyelids (Fifer et al., 2010).
During the training phase, the newborns were repeatedly presented with a tone just
before each puff of air. Given this experience, they quickly learned to expect the air
puff after the tone, as evidenced by their making an eye movement in response to
the tone alone. Newborns seem able to learn in their sleep because their slumbering
brains do not become disconnected from external stimulation to the same extent
that the brains of older individuals do.
FIGURE 2.22 Total sleep and propor-
tion of reM and non-reM sleep across
the life span Newborns average a total of
16 hours of sleep, roughly half of it in reM
sleep. The total amount of sleep declines
sharply throughout early childhood and
continues to decline much more slowly
throughout life. From adolescence on, reM
sleep constitutes only about 20% of total
sleep time. (adapted from roffwarg et al.,
1966, and from a later revision by these
3 – 5
6 – 23
3 –
5 –
10 –
14 –
19 – 30 33 – 45 50 – 70 70 – 85
14 13 12 11 10.5 10 8.5 7.75 7 6 5.75
l a
InfantsNeonate Children
Age (in years unless labeled otherwise)
Adolescents Adults Old Age
NREM sleep
REM sleep

72 n chapTer 2 PREnAtAl DEvElOPMEnt AnD thE nEwBORn PERIOD
Another difference between the sleep of young infants and older individuals (not
reflected in Figure 2.22) is in sleep–wake cycles. Newborns generally cycle between
sleep and waking states several times in a 24­hour period, sleeping slightly more at
night than during the day (Whitney & Thoman, 1994). Although newborns are
likely to be awake during part of their parents’ normal sleep time, they gradually
develop the more mature pattern of sleeping through the night.
The age at which infants’ sleep patterns come to match those of adults depends
very much on cultural practices and pressures. For example, many infants in the
United States sleep through the night by around 4 months of age—a development
actively encouraged by their parents. Indeed, tired parents employ many different
strategies to get their infants to sleep through the night—from adopting elaborate,
often extended bedtime rituals intended to lull the baby into dreamland to gritting
their teeth and letting the baby cry himself or herself to sleep. (Note: one little­
known but particularly useful strategy for encouraging longer periods of nighttime
sleeping is exposing the infant to bright sunlight during the day [Harrison, 2004].)
In contrast with U.S. parents, Kipsigis parents in rural Kenya are relatively un­
concerned about their infants’ sleep patterns. Kipsigis babies are almost always
with their mothers. During the day, infants are often carried on their mother’s back
as she goes about her daily activities, and at night they sleep with her and are al­
lowed to nurse whenever they awaken. As a consequence, these babies distribute
their sleeping throughout the night and day for several months (Harkness & Super,
1995; Super & Harkness, 1986). Thus, cultures vary not only in terms of where ba­
bies sleep, as you learned in Chapter 1, but also in terms of how strongly parents
attempt to influence when their babies sleep.
How do you feel when you hear a baby cry? We imagine that, like most people,
you find the sound of a crying infant extremely unpleasant. Why is an infant’s cry
so aversive?
From an evolutionary point of view, adults’ aversion to infants’ crying could have
adaptive value. Infants cry for many reasons—including illness, pain, and hunger—
that require the attention of caregivers. Parents are likely to attempt to quiet their
crying infant by taking care of the infant’s needs, thereby promoting the infant’s
/ A
Most american parents want to avoid the
2 a.m. fate of this young father. They regard
their baby’s sleeping through the night as
a developmental triumph—the sooner, the

thE nEwBORn InFAnt n 73
survival. This fact has led some researchers to suggest that in times of hardship,
such as famine, cranky babies are more likely to survive than are placid ones, pos­
sibly because their distress elicits adult attention and they consequently get more
than their share of scarce food resources (DeVries, 1984).
Parents, especially first­timers, are often puzzled and anxious about why their
baby is crying. Indeed, one of the most frequent complaints pediatricians hear from
parents concerns crying that the parents think is excessive but is actually common
(Barr, 1998; Harkness et al., 1996). With experience, parents become better at in­
terpreting their infants’ crying, identifying characteristics of the cry itself (a sharp,
piercing cry usually signals pain, for example) and considering the context (such as
when the infant’s last feeding was) (Green, Jones, & Gustafson, 1987).
Do all newborns’ cries sound alike? Parents certainly do not think so. In fact,
within the first week after birth, mothers are able to distinguish their own new­
born’s cries from those of other infants (e.g., Cismaresco & Montagner, 1990).
Newborns’ cries are also differentially shaped by the sounds of the language in their
environment. A recent study that compared the crying patterns of French and Ger­
man newborns found that the infants’ cries followed different acoustic patterns that
mimicked the pitch patterns in their home language (Mampe et al., 2009).
After the newborn period, crying behavior typically increases, cresting at about
6 weeks of age, and then declines to about an hour a day for the rest of the first year
(St James­Roberts & Halil, 1991). On a daily basis, the peak time for crying is late
afternoon or evening, which can be quite disappointing to parents looking forward
to interacting with their baby at the end of the workday. Increased crying late in the
day may be due to an accumulation of excess stimulation during the daytime hours.
The nature of crying and the reasons for it change with development. Early on,
crying reflects discomfort from pain, hunger, cold, or overstimu lation, although,
from the beginning, infants also cry from frustration (Lewis, Alessandri, & Sullivan,
1990; Stenberg, Campos, & Emde, 1983). Over time, crying becomes more com­
municative, often seeming geared to “tell” caregivers something and to get them to
respond (Gustafson & Green, 1988).
Soothing What are the best ways to console a crying baby? Most of the
traditional standbys—rocking, singing lullabies, holding the baby up to the
shoulder, giving the baby a pacifier—work reasonably well (R. Campos,
1989; Korner & Thoman, 1970). Many effective soothing techniques involve
moderately intense and continuous or repetitive stimulation. The combina­
tion of holding, rocking, and talking or singing relieves an infant’s distress
better than any one of them alone ( Jahromi, Putnam, & Stifter, 2004).
One very common soothing technique is swaddling, which involves
wrapping a young baby tightly in cloths or a blanket, thereby restricting
limb movement. The tight wrapping provides a constant high level of tactile
stimulation and warmth. This technique is practiced in cultures as diverse
and widespread as those of the Navajo and Hopi in the American Southwest
(Chisholm, 1983), the Quechua in Peru (Tronick, Thomas, & Daltabuit,
1994), and rural villagers in Turkey (Delaney, 2000). Another traditional
approach, distracting an upset infant with interesting objects or events, can
also have a soothing effect, but the distress often resumes as soon as the in­
teresting stimulus is removed (Harman, Rothbart, & Posner, 1997).
Touch can also have a soothing effect on infants. In interactions with
an adult, infants fuss and cry less, and they smile and vocalize more, if the
adult pats, rubs, or strokes them (Field et al., 1996; Peláez­Nogueras et al.,
1996; Stack & Arnold, 1998; Stack & Muir, 1992). Carrying young infants,
carrying infants close to the parent’s body
results in less crying. Many Western parents
are now emulating the traditional carrying
methods of other societies around the world.
/ D
swaddling n a soothing technique, used
in many cultures, that involves wrapping
a baby tightly in cloths or a blanket

74 n chapTer 2 PREnAtAl DEvElOPMEnt AnD thE nEwBORn PERIOD
as is routinely done in many societies around the world, reduces the amount of cry­
ing that they do (Hunziker & Barr, 1986). In fact, a recent study found that cry­
ing infants showed sharper decreases in heart rate, physical movement, and crying
when carried about by their mother than when held in her lap. Similar quieting re­
sponses are seen in maternal carrying in other species (think of how still lion cubs
become when carried by their mother) and are conjectured to be innate coopera­
tive mechanisms that facilitate the mother’s carrying efforts (Esposito et al., 2013).
In other laboratory studies, placing a small drop of something sweet on a dis­
tressed newborn’s tongue has been shown to have a dramatic calming effect (Barr
et al., 1994; Blass & Camp, 2003; Smith & Blass, 1996). A taste of sucrose has an
equally dramatic effect on pain sensitivity; newborn boys who are given a sweet­
ened pacifier to suck during circumcision cry much less than babies who do not
receive this simple intervention (Blass & Hoffmeyer, 1991).
response to distress One question that often concerns parents is how to respond
to their infant’s signals of distress. They wonder whether quick and consistent sup­
portive responses will reward the infant for fussing and crying, and hence increase
these behaviors, or will instead give the infant a sense of security that leads to less
fussing and crying. An answer to this question comes from a longitudinal study
that found that infants whose cries were ignored during the first 9 weeks actually
cried less during the next 9 weeks (Hubbard & van IJzendoorn, 1991). Assessing
the severity of the infant’s distress before responding may be the key factor. If a par­
ent responds quickly to severe distress but delays responding to minor upset, the
infant may learn to cope with less serious problems on his or her own and hence
end up crying less overall.
colic No matter how or how much their parents try to soothe them, some infants
are prone to excessive, inconsolable crying for no apparent reason during the first
few months of life, a condition referred to as colic. Not only do “colicky” babies cry
a lot, but they also tend to have high­pitched, particularly unpleasant cries (Stifter,
Bono, & Spinrad, 2003). The causes of colic are unknown, and may include aller­
gic responses to their mothers’ diets (ingested via breast milk), formula intolerance,
immature gut development, and/or excessive gassiness. Unfortunately, colic is not
a rare condition: more than 1 in 10 young U.S. infants—and their parents—suffer
from it. Fortunately, it typically ends by around 3 months of age and leaves no ill
effects (Stifter & Braungart, 1992; St James­Roberts, Conroy, & Wilsher, 1998).
One of the best things parents with a colicky infant can do is seek social support,
which can provide relief from the stress, frustration, and sense of inadequacy and
incompetence they may feel because they are unable to relieve their baby’s distress.
Negative Outcomes at Birth
Although most recognized pregnancies in an industrialized society result in the
full­term birth of a healthy baby, sometimes the outcome is less positive. The worst
result, obviously, is the death of an infant. A much more common negative outcome
is low birth weight, which can have long­term consequences.
Infant Mortality
Infant mortality—death during the first year after birth—is now relatively rare in
the industrialized world, thanks to decades of improvements in public health and
general economic levels. In the United States, the 2010 infant mortality rate was 6.14
deaths per 1000 live births, the lowest in U.S. history (Miniño & Murphy, 2012).
colic n excessive, inconsolable crying by
a young infant for no apparent reason
infant mortality n death during the first
year after birth

thE nEwBORn InFAnt n 75
Although the U.S. infant mortality rate is at an all­time
low in absolute terms, it is high compared with that of other
industrialized nations. (Table 2.3 shows where the United
States’ infant mortality rate stood relative to the rates of a se­
lection of developed countries in 2008.) The relative ranking
of the United States has generally gotten worse over the past
several decades, because the infant mortality rates in many
other countries have had a higher rate of improvement.
The rates of infant mortality are starkly different for sub­
sets of the U.S. population. African American infants are
more than twice as likely to die before their first birthday
as European American infants are. Indeed, the infant mor­
tality rate for African Americans is similar to the rates ob­
served in many underdeveloped countries.
Why do so many babies die in the United States—the
richest country in the world? Why are African American
infants’ chances of survival so much poorer than those of
White American infants? There are many reasons, most
having to do with poverty. For example, many low­ income
mothers­to­be, including a disproportionate number of Af­
rican Americans, have no health insurance and thus lim­
ited access to good medical and prenatal care (Cohen &
Martinez, 2006). In contrast, the countries that rank above
the United States with respect to infant mortality usually
provide government­sponsored health care that guarantees
prenatal care at low or minimal cost.
In less developed countries, especially those suffering from a breakdown in social
organization due to war, famine, major epidemics, or persistent extreme poverty, the
infant mortality rates can be staggering. In countries like Afghanistan, Mali, and
Somalia, for example, roughly one of every 10 infants dies before age 1 (Central
Intelligence Agency, 2012).
Infant Mortality rates (IMr)* for Selected Developed Nations
with Lower rates than Those of the United States, 2008
Country Infant
Mortality Rate
Country Infant
Mortality Rate
Luxembourg 1.8 France 3.8
Slovenia 2.1 Israel 3.8
Iceland 2.5 Netherlands 3.8
Sweden 2.5 Denmark 4.0
Japan 2.6 Switzerland 4.0
Finland 2.6 Australia 4.1
Norway 2.7 Korea 4.7
Greece 2.7 United Kingdom 4.7
Czech Republic 2.8 New Zealand 4.9
Ireland 3.0 Estonia 5.0
Portugal 3.3 Hungary 5.6
Belgium 3.4 Poland 5.6
Germany 3.5 Canada 5.7
Spain 3.5 Slovak Republic 5.9
Austria 3.7 United States 6.6
Italy 3.7
*Infant Deaths per 1000 Live Births
Source: Adapted from Heisler, 2012
afghanistan has one of the highest infant
mortality rates in the world. among the
causes are extreme poverty, poor nutrition,
and poor sanitation. The great majority of
the population lacks access to clean water,
leading to a great many infant deaths
related to dysentery, severe diarrhea, and
other illnesses.

76 n chapTer 2 PREnAtAl DEvElOPMEnt AnD thE nEwBORn PERIOD
Low Birth Weight
The average newborn in the United States weighs 7½ pounds (most are between 5½
and 10 pounds). Infants who weigh less than 5½ pounds (2500 grams) at birth are
considered to be of low birth weight (LBW). Some LBW infants are premature, or
preterm; that is, they are born at 35 weeks after conception or earlier, instead of the
normal term of 38 weeks. Other LBW infants are referred to as small for gestational
age: they may be either preterm or full­term, but they weigh substantially less than is
normal for their gestational age, which is based on weeks since conception.
Slightly more than 8% of all U.S. newborns are of LBW (Martin et al., 2012). The
rate for African American LBW newborns is nearly twice as high (13.6%), and ap­
proaches the LBW rate observed in developing countries (16.5%) (United Nations
Children’s Fund and World Health Organization, 2004). As a group, LBW new­
borns have a heightened level of medical complications, as well as higher rates of
neurosensory deficits, more frequent illness, lower IQ scores, and lower educational
achievement. Very LBW babies (those weighing less than 1500
grams, or 3.3 pounds) are particularly vulnerable; these infants
accounted for 1.45% of live births in the United States in 2009
(Martin et al., 2011).
There are numerous causes of LBW and prematurity, includ­
ing many of the infant­mortality risk factors discussed earlier.
Another cause is the skyrocketing rate of twin, triplet, and other
multiple births as a result of the development of increasingly
successful treatments for infertility. (The use of fertility drugs
typically results in multiple eggs being released during ovulation;
the use of in vitro fertilization [IVF] usually involves the place­
ment of multiple laboratory­fertilized embryos in the uterus.) In
1980, 1 in every 53 infants born in the United States was a twin;
in 2009, 1 in every 30 infants was a twin (Martin, Hamilton, &
Osterman, 2012). The numbers for higher­order births (triplets
and up) have also increased dramatically in recent years. This is
a concern because the rates of LBW among multiples are quite
high: 56% for twins and higher than 90% for triplets and above
(Martin et al., 2011). (Box 2.5 discusses some of the challenges
faced by parents of LBW infants.)
Long-term outcomes What outcome can be expected for LBW newborns who
survive? This question becomes increasingly important as newborns of ever lower
birth weights—some as low as 800 grams (about 1.76 pounds)—are kept alive by
modern medical technology. The answer includes both bad news and good news.
The bad news is that, as a group, children who were LBW infants have a
higher incidence of developmental problems: the lower their birth weight, the
more likely they are to have persistent difficulties (e.g., Muraskas, Hasson, &
Besinger, 2004). They suffer from somewhat higher levels of hearing, language,
and cognitive impairments. In preschool and elementary school, they are more
likely to be distractible and hyperactive and to have learning disabilities. This
group is also more likely to experience a variety of social problems, including
poor peer and parent–child relations (Landry et al., 1990). Finally, adolescents
who were LBW babies are less likely than their siblings to complete high school
(Conley & Bennett, 2002). This result holds even within twin pairs; the twin
with higher birth weight is more likely to complete high school than is his or her
smaller co­twin (Black et al., 2007).
. /
These newborns were among 5503 triplet
births in the United States in 2010. That
year, there were also 313 quadruplet births
and 37 quintuplet and other higher-order
low birth weight (LBW) n a birth
weight of less than 5½ pounds (2500
premature n any child born at 35 weeks
after conception or earlier (as opposed to
the normal term of 38 weeks)
small for gestational age n babies
who weigh substantially less than is
normal for whatever their gestational age

thE nEwBORn InFAnt n 77
FIGURE 2.23 Small miracles Shown here is (a) one of the smallest newborns ever to survive
and (b) the same child at 14 years of age. Born in 1989 after just 27 weeks of gestation, Madeline
weighed a mere 9.9 ounces—approximately the equivalent of three bars of soap. extremely LBW
infants tend to suffer serious disabilities, but Madeline is remarkably healthy, other than being a bit
small for her age and having asthma. She entered high school as an honor student and enjoys playing
her violin and rollerblading.
(a) (b)
. h
I /
The good news is that the majority of LBW children turn out quite well. The
negative effects of their birth status gradually diminish, with children who were
slightly to moderately underweight as newborns generally ending up within the
normal range on most developmental measures (Kopp & Kaler, 1989; Liaw &
Brooks­Gunn, 1993; Meisels & Plunkett, 1988; Vohr & Garcia­Coll, 1988). Fig­
ure 2.23 depicts a particularly striking example of this fact (Muraskas et al., 2004).
Indeed, one recent follow­up study of extremely LBW infants (,1000 grams)
found that by 18 to 22 months of age, 16% were unimpaired and 22% were only
mildly impaired (Gargus et al., 2009).
Intervention programs What can be done to help an LBW infant overcome his
or her poor start in life? A variety of intervention programs for LBW newborns
offer a prime example of our theme about the role of research in improving the wel­
fare of children. In many of them, parents are active participants, a marked change
from past practice. Hospitals formerly did not allow parents to have any contact
with their LBW infants, mainly because of fear of infection. Parents are now en­
couraged to have as much physical contact and social interaction with their hospi­
talized infant as the baby’s condition allows.
One widely implemented intervention for hospitalized newborns is based on the
idea that being touched—cuddled, caressed, and carried—is a vital part of a new­
born’s life. Many LBW infants experience little stimulation of this kind because
of the precautions that must be taken with them, including keeping them in spe­
cial isolettes, hooked up to various life­support machines. To compensate for this
lack of everyday touching experience, Field and her colleagues (Field, 2001; Field,
Hernandez­Reif, & Freedman, 2004) developed a special therapy that involves

78 n chapTer 2 PREnAtAl DEvElOPMEnt AnD thE nEwBORn PERIOD
BOX 2.5: applications
Parenthood is challenging under the best of
circumstances, but it is especially so for the
parents of a preterm or LBW baby. First, they
have to accept their disappointment over the
fact that they do not have the perfect baby
they had hoped for, and they may also have
to cope with feelings of guilt (“What did I
do wrong?”), inadequacy (“How can I possi-
bly take care of such a tiny, fragile baby?”),
and fear (“Will my baby survive?”). In addi-
tion, caring for an LBW baby can be espe-
cially time-consuming and stressful and, if
the infant requires extended treatment, very
While all new parents have a great deal
to learn about caring for their infants, par-
ents of an LBW baby face special challenges
from the outset. In the hospital, they need to
learn how to interact successfully with their
fragile baby, who may be confined to an iso-
lette and hooked up to life-support equip-
ment. When their infant comes home, they
may have to cope with a baby who is fairly
passive and unresponsive, while being care-
ful not to overstimulate the infant in an effort
to elicit some response (Brazelton, Nugent,
& Lester, 1987; Patteson & Barnard, 1990).
LBW infants also tend to be fussier than the
average baby and more difficult to soothe
when they become upset (Greene, Fox, &
Lewis, 1983). To compound matters, they
often have a high-pitched cry that is particu-
larly unpleasant (Lester et al., 1989).
Another problem for parents is the fact
that LBW infants have more trouble falling
asleep, waking up, and staying alert than
do infants of normal birth weight, and their
feeding schedules are less regular (DiVitto &
Goldberg, 1979; Meisels & Plunkett, 1988).
Thus, it takes longer for the baby to get on
a predictable schedule, making the parents’
lives more hectic.
Parents of a preterm infant also need to
understand that their baby’s early develop-
ment will not follow the same timetable as a
full-term infant’s: developmental milestones
will be delayed, often linked more tightly to
gestational age at birth than to chronologi-
cal age after birth. For example, their infant
will not begin to smile at them at around 6
weeks of age, the time when full-term in-
fants usually reach this milestone. Instead,
they may have to wait several more weeks for
their baby to look them in the eye and break
into a heart-melting smile. Thus, preterm
infants are potentially more challenging to
care for while being less rewarding to inter-
act with. One consequence is that children
who were born preterm are more likely to be
victims of parental child abuse than are full-
term infants (e.g., Spencer et al., 2006).
One step that can be helpful to parents of
an LBW or preterm infant is learning more
about infant development. One intervention
program trained mothers—in the hospital
and after returning home—to interpret their
preterm babies’ signals (Achenbach et al.,
1990). When tested at age 7 years, their
children showed significantly better cogni-
tive skills than those of a comparison group
of LBW children whose parents did not re-
ceive training.
In a more recent longitudinal study, re-
searchers randomly assigned a group of
mothers of preterm infants to either receive
an intervention focused on increasing paren-
tal self-confidence and responsiveness or to
be in a control group that received no inter-
vention (Nordhov et al., 2012). At age 5, a
comparison of behavioral outcomes for the
children in each group (as rated by parents
and preschool teachers) indicated that the
children whose mothers experienced the
intervention had fewer behavior problems
than did the children whose mothers did not
experience the intervention. This was par-
ticularly the case in the areas of aggressive
behavior and attention deficits, which are
often associated with preterm birth. This re-
sult is especially informative because the
study’s randomized control design means
that the findings cannot be readily explained
by preexisting differences among the infants
and their families.
In addition, any parent who is trying to
deal with an LBW baby or an infant with
other problems would do well to seek social
support—from a spouse or partner, other
family members, friends, or a formal sup-
port group. One of the best-documented
phenomena in psychology is that we all
cope better with virtually any life problem
when we have support from other people. In-
deed, one potentially important component
of the successful intervention described in
the preceding paragraph is that it included
support sessions, in the hospital and during
home visits, designed to encourage parents
to talk about their experiences and express
their feelings.
parents of an LBW baby usually have to wait longer to experience the joy
of their child’s first social smile.

thE nEwBORn InFAnt n 79
massaging LBW babies and flexing their arms and legs (Figure
2.24). LBW babies who receive this therapy are more active and
alert and gain weight faster than those who are not massaged. As a
consequence, they get to go home earlier. Recent results also suggest
that having parents sing to their LBW newborns during their stay
in the hospital similarly improves the newborns’ health, while also
calming parents’ fears (Loewy et al., 2013).
Many intervention programs for LBW newborns extend beyond
their hospital stay, some for several years (e.g., Ramey & Campbell,
1992). The potential of such interventions was highlighted by the
Infant Health and Development Project (IHDP), which involved
985 children in eight major U.S. cities. This program was especially
well designed. For one thing, the infants were randomly assigned
to either the intervention group or the control group. For another,
all the children were provided good health care, which ensured that
this crucial factor could not affect the outcome of the research. The
intervention lasted for 3 years and included an intensive early­childhood education
program, as well as home visits that, among other things, encouraged the parents’
continued participation in the program.
Repeated assessments of the children in this study have consistently revealed
a positive effect of intervention, at least for infants who weighed more than 2000
grams. At 3 years of age, the intervention group had an advantage of 14 IQ points
over the control group, although the difference was larger for the LBW children
who had been relatively heavier at birth—2000 to 2500 grams versus less than 2000
grams. In follow­ups at 5 and 8 years of age, the intervention group continued to
show advantages, though these were limited to those participants who had weighed
more than 2000 grams at birth. In the most recent assessment, when the partici­
pants were 18 years old, differences favoring the intervention group—better aca­
demic performance and fewer behavior problems—were still observed, but, again,
only for those teenagers who had been the heavier LBW newborns (McCormick
et al., 2006). The researchers concluded that their results provide support for early
intervention to promote the development of at­risk LBW infants, but they also
noted that such interventions are less likely to be successful with children who were
extremely small newborns.
The IHDP story illustrates three important general points relevant to inter­
vention efforts designed for high­risk infants. First, many intervention programs
produce gains, but often those gains are relatively modest and diminish over time.
Second, the success of any intervention depends on the initial health status of the
infant. Like the IHDP, many programs for LBW babies have been most beneficial
to those infants who are less tiny at birth. This fact is cause for concern, as modern
medical technology makes it increasingly possible to save the lives of ever­smaller
infants who have a high risk of permanent, serious impairment. The third point is
the importance of cumulative risk: the more risks the infant endures, the lower the
chances of a good outcome. Because this principle is so important for all aspects of
development, we examine it in greater detail in the following section.
Multiple-Risk Model
Risk factors tend to occur together. For example, a woman who is so addicted to
alcohol, cocaine, or heroin that she continues to abuse the substance even though
she is pregnant is likely to be under a great deal of stress and unlikely to eat well,
. /
FIGURE 2.24 Infant massage every-
body enjoys a good massage, but hospital-
ized newborns particularly benefit from extra

80 n chapTer 2 PREnAtAl DEvElOPMEnt AnD thE nEwBORn PERIOD
take vitamins, earn a good income, seek prenatal care, have a strong social support
network, or take good care of herself in other ways. Furthermore, whatever the cu­
mulative effects of these prenatal risk factors, they will likely be compounded after
birth by the mother’s continuation of her unhealthy lifestyle and by her resulting
inability to provide good care for her child (e.g., Weston et al., 1989).
As you will see repeatedly throughout this book, a negative developmental
outcome—whether in terms of prenatal or later development—is more likely when
there are multiple risk factors. In a classic demonstration of this fact, Michael Rutter
(1979) reported a heightened incidence of psychiatric problems among English
children growing up in families with four or more risk factors (including marital
distress, low SES, paternal criminality, and maternal psychiatric disorder) (Figure
2.25). Thus, the likelihood of developing a disorder is slightly elevated for the child
of parents who fight a lot; but if the child’s family is also poor, the father engages
in criminal behavior, and the mother suffers from emotional problems, the child’s
risk is multiplied nearly tenfold. Similar risk patterns have been reported for IQ
(Sameroff et al., 1993) and social­emotional competence (Sameroff et al., 1987).
Poverty as a Developmental Hazard
Because it is such an important point, we cannot emphasize enough that the ex­
istence of multiple risks is strongly related to SES. Consider some of the factors
we have discussed that are known to be dangerous for fetal development: inade­
quate prenatal care, poor nutrition, illness, emotional stress, cigarette smoking, drug
abuse, and exposure to environmental and occupational hazards. All these factors
are more likely to be experienced by a woman living below the poverty line than
by a middle­class woman. It is no wonder, then, that on the whole, the outcome
of pregnancy is less positive for infants of lower­SES parents than for babies born
to middle­class parents (Kopp, 1990; Minde, 1993; Sameroff, 1986). Nor should
it be surprising that among LBW infants, the eventual developmental outcome is
poorer for those in lower­SES families (Drillien, 1964; Gross et al., 1997; Kalmár,
1996; Largo et al., 1989; Lee & Barratt, 1993; McCarton et al., 1997; Meisels &
Plunkett, 1988).
An equally sad fact is that in many countries, minority families are overrepre­
sented in the lowest SES levels. According to a study by the National Center for
Children in Poverty, in 2011, 22% of all U.S. children lived in families whose in­
come placed them below the poverty line ($22,350 for a family of four in that year).
However, among African American and Hispanic children, the percent living in
poverty was 39% and 34%, respectively (Addy, Engelhardt, & Skinner, 2013).
Thus, their SES places many minority fetuses, newborns, and children at increased
risk for developmental difficulties.
Risk and Resilience
There are, of course, individuals who, faced with multiple and seemingly over­
whelming developmental hazards, nevertheless do well. In studying such children,
researchers employ the concept of developmental resilience (Garmezy, 1983;
Masten, Best, & Garmezy, 1990; Sameroff, 1998). Resilient children—like those
in the Kauai study discussed in Chapter 1—often have two factors in their favor:
(1) certain personal characteristics, especially intelligence, responsiveness to others,
and a sense of being capable of achieving their goals; and (2) responsive care from
developmental resilience n successful
development in spite of multiple and
seemingly overwhelming developmental
Number of risk factors
1 2 3 4+
FIGURE 2.25 Multiple risk factors
children who grow up in families with mul-
tiple risk factors are more likely to develop
psychiatric disorders than are children from
families with only one or two problematic
characteristics (rutter, 1979).

chapter summary:
Prenatal Development
n Nature and nurture combine forces in prenatal development.
Much of this development is generated by the fetus itself,
making the fetus an active player in its own progress. Substan­
tial continuity exists between what goes on before and after
birth in that infants demonstrate the effects of what has hap­
pened to them in the womb.
n Prenatal development begins at the cellular level with
conception, the union of an egg from the mother and a
sperm from the father to form a single­celled zygote. The
zygote multiplies and divides on its way through a fallopian
n The zygote undergoes the processes of cell division, cell migra­
tion, cell differentiation, and cell death. These processes con­
tinue throughout prenatal development.
n When the zygote becomes implanted on the uterine wall, it
becomes an embryo. From that point, it is dependent on the
mother to obtain nourishment and oxygen and to get rid of
waste products through the placenta.
n Fetal behavior begins 5 or 6 weeks after conception with
simple movements, undetected by the mother, that become
increasingly complex and organized into patterns. Later,
the fetus practices behaviors vital to independent living,
including swallowing and a form of intrauterine “breathing.”
n The fetus experiences a wealth of stimulation both from
within the womb and from the external environment.
The fetus learns from this experience, as demonstrated by
studies showing that both fetuses and newborns can dis­
criminate between familiar and novel sounds, especially in
speech, and exhibit persistent taste preferences developed in
the womb.
n There are many hazards to prenatal development. The most
common fate of a fertilized egg is spontaneous abortion
(miscarriage). A wide range of environmental factors can be
In summary, development is highly complex, from the moment of conception
to the moment of birth. As you will see throughout this book, that complexity
continues over the ensuing years. Although early events and experiences can pro­
foundly affect later development, developmental outcomes are never a foregone
The experience of newborn infants is mediated by internal states of arousal, ranging from
deep sleep to intense crying, with large individual differences in the amount of time spent in
the different states. Newborns spend roughly half their time asleep, but after early infancy,
the amount of sleep declines steadily over many years. Researchers believe that the large
proportion of sleep time that newborns spend in REM sleep is important for the development
of the visual system and brain. Infants’ crying is a particularly salient form of behavior for
parents, and it generally elicits attention and caretaking. Effective soothing techniques pro-
vide moderately intense, continuous, or repetitive stimulation. How parents respond to their
young infant’s distress is related to later crying.
Negative outcomes of pregnancy are higher for minorities and for families living in pov-
erty. The United States has higher rates of infant mortality than do many other developed
nations. Just more than 8% of all infants born in the United States are LBW. Although most
will suffer few lasting effects, the long-term outcome of extremely LBW babies is often prob-
lematic. Several large-scale intervention programs have successfully improved the outcome
of LBW infants.
According to the multiple-risk model, the more risks that a fetus or child faces, the more
likely the child is to suffer from a variety of developmental problems. Low SES is associated
with many developmental hazards. Despite facing multiple risks, many children nevertheless
show remarkable resiliency and thrive.

82 n chapTer 2 PREnAtAl DEvElOPMEnt AnD thE nEwBORn PERIOD
Critical Thinking Questions
1. A recent cartoon showed a pregnant woman walking down a
street carrying an MP3 player with a set of very large head­
phones clamped around her protruding abdomen. What
point was it making? What research might have provided
the basis for the woman’s behavior, and what assumptions is
she making about what the result might be? If you or your
partner were pregnant, do you think you would do something
like this?
2. We hear a great deal about the terrible and tragic effects that
illegal drugs like cocaine and diseases like AIDS can have on
fetal development. But what two maternal behaviors associ­
ated with prenatal harm are actually the most common in the
United States today, and what are some of the effects they
can have?
3. Suppose you were in charge of a public health campaign to
improve prenatal development in the United States and you
could focus on only one factor. What would you target and
4. Describe some of the cultural differences that exist in beliefs
and practices with respect to conception, pregnancy, and
childbirth. Is there any practice of another culture that
appeals to you more than the practices with which you are
5. Are you more encouraged or more discouraged by the
results of intervention programs such as the IHDP?
What would it take to make their gains larger and longer
6. Speculate on why the infant mortality rate in the United
States has steadily gotten worse compared with that of other
7. Explain the basic idea of the multiple­risk model and how it
relates to poverty in terms of prenatal development and birth
hazardous to prenatal development. These include teratogens
from the external world and certain maternal characteris­
tics, such as age, nutritional status, physical health, behavior
(especially the use of legal or illegal drugs), and emotional
The Birth Experience
n Approximately 38 weeks after conception, the baby is ready to
be born. Usually, the behavior of the fetus helps to initiate the
birth process.
n Being squeezed through the birth canal has several beneficial
effects on the newborn, including preparing the infant to take
his or her first breath.
n Cultural practices surrounding childbirth vary greatly and
are in part related to the goals and values emphasized by the
The Newborn Infant
n Newborns’ states of arousal range from deep sleep to active
n The amount of time infants spend in the different arousal
states varies greatly, both across individuals and across
n REM sleep seems to compensate for the lack of visual stimu­
lation that results from the darkness of the womb, and for the
fact that newborns spend much of their time with their eyes
shut, asleep.
n The sound of a baby crying can be very aversive, and adults
employ many strategies to soothe distressed infants.
n The infant mortality rate in the United States is high rela­
tive to that of other developed countries. It is much higher for
babies born to low­SES parents.
n Infants born weighing less than 5½ pounds (2500 grams)
are referred to as being of low birth weight. LBW infants are
at risk for a variety of developmental problems, and the
lower the birth weight, the greater the risk of lasting
n A variety of intervention programs have been designed to
improve the course of development of LBW babies, but the
success of such programs depends very much on the number of
risk factors that threaten the baby.
n The multiple­risk model refers to the fact that infants with a
number of risk factors have a heightened likelihood of con­
tinued developmental problems. Poverty is a particularly insid­
ious risk to development, in part because it is associated with
numerous negative factors.
n Some children display resilience even in the face of sub­
stantial challenges. Resilience seems to result from cer­
tain personal characteristics and from responsive care from

Key Terms
amniotic sac, p. 48
apoptosis, p. 46
cephalocaudal development, p. 48
colic, p. 74
conception, p. 42
developmental resilience, p. 80
dose–response relation, p. 59
embryo, p. 45
embryonic stem cells, p. 45
epigenesis, p. 42
fetal alcohol spectrum disorder (FASD), p. 62
fetus, p. 45
fraternal twins, p. 47
gametes (germ cells), p. 42
habituation, p. 54
identical twins, p. 47
infant mortality, p. 74
low birth weight (LBW), p. 76
meiosis, p. 42
mitosis, p. 45
neural tube, p. 47
non­REM sleep, p. 70
phylogenetic continuity, p. 46
placenta, p. 48
premature, p. 76
rapid eye movement (REM) sleep, p. 70
sensitive period, p. 57
small for gestational age, p. 76
state, p. 70
sudden infant death syndrome (SIDS), p. 61
swaddling, p. 73
teratogen, p. 57
umbilical cord, p. 48
zygote, p. 44

TILLY WILLIS , Waiting, 2005 (oil on canvas)

Biology and Behavior
n Nature and Nurture
Genetic and Environmental Forces
Box 3.1: Applications Genetic Transmission of Disorders
Behavior Genetics
Box 3.2: Individual Differences Identical Twins
Reared Apart
n Brain Development
Structures of the Brain
Developmental Processes
Box 3.3: A Closer Look Mapping the Mind
The Importance of Experience
Brain Damage and Recovery
n The Body: Physical Growth and
Growth and Maturation
Nutritional Behavior
n Chapter Summary
chapter 3:

Several years ago, one of your authors received a call from the police. A city detective wanted to come by for a chat about some street and traffic signs that had been stolen—and also about the fact that one of the culprits was the author’s 17-year-old son. In an evening of hilarious fun and poor judgment, the son, along with two friends, had stolen more than a dozen
city signs and then concealed them in the family attic. His upset parents wondered
how their sweet, sensitive, kind, soon-to-be Eagle Scout son (who can be seen in
his innocent days on pages 137 and 594) could have failed to foresee the conse-
quences of his actions.
Many parents have similarly wondered how their once-model children could
have morphed into thoughtless, irresponsible, self-absorbed, impolite, bad-
tempered individuals simply by virtue of entering adolescence. Parents are not
the only ones surprised by the change in the behavior of their offspring: teen-
agers themselves are often taken aback and mystified as to what has come over
them. One 14-year-old girl lamented: “Sometimes, I just get overwhelmed now. . . .
There’s all this friend stuff and school and how I look and my parents. I just go in
my room and shut the door. . . . I don’t mean to be mean, but sometimes I just have
to go away and calm down by myself.” And a 15-year-old boy expressed similar
concerns: “I get in trouble a lot more now, but it’s for stuff I really didn’t mean. . . .
I forget to call home. I don’t know why. I just hang out with friends, and I get in-
volved with that and I forget. Then my parents get really mad, and then I get really
mad, and it’s a big mess” (Strauch, 2003).
New insights into these often abrupt developmental changes have come through
research into the biological underpinnings of behavioral development. Researchers
now suspect that many of the behavioral changes that are distressing both to ado-
lescents and their parents may be related to dramatic changes in brain structure and
functioning that occur during adolescence. In addition, there is growing evidence
that some genetic predispositions do not emerge until adolescence and that they
may contribute to these seemingly abrupt developmental changes.
Understanding the biological underpinnings of behavioral development is, of
course, essential to understanding development at any point in the life span. The
focus of this chapter is on the key biological factors that are in play from the mo-
ment of conception through adolescence, including the inheritance and influence
of genes, the development and early functioning of the brain, and important as-
pects of physical development and maturation. Every cell in our bodies carries the
genetic material that we inherited at our conception and that continues to influ-
ence our behavior throughout life. Every behavior we engage in is directed by our
brain. Everything we do at every age is mediated by a constantly changing physical
body—one that changes very rapidly and dramatically in the first few years of life
and in adolescence, but more slowly and subtly at other times.
Several of the themes that were set out in Chapter 1 figure prominently in this
chapter. Issues of nature and nurture, as well as individual differences among children,
are central throughout this whole chapter and especially the first section, which fo-
cuses on the interaction of genetic and environmental factors in development. Mech-
anisms of change are prominent in our discussions of the developmental role of genetic
factors and of the processes involved in the relationship between brain functioning
and behavior. Continuity in development is also highlighted throughout the chapter.
We again emphasize the activity-dependent nature of developmental processes and
the role of the active child in charting the course of his or her own development.
n Nature and Nurture
n The Active Child
n Continuity/Discontinuity
n Mechanisms of Change
n Individual Differences
n Research and Children’s

Nature and Nurture
Everything about you—from your physical structure, intellectual capacity, and per-
sonality characteristics to your preferences in hobbies and food—is a joint conse-
quence of the interaction between the genetic material you inherited from your
parents and the environments you have experienced from conception to the pres-
ent moment. These two factors—heredity and environment—work in concert to
influence both the ways in which you are like other people and the ways in which
you are unique.
Long before there was any understanding of the principles of heredity, people
were aware that some traits and characteristics “run in families” and that this ten-
dency was somehow related to procreation. For as long as there have been domes-
ticated animals, for example, farmers have practiced selective breeding to improve
certain characteristics of their livestock, such as the size of their horses and the milk
yield of their goats, cows, or yaks. People have also long been aware that the environ-
ment plays a role in development—that a nutritious diet, for example, is necessary
for livestock to produce a good milk supply or fine-quality wool. When scientists
first began to investigate the contributions of heredity and environment to develop-
ment, they generally emphasized one factor or the other as the prime influence—
heredity or environment, nature or nurture. In nineteenth-century En gland, for
example, Francis Galton (1869/1962), a cousin of Charles Darwin, identified men
who had achieved “eminence” in a variety of fields and concluded that talent runs
in families, because very close relatives of an eminent man (his father, brother, son)
were more likely to be high achievers themselves than were less close relatives.
Among Galton’s cases of closely related eminent men were John Stuart Mill and
his father, both respected English philosophers. However, Mill himself pointed out
that most of Galton’s eminent men were members of well-to-do families. In his
view, the relation between the achievement of these eminent men and their kinship
had less to do with biological ties than with the fact that they were similar in eco-
nomic well-being, social status, education, and other advantages and opportunities.
The phenomenal athletic ability of tennis
greats Venus and Serena Williams is almost
certainly due to the combination of nature—
the genes they inherited from their par-
ents—and nurture—the extensive coaching
they received from their father and the tire-
less emotional support provided by their

In short, according to Mill, Galton’s subjects rose to eminence more because of en-
vironmental factors than hereditary ones.
Our modern understanding of how characteristics are transmitted from parent
to offspring originated with insights achieved by Gregor Mendel, a nineteenth-
century Austrian monk who observed distinct patterns of inheritance in the pea
plants that he cross-bred in his monastery garden. Some aspects of these inheri-
tance patterns were later discovered to occur in all living things (see pages 92–93).
A much deeper understanding of how genetic influences operate came with James
Watson and Francis Crick’s 1953 identification of the structure of DNA, the basic
component of hereditary transmission.
Since that landmark discovery, enormous progress has been made in deciphering
the genetic code. Researchers have mapped the entire genome—the complete set
of genes—of myriad species of plants and animals, including chickens, mice, chim-
panzees, and humans, and even several extinct species,
including our closest evolutionary relative, Neander-
thals (R. E. Green et al., 2010). In 2010, a consortium
of geneticists began working to sequence the genomes
of 10,000 vertebrate species (Lander, 2011), the expec-
tation being that examining the genomes of such a di-
verse set of species will provide knowledge not only
about those species but also about human evolution
and the way genes function. Comparisons of the ge-
nomes of various species have already revealed much
about our human genetic endowment, and they have
provided numerous surprises.
One surprise was the number of genes that humans
have: the current estimate of around 21,000 genes is
far fewer than previous estimates, which ranged from
35,000 to more than 100,000 genes (Clamp et al.,
2007). A second major surprise was that most of those
genes are possessed by all living things. We humans
share a large proportion of our genes with bears, barnacles, beans, and bacteria. Most
of our genes are devoted, in decreasing order, to making us animals, vertebrates,
mammals, primates, and—finally—humans. In the next section, we will look at a
third surprise, one that may turn out to be a blockbuster.
As researchers have achieved better understanding of the role of hereditary fac-
tors in development, they have also come to appreciate the limits of what these
factors can account for on their own. Similarly, as knowledge has grown concern-
ing the influence of experience on development, it has become clear that experience
alone rarely provides a satisfactory account. Development results from the close and
continual interplay of nature and nurture—of genes and experience—and this in-
terplay is the focus of the following section.
Genetic and Environmental Forces
The interplay of genes and experience is exceedingly complex. To simplify our dis-
cussion of interactions among genetic and environmental factors, we will organize
it around the model of hereditary and environmental influences shown in Figure
3.1. Three key elements of the model are the genotype—the genetic material an
individual inherits; the phenotype—the observable expression of the genotype,
including both body characteristics and behavior; and the environment—every

. A
“We think it has something to do with your genome.”
genome n the complete set of genes of
any organism
genotype n the genetic material an indi-
vidual inherits
phenotype n the observable expres-
sion of the genotype, including both body
characteristics and behavior
environment n every aspect of an indi-
vidual and his or her surroundings other
than genes

aspect of the individual and his or her surroundings (including prenatal experience)
other than the genes themselves.
These three elements are involved in five relations that are fundamental in the
development of every child: (1) the parents’ genetic contribution to the child’s
genotype; (2) the contribution of the child’s genotype to his or her own phenotype;
(3) the contribution of the child’s environment to his or her phenotype; (4) the in-
fluence of the child’s phenotype on his or her environment; and (5) the influence
of the child’s environment on his or her genotype. We will now consider each of
these relations in turn.
1. Parent’s Genotype–Child’s Genotype
Relation 1 involves the transmission of genetic material—chromosomes and
genes—from parent to offspring. You caught a glimpse of this process in Chapter
2, when we discussed the gametes (one from the mother and one from the father)
that conjoin at conception to create a zygote. The nucleus of every cell in the body
contains chromosomes, long threadlike molecules made up of two twisted strands
of DNA (deoxyribonucleic acid). DNA carries all the biochemical instructions
involved in the formation and functioning of an organism. These instructions are
“packaged” in genes, the basic unit of heredity in all living things. Genes are sec-
tions of chromosomes. More specifically, each gene is a segment of DNA that is the
code for the production of particular proteins. Some proteins are the building blocks
of the body’s cells; others regulate the cells’ functioning. Genes affect development
and behavior only through the manufacture of proteins: “DNA’s information trans-
lated into flesh and blood” ( J. S. Levine & Suzuki, 1993, p. 19).
But here is the blockbuster surprise we mentioned earlier: researchers have dis-
covered that genes—at least “genes” as they have been traditionally defined—make
up only about 2% of the human genome (Mouse Genome Sequencing Consortium,
2002). Much of the rest of our genome—once thought to be “junk” DNA—turns
out to play a supporting role in influencing genetic transmission by regulating the
activity of protein-coding genes (e.g., Mendes Soares & Valcárcel, 2006). Just how
much of this noncoding DNA is vital to functioning, and precisely how it works,
is, as of today, shrouded in mystery and controversy. Given the pace of genetic re-
search, however, tomorrow may be a different story.
human heredity Humans normally have a total of 46 chromosomes in the nu-
cleus of each cell, except egg and sperm cells. (Recall from Chapter 2 that, as a
result of the type of cell division that produces gametes, eggs and sperm each
1. Parent’s Genotype–Child’s Genotype
2. Child’s Genotype–Child’s Phenotype
3. Child’s Environment–Child’s Phenotype
4. Child’s Phenotype–Child’s Environment
5. Child’s Environment–Child’s Genotype
FIGURE 3.1 Development Development
is a combined function of genetic and envi-
ronmental factors. The five numbered rela-
tions are discussed in detail in the text.
chromosomes n molecules of DNA that
transmit genetic information; chromo-
somes are made up of DNA
DNA (deoxyribonucleic acid) n mol-
ecules that carry all the biochemical
instructions involved in the formation and
functioning of an organism
genes n sections of chromosomes that
are the basic unit of heredity in all living

contain only 23 chromosomes.) These 46 chromosomes are
actually 23 pairs (Figure 3.2). With one exception—the sex
chromosomes—the two members of each chromosome pair are
of the same general size and shape (roughly the shape of the
letter X). Furthermore, each chromosome pair carries, usually
at corresponding locations, genes of the same type—that is,
sequences of DNA that are relevant to the same traits. One
member of each chromosome pair was inherited from each
parent. Thus, every individual has two copies of each gene, one
on the chromosome inherited from the father and one on the
chromosome from the mother. Your biological children will
each receive half of your genes, and your grandchildren will
have one-quarter (just as you have half your genes in common
with each of your biological parents and one-fourth with each
Sex determination As noted, the sex chromosomes, which
determine an individual’s sex, are an exception to the general
pattern of chromosome pairs being the same size and shape
and carrying corresponding genes. Females have two identi-
cal, largish sex chromosomes, called X chromosomes, but males
have one X chromosome and one much smaller Y chromo-
some (so called because it has the shape of the letter Y). Be-
cause a female has only X chromosomes, the division of her
germ cells results in all her eggs having an X. However, be-
cause a male is XY, half his sperm contain an X chromosome
and half contain a Y. For this reason, it is always the father who
determines the sex of offspring: if an X-bearing sperm fertil-
izes an egg, a female (XX) zygote results; if an egg is fertilized
by a Y-bearing sperm, the zygote is male (XY). It is the pres-
ence of a Y chromosome—not the fact of having only one X
chromosome—that makes an individual male. A gene on the
Y chromosome encodes the protein that triggers the prenatal
formation of testes by activating genes on other chromosomes. Subsequently, the
testes produce the hormone testosterone, which takes over the molding of male-
ness ( Jegalian & Lahn, 2001).
Diversity and individuality As we have noted, genes guarantee that humans will
be similar to one another in certain ways, both at the species level (we are all bipedal
and have opposable thumbs, for example) and at the individual level (i.e., family
resemblances). Genes also guarantee differences at both levels. Several mechanisms
contribute to genetic diversity among people.
One such mechanism is mutation, a change that occurs in a section of DNA.
Some mutations are random, spontaneous errors; others are caused by environ-
mental factors. Most are harmful. Those that occur in germ cells can be passed
on to offspring; many inherited diseases and disorders originate from a mutated
gene. (Box 3.1 on pages 94–95 discusses the genetic transmission of diseases and
Occasionally, however, a mutation that occurs in a germ cell or early in prena-
tal development makes individuals more viable, that is, more likely to survive—
perhaps by increasing their resistance to some disease or by increasing their ability
sex chromosomes n the chromosomes
(X and Y) that determine an individual’s
mutation n a change in a section of
FIGURE 3.2 Karyotype This color-
enhanced micrograph, called a karyotype,
shows the 23 pairs of chromosomes in a
healthy human male. as you can see, in
nearly all cases, the chromosomes of each
homologous pair are roughly the same size.
The notable exception is the sex chro-
mosomes (middle of bottom row): the Y
chromosome that determines maleness is
much smaller than the X chromosome. a
woman’s karyotype would contain two X
/ S

to adapt to some crucial aspect of their environment. Such mutations provide the
basis for evolution. This is because a person with the favorable mutated gene is
more likely to survive long enough to produce offspring, who, in turn, are likely to
possess the mutated gene, thus heightening their own chance of surviving and re-
producing. Across generations, these favorable genes proliferate in the gene pool
of the species.
A second mechanism that promotes variability among individuals is the random
assortment of chromosomes in the formation of egg and sperm. During germ-cell
division, the 23 pairs of chromosomes are shuffled randomly, with chance deter-
mining which member of each pair goes into each new egg or sperm. This means
that, for each germ cell, there are 223, or 8.4 million, possible combinations of chro-
mosomes. Thus, when a sperm and an egg unite, the odds are essentially zero that
any two individuals—even members of the same family—would have the same
genotype (except, of course, identical twins). Further variation is introduced by
the fact that when germ cells divide, the two members of a pair of chromosomes
sometimes swap sections of DNA. As a result of this process, referred to as cross-
ing over, some of the chromosomes that parents pass on to their offspring are con-
stituted differently from their own.
2. Child’s Genotype–Child’s Phenotype
We now turn to Relation 2 in Figure 3.1, the relation between one’s genotype and
one’s phenotype. Our examination of the genetic contribution to the phenotype be-
gins with a key fact: although every cell in your body contains copies of all the genes
you received from your parents, only some of those genes are expressed. At any
given time in any cell in the body, some genes are active (turned on), while others
are not. Some genes that are hard at work in neurons, for example, are totally at rest
in toenail cells. As you will see, there are several reasons for this.
Gene expression: Developmental changes Genes influence development and
behavior only when they are turned on, and human development proceeds nor-
mally, from conception to death, only if genes get switched on and off in the right
place, at the right time, and for the right length of time. Some genes are turned on
in only a few cells and for only a few hours and then are switched off permanently.
This pattern is typical during embryological development when, for example, the
genes that are turned on in certain cells lead them to specialize for arm, hand, and
fingerprint formation. Other genes are involved in the basic functioning of almost
all cells almost all the time.
The switching on and off of genes is controlled primarily by regulator genes.
The activation or inactivation of one gene is always part of a chain of genetic
events. When one gene is switched on, it causes another gene to turn on or off,
which has an impact on the status of yet other genes. Thus, genes never function
in isolation. Instead, they belong to extensive networks in which the expression of
one gene is a precondition for the expression of another, and so on. The continuous
switching on and off of genes underlies development throughout life, from the ini-
tial prenatal differentiation of cells to the gene-induced events of puberty to many
of the changes related to aging.
External factors can affect the switching on and off of genes. A dramatic exam-
ple is the effect of thalidomide on limb development (described in Chapter 2), in
which the sedative interferes with the functioning of genes underpinning normal
growth factors (Ito et al., 2010). Another example comes from the fact that early
These elvis impersonators look like elvis,
sneer like elvis, and even sing like elvis
(sort of). But they are not the King. The
probability that any two humans (other than
identical twins) have the same genotype is
essentially zero.
crossing over n the process by which
sections of DNA switch from one chromo-
some to the other; crossing over promotes
variability among individuals
regulator genes n genes that control
the activity of other genes

visual experience is necessary for the normal development of the visual system, be-
cause it causes the switching on of certain genes, which, in turn, switch on other
genes in the visual cortex (Maya-Vetencourt & Origlia, 2012). The ramifications
of decreased visual experience are observed in cases of children with cataracts that
are not removed early in life, as discussed later in this chapter.
The fact that regulator genes can repeatedly switch other genes on and off in
different patterns means that a given gene can function multiple times in multiple
places during development. All that is required is that the gene’s expression be
controlled by different regulator genes at different times. This on-again, off-again
functioning of individual genes results in enormous diversity in genetic expression.
By analogy, consider the fact that this book is written with only 26 letters and prob-
ably only a few thousand different words made up of combinations of those letters.
The meaning comes from the order in which the letters occur, the order in which
they have been “switched on and off ” by the authors.
Gene expression: Dominance patterns Many of an individual’s genes are never
expressed; some others are only partially expressed. One reason for this is the fact
that about one-third of human genes have two or more different forms, known as
alleles. The alleles of a given gene influence the same trait or characteristic (e.g.,
eye color), but they contribute to different developmental outcomes (e.g., brown,
blue, hazel, gray eyes).
Let’s consider the simplest pattern of gene expression—the one discovered
by Mendel and referred to as the dominant–recessive pattern. The explanation for
this pattern (unknown to Mendel) is that some genes have only two alleles, one
of which is dominant and the other recessive. In this pattern, there are two pos-
sibilities: (1) a person can inherit two of the same allele—
two dominant or two recessive—and thus be homozygous
for the trait in question; or (2) the person can inherit two
different alleles—one dominant and the other recessive—
and thus be heterozygous for the trait. When an individual
is homozygous, with either two dominant or two recessive
alleles, the corresponding trait will be expressed. When an
individual is heterozygous for a trait, the instructions of the
dominant allele will be expressed (see Figure 3.3).
To illustrate, let us consider two traits of no importance
to human survival: the ability to roll one’s tongue lengthwise
and curliness of hair. If you can roll your tongue lengthwise
into the shape of a tube, then at least one, but not necessar-
ily both, of your parents must also possess this remarkable
but useless talent. From this statement (and Figure 3.3),
you should be able to figure out that tongue rolling is gov-
erned by a dominant allele. In contrast, if you have straight
hair, then both of your parents must carry an allele for this
trait, although it is possible that neither of them actually has
straight hair. This is because straight hair is governed by a recessive gene, and curly
hair is governed by a dominant gene.
The sex chromosomes present an interesting wrinkle in the story of dominance
patterns. The X chromosome carries roughly 1500 genes, whereas the much smaller
Y chromosome carries only about 200. Thus, when a female inherits a recessive al-
lele on the X chromosome from her mother, she is likely to have a dominant allele
on the chromosome from her father to suppress it, so she will not express the trait
B b
B = dominant gene for brown hair b = recessive gene for blond hair
b B b b b
B b
FIGURE 3.3 Mendelian inheritance
patterns pictured here are the Mendelian
inheritance patterns for the offspring of two
brown-haired parents who are both heterozy-
gous for hair color. The allele for brown hair
(B) is dominant, and that for blond hair (b)
is recessive. Note that these parents have
three chances out of four of producing chil-
dren with brown hair. They have two chances
in four of producing brown-haired children
who carry the gene for blond hair.
alleles n two or more different forms of
a gene
dominant allele n the allele that, if
present, gets expressed
recessive allele n the allele that is not
expressed if a dominant allele is present
homozygous n having two of the same
allele for a trait
heterozygous n having two different
alleles for a trait

in question. In contrast, when a male inherits the same recessive allele on the X
chromosome from his mother, he likely will not have a dominant allele from his
father to override it, so he will express the trait. This difference in sex-linked in-
heritance is one reason for the greater vulnerability of males described in Chapter
2 (Box 2.2): they are more likely to suffer a variety of inherited disorders caused by
recessive alleles on their X chromosome (see also Box 3.1).
Despite the traditional emphasis given to it, the dominant–recessive pattern of
inheritance, in which a single gene affects a particular trait, pertains to relatively
few human traits—such as hair color, blood type, abundance of body hair, and the
like—as well as to a large number of genetic disorders Much more commonly, a
single gene can affect multiple traits; both alleles can be fully expressed or blended
in heterozygous individuals; and some genes are expressed differently, depending
on whether they are inherited from the mother or from the father.
Inheritance patterns are vastly more complicated for most of the traits and
behaviors that are of primary interest to behavioral scientists. These traits, such
as shyness, aggression, thrill-seeking, and language learning, involve polygenic
inheritance, in which several different genes contribute to any given phenotypic
outcome. Gene-outcome linkages are particularly difficult to detect when many
genes are involved. For this reason, you should be skeptical whenever you encounter
newspaper headlines announcing the discovery of “a gene for” a complex human
trait or predisposition.
3. Child’s Environment–Child’s Phenotype
We now come to Relation 3 in our model—the impact of the environment on
the child’s phenotype. (Remember, the environment includes everything not in
the genetic material itself, including the variety of prenatal experiences discussed
in Chapter 2.) As the model indicates, the child’s observable characteristics re-
sult from the interaction between environmental factors and the child’s genetic
Because of the continuous interaction of genotype and environment, a given
genotype will develop differently in different environments. This idea is expressed
by the concept of the norm of reaction (Dobzhansky, 1955), which refers to all the
phenotypes that could theoretically result from a given genotype in relation to all
the environments in which it could survive and develop. According to this concept,
for any given genotype developing in varying environments, a range of outcomes
would be possible. A child with a given genotype would probably develop quite dif-
ferently in a loving, supportive family than he or she would in an alienating, abusive
family. (Figure 3.4 offers a classic illustration of the norm of reaction in a genotype–
environment interaction.)
examples of genotype–environment interaction Genotype–environment in-
teractions can be studied directly by randomly assigning nonhuman animals with
known genotypes to be raised in a wide variety of environmental conditions. If
genetically identical animals develop differently in different environments, re-
searchers can infer that environmental factors must be responsible for the different
developmental outcomes. Scientists cannot, of course, randomly assign humans to
different rearing conditions, but there are powerful naturally occurring examples of
genotype–environment interactions for humans.
One such example is phenylketonuria (PKU), a disorder related to a defective
recessive gene on chromosome 12. Individuals who inherit this gene from both
polygenic inheritance n inheritance
in which traits are governed by more than
one gene
norm of reaction n all the phenotypes
that can theoretically result from a given
genotype in relation to all the environ-
ments in which it can survive and develop
phenylketonuria (PKU) n a disorder
related to a defective recessive gene on
chromosome 12 that prevents metabolism
of phenylalanine

Thousands of human disorders—many of
them extremely rare—are presently known to
have genetic origins. Although our discussion
here will focus on the behaviors and psycho-
logical symptoms associated with such dis-
orders, most of them also involve a variety
of physical symptoms, often including un-
usual physical appearance (e.g., distorted
facial features), organ defects (e.g., heart
problems), and atypical brain development.
These and other genetically based conditions
can be inherited in several different ways.
Dominant–Recessive Patterns
Many genetic disorders involve the
dominant–recessive pattern of inheritance,
occurring only when an individual has two
recessive alleles for the condition. To date,
more than 2850 such disorders have been
identified (Lander, 2011). Recessive-gene
disorders include PKU (discussed on pages
94 and 96) and sickle-cell anemia (dis-
cussed below), as well as Tay-Sachs disease,
cystic fibrosis, and many others. Disorders
that are caused by a dominant gene include
Huntington disease (a progressive and al-
ways fatal degenerative condition of the
brain) and neurofibromatosis (a disorder in
which nerve fibers develop tumors). A com-
bination of severe speech, language, and
motor difficulties that is common in a par-
ticular family in England has been traced to
a mutation of a single gene (referred to as
FOXP2) that acts in a dominant fashion (see
S. E. Fisher & Scharff, 2009).
In some cases, a single gene can have
both harmful and beneficial effects. One
such case is sickle-cell disease, in which
red blood cells are sickle-shaped rather
than round, diminishing their capacity to
transport oxygen. This disease, which can
be debilitating and sometimes fatal, affects
about 1 of every 500 African Americans. It
is a recessive-gene disorder, so individuals
who are homozygous for this trait (inheriting
two sickle-cell genes, one from each parent)
will suffer from the disease. Individuals who
are heterozygous for this trait (carrying one
normal and one sickle-cell gene) have some
abnormality in their blood cells but usually
experience no negative effects. In fact, if
they live in regions of the world—like West
Africa—where malaria is common, they ben-
efit, because the sickle cells in their blood
confer resistance against this deadly dis-
ease. In nineteenth-century Africa, malaria
came to be known as the “White man’s dis-
ease” because so many European explorers,
lacking the sickle-cell gene, died of it.
Note that even when the root cause of a
disorder is a single gene, it does not mean
that that one gene is responsible for all man-
ifestations of the disorder. The single gene
simply starts a cascade of events, turning on
and turning off multiple genes with effects
on many different aspects of the individual’s
subsequent development.
Polygenic Inheritance
Many common human disorders are believed
to result from interactions among multiple in-
herited genes, often in conjunction with envi-
ronmental factors. Among the many diseases
in this category are some forms of cancer and
heart disease, Type 1 and Type 2 diabetes,
and asthma. Psychiatric disorders, such as
schizophrenia, and behavior disorders, such
as attention-deficit hyperactivity disorder,
probably also involve multiple genes. More
than 1100 gene loci affecting common traits
and diseases have been identified to date,
due largely to continually improving methods
for genetic epidemiology (Lander, 2011).
Sex-Linked Inheritance
As mentioned in the text, some single-gene
conditions are carried on the X chromosome
and are much more common in males. (Fe-
males can inherit such conditions, but only
if they inherit the culprit recessive alleles on
both of their X chromosomes.) Sex-linked dis-
orders range from relatively minor problems,
like male-pattern baldness and red–green
color blindness, to very serious problems, in-
cluding hemophilia and Duchenne muscu-
lar dystrophy. Another sex-linked disorder is
fragile-X syndrome, which involves mutations
in the X chromosome and is the most com-
mon inherited form of intellectual disability.
Chromosomal Anomalies
Some genetic disorders originate with errors
in germ-cell division that result in a zygote
that has either more or less than the normal
complement of chromosomes. Most such
zygotes cannot survive, but some do. Down
syndrome most commonly originates when
the mother’s egg cells do not divide prop-
erly, and an egg that is fertilized contains an
extra copy of chromosome 21. The probabil-
ity of such errors in cell division increases
with age, with the incidence of giving birth
to a child with Down syndrome being mark-
edly higher for women older than 35. (In-
creased paternal age has also been linked to
the incidence of Down syndrome, though to
a lesser extent [De Souza, Alberman, & Mor-
ris, 2009; Hurles, 2012]). The boy pictured
on the next page shows some of the facial
features common to individuals with Down
syndrome, which is also marked by intellec-
tual disability (ranging from mild to severe),
a number of physical problems, and a sweet
Other genetic disorders arise from extra
or missing sex chromosomes. For exam-
ple, Klinefelter syndrome, which affects
between 1 in 500 to 1000 males in the
United States, involves an extra X chromo-
some (XXY). The physical signs of this syn-
drome, which can include small testes and
elongated limbs, often go unnoticed, but in-
fertility is common. Turner syndrome, which
affects 1 in 2500 U.S. women, involves a
missing X chromosome (XO) and is usually
characterized by short stature, stunted sex-
ual development at puberty, and infertility.
Gene Anomalies
Just as genetic disorders can originate from
extra or missing chromosomes, so too can
they result from extra, missing, or abnormal
genes. One intriguing instance is Williams
syndrome. This rare genetic disorder in-
volves a variety of cognitive impairments,
most noticeably in spatial and visual skills,
but relatively less impairment in language
ability (e.g., Musolino & Landau, 2012;
Skwerer & Tager-Flusberg, 2011). Individu-
als with Williams syndrome are also typically
characterized by outgoing personalities and
friendliness paired with anxiety and pho-
bias. This condition has been traced to the
deletion of a small section of approximately
25 genes on chromosome 7. Some individ-
uals, however, have a smaller deletion; in
BOX 3.1: applications

these cases, the degree of impairment is
decreased, suggesting a clear relationship
between the number of genes deleted and
the resulting phenotype (Karmiloff-Smith et
al., 2012). Interestingly, some individuals
show a duplication of the same section of
genes that is deleted in Williams syndrome.
In this disorder, known as 7q11.23 duplica-
tion syndrome, the pattern of abilities and
disabilities is flipped, with individuals ex-
hibiting relatively weak speech and language
abilities paired with relatively strong visuo-
spatial skills (Mervis & Velleman, 2011;
Osborne & Mervis, 2007).
Regulator Gene Defects
Many disorders are thought to originate
from defects in regulator genes, which, as
discussed on page 91, control the expres-
sion of other genes. For example, a defect
in the regulator gene that initiates the de-
velopment of a male can interrupt the nor-
mal chain of events, occasionally resulting
in a newborn who has female genitalia but
is genetically male. Such cases often come
to light when a young woman fails to begin
menstruating or when a fertility clinic dis-
covers that the reason a couple has failed
to conceive is that the person trying to get
pregnant is genetically male.
Unidentified Genetic Basis
In addition to the known gene-disorder links,
there are many syndromes whose genetic or-
igins are clear from their inheritance pat-
terns but whose specific genetic cause has
yet to be identified. For example, dyslexia
is a highly heritable reading disability that
probably stems from a variety of gene-based
conditions. Another example is Tourette syn-
drome. Individuals with this disorder gener-
ally display a variety of tics, ranging from
involuntary twitching and jerking to com-
pulsively blurting out obscenities. Research
suggests that Tourette syndrome probably
involves a complex pattern of inheritance,
making precise determination of the cause
very difficult (O’Rourke et al., 2009).
The same is true for autism spectrum dis-
order (ASD), which includes both autism
and Asperger syndrome and involves a wide
range of deficits in social skills and commu-
nication. In 2008, in various U.S. districts
monitored by the Centers for Disease Con-
trol, it was estimated that the ASD preva-
lence rate among 8-year-olds was 1 in 88
children (age 8 is thought to be the age of
peak prevalence), with boys being 5 times
more likely than girls to be identified as hav-
ing the disorder (Baio, 2012). The diagno-
sis of ASD is based on major impairments
in social interaction and communication
skills and a limited set of interests or re-
petitive behaviors. Individuals with Asperger
syndrome tend to have a milder array of
symptoms and usually do not experience dif-
ficulties in language development.
ASD includes individuals with not only a
range of disabilities but also, in some cases,
remarkable talents in a narrowly focused
area, such as mathematics or drawing. ASD
is known to be highly heritable: twin studies
have revealed that identical twins (who share
100% of their genes) are more than twice
as likely as fraternal twins (who share 50%
of their genes) to share an autism diagnosis
(Ronald & Hoekstra, 2011). The difficulty
in identifying the specific genetic basis for
autism spectrum disorder is highlighted by
the fact that, at present, there are more than
100 candidate genes associated with ASD
(Geschwind, 2011; L. M. Xu et al., 2012).
The number of children diagnosed with
ASD has increased dramatically in recent
years. Indeed, in the districts tracked by the
Centers for Disease Control, the ASD prev-
alence estimates for 8-year-olds in 2008
represented a 78% increase over those for
2002 (Baio, 2012). Part of the increase is
believed to be due to greater public aware-
ness of the syndrome, leading to a higher
level of detection by parents, teachers, and
doctors. In addition, current diagnostic cri-
teria are broader than those of the past. It is
thus unclear to what degree the increased
level of diagnoses accurately reflects a
change in the actual incidence of ASD (e.g.,
Gernsbacher, Dawson, & Goldsmith, 2005).
One factor that was highly publicized as
a possible cause of the so-called autism ep-
idemic—the MMR vaccine that is routinely
given to young children to prevent measles,
mumps, and rubella—has been definitively
ruled out (A. W. McMahon et al., 2008; Price
et al., 2010). Indeed, the original study re-
porting a link between the MMR vaccine and
ASD (Wakefield et al., 1998) has been shown
to be fraudulent and has been retracted
(Godlee, Smith, & Marcovitch, 2011). Un-
fortunately, however, some parents continue
to deny their children this important vaccine,
needlessly putting them at risk for the ill-
nesses that the vaccine prevents.
One of the most common
identifiable causes of intel-
lectual disability is Down
syndrome, which occurs in
about 1 of every 1000 births
in the United States. The risk
increases dramatically with
the age of the parents, espe-
cially the mother; by the age
of 45, a woman has 1 chance
in 32 of having a baby with
Down syndrome. The degree
of disability varies greatly and
depends in part on the kind
of care and early intervention
children receive.

parents cannot metabolize phenylalanine, an amino acid present in many foods
(especially red meats) and in artificial sweeteners. If they eat a normal diet, phe-
nylalanine accumulates in the bloodstream, causing impaired brain development
that results in severe intellectual impairment. However, if infants
with the PKU gene are identified shortly after birth and placed on
a stringent diet free of phenylalanine, intellectual impairment can
be avoided, as long as the diet is carefully maintained. Thus, a given
genotype results in quite different phenotypes—cognitive disabil-
ity or relatively normal intelligence—depending on environmen-
tal circumstances. Because early detection of this genetic disorder
has such a positive effect on children’s developmental outcomes,
all newborn infants in the United States are routinely screened for
PKU, as well as for a number of other severe and easily detected ge-
netic disorders.
A second example of a genotype–environment interaction comes
from an important study showing that the effects of abusive parent-
ing vary in severity as a function of the child’s genotype (Caspi et
al., 2002). The researchers wanted to determine why some children
who experience severe maltreatment become violent and antisocial
as adults, whereas others who are exposed to the same abuse do
not. The results, shown in Figure 3.5, revealed the importance of a
High elevation
Medium elevation
Low elevation
FIGURE 3.4 The norm of reaction con-
cept This classic figure illustrates how a
given genotype can develop differently in
different environments. Three cuttings were
made from each of seven individual plants;
thus, the cuttings in each set of three had
identical genes. The three cuttings from each
plant were then planted at three different ele-
vations, ranging from sea level to high moun-
tains. The question of interest was whether
the orderly differences in height that were
observed at the low elevation would persist at
the two higher elevations. as you can see, the
order of the heights of the plants is neither
orderly nor consistent across the different
environments. For example, the first plant
on the left that is the tallest one at sea level
and at high elevation is one of the shortest at
medium elevation. The fourth plant is tallest
at the medium elevation and shortest at the
highest. Notice that not a single plant is
always either the tallest or the shortest across
the three elevations. “The phenotype is the
unique consequence of a particular geno-
type developing in a particular environment”
(Lewontin, 1982, pp. 22–23).
Childhood maltreatment
l b
activity, n = 163
activity, n = 279
FIGURE 3.5 Genotype and environ-
ment This graph shows the level of anti-
social behavior observed in young men as
a function of the degree to which they had
been maltreated in childhood. as this figure
shows, those young men who had experi-
enced severe maltreatment were in general
more likely to engage in antisocial behavior
than were those who had experienced none.
however, the effect was much stronger for
those individuals who had a relatively inac-
tive MaOa gene. (adapted from caspi et al.,
2002, p. 852)

combination of environmental and genetic factors leading to antisocial outcomes—
suffering abusive treatment as a child and possessing a particular variant of MAOA,
an X-linked gene known to inhibit brain chemicals associated with aggression.
Young men who had a relatively inactive version of the MAOA gene, and who had
experienced severe maltreatment, grew up to be more antisocial than other men.
More concretely, 85% of the maltreated group with the relatively inactive gene
developed some form of antisocial behavior, and they were almost 10 times more
likely to be convicted of a violent crime. The important point here is that neither
factor by itself (possessing the inactive MAOA gene or being abused) predisposed
boys to become highly aggressive; the higher incidence of antisocial behavior was
observed only for the group with both factors. As the authors of that study note,
knowledge about specific genetic risk factors that make people more susceptible
to particular environmental effects could strengthen multiple-risk models, such as
those discussed in the previous two chapters.
parental contributions to the child’s environment Obviously, a highly salient
and important part of a child’s environment is the parents’ relationship with the
child—the manner in which they interact with him or her, the general
home environment they provide, the experiences they arrange for the
child, the encouragement they offer for particular behaviors, attitudes,
and activities, and so on. Less obvious is the idea that the environment
that parents provide for their children is due in part to the parents’ own
genetic makeup. Parents’ behavior toward their children (e.g., how warm
or reserved they are, how patient or short-fused) is genetically influ-
enced, as are the kinds of preferences, activities, and resources to which
they expose their children (Plomin & Bergeman, 1991). For example,
the child of a highly musical parent is likely to hear more music while
growing up than are children whose parents are less musically inclined.
Parents who are skilled readers and enjoy and value reading are likely
to read often for pleasure and information and are likely to have lots of
books around the house. They are also more likely to read frequently to
their children and to take them to the library. In contrast, parents for
whom reading is challenging and not a source of pleasure are less likely
to provide a highly literate environment for their children (Scarr, 1992).
4. Child’s Phenotype–Child’s Environment
Relation 4 in our model restates the active child theme—the child as a source of his or
her own development. As noted in Chapter 1, children are not just the passive recipi-
ents of a preexisting environment. Rather, they are active creators of the environment
in which they live in two important ways. First, by virtue of their nature and behav-
ior, they actively evoke certain kinds of responses from others (Scarr, 1992; Scarr &
McCartney, 1983). Babies who enjoy being cuddled are more likely to receive cud-
dling than are squirmy babies. Impulsive children hear “No,” “Don’t,” “Stop,” and “Be
careful” more often than inhibited children do. Indeed, the degree to which parent–
child relationships are mutually responsive is largely a function of the child’s geneti-
cally influenced behavioral characteristics (Deater-Deckard & O’Connor, 2000).
The second way in which children create their own environment is by actively
selecting surroundings and experiences that match their interests, talents, and per-
sonality characteristics (Scarr, 1992). As soon as infants become capable of self-
locomotion, for example, they start selecting certain objects in the environment for
This parent enjoys reading novels for plea-
sure and reads extensively for her work.
She is providing a rich literary environment
for her young child. The child may become
an avid reader both because his mother’s
genetic makeup contributed to his enjoy-
ment of reading and because of the physical
environment (lots of books) and the social
environment (encouragement of an interest
in books) that the mother has provided.

exploration. Some very young children (especially boys) develop extremely intense
interests in particular kinds of objects or activities that do not stem from parental
encouragement (DeLoache, Simcock, & Macari, 2007). For example, many little
boys become obsessed with vehicles and construction equipment. Other young
children develop idiosyncratic and even quite peculiar interests (e.g., blenders,
roadkill). For many parents, the origin of these preschool passions is totally ob-
scure, and occasionally worrisome, because they do not realize how common these
intense interests actually are.
Beginning in the preschool years, children’s friendship opportunities increasingly
depend on their own characteristics, as they choose playmates and pals with whom
they feel compatible—the “birds of a feather flock together” phenomenon. And, as
noted in Chapter 1, with age, children play an ever more active role in selecting their
own environment. As they gain more autonomy, they increasingly select aspects of
the environment that fit their temperament and abilities. Returning to the reading
example, children who enjoy reading will read more books than will children who
find reading tedious. The more they read, the more skillful readers they become,
leading them to choose increasingly more challenging books, which, in turn, leads
them to acquire advanced vocabulary, improve their language comprehension, and
enhance their general knowledge base, resulting in greater success in school.
5. Child’s Environment–Child’s Genotype
The fifth relationship in our model is perhaps the most surprising. Until fairly re-
cently, geneticists thought of the genotype as being “fixed” at birth. But as discussed
in Chapter 1 (page 11), the new field of epigenetics has turned this conventional
wisdom on its head. That is, it is now known that although the structure of DNA
remains “fixed” (mutations aside), certain epigenetic mechanisms, mediated by the
environment, can alter the functioning of genes and create stable changes in their
expression—and some of these changes can be passed on to the next generation.
Epigenetic factors can help explain why identical twins do not have identical
pathways through life: different environments can alter gene expression in subtle
ways across developmental time. These stable changes in gene expression that are
mediated by the environment involve processes of methylation, which silence gene
expression. Differences in experience over the course of development are reflected
in differences in methylation levels. Consider identical twin pairs at the age of 3
and at the age of 50, for example. Three-year-old co-twins have had highly over-
lapping life experiences, whereas many 50-year-old co-twins are likely to have had
a far more divergent range of experiences. In a study that measured differences
in DNA methylation levels in 3- and 50-year-old identical co-twins, researchers
found that, whereas there were virtually no differences in the 3-year-olds’ levels,
roughly one-third of the 50-year-olds showed “remarkable” differences—and the
greater the differences in the twins’ lifestyle and experiences, the greater the differ-
ences in their methylation levels (Fraga et al., 2005).
How might the environment exert its effects through epigenetic mechanisms?
To date, the bulk of the behavioral research on this topic has focused on nonhuman
animal models, with clear evidence that low-quality maternal care has epigenetic
effects, permanently changing the animal’s pattern of gene expression (for a recent
review, see van IJzendoorn, Bakermans–Kranenburg, & Ebstein, 2011). In particu-
lar, poor maternal care affects the methylation of genes involved in glucocorticoid
receptors, which influence how the animal copes with stress (e.g., T.-Y. Zhang &
Meaney, 2010). As you saw in Chapter 1, there is emerging evidence suggesting

similar effects of early stress on methylation in humans (e.g., Essex et al., 2013).
The myriad risk factors associated with growing up in poverty appear to act on de-
veloping children via epigenetic processes as well; adults who grew up in impover-
ished households exhibit different patterns of gene expression decades later than
do adults who grew up in high-SES homes, regardless of their SES as adults (e.g.,
G. E. Miller et al., 2009).
Our discussion of the five kinds of gene–environment interactions has empha-
sized the myriad challenges in understanding how genes function in the devel-
opment of individuals. Nevertheless, the conceptualization we have presented is
greatly simplified. This is particularly true for the fifth relationship—epigenetics—
which, when considered in full, suggests that the line between genes and environ-
ment is blurry at best. The complexity of gene–environment relationships raises
both challenges and opportunities for developmental scientists. One challenge is
that the genome can no longer comfortably be considered immutable irrespective
of the widely varying environments in which children develop. One opportunity is
that as this field continues to develop, it may become possible to determine which
aspects of the environment are most likely to have a lasting impact on children’s
eventual health and well-being.
Behavior Genetics
The rapidly expanding field known as behavior genetics is concerned with how
variation in behavior and development results from the interaction of genetic and en-
vironmental factors. Behavior geneticists ask the same sort of question Galton asked
about eminence: “Why are people different from one another?” Why, in any group
of human beings, do we vary in terms of how smart, sociable, depressed, aggressive,
and religious we are? The answer given by behavior geneticists is that all behavioral
traits are heritable; that is, they are all influenced to some degree by hereditary fac-
tors (Bouchard, 2004; Turkheimer, 2000). As noted, the kind of traits that have been
of particular interest to behavior geneticists—intelligence, sociability, mood, aggres-
sion, and the like—are polygenic, that is, affected by the combination of many genes.
They are also multifactorial, that is, affected by a host of environmental factors as
well as genetic ones. Thus, the potential sources of variation are vast.
To fully answer Galton’s question, behavior geneticists try to tease apart genetic
and environmental contributions to the differences observed among a population
of people or other animals. Two premises underlie this endeavor:
1. To the extent that genetic factors are important for a given trait or behavior,
individuals who are genotypically similar should be phenotypically similar. In
other words, behavior patterns should “run in families”: children should be
more similar to their parents and siblings than to second- or third-degree rel-
atives or unrelated individuals.
2. To the extent that shared environmental factors are important, individuals who
were reared together should be more similar than people who were reared apart.
Behavior Genetic Research Designs
As it was for Galton, the mainstay of modern behavior-genetics research is the
family study. In order to examine genetic and environmental contributions to a
given trait or characteristic, behavior geneticists first measure that trait in people
who vary in terms of genetic relatedness—parents and their children, identical and
behavior genetics n the science con-
cerned with how variation in behavior and
development results from the combina-
tion of genetic and environmental factors
heritable n refers to any characteristics
or traits that are influenced by heredity
multifactorial n refers to traits that are
affected by a host of environmental fac-
tors as well as genetic ones

fraternal twins, nontwin siblings, and so on. Next, they assess
how highly correlated the measures of the trait are among in-
dividuals who vary in the degree to which they are genetically
related. (As you may recall from Chapter 1, the strength and
direction of a correlation express the extent to which two vari-
ables are related; the higher the correlation, the more precisely
scores on one variable can be predicted from scores on the
other.) Finally, behavior geneticists compare the resulting cor-
relations to see if they are (1) higher for more closely related
individuals than for less closely related people, and (2) higher
for individuals who share the same environment than for in-
dividuals who do not.
There are several specialized family-study designs that are
particularly helpful in assessing genetic and environmental
influences. One is the twin-study design, which compares the
correlations for identical (monozygotic, or MZ) twins with
those for same-sex fraternal (dizygotic, or DZ) twins. As you will recall, identical
twins have 100% of their genes in common (though the expression of these genes
are affected by epigenetic factors over the course of development, as discussed in
the previous section), whereas fraternal twins are only 50% genetically similar (just
like nontwin siblings). For twins who grow up together, the degree of similarity of
the environment is generally assumed to be equal. Both types of twins shared the
same womb, were born at the same time, have lived in the same family and com-
munity, and are always the same age when tested. Thus, with different levels of
genetic similarity and essentially equal environmental similarity, the difference be-
tween the correlations for the two types of twins is treated as an index of the im-
portance of genetic factors. If the correlation between identical twins on a given
trait or behavior is substantially higher than that between fraternal
twins, it is assumed that genetic factors are substantially responsible
for the difference.
Another family-study design used for assessing genetic and envi-
ronmental influences is the adoption study. In this approach, research-
ers examine whether adopted children’s scores on a given measure
are correlated more highly with those of their biological parents and
siblings or with those of their adoptive parents and siblings. Genetic
influences are inferred to the extent that children resemble their bio-
logical relatives more than they do their adoptive ones.
The ideal behavior-genetics design—the adoptive twin study—
compares identical twins who grew up together versus identical twins
who were separated shortly after birth and raised apart. If the correla-
tions for twins reared apart are similar to those for twins reared together,
it suggests that environmental factors have little effect. Conversely, to
the extent that the correlations between identical twins who grew up
in different environments are lower than those for identical twins who
grew up together, environmental influence is inferred. Box 3.2 describes
some of the remarkable findings that have emerged from studies of
twins reared apart, as well as some of the problems with such research.
Family studies of intelligence The most common focus of
behavior-genetics family studies has been intelligence. Table 3.1 sum-
marizes the results of more than 100 family studies of IQ through

. A
“The title of my science project is ‘My LIttle Brother: Nature or Nurture.’”
Summary of Family Studies of Intelligence
Average Familial IQ Correlations (R)
Relationship Average R Reared-together
biological relatives
Number of Pairs
MZ twins 0.86 4672
DZ twins 0.60 5533
Siblings 0.47 26,473
Parent–offspring 0.42 8433
Half siblings 0.35 200
Cousins 0.15 1176
biological relatives
MZ twins 0.72 65
Siblings 0.24 203
Parent–offspring 0.24 720
nonbiological relatives
Siblings 0.32 714
Parent–offspring 0.24 720
Note: MZ 5 monozygotic; DZ 5 dizygotic.
Source: McGue et al. (1993)

adolescence. The pattern of results reveals both genetic and environmental in-
fluences. Genetic influence is shown by generally higher correlations for higher
degrees of genetic similarity. Most notable is the finding that identical (MZ) twins
resemble one another in IQ more than do same-sex fraternal (DZ) twins. At the
same time, environmental influences are reflected in the fact that iden tical twins are
not identical in terms of IQ. Further evidence for an environmental role is that MZ
twins who are reared together are more similar than those reared apart.
Oskar Stohr and Jack Yufa are identical
twins who were separated shortly after their
birth in Trinidad. Oskar was raised by his
grandmother in Germany as a Catholic and
a Nazi. Jack was raised by his father, in the
Caribbean, as a Jew. Despite their very dif-
ferent backgrounds, when the brothers first
met as middle-aged men recruited for a re-
search study in Minneapolis, they discov-
ered a remarkable number of similarities
between them:
They like spicy foods and sweet li-
queurs, are absent-minded, have a
habit of falling asleep in front of the
television, think it’s funny to sneeze
in a crowd of strangers, flush the toi-
let before using it, store rubber bands
on their wrists, read magazines back
to front, dip buttered toast in their
coffee. Oskar is domineering toward
women and yells at his wife, which
Jack did before he was separated.
(Holden, 1980, p. 1324)
Jack and Oskar are participants in the
Minnesota Study of Twins Reared Apart, an
extensive research project on identical twins
separated early in life (Bouchard et al.,
1990). More than 100 pairs of such twins
have been located, recruited for the study,
and brought to Minneapolis to undergo an
extensive battery of physiological and psy-
chological tests. Many twin siblings were
meeting for the first time since infancy. (The
reunited twins in the photo at right showed
almost as many striking similarities as did
Jack and Oskar, including their having held
several very similar jobs and being volunteer
firemen.) The motivation for this large-scale
study is to examine genetic and environ-
mental contributions to development and
behavior by comparing individuals who are
genetically identical but who grew up in dif-
ferent environments.
The Minnesota team of investigators has
been struck by the extent of the similari-
ties they have found in the separated twins;
they have identified genetic contributions
to “almost every behavioral trait so far in-
vestigated from reaction time to religiosity”
(Bouchard et al., 1990).
As striking as the similarities between
separated twins may be, there are several
problems with automatically
assuming that these similar-
ities are attributable to ge-
netic factors. One issue is
that it would be a great over-
simplification to suggest that
all of the similar traits shared
by separated twins are ge-
netic. For example, it would
be a stretch to argue that the
men in the photograph share
a set of genes that predeter-
mined that they both would
become firemen. As previ-
ously noted, genes code for
proteins, not for anything as complex as
an occupation (or choice of facial hair). An
additional issue is the practice of selective
placement: adoption agencies generally try
to place children with families of the same
general background and race, so the envi-
ronments of the separated siblings are often
similar in many ways. It is extremely rare
for separated twins to be raised like Jack
and Oskar, with different languages, reli-
gions, and cultures. In fact, the majority of
the twins in most behavior-genetics studies
are from predominantly White, middle-class
families in Western countries. As behav-
ior geneticists Levine and Suzuki (1993)
Take one of those kids and put him in
a really different environment, like
in a family of bushmen in Africa, or in
a farming village in mainland China,
and then come back twenty years
later and see if you find two firemen
who dress the same!
(p. 241)
BOX 3.2: individual differences
Identical twins Gerald Levey and Mark
Newman were separated at birth and reared
separately in middle-class Jewish homes in the
New York area. When reunited at the age of
31, they discovered, among many other simi-
larities, that they were both volunteer firemen
with droopy moustaches; long sideburns; and a
penchant for hunting, fishing, and John Wayne
movies. They even drank the same brand of
beer, from a can, which they held with their
pinkie tucked under the bottom and crushed
when they had emptied it.

Does the relative influence that genes and environment have on intelligence
change over the course of development? One might expect that as children get
older and have ever more (and more varied) experiences in the world, genetic in-
fluences on IQ would decrease. Surprisingly, recent studies have revealed exactly
the opposite pattern: as twins get older, the degree of variance in IQ accounted for
by their genetic similarity increases. In a study of 11,000 MZ and DZ twin pairs
across four countries, researchers found that the correlations in IQ between co-
twins increased with age for MZ twins and decreased with age for DZ twins. These
divergent patterns were observed first from childhood to adolescence, and again
from adolescence to young adulthood (Haworth et al., 2009). The same pattern of
results was revealed in a large longitudinal study that compared MZ and DZ twin
pairs in early childhood (2- to 4-year-olds) and middle childhood (7- to 10-year-
olds): for the younger children, shared environment accounted for more variance
than did shared genes, with the opposite pattern observed for the older children
(O. S. P. Davis, Haworth, & Plomin, 2009).
This surprising pattern of results—namely, that genetic influences increase with
age—is consistent with the idea that people actively construct their own envi-
ronment: the phenotype–environment correlation (Relation 3) discussed earlier
(McGue et al., 1993; Scarr & McCartney, 1983). As children get older, they in-
creasingly control their own experiences, and their parents have less influence over
their activities. The effects of education may be particularly relevant to this pattern
of results, given that educational experiences and achievements influence children’s
performance on measurements of intelligence. Younger children have little or no
choice about their educational setting and opportunities, whereas older children,
teens, and young adults have increasingly greater choices with regard to their edu-
cational experiences (choosing more or less challenging courses of study, more or
less academically oriented peer groups, and so on). It may be that identical twins’
IQs become more similar into adulthood because their common genetic predisposi-
tions lead them to select similar intellectual stimulation, whereas the IQs of frater-
nal twins become increasingly dissimilar because they choose divergent experiences
for themselves (Scarr & McCartney, 1983).
In their approach to the nature–nurture question, many behavior geneticists at-
tempt to quantify the degree to which genes contribute to various traits. To es-
timate how much of the variability in measures of a given trait is attributable to
genetic and environmental factors, they derive heritability estimates from correla-
tions of the type shown in Table 3.1. Heritability is a statistical estimate of how
much of the measured variance on a trait among individuals in a given population
is attributable to genetic differences among those individuals.
A crucial point to understand about heritability estimates is that they tell us
nothing about the relative contributions of genetic and environmental factors to
the development of an individual. Instead, they estimate how much of the varia-
tion among a given population of people is due to differences in their genes. The
heritability estimate for intelligence, for example, is generally considered to be ap-
proximately 50% (Bouchard, 2004; Plomin, 1990). This means that, for the popula-
tion studied, roughly 50% of the variation in IQ scores is due to genetic differences
among the members of the population. (It does not mean that 50% of your IQ score
is due to your genetic makeup and 50% is due to your experience.) Note that this
heritability estimate indicates that the environmental contribution to the variation
in IQ is also approximately 50%.
heritability n a statistical estimate of
the proportion of the measured variance
on a trait among individuals in a given
population that is attributable to genetic
differences among those individuals

Behavior-genetic analyses have been applied to many diverse aspects of human
behavior, several of which you will encounter in other chapters of this book. To cite
just a few examples, substantial heritability has been reported for infant activity
level (Saudino & Eaton, 1991), temperament (Goldsmith, Buss, & Lemery, 1997),
reading disability (DeFries & Gillis, 1993), and antisocial behavior (Gottesman
& Goldsmith, 1994). Substantial heritability has even been reported for divorce
(McGue & Lykken, 1992), TV viewing (Plomin et al., 1990), and other factors that
previously seemed more likely to be influenced by the environment than by genetics
(e.g., Jaffee & Price, 2007).
The implausibility of “divorcer” or “couch potato” genes brings us back to a
point we made earlier: despite the common use of the phrase, there are no genes
“for” particular behavior patterns. As have we stressed, genes do nothing more than
code for proteins, so they affect behavior only insofar as those proteins affect the
sensory, neural, and other physiological processes involved in behavior. Thus, the
heritability estimate for divorce may be related to a genetic predisposition to, say,
seek out novelty, and the estimate for TV viewing may be related to a genetically
based low activity level or short attention span.
Heritability estimates have been criticized, both from within psychology
(e.g., G. Gottlieb, Wahlsten, & Lickliter, 1998; Lerner, 1995) and from outside
it (e.g., J. S. Levine & Suzuki, 1993; Lewontin, 1982). Part of the criticism stems
from ways that the term “heritability” is often misinterpreted or misused by the
public. One very common misuse involves the application of the concept of heri-
tability to individuals, despite the fact that, as we have emphasized, heritability ap-
plies only to populations.
In addition, a heritability estimate applies only to a particular population living in
a particular environment. Consider the case of height. Research conducted almost
exclusively with North Americans and Europeans—most of them White and ad-
equately nourished—puts the heritability of height at around 90%. But what if
some segment of this population had experienced a severe famine during child-
hood, while the rest remained well fed? Would the heritability estimate for height
still be 90%? No—because the variability due to environmental factors (poor nutri-
tion) would increase dramatically and, therefore, the variability that could be attrib-
uted to genetic factors would decrease to the same degree. The principle of variable
heritability also appeared in the discussion of IQ correlations earlier in this chapter,
with the heritability estimates derived from them differing for the same individuals
at different points in development (O. S. P. Davis et al., 2009).
Furthermore, it is known that heritability estimates can differ markedly for
groups of people who grow up in very different economic circumstances. In the
United States, for instance, heritability estimates differ considerably as a function
of socioeconomic status (SES), as shown by a large twin study that included fami-
lies across the SES spectrum (Turkheimer et al., 2003). In this study, almost 60% of
the variance in IQ among a sample of 7-year-olds living in poverty was accounted
for by shared environment, with almost none of it attributable to genetic similar-
ity. Affluent families follow the opposite pattern, with genetic factors contribut-
ing more than environmental ones. In a related study focused on the test scores of
adolescent twins, the same pattern was observed: environmental factors trumped
genetic factors for poorer teens, while genetic factors trumped environmental fac-
tors for wealthier teens (Harden, Turkheimer, & Loehlin, 2007). Although it is not
fully clear what causes these differing levels of heritability, both studies suggest that
qualitatively different developmental forces may be operating in poor versus afflu-
ent environments.

A related, frequently misunderstood point is that high heritability does not imply
immutability. The fact that a trait is highly heritable does not mean that there is lit-
tle point in trying to improve the course of development related to that trait. Thus,
for example, the fact that the heritability estimate for IQ is relatively high does not
mean that the intellectual performance of young children living in poverty cannot
be improved by appropriate intervention efforts (see Chapter 8, pages 317–320).
Finally, because they are relevant only within a given population, heritability es-
timates tell us nothing about differences between groups. The heritability score for
IQ , for example, provides little insight into the meaning of differences in the IQ
scores of different groups of Americans. European Americans, on average, score
15 points higher on IQ tests than do African Americans. Some people mistakenly
assume that because IQ is estimated to be 50% heritable, the difference between
these two groups’ IQ scores is genetically based. This assumption is unwarranted,
given the large overall disparities between the two groups in family income and
education, quality of neighborhood schools, health care, and myriad other factors.
Environmental Effects
Every examination of genetic contributions to behavior and development is also,
necessarily, a study of environmental influences: estimating heritability automati-
cally estimates the proportion of variance not attributable to genes. Because herita-
bility estimates rarely exceed 50%, a large contribution from environmental factors
is usually indicated.
Behavior geneticists try to assess the extent to which aspects of an environment
shared by biologically related people make them more alike and to what extent non-
shared experiences make them different. The most obvious source of shared envi-
ronment is growing up in the same family. Shared-environment effects can also be
inferred when twins or other relatives are more similar on some trait than would be
expected on the basis of their genetic relatedness. For example, substantial shared-
environmental influence has been inferred for positive emotion in toddlers and
young children because fraternal and identical twins who were reared together were
equally similar in the degree to which they showed pleasure (Goldsmith et al., 1997).
The similarity between these identical twins
may be enhanced by environmental factors.
Sharing similar abilities, they may enjoy
similar activities and be exposed to similar
environmental influences. Being of similar
intelligence, they are likely to have relatively
similar experiences in school. Later, they
may enjoy similar success in dating and end
up with spouses of similar social class. TO
/ I

Shared-environment effects are also being discovered for disorders that have a clear
genetic component. For instance, as discussed in Box 3.1, twin studies of autism
spectrum disorder (ASD) have consistently provided evidence for genetic effects
(with heritability of the disorder being greater for MZ twins than for DZ twins).
However, in a recent large-scale study of twin pairs in which at least one co-twin had
an ASD diagnosis, researchers found a substantial shared-environment effect on the
likelihood that the second twin also had an ASD diagnosis (Hallmayer et al., 2011).
Surprisingly, behavior geneticists have reported little evidence of shared-
environment effects for some other aspects of development. For example, with
respect to personality, the correlations for adoptive siblings are often near zero
(D. C. Rowe, 1994). The same is true for some types of psychopathology, includ-
ing schizophrenia (Gottesman, 1991). As noted in Chapter 1, being adopted into
a family with a schizophrenic sibling does not increase the risk that a child will be-
come schizophrenic. In addition, the risk of schizophrenia is the same for the bio-
logical child of a schizophrenic parent regardless of whether the child is raised by
that parent or is adopted away at birth (Kety et al., 1994).
Behavior geneticists’ investigations of the effects of nonshared environments
arise from the recognition that even children who grow up in the same family do
not have all their experiences in common—either inside or outside the family.
Within the family, birth order may result in quite different experiences for siblings.
The oldest child in a large family, for example, may have been reared by young, en-
ergetic, but inexperienced, parents, whereas that child’s much younger sibling will
be parented by older and more sedentary, but more knowledgeable, individuals who
are likely to have more resources available than they did as first-time parents. In
addition, as discussed in Chapter 1, siblings may experience their parents’ behavior
toward them differently (the “Mom always loved you best” syndrome). They may
also be affected quite differently by an event they experience in common, such as
the divorce of their parents (Hetherington & Clingempeel, 1992). Finally, siblings
may be highly motivated to differentiate themselves from one another (Sulloway,
1996). The younger sibling of a star student may strive to be a star athlete instead,
and a child who observes a sibling disappearing into a self-destructive pattern of
drug and alcohol abuse may become determined to follow a different path. As these
examples illustrate, siblings themselves are an important part of the environment,
and each provides a different constellation of experiences for the others. This is an-
other factor that makes each child’s experience within the family different.
Outside the family, siblings can also have highly divergent experiences, partly
as a result of belonging to different peer groups. Highly active siblings who both
like physical challenges and thrills will have very different experiences if one takes
up rock climbing while the other hangs out with delinquents. Idiosyncratic life
events—suffering a serious accident, having an inspiring teacher, being bullied on
the playground—can contribute further to making siblings develop differently. The
primary effect of nonshared environmental factors is to increase the differences
among family members (Plomin & Daniels, 1987).
The five relations shown in Figure 3.1 depict the complex interplay of genetic and environ-
mental forces in development. (1) The course of children’s development is influenced by the
genetic heritage they receive from their mother and father, with their sex determined solely
by their father’s chromosomal contribution. (2) The relation between children’s genotype and
phenotype depends in part on dominance patterns in the expression of some genes, but most

traits of primary interest to behavioral scientists are influenced by multiple genes (polygenic
inheritance). (3) As the concept of norm of reaction specifies, any given genotype will develop
differently in different environments. A particularly salient part of children’s environment is
their parents, including their parents’ own genetic makeup, which influences how parents be-
have toward their children. (4) Children’s own genetic makeup influences how they select and
shape their own environment and the experiences they have in it. (5) Conversely, children’s
experiences can change their genetic expression through epigenetic mechanisms.
The field of behavior genetics is concerned with how development results from the inter-
action of genetic and environmental factors. Using the family-study methodology, behavior
geneticists compare the correlations among individuals who vary in the degree of genetic re-
latedness and in similarity of their rearing environments. Heritability estimates indicate the
proportion of the variance among individuals in a given population on a given trait that is
attributable to genetic differences among them. Most behavioral traits that have been mea-
sured show substantial heritability; at the same time, heritability estimates reveal the close
partnership of heredity and environment in development and the fallacy of considering the
influences of nature and nurture as independent of one another.
Brain Development
As you will see, the collaboration between nature and nurture takes center stage in
the development of the brain and nervous system. Before discussing developmental
processes in the formation of the brain, however, we need to consider the basic com-
ponents of this “most complex structure in the known universe” (R. F. Thompson,
2000, p. 1).
Fundamental to all aspects of behavioral development is the development of the
central nervous system and especially the brain. The brain is the font of all thought,
memory, emotion, imagination, personality—in short, the behavior, capacities, and
characteristics that make us who we are.
Structures of the Brain
In our examination of the structures of the brain, we focus our discussion on two
that are central to behavior—the neuron and the cortex, as well as some of their
The business of the brain is information. The basic units of the brain’s remarkably
powerful informational system are its more than 100 billion neurons (Figure 3.6),
which constitute the gray matter of the brain. These cells are specialized for send-
ing and receiving messages between the brain and all parts of the body, as well as
within the brain itself. Sensory neurons transmit information from sensory receptors
that detect stimuli in the external environment or within the body itself; motor neu-
rons transmit information from the brain to muscles and glands; and interneurons
act as intermediaries between sensory and motor neurons.
Although they vary substantially in size, shape, and function, all neurons are
made up of three main components: (1) a cell body, which contains the basic bio-
logical material that keeps the neuron functioning; (2) dendrites, fibers that receive
input from other cells and conduct it toward the cell body in the form of electrical
impulses; and (3) an axon, a fiber (anywhere from a few micrometers to more than
a meter in length) that conducts electrical signals away from the cell body to con-
nections with other neurons.
neurons n cells that are specialized for
sending and receiving messages between
the brain and all parts of the body, as well
as within the brain itself
cell body n a component of the neuron
that contains the basic biological material
that keeps the neuron functioning
dendrites n neural fibers that receive
input from other cells and conduct it
toward the cell body in the form of elec-
trical impulses
axons n neural fibers that conduct elec-
trical signals away from the cell body to
connections with other neurons

Neurons communicate with one another at synapses, which are microscopic
junctions between the axon terminal of one neuron and the dendritic branches of
another. In this communication process, electrical and chemical messages cross
the synapses and cause the receiving neurons either to fire, sending a signal on
to other neurons, or to be inhibited from firing. The total number of synapses is
staggering—hundreds of trillions—with some neurons having as many as 15,000
synaptic connections with other neurons.
Glial Cells
Glial cells, the brain’s white matter, make up nearly half the human brain, out-
numbering neurons 10 to 1. They perform a variety of critical functions, includ-
ing the formation of a myelin sheath around axons, which insulates them and
increases the speed and efficiency of information transmission. The importance
of myelin is highlighted by the severe consequences that can arise from disorders
that affect it. For example, multiple sclerosis is a disease in which the immune
Myelin sheath
Cell body
Axon terminals
Transmitting neuron
Receiving neuron
FIGURE 3.6 The neuron The cell body
manufactures proteins and enzymes, which
support cell functioning, as well as the
chemical substances called neurotransmit-
ters, which facilitate communication among
neurons. The axon is the long shaft that con-
ducts electrical impulses away from the cell
body. Many axons are covered with a myelin
sheath, which enhances the speed and effi-
ciency with which signals travel along the axon.
Branches at the end of the axon have termi-
nals that release neurotransmitters into the
synapses—the small spaces between the axon
terminals of one neuron and the dendrites or
cell body of another. The dendrites conduct
impulses toward the cell body. an axon can
have synapses with thousands of other neurons.
(adapted from Banich, 1997)
synapses n microscopic junctions
between the axon terminal of one neuron
and the dendritic branches or cell body
of another
glial cells n cells in the brain that
provide a variety of critical supportive
myelin sheath n a fatty sheath that
forms around certain axons in the body
and increases the speed and efficiency of
information transmission

system attacks myelin, interfering with neuronal signaling and producing varying
degrees of physical and cognitive impairment. Several psychiatric disorders, includ-
ing schizophrenia and bipolar disorder, are also linked to defects in the gene that
regulates production of myelin (e.g., Hakak et al., 2001; Tkachev et al., 2003).
Glial cells play a further role in communication within the brain by influencing
the formation and strengthening of synapses and by communicating biochemically
among themselves in a network separate from the neural network, and allowing
them to efficiently regulate many aspects of brain activity (Fields, 2004).
The Cortex
The cerebral cortex, the surface of which is shown in Figure 3.7, is considered the
“most human part of the human brain” (McEwen & Schmeck, 1994). Over the
course of human evolution, the brain expanded greatly in size. Almost all of this
increase occurred in the cerebral cortex, which constitutes 80% of the brain, a much
greater proportion than in other species. The folds and fissures that are apparent in
Figure 3.7 form during development as the brain grows within the confined space
of the skull; these convolutions make it possible to pack more cortex into the lim-
ited space.
The cortex plays a primary role in a wide variety of mental functions, from seeing
and hearing to reading, writing, and doing arithmetic and to feeling compassion and
communicating with others. As Figure 3.7 shows, the major areas of the cortex—
the lobes—can be characterized in terms of the general behavioral categories with
which they are associated. The occipital lobe is primarily involved in processing vi-
sual information. The temporal lobe is associated with memory, visual recognition,
speech and language, and the processing of emotion and auditory information. The
parietal lobe is important for spatial processing. It is also involved in the integration
of information from different sensory modalities, and it plays a role in integrating
Frontal lobe
Primary olfactory cortex
(mostly hidden from view)
Primary auditory cortex
(mostly hidden from view)
Temporal lobe
Prefrontal cortex
Parietal lobe
Primary visual
cortex (mostly
hidden from view)
Occipital lobe
Primary motor cortex Primary somatosensory cortex
FIGURE 3.7 The human
cerebral cortex This view of the
left hemisphere of an adult brain
shows the four major cortical
regions—known as the lobes—
which are divided from one
another by deep fissures. each
of the primary sensory areas
receives information from a par-
ticular sensory system, and the
primary motor cortex controls the
body’s muscles. Information from
multiple sensory areas is pro-
cessed in association areas.
cerebral cortex n the “gray matter” of
the brain that plays a primary role in what
is thought to be particularly humanlike
functioning, from seeing and hearing to
writing to feeling emotion
lobes n major areas of the cortex associ-
ated with general categories of behavior
occipital lobe n the lobe of the cortex
that is primarily involved in processing
visual information
temporal lobe n the lobe of the cortex
that is associated with memory, visual
recognition, and the processing of emo-
tion and auditory information
parietal lobe n governs spatial pro-
cessing as well as integrating sensory
input with information stored in memory

sensory input with information stored in memory and with information about inter-
nal states. The frontal lobe, the brain’s “executive,” is involved in cognitive control,
including working memory, planning, decision making, and inhibitory control. In-
formation from multiple sensory systems is processed and integrated in the associa-
tion areas that lie in between the major sensory and motor areas.
Although it is convenient to think of different cortical areas as if they were func-
tionally specific, they are not. It has become increasingly clear that complex mental
functions are mediated by multiple areas of the brain, with an extraordinary degree
of interactivity both within and across brain regions. A given area may be critical
for some ability, but that does not mean that control of that ability is located in that
one area. (Box 3.3 examines some of the techniques that researchers use to learn
about brain functioning.)
cerebral lateralization The cortex is divided into two separate halves, or cerebral
hemispheres. For the most part, sensory input from one side of the body goes to
the opposite side of the brain, and the motor areas of the cortex control movements
of the opposite side of the body. Thus, if you pick up a hot pot with your right hand,
it is the left side of the brain that receives the sensory response, registers the pain,
and initiates the motor response to let go immediately.
The left and right hemispheres of the brain communicate with each other pri-
marily by way of the corpus callosum, a dense tract of nerve fibers that connect
them. The two hemispheres are specialized for different modes of processing, a
phenomenon referred to as cerebral lateralization. There are notable similarities
across species in hemispheric specialization. For example, most aspects of speech
and language are lateralized to the left hemisphere in humans, with a similar asym-
metry observed for communicative signals in nonhuman species from mice to pri-
mates (Corballis, 2009).
Developmental Processes
How does the incredibly complex structure of the human brain come into being?
You will not be surprised to hear that, once again, a partnership of nature and nur-
ture is involved. Some aspects of the construction of the brain are set in motion and
tightly controlled by the genes, relatively independent of experience. But, as you
will see, other aspects are profoundly influenced by experience.
Neurogenesis and Neuron Development
In the 3rd or 4th week of prenatal life, cells in the newly formed neural tube begin
dividing at an astonishing rate—at peak production, 250,000 new cells are born
every minute. Neurogenesis, the proliferation of neurons through cell division, is
virtually complete by around 18 weeks after conception (Rakic, 1995; Stiles, 2008).
Thus, most of the roughly 100 billion neurons you currently possess have been with
you since before you were born. Notably, however, we do continue to generate new
neurons throughout life. During bouts of learning, for example, neurogenesis oc-
curs in the hippocampus, a brain region important for memory processes (E. Gould
et al., 1999). Neurogenesis does not always occur, however: it can be inhibited by
stress (Mirescu & Gould, 2006). This pattern of results suggests that neurogenesis
later in life is not fixed and predetermined but is instead adaptive, increasing under
rewarding conditions and decreasing in threatening environments (e.g., Glasper,
Schoenfeld, & Gould, 2012).
frontal lobe n associated with orga-
nizing behavior; the one that is thought
responsible for the human ability to plan
association areas n parts of the brain
that lie between the major sensory and
motor areas and that process and inte-
grate input from those areas
cerebral hemispheres n the two
halves of the cortex; for the most part,
sensory input from one side of the body
goes to the opposite hemisphere of the
corpus callosum n a dense tract of
nerve fibers that enable the two hemi-
spheres of the brain to communicate
cerebral lateralization n the special-
ization of the hemispheres of the brain for
different modes of processing
neurogenesis n the proliferation of neu-
rons through cell division

After their “birth,” neurons begin the second developmental process, which in-
volves migration to their ultimate destinations. Some neurons are pushed along
passively by the newer cells formed after them, whereas others actively propel
themselves toward their ultimate location.
Once neurons reach their destination, cell growth and differentiation occur.
Neurons first grow an axon and then a “bush” of dendrites (refer back to Figure
Developmental scientists employ a variety of
techniques to determine what areas of the
brain are associated with particular behav-
iors, thoughts, and feelings and how brain
functions change with age. The existence of
increasingly powerful techniques for investi-
gating brain function has sparked a revolu-
tion in the understanding of the brain and its
development. Here, we provide examples of
some of the techniques most often used to
map the mind and its workings in children.
Electrophysiological Recording
One of the techniques most often used by de-
velopmental researchers to study brain func-
tion is based on electroencephalographic
(EEG) recordings of electrical activity gener-
ated by neurons. EEG is completely noninva-
sive (the recordings are obtained through an
electrode cap that simply rests on the scalp,
and can contain hundreds of electrodes), so
this method can be used successfully even
with infants (see photo at right). EEG record-
ings provide detailed information about the
time course of neural events, and have pro-
vided valuable information about a variety of
brain-behavior relations.
An electrophysiological technique that is
very useful for studying the relation between
brain activity and specific kinds of stimula-
tion is the recording of event-related poten-
tials (ERPs), that is, changes in the brain’s
electrical activity that occur in response to
the presentation of a particular stimulus.
One contribution these measures have made
is that they reveal continuity over time. For
instance, studies of infants’ ERPs in re-
sponse to native-speech sounds have shown
that infants’ ability to discriminate among
these sounds predicts their language growth
over the next few years (Kuhl et al., 2008). A
related method, called magnetoencephalog-
raphy (MEG), detects magnetic fields gener-
ated by electrical currents in the brain. MEG
has the added benefit of being the only non-
invasive imaging method that can be used
to study the fetal brain. Although the use of
MEG for this purpose is in its early stages,
researchers have so far been able to detect
fetal neural responses to auditory stimuli and
flashes of light displayed on the mother’s ab-
domen, as well as habituation responses to
repeated stimuli (Sheridan et al., 2010).
Functional Magnetic Resonance Imaging
Functional magnetic resonance imaging
(fMRI) uses a powerful electromagnet to de-
tect fluctuations in cerebral blood flow in
different areas of the brain. Increased blood
flow indicates increased activity, so this tech-
nology allows researchers to determine which
areas of the brain are activated by different
tasks and stimuli. Because a person must be
able to tolerate the noise and close confine-
ment of an MRI machine and must also be
able to remain very still, most developmental
fMRI studies have been done with children
aged 6 years or older, often using practice
sessions in a mock scanner to help children
acclimate to the MRI environment. However,
recent studies have used fMRI methods to
investigate neural processes in sleeping in-
fants as young as 2 days old. One such study
demonstrated that the areas of the brain that
are activated by spoken language from later
infancy onward are also activated by speech
in neonates (Perani et al., 2011).
Other Techniques
Positron emission tomography (PET) mea-
sures brain activity by detecting the brain’s
metabolic processes and has provided im-
portant information about brain develop-
ment. However, because PET scans involve
injecting radioactive material into the brain,
this technique is used primarily for diagnos-
tic purposes.
One of the newest methods to be used
in developmental studies is near-infrared
spectroscopy (NIRS), an optical imaging
technique that measures neural activity by
detecting metabolic changes that lead to
differential absorption of infrared light in
brain tissue. The infrared light is transmit-
ted to the brain, and its absorption is de-
tected by means of an optical-fiber skullcap
or headband. Because NIRS is silent, non-
invasive, and does not require rigid stabiliza-
tion of the head, it is particularly promising
BOX 3.3: a closer look
eeG This eeG cap holds electrodes snugly
against the baby’s scalp, enabling researchers
to record electrical activity generated from all
over the baby’s brain.
. N
event-related potentials (ERPs) n
changes in the brain’s electrical activity
that occur in response to the presentation
of a particular stimulus

3.6). Thereafter, they take on the specific structural and functional characteristics
of the different structures of the brain. Axons elongate as they grow toward specific
targets, which, depending on the neuron in question, might be anything from an-
other neuron in the brain to a bone in the big toe. The main change in dendrites is
“arborization”—an enormous increase in the size and complexity of the dendritic
“tree” that results from growth, branching, and the formation of spines on the
for research with infants and young chil-
dren. Thus far, a number of attempts to pin-
point infants’ brain activation in response
to particular stimuli have shown mixed re-
sults, in part because the technology is still
in its early stages (Aslin, 2012). One use
of NIRS that has already proved success-
ful is the monitoring of brain-oxygen levels
in premature newborns. Another particularly
interesting and successful application of
NIRS involved a study of deaf children who
had just received a cochlear implant, a sur-
gically implanted electronic hearing device
that we will discuss in Chapter 6. Because
of concerns about the effects of its mag-
netic field, fMRI cannot be used to study
brain processes in individuals with implants.
NIRS was thus used to determine whether
the auditory cortices of these children could
respond to auditory stimulation. The NIRS
showed that, rather remarkably, the auditory
cortex of deaf children responded to sound
within hours after the implant was activated,
even though the cortex had never before
been exposed to sound (Sevy et al., 2010).
fMrI images The figure shows fMrI images of the brains
of a 9-year-old (panel a) and a 24-year-old (panel B) in a
standard cognitive task that requires responding to some
stimuli but inhibiting responding to others. (The images to
the left show the “slices” of the brain averaged together in
the images on the right.) The results show that the location
of activation in the prefrontal cortex did not differ between
children and adults, but the overall extent of activation was
greater for the children (casey, 1999). RE
. J
. C
spines n formations on the dendrites
of neurons that increase the dendrites’
capacity to form connections with other
erp responses This figure shows erp wave-
forms in response to novel (red line) and
familiar (yellow line) stimuli. The infants
who later recalled how to assemble a toy (left
panel) had clearly discriminated between the
familiar and novel items on an earlier recogni-
tion test. The infants who did not recall the
assembly sequence (right panel) had not dis-
criminated between the components on the
earlier test. (adapted from L. J. carver, Bauer,
& Nelson, 2000)

branches. Arborization enormously increases the dendrites’ capacity to form con-
nections with other neurons. In the cortex, the period of most intense growth and
differentiation comes after birth.
The process of myelination, the formation of the insulating myelin sheath around
some axons, begins in the brain before birth and continues into early adulthood. As
noted earlier, a crucial function of myelin is to increase the speed of neural conduc-
tion. Myelination begins deep in the brain, beginning with the brainstem, and moves
upward and outward into the cortex at a fairly steady rate throughout childhood and
adolescence and into early adulthood (Lenroot & Giedd, 2006). The various cortical
areas thus become myelinated at very different rates, possibly contributing to the dif-
ferent rates of development for various behaviors.
This pattern diverges in interesting ways from the pattern found in our primate
relative, the chimpanzee. Initially, white matter develops even more slowly in the
prefrontal lobes of infant and juvenile chimpanzees than it does in young humans,
suggesting one possible mechanism whereby evolutionary pressure has improved
human brain function relative to that of other primates (Sakai et al., 2011). Interest-
ingly, however, the chimpanzee shows a mature pattern of myelination at the point
of sexual maturity, far earlier than that observed in humans (D. J. Miller et al., 2012).
The reasons for the extended period of human myelination remain unknown, and
might be both positive (facilitating improvements in executive functions after sexual
maturity) and negative (making the human brain more vulnerable to disorders re-
lated to myelination discussed on pages 107–108).
One result of the extraordinary growth of axonal and dendritic fibers is a wildly exu-
berant generation of neuronal connections. In a process called synaptogenesis, each
neuron forms synapses with thousands of others, resulting in the formation of the
trillions of connections referred to earlier. Figure 3.8 shows the time course of synap-
togenesis in the cortex. As you can see, it begins prenatally and proceeds very rapidly
2 yrs.
BirthConception 4 yrs. 10 yrs.
Adolescence Adult
Visual CortexPrefrontal Cortex
FIGURE 3.8 Synapse production and
elimination Mean synaptic density (the
number of synapses in a given space) first
increases sharply as new synapses are
overproduced and later declines gradu-
ally as excess synapses are eliminated.
Note that the time scale is compressed at
later stages. (From p. r. huttenlocher &
Dabholkar, 1997)
myelination n the formation of myelin
(a fatty sheath) around the axons of
neurons that speeds and increases
information-processing abilities
synaptogenesis n the process by which
neurons form synapses with other neu-
rons, resulting in trillions of connections

both before birth and for some time afterward. Note that both the timing and rate
of synapse production vary for different cortical areas; synapse generation is com-
plete much earlier in the visual cortex, for example, than in the frontal area. As with
myelination, the differential timing of synapse generation across areas of the brain
likely contributes to the developmental timing of the onset of various abilities and
Synapse Elimination
The explosive generation of neurons and synapses during synaptogenesis, which is
largely under genetic control, results in a huge surplus—many more neural connec-
tions than any one brain can use. This overabundance of synapses includes an ex-
cess of connections between different parts of the brain: for instance, many neurons
in what will become the auditory cortex are linked with those in the visual area, and
both of these areas are overly connected to neurons involved in taste and smell. As
a consequence of this hyperconnectivity, newborns may experience synesthesia—
the blending of different types of sensory input (Maurer & Mondloch, 2004). In
the case of the extra connections between auditory and visual cortex, for example,
auditory stimulation may produce a visual experience, with the infant’s perceiving
a sound as being of a particular color.
We now come to what is one of the most remarkable facts about the develop-
ment of the human brain. Approximately 40% of this great synaptic superfluity gets
eliminated in a developmental process known as synaptic pruning. As you learned
in the previous chapter, cell death is a normal part of development, and nowhere is
that more evident than in the systematic pruning of excess synapses that continues
for years after birth. This pruning occurs at different times in different areas of the
brain (P. R. Huttenlocher & Dabholkar, 1997). You can see from Figure 3.8 that
the elimination of synapses in the visual cortex begins near the end of the first year
of life and continues until roughly 10 years of age, whereas synapse elimination in
the prefrontal area shows a slower time course. During peak pruning periods, as
many as 100,000 synapses may be eliminated per second (Kolb, 1995)!
Not known until fairly recently is the fact that the brain undergoes explosive
changes during adolescence, including a wave of overproduction and pruning akin
to that in the first years of life (Giedd et al., 1999; Gogtay et al., 2004). Although
the amount of white matter in the cortex shows a steady increase from childhood
well into adulthood, the amount of gray matter increases dramatically starting
around 11 or 12 years of age. The increase in gray matter proceeds rapidly, peaks
around puberty, and then begins to decline as some of it is replaced by white matter
(see Figure 3.9). The last area of the cortex to mature is the dorsolateral prefrontal
cortex, which is vital for regulating attention, controlling impulses, foreseeing con-
sequences, setting priorities, and other executive functions. It does not reach adult
dimensions until after the age of 20.
You will notice that Figure 3.8 does not show a second proliferation and reduc-
tion of synaptic density in adolescence. One of the reasons for this is that the figure
is based on cross-sectional research in which the brains of individuals of different
ages were examined only at autopsy. The new data showing substantial develop-
ment in the adolescent brain come from longitudinal studies in which the same in-
dividuals’ brains were scanned repeatedly over several years. The dramatic changes
that appear in individuals were not evident when the brains of separate groups of
different ages were studied. (See the discussion of developmental research designs
in Chapter 1, pages 32–33.)
synaptic pruning n the normal devel-
opmental process through which synapses
that are rarely activated are eliminated

The Importance of Experience
What factors determine which of the brain’s excess synapses will be pruned and
which maintained? Experience plays a central role in what is essentially a case of
“use it or lose it.” In a competitive process that has been dubbed “neural Darwin-
ism” (Edelman, 1987), those synapses that are frequently activated are selectively
preserved (Changeux & Danchin, 1976). The more often a synapse is activated, the
stronger the connection becomes between the neurons involved: in short, neurons
that fire together wire together (Hebb, 1949). Conversely, when a synapse is rarely
active, it is likely to disappear: the axon of one neuron withdraws and the dendritic
spine of the other is “pruned away.”
The obvious question now is: Why does the human brain—the product of mil-
lions of years of evolution—take such a devious developmental path, producing a
huge excess of synapses, only to get rid of a substantial proportion of them? The an-
swer appears to be evolutionary economy. The capacity of the brain to be molded or
changed by experience, referred to as plasticity, means that less information needs
to be encoded in the genes. This economizing may, in fact, be a necessity: the num-
ber of genes involved in the formation and functioning of the nervous system is
enough to specify only a very small fraction of the normal complement of neurons
and neural connections. In addition, if brain structures were entirely hard-wired,
organisms would be unable to adapt to their postnatal environment. To complete
the final wiring of the brain, nurture joins forces with nature.
The collaboration between nature and nurture in building the brain occurs dif-
ferently for two kinds of plasticity. One kind involves the general experiences that
almost all infants have just by virtue of being human. The second kind involves
specific, idiosyncratic experiences that children have as a result of their particular
life circumstances—such as growing up in the United States or in the Amazon rain
forest, experiencing frequent cuddling or abuse, being an only child or one of many
siblings, and so on.
plasticity n the capacity of the brain to
be affected by experience
FIGURE 3.9 Brain maturation
These views of the right side and
top of the brain of 5- to 20-year-
olds illustrate maturation over the
surface of the cortex. The averaged
MrI images come from participants
whose brains were scanned repeat-
edly at 2-year intervals. The bluer
the image, the more mature that part
of the cortex is (i.e., the more gray
matter has been replaced with white
matter). Notice that the parts of the
cortex associated with more basic
functions (i.e., the sensory and motor
areas toward the back) mature ear-
lier than the areas involved in higher
functions (i.e., attention, executive
functioning). Notice particularly that
the frontal areas, involved in executive
functioning, approach maturity only
in early adulthood. (From Gogtay et
al., 2004)

Experience-Expectant Processes
William Greenough refers to the role of general human experience in shaping brain
development as experience-expectant plasticity. According to this view, the nor-
mal wiring of the brain is in part a result of the kinds of general experiences that
have been present throughout human evolution, experiences that every human with
an intact sensory-motor system who inhabits a reasonably normal environment
will have: patterned visual stimulation, voices and other sounds, movement and
manipulation, and so forth (Greenough & Black, 1992). Consequently, the brain
can “expect” input from these reliable sources to fine-tune its circuitry; synapses
that are frequently activated will be strengthened and stabilized and those that are
rarely activated will be “pruned.” Thus, our experience of the external world plays
a fundamental role in shaping the most basic aspects of the structure of our brain.
One fundamental benefit of experience-expectant plasticity is that, because experi-
ence helps shape the brain, fewer genes need to be dedicated to normal development.
Another is that the brain is better able to recover from injury to certain areas, because
other brain areas can take over the function that would have been performed by the
damaged area. The younger the brain when damaged, the more likely recovery is.
The downside of experience-expectant plasticity is that it is accompanied by vul-
nerability. If for some reason the experience that the developing brain is “expecting”
for fine-tuning its circuits does not occur, whether because of inadequate stimu-
lation or impaired sensory receptors, development may be compromised. A good
example of this vulnerability comes from children who are born with cataracts that
obscure their vision. The longer a cataract remains in place after birth, the more
impaired the child’s visual acuity will be once it is removed. Dramatic improvement
typically follows early removal, although some aspects of visual processing (espe-
cially of faces) remain affected even into adulthood (de Heering & Maurer, 2012;
Maurer, Mondloch, & Lewis, 2007). Presumably, the lasting deficits of late cataract
removal occur because synapses that would normally have been activated by visual
stimulation after birth were pruned because of the lack of that stimulation.
When an expected form of sensory experience is absent, what happens to areas
of the brain that normally would have become specialized as a result of that experi-
ence? A wealth of data from animals indicates that such areas can become at least
partially reorganized to serve some other function. Evidence of such plasticity and
reorganization in humans comes from studies of congenitally deaf adults who, as
children, had learned American Sign Language, a full-fledged, visually based, lan-
guage (Bavelier, Dye, & Hauser, 2006; Bavelier & Neville, 2002). Deaf individuals
rely heavily on peripheral vision for language processing; they typically look into
the eyes of a person who is signing to them, while using their peripheral vision to
monitor the hand and arm motions of the signer. ERP recordings of brain activ-
ity (see Box 3.3) showed that deaf individuals’ responses to peripheral visual stimuli
are several times stronger than those of hearing people. In addition, their responses
are distributed differently across brain regions. Thus, because of the lack of audi-
tory experience, brain systems that would normally be involved in hearing and in
spoken-language processing become organized to process visual information instead.
Similar evidence of early brain reorganization comes from research with blind
adults. When tested for their ability to discriminate changes in musical pitch, adults
who were born blind or became blind quite early performed much better than those
who had become blind later in life (Gougoux et al., 2004). Presumably, connections
between visual and auditory cortex were preserved in individuals with early-onset
blindness, giving them extra “brain power” to apply to the auditory task. Consis-
tent with this idea, brain-imaging research suggests that parts of the visual cortex
experience-expectant plasticity n the
process through which the normal wiring
of the brain occurs in part as a result
of experiences that every human who
inhabits any reasonably normal environ-
ment will have

contribute to superior sound localization ability in adults with early-onset blind-
ness. A related result is that congenitally blind individuals show activation in the
“visual” cortex both when reading Braille (Sadato et al., 1998) and when processing
spoken language (Bedny et al., 2011).
Sensitive periods As suggested by the foregoing examples, a key element in
experience-expectant plasticity is timing. There are a few sensitive periods when
the human brain is especially sensitive to particular kinds of external stimuli. It is
as though a time window were temporarily opened, inviting environmental input to
help organize the brain. Gradually, the window closes. The neural organization that
occurs (or does not occur) during sensitive periods is typically irreversible.
As discussed in Chapter 1, the extreme deprivation that the Romanian orphans
suffered early in life, when children normally experience a wealth of social and
other environmental stimulation, is considered by some to be an example of a
sensitive-period effect. Some investigators speculate that adolescence, during which
rapid changes are occurring in the brain, may be another sensitive period for various
aspects of development. Yet another sensitive period, for language learning, will be
discussed in Chapter 6.
Experience-Dependent Processes
The brain is also sculpted by idiosyncratic experience through what Greenough
calls experience-dependent plasticity. Neural connections are created and re-
organized constantly, throughout life, as a function of an individual’s experiences.
(If you remember anything of what you have been reading in this chapter, it’s be-
cause you have formed new neural connections.)
Much of the research on experience-dependent plasticity has
been focused on nonhuman animals, whose environments can be
readily manipulated. One such method has involved comparisons
between animals reared in complex environments full of objects
to explore and use versus animals reared in bare laboratory cages.
The brains of rats (and cats and monkeys) that grow up in a com-
plex environment have more dendritic spines on their cortical
neurons, more synapses per neuron, and more synapses overall, as
well as a generally thicker cortex and more of the supportive tis-
sues (such as blood vessels and glial cells) that maximize neuro-
nal and synaptic function. All this extra hardware seems to have a
payoff: rats (and other animals) reared in a complex environment
(which is more akin to their natural environment) perform better
in a variety of learning tasks than do their counterparts raised in
bare cages (e.g., Sale, Berardi, & Maffei, 2009).
Highly specific effects of experience on brain structure also
occur. For example, rats that are trained to use just one forelimb
to get a food reward have increased dendritic material in the par-
ticular area of the motor cortex that controls the movement of
the trained limb (Greenough, Larson, & Withers, 1985). In hu-
mans, research on musicians has revealed that, compared with a
control group, violinists and cellists had increased cortical rep-
resentation of the fingers of the left hand (Elbert et al., 1995).
In other words, after years of practice, more cortical cells were
devoted to receiving input from and controlling the fingers that
manipulate the strings of the instruments. Similarly, in skilled
experience-dependent plasticity n
the process through which neural con-
nections are created and reorganized
throughout life as a function of an indi-
vidual’s experiences
, T
as a result of growing up in a complex
environment full of stimulating objects to
explore and challenges to master, the brains
of the rats in the top photo will contain
more synapses than if they had been reared
in unstimulating laboratory cages (bottom


Braille readers, the cortical representation of the left hand—which is used to read
Braille text—is enlarged (Pascual-Leone et al., 1993).
Effects of specific experience are also evident in fMRI studies of individuals with
dyslexia, a severe reading problem in people with normal intelligence and schooling
(see Chapter 8). One example involves a remedial reading program in which 2nd-
and 3rd-graders with dyslexia received training in recognizing the correspondence
between speech sounds and letters (Blachman et al., 2004). After the training, not
only did the children show marked improvement in their reading ability, but fMRI
imaging revealed increased activity in their left-brain areas that was similar to the
activity in the brains of good readers. The specific effects of one’s reading experience
also show up in the fact that reading Chinese characters recruits distinctly different
brain networks than those involved in reading an alphabetic script (such as English).
Brain Damage and Recovery
As noted previously, because of its plasticity (especially early in life), the brain can
become rewired—at least to some degree—after suffering damage. Children who
suffer from brain damage thus have a better chance of recovering lost function
than do adults who suffer similar damage. The strongest evidence for this comes
from young children who suffer damage to the language area of the cortex and who
generally recover most, if not all, of their language functions. This is because after
the damage has occurred, other areas of the immature brain can take over language
functions. As a result, language is largely spared, though specific linguistic impair-
ments may remain (e.g., Zevin, Datta, & Skipper, 2012).
In contrast, adults who sustain the same type of brain damage undergo no such
reorganization of language functions and may have a permanent loss in the ability
to comprehend or produce speech. Greater recovery from early brain injury has also
been observed for functions other than language. For example, producing appropri-
ate facial expressions is more difficult for adults who had damage to the frontal area
of the cortex during adulthood than for adults whose frontal lobe injury occurred
in childhood (Kolb, 1995).
It is not always true, however, that the chance of recovery from early brain in-
jury is greater than it is for later injury. Likelihood of recovery depends on how
extensive the damage is and what aspect of brain development is occurring at the
time of the damage. Consider, for example, the offspring of Japanese women who,
while pregnant, were exposed to massive levels of radiation from the atomic bombs
dropped on Hiroshima and Nagasaki in 1945. The rate of intellectual impairment
/ G
how would the cortical representations of
their fingers be likely to differ for these two
professional musicians?

was much higher for surviving children whose exposure had occurred very early in
prenatal development, during the time of rapid neurogenesis and migration of neu-
rons (Otake & Schull, 1984). Similarly, brain injury during early childhood gener-
ally results in more severe cognitive impairment in IQ than does later comparable
injury (V. Anderson et al., 2012).
Furthermore, even when children appear to have made a full recovery from an
early brain injury, deficits may emerge later. This was demonstrated in a cross-
sectional study that compared cognitive performance in a group of children who
had been born with cerebral damage and a control group of children with no brain
damage (Banich et al., 1990). As Figure 3.10 shows, the children with brain damage
did not differ from the control group in their performance on two subscales of an IQ
test at 6 years of age. However, as the normal children’s performance improved with
age, the brain-damaged children’s performance fell progressively behind. The same
pattern of results—decline in IQ over age for children with brain damage—was also
demonstrated in a longitudinal study, in which children who had sustained early
damage were tested before and after age 7 (S. C. Levine et al., 2005). These results
illustrate the difficulty of predicting the development of children with cerebral inju-
ries: behavior that appears normal early in development may deteriorate.
On the basis of these various aspects of plasticity, we can generalize that the
worst time to suffer brain damage is very early, during prenatal development and
the first year after birth, when neurogenesis is occurring and basic brain structures
are being formed. Damage at this point may have cascading effects on subsequent
aspects of brain development, with potentially wide-ranging negative effects. In
contrast, when brain damage is sustained in early childhood—that is, when synapse
generation and pruning are occurring and plasticity is highest—the chances for the
brain’s rewiring itself and recovering lost function are best.
Nature and nurture cooperate in the construction of the human brain. Some important brain
structures include the neurons, which communicate with one another at synapses; the cortex,
in which different functions are localized in different areas; and the cerebral hemispheres,
which are specialized for different kinds of processing. The processes involved in the devel-
opment of the brain include neurogenesis and synaptogenesis, followed by the systematic
elimination of some synapses and the preservation of others as a function of experience.
Two forms of plasticity contribute to the development of behavior. As a result of
experience-expectant plasticity, the brain is shaped by experiences that are available to every
Age at testing
16 18141210864
Age at testing
Block design
16 18141210864
Congenital lesion
Congenital lesion
Control Control
FIGURE 3.10 emergent effects of early
brain damage at 6 years of age, children
with congenital brain damage scored the
same as normal children on two subscales of
an intelligence test. however, the children
with brain damage failed to improve and
fell progressively farther behind the normal
children, so that by adolescence there were
large differences between the two groups.
(Data from Banich et al., 1990; figure from
Kolb, 1995)

typically developing individual in interaction with every species-typical environment. Through
experience-dependent plasticity, the brain is also structured by an individual’s idiosyncratic
life experiences. Because of the importance of experience in brain development, sensitive
periods exist during which specific experience must be present for normal development. Tim-
ing is also a crucial factor in the ultimate impact of brain damage.
The Body: Physical Growth and Development
In Chapter 1, we emphasized the multiple contexts in which development occurs.
Here we focus on the most immediate context for development—the body itself.
Everything we think, feel, say, and do involves our physical selves, and changes in
the body lead to changes in behavior. In this section, we present a brief overview
of some aspects of physical growth, including some of the factors that can disrupt
normal development. Nutritional behavior, a vital aspect of physical development,
is featured as we consider the regulation of eating. We concentrate particularly on
one of the consequences of poor regulation—obesity. Finally, we focus on the op-
posite problem—undernutrition.
Growth and Maturation
Compared with most other species, humans undergo a prolonged period of physi-
cal growth. The body grows and develops for 20% of the human life span, whereas
mice, for example, grow during only 2% of their life span. Figure 3.11 shows the
most obvious aspects of physical growth: we get 3 times taller and 15 to 20 times
heavier between birth and age 20. The figure shows averages, of course, and there
Age (in years)
Age (in years)
FIGURE 3.11 Growth curves These
growth curves for height and weight from
ages 2 to 20 years are based on large
national samples of children from across
the United States. each curve indicates the
percent of the reference population that
falls below the indicated weight and height.
(centers for Disease control and prevention,

are obviously huge individual differences in height and weight, as well as in the
timing of physical development.
Growth is uneven over time, as you can tell from the differences in the slopes in
Figure 3.11. The slopes are steepest when the most rapid growth is occurring—in
the first 2 years and in early adolescence. Early on, boys and girls grow at roughly
the same rate, and they are essentially equal in height and weight until around 10
to 12 years of age. Then girls experience their adolescent growth spurt, at the end of
which they are somewhat taller and heavier than boys. (Remember those awkward
middle-school years when the girls towered over the boys, much to the discomfort
of both?) Adolescent boys experience their growth spurt about 2 years after the
girls, permanently passing them in both height and weight. Full height is achieved,
on average, by around the age of 15½ for girls and 17½ for boys.
Growth is also uneven across the different parts of the body. Following the prin-
ciple of cephalocaudal development described in Chapter 2 (page 48), the head re-
gion is initially relatively large—fully 50% of body length at 2 months of age—but
only about 10% of body length in adulthood. The gawkiness of young adolescents
stems in part from the fact that their growth spurt begins with dramatic increases
in the size of the hands and feet; it’s easy to trip over your own feet when they are
disproportionately larger than the rest of you.
Body composition also changes with age. The proportion of body fat is highest
in infancy, gradually declining thereafter until around 6 to 8 years of age. In adoles-
cence, it decreases in boys but increases in girls, and that increase helps trigger the
onset of menstruation. The proportion of muscle grows slowly until adolescence,
when it increases dramatically, especially in boys.
There is great variability across individuals and groups in all aspects of physical de-
velopment. This variability in physical development is due to both genetic and en-
vironmental factors. Genes affect growth and sexual maturation in large part by
influencing the production of hormones, especially growth hormone (secreted by the
pituitary gland) and thyroxine (released by the thyroid gland). The influence of envi-
ronmental factors is particularly evident in secular trends, marked changes in physi-
cal development that have occurred over generations. In contemporary industrialized
nations, adults are several inches taller than their same-sex great-grandparents were.
This change is assumed to have resulted primarily from improvements in nutrition
and general health. Another secular trend in the United States today involves girls’
beginning to menstruate a few years earlier than their ancestors did, a change attrib-
uted to the general improvement in nutritional status of the population.
Environmental factors can also play a role in disturbances of normal growth. For
example, severe chronic stress, such as that associated with a home environment
involving serious marital discord, alcoholism, or child abuse can impair growth by
lowering the pituitary gland’s production of growth hormone (Powell, Brasel, &
Blizzard, 1967). Children raised in institutions also have a higher risk of growth
impairment, likely due to the combination of social stressors and poor nutrition
(D. E. Johnson & Gunnar, 2011). A combination of genetic and environmental
factors is apparently involved in failure to thrive, a condition in which infants be-
come malnourished and fail to grow or gain weight for no obvious medical reason.
Because the reason for a particular infant’s failure to thrive is often difficult to de-
termine, treatment may range from hospitalization to dietary supplementation to
behavioral interventions, such as rewards for positive eating behaviors ( Jaffe, 2011).
secular trends n marked changes in
physical development that have occurred
over generations
failure to thrive n a condition in which
infants become malnourished and fail to
grow or gain weight for no obvious med-
ical reason

Nutritional Behavior
The health of our bodies depends on what we put into them, including the amount
and kind of food we eat. Thus, the development of eating or nutritional behavior is
a crucial aspect of child development from infancy onward.
Infant Feeding
Like all mammals, human newborns obtain life-sustaining nourishment through
suckling, although they require more assistance in this endeavor than do most other
mammals. Throughout nearly the entire history of the human species, the only or
primary source of nourishment for infants was breast milk. Mother’s milk has many
virtues ( J. Newman, 1995). It is naturally free of bacteria, strengthens the infant’s
immune system, and contains the mother’s antibodies against infectious agents the
baby is likely to encounter after birth.
There have also been suggestions in the literature that the fatty acids in breast
milk have a positive effect on cognitive development, with some studies indicating
higher IQ scores for children and adults who were breastfed as infants (for review,
see Nisbett et al., 2012). The challenge in this area of research in the United States
is that the choice to breastfeed is correlated with social class (due to factors rang-
ing from maternal education to working conditions that make it difficult to nurse
or pump breast milk on the job). However, several recent studies that controlled
for social class still found cognitive benefits associated with breastfeeding. In one
of those studies, mother–infant dyads were randomly assigned either to an inter-
vention encouraging breastfeeding or to a control condition without intervention.
The results indicated that prolonged and exclusive breastfeeding in infancy led to
increased IQ scores at 6½ years of age (Kramer et al., 2008). Another study that
examined genetic factors found that children who carry one of two specific alleles
that regulate fatty acids showed a substantial cognitive benefit from breastfeed-
ing, while individuals with a different allele showed a smaller benefit (Caspi et
al., 2007). These results reflect the kind of genotype–environment interaction dis-
cussed earlier in this chapter, with the benefits of a particular environment (in this
case, breast milk) delimited by the child’s genotype.
However, in spite of the well-established nutritional superiority of breast milk,
as well as the fact that it is free, many infants in the United States are exclusively
or predominantly formula-fed. Recent public health efforts have begun to shift this
longtime feeding trend, by educating parents about the benefits of breast milk and
encouraging employers to provide private space for working mothers to pump breast
milk. Since these efforts were initiated, the number of newborns fed breast milk in
the United States has increased annually and, by 2009, had risen to 76.9% of neo-
nates (Centers for Disease Control and Prevention, 2012). However, this good nu-
tritional start was difficult for parents to maintain; by 6 months of age, only 47.2%
of infants were still being breastfed, and by 12 months of age, only 25.5% were.
In developed countries, infant formula can support normal growth and devel-
opment, although infants who are formula-fed have somewhat higher rates of in-
fection than do those who are fed breast milk. In undeveloped countries, however,
formula feeding can exact a costly toll. Much of the undeveloped world does not
have safe water, so infant formula is often mixed with polluted water in unsanitary
containers. Furthermore, poor, uneducated parents often dilute the formula in an
effort to make the expensive powder last longer. In such circumstances, parents’
attempts to promote the health of their babies end up having the opposite effect
(Popkin & Doan, 1990).
By breastfeeding her infant, this mother is
providing her baby with many benefits that
are not available in formula.

Development of Food Preferences and the Regulation of Eating
Food preferences are a primary determinant of what we eat throughout life, and some
of these preferences are clearly innate. Infants display some of the same reflexive fa-
cial expressions that older children and adults display in response to three basic tastes:
sweet, sour, and bitter. The first produces a hint of a smile; the second, a pucker; the
third, a grimace (Rosenstein & Oster, 1988; Steiner, 1979). Newborns’ strong prefer-
ence for sweetness is reflected both in their smiling in response to sweet flavors and
in the fact that they will drink larger quantities of sweetened water than plain water.
These innate preferences may have an evolutionary origin, since poisonous substances
are often bitter or sour but almost never sweet. At the same time, recall from Chapter
2 (page 53) that taste preferences can also be influenced by the prenatal environment,
suggesting an important role for experience even in the earliest flavor preferences.
Infants’ taste sensitivity is evident in their reactions to their mother’s milk,
which can take on the flavor of what she eats. Babies nurse longer and take more
breast milk when their mother has ingested either garlic or vanilla flavors, but
they drink less breast milk after she has downed a beer (Mennella & Beauchamp,
1993a, 1993b, 1996).
From infancy on, experience has a major influence on what foods children like
and dislike and on what and how much they eat. For instance, preschool children’s
liking for particular foods increases if they observe other children enjoying them
(Birch & Fisher, 1996). Children’s eating is also influenced by what foods their
parents encourage and discourage. This influence does not always work in the way
the parents intend, however. For example, standard parental strategies of cajoling
and bribing young children to eat new or healthier foods—“If you eat your spinach,
you can have some ice cream”—can be doubly counterproductive. The most prob-
able result is that the child will dislike the healthy food even more and have an even
stronger preference for the sweet, fatty food used as a reward (Birch & Fisher, 1996).
Many parents become needlessly concerned with how much their young chil-
dren eat. They might, however, put less effort into trying to control their children’s
eating behavior if they realized that young children are actually quite good at regu-
lating the amount of food they consume. Research has shown that preschool chil-
dren adjust how much they eat at a given time based on how much they consumed
earlier. For example, children were found to eat less for lunch if they had been
served a snack earlier than if they had not had the snack (Birch & Fisher, 1996).
(In contrast, a group of adults ate pretty much the same amount of a meal whether
or not they had been served a snack earlier.)
In general, children whose parents try to control their eating habits tend to be
worse at regulating their food intake themselves than are children whose parents
allow them more control over what and how much they eat (S. L. Johnson & Birch,
1994). Parents’ overregulation of their children’s eating behavior can have continu-
ing effects. Adults who reported that their parents used food to control their be-
havior were more likely to be struggling with their weight and with binge eating
(Puhl & Schwartz, 2003).
So many people have difficulty regulating their eating appropriately that the most
common dietary problems in the United States are related to overeating and its
many consequences. In an epidemic of obesity, one-third of American adults are
currently considered obese (Ogden et al., 2012). It is an increasing problem, not just
among Americans but also among indigenous people in many developing coun-
tries (Abelson & Kennedy, 2004). This situation exists largely because societies

all over the world are increasingly adopting
a “Western diet” of foods high in fat and
sugar and low in fiber. Fast-food restaurants
have proliferated around the globe; indeed,
after Santa Claus, Ronald McDonald is the
second most recognized figure worldwide
(K. Brownell, 2004).
The proportion of American children and
adolescents who are overweight has tripled in
the past four decades (see Figure 3.12), with
the increase being greatest for Latinos and Af-
rican Americans. The outlook for these heavy
children is troubling, because they are likely
to struggle with weight problems through-
out their lives. Furthermore, there is a good
chance they will adopt a variety of unhealthy
measures to fight their weight problems—
skipping meals, fasting, smoking, taking diet
pills, and even undergoing liposuction—all of
which can lead to further health problems.
Two important questions need to be addressed: Why do some people but not
others become overweight, and why is there an epidemic of obesity? Both genetic
and environmental factors play roles. Genetic factors are reflected in the findings
that (1) the weight of adopted children is more strongly correlated with that of their
biological parents than with that of their adoptive parents, and (2) identical twins,
including those reared apart, are more similar in weight than fraternal twins are
(Plomin et al., 2013). Even the speed of eating, which is related both to how much
is eaten in a given meal and to the weight of the eater, shows substantial heritabil-
ity (Llewellyn et al., 2008). Thus, genes affect individuals’ susceptibility to gaining
weight and how much food they eat in the first place, making it relatively difficult or
easy for them to avoid becoming part of the obesity epidemic.
Environmental influences also play a major role in this epidemic, as is obvious
from the fact that a much higher proportion of the population of the United States
is overweight now than in previous times. Indeed, some have argued that becoming
obese in the United States could be considered a normal response to the contempo-
rary American taste for high-fat, high-sugar foods
in ever larger portion sizes (K. D. Brownell, 2003).
A host of other factors fuel the ever expanding
waistlines of today’s children. Children spend less
time playing outside than their counterparts did in
previous generations: fully half of today’s preschool-
aged children spend less than an hour a day engaged
in outdoor play (Tandon et al., 2012). Children
today also get less exercise because they rarely walk
or bike to school. At school, they frequently have
no physical education programs or recess activities
and often purchase cafeteria lunches consisting of
high-fat foods (e.g., pizza, hamburgers) and high-
calorie soft drinks. Young couch potatoes—many
of whom spend more than 5 hours a day in front of
the TV consuming junk food as they are subjected
to a barrage of advertisements for more high-fat,
This photo clearly reflects the genetic
aspects of the problem of obesity. The ice
cream cone is emblematic of the environ-
mental factors that may contribute to it.
6–11 years
12–19 years
2–5 years
1963–65 1971–74 1976–80 1988–94 1999–00 2003–42001–21966–70
FIGURE 3.12 Overweight—a growing
problem The proportion of children in the
United States who are overweight has tripled
in the past four decades.
Source: National Health Examination Surveys II (Ages 6–11) and III (Ages
12–17), 1999–2004

nonnutritious fast food—are much more likely to be obese than
are children who watch for 2 hours or fewer (T. N. Robinson,
2001). In addition, many U.S. families often dine out at fast-food
or “all you can eat” buffet-style restaurants where they consume
large portions of relatively high-calorie foods (Krishnamoorthy,
Hart, & Jelalian, 2006). Finally, unhealthy foods are often less
expensive and more readily available than healthier foods, espe-
cially in inner-city areas that lack full-service supermarkets. In
such areas, known as “food deserts,” poorer residents often must
rely on convenience stores that stock primarily high-calorie pre-
packaged foods, making it difficult even for motivated parents to
provide healthy foods to their children.
Obesity puts children and adolescents at risk for a wide variety
of serious health problems, including heart disease and diabetes.
In addition, many obese youth suffer the consequences of nega-
tive stereotypes and discrimination in a variety of areas, even col-
lege admissions (M. A. Friedman & Brownell, 1995). Overweight
children and teenagers suffer a variety of other social problems as
well. For example, overweight adolescents tend to be either socially
isolated or on the fringe of their social networks (Strauss & Pol-
lack, 2003). Also, in a large-scale survey of middle school and high school students,
teens who reported being teased about their weight had considered suicide more often
than had their slimmer peers (M. Eisenberg, Neumark-Sztainer, & Story, 2003).
There is, unfortunately, no easy cure for obesity in children. However, some hope
for the general obesity problem comes from the fact that public awareness is now
focused on the severity of the problem and the variety of factors that contribute to
it. Many schools have begun serving more nutritious, less caloric foods, including
those available in vending machines, and fast-food chains have begun to include at
least some low-calorie options on their menus. Prominent national figures, such as
First Lady Michelle Obama, have targeted childhood obesity as a key public health
issue, raising hope that campaigns focused on healthy eating and exercise will help
families make positive lifestyle choices. Another helpful step, proposed by the In-
stitute of Medicine (2004), would be for the food, beverage, and entertainment in-
dustries to discontinue targeting their advertising of high-fat, high-sugar foods and
drinks to children and adolescents.
At the same time that many people in relatively rich countries are overeating their
way to poor health, the health of people in developing nations is compromised by
their not getting enough to eat. Fully one-fourth of all children (and 40% of those
younger than 5) living in these countries are undernourished. The nutritional defi-
cits they experience can involve an inadequate supply of total calories, of protein, of
vitamins and minerals, or any combination of these deficiencies. Severe malnutri-
tion of infants and young children is most common in developing and/or war-torn
countries. Analyses of child mortality data suggest that suboptimum nutrition (in-
cluding nonexclusive breastfeeding) is an underlying cause of 35% of child deaths
worldwide (R. E. Black et al., 2008).
Undernutrition and malnutrition are virtually always associated with poverty
and myriad related factors, ranging from limited access to health care (the primary
cause in the United States) to warfare, famine, and natural disasters. The interac-
tion of malnutrition with poverty and other forms of deprivation adversely affects
By exercising together, this father and son
may be taking one of the most effective
steps they can toward weight control.
/ P

all aspects of development. Figure 3.13 presents a model of how the complex in-
teraction of these multiple factors impairs cognitive development ( J. L. Brown &
Pollitt, 1996). As you can see, malnutrition can have direct effects on the structural
development of the brain, general energy level, susceptibility to infection, and
physical growth. With inadequate energy, malnourished children tend to reduce
their energy expenditure and withdraw from stimulation, making them quiet and
passive in general, less responsive in social interactions, less attentive in school,
and so on. Apathy, slowed growth, and delayed development of motor skills also
retard the children’s exploration of the environment, further limiting their oppor-
tunities to learn.
Can anything be done to help malnourished and undernourished youngsters?
Because so many interacting factors are involved in the problem, addressing it ef-
fectively is not easy—but neither is it impossible, as shown by several large-scale
intervention efforts throughout the world. For example, in one long-term proj-
ect led by Ernesto Pollitt in Guatemala, a high-protein dietary supplement ad-
ministered starting in infancy correlated with an increase in performance on tests
of cognitive functioning in adolescence (Pollitt et al., 1993). Follow-ups on the
participants in adulthood produced strong evidence for the continuing benefits
of dietary supplements 25 years after the intervention (Maluccio et al., 2009).
Although it is possible to improve the developmental status of malnourished
children, it would be better, both for the children themselves and for society in
general, to prevent the occurrence of malnutrition in the first place. As Brown and
Pollitt (1996) note: “On balance, it seems clear that prevention of malnutrition
among young children remains the best policy—not only on moral grounds but
on economic ones as well” (p. 702).
Brain damage
(sometimes reversible)
of environment
Lethargy and
Malnutrition Illness
Delayed physical
Lack of educational
and medical resources
Delayed development
of motor skills such
as crawling and walking
of child from
adults because
child appears
FIGURE 3.13 Malnutrition and cogni-
tive development Malnutrition, combined
with poverty, affects many aspects of devel-
opment and can lead to impaired cognitive
abilities. (From J. L. Brown & pollitt, 1996)

Sound nutritional behavior is vital to general health. Preferences for certain foods are evident
from birth on, and, as children develop, what they choose to eat is influenced by many factors,
including the preferences of their friends and their parents’ attempts to influence their eating
behavior. Obesity among both adults and children has increased dramatically in the United
States and much of the rest of the world in recent decades, as exposure to rich foods in large
portions has increased and physical activity has decreased. However, throughout the world, the
most common nutritional problem is undernutrition, which is very closely associated with pov-
erty. The combination of malnutrition and poverty is particularly devastating to development.
chapter summary:
Nature and Nurture
n The complex interplay of nature and nurture was the constant
theme of this chapter. In the drama of development, genotype,
phenotype, and environment all play starring roles, and the
plot moves forward as they interact in many obvious and many
not-so-obvious ways.
n The starting point for development is the genotype—the genes
inherited at conception from one’s parents. Only some of those
genes are expressed in the phenotype, one’s observable charac-
teristics. Whether some genes are expressed at all is a function
of dominance patterns. Most traits studied by developmental
scientists are influenced by multiple genes. The switching on
and off of genes over time underlies many aspects of develop-
ment. This process is affected by experience via methylation.
n The eventual outcome of a given genotype is always contin-
gent on the environment in which it develops. Parents and
their behavior toward their children are a salient part of the
children’s environment. Parents’ behavior toward their chil-
dren is influenced by their own genotypes. Similarly, the child’s
development is influenced by the aspects of the environment
he or she seeks out and the different responses the child’s char-
acteristics and behavior evoke from other people.
n The field of behavior genetics is concerned with the joint
influence of genetic and environmental factors on behavior.
Through the use of a variety of family-study designs, behavior
geneticists have discovered a wide range of behavior patterns
that “run in families.” Many behavior geneticists use herita-
bility estimates to statistically evaluate the relative contribu-
tions of heredity and environment to behavior.
Brain Development
n A burgeoning area of developmental research focuses on the
development of the brain—the most complex structure in
the known universe. Neurons are the basic units of the brain’s
informational system. These cells transmit information via
electrical signals. Impulses are transmitted from one neuron to
another at synapses.
n The most human part of the human brain is the cortex,
because it is involved in a wide variety of higher mental func-
tions. Different areas of the cortex are specialized for general
behavioral categories. The cortex is divided into two cerebral
hemispheres, each of which is specialized for certain modes of
processing, a phenomenon known as cerebral lateralization.
n Brain development involves several processes, beginning with
neurogenesis and differentiation of neurons. In synaptogen-
esis, an enormous profusion of connections among neurons is
generated, starting prenatally and continuing for the first few
years after birth. Through synaptic pruning, excess connections
among neurons are eliminated.
n Experience plays a crucial role in the strengthening or elimina-
tion of synapses and hence in the normal wiring of the brain.
The fine-tuning of the brain involves experience-expectant
processes, in which existing synapses are preserved as a func-
tion of stimulation that virtually every human encounters, and
experience-dependent processes, in which new connections are
formed as a function of learning.
n Plasticity refers to the fact that nurture is the partner of nature
in the normal development of the brain. This fact makes it
possible in certain circumstances for the brain to rewire itself
in response to damage. It also makes the developing brain vul-
nerable to the absence of stimulation at sensitive periods in
n The ability of the brain to recover from injury depends on the
age of the child. Very early damage, during the time when
neurogenesis and synaptogenesis are occurring, can have espe-
cially devastating effects. Damage during the preschool years,
when synapse elimination is occurring, is less likely to have
permanent harmful effects.
The Body: Physical Growth and Development
n Humans undergo a particularly prolonged period of physical
growth, during which growth is uneven, proceeding more rap-
idly early in life and in adolescence. Secular trends have been
observed in increases in average height and weight.

Key Terms
alleles, p. 92
association areas, p. 109
axons, p. 106
behavior genetics, p. 99
cell body, p. 106
cerebral cortex, p. 108
cerebral hemispheres, p. 109
cerebral lateralization, p. 109
chromosomes, p. 89
corpus callosum, p. 109
crossing over, p. 91
dendrites, p. 106
DNA (deoxyribonucleic acid), p. 89
dominant allele, p. 92
environment, p. 88
event-related potentials (ERPs), p. 110
experience-dependent plasticity, p. 116
experience-expectant plasticity, p. 115
failure to thrive (nonorganic), p. 120
frontal lobe, p. 109
genes, p. 89
genome, p. 88
genotype, p. 88
glial cells, p. 107
heritability, p. 102
heritable, p. 99
heterozygous, p. 92
homozygous, p. 92
lobes, p. 108
multifactorial, p. 102
mutation, p. 90
myelin sheath, p. 107
myelination, p. 112
neurogenesis, p. 109
neurons, p. 106
norm of reaction, p. 93
occipital lobe, p. 108
parietal lobe, p. 108
phenotype, p. 88
phenylketonuria (PKU), p. 93
plasticity, p. 114
polygenic inheritance, p. 93
recessive allele, p. 92
regulator genes, p. 91
secular trends, p. 120
sex chromosomes, p. 90
spines, p. 111
synapses, p. 107
synaptic pruning, p. 113
synaptogenesis, p. 112
temporal lobe, p. 108
n Food preferences begin with innate responses by newborns to
basic tastes, but additional preferences develop as a result of
experience. Problems with the regulation of eating are evident
in the United States, where an epidemic of obesity is clearly
related to both environmental and genetic factors.
n In much of the rest of the world, the dominant problem is
getting enough food, and nearly half of all the children in
the world suffer from undernutrition. Inadequate nutrition
is closely associated with poverty, and it leads to a variety of
behavioral and physical problems in virtually every aspect
of the child’s life. Prevention of undernutrition is needed
to allow millions of children to develop normal brains and
Critical Thinking Questions
1. A major focus of this chapter was the interaction of nature
and nurture. Consider yourself and your family (regard-
less of whether you were raised by your biological parents).
Identify some aspect of who you are that illustrates each
of the five relations depicted in Figure 3.1 and answer
these questions: (a) How and when was your sex deter-
mined? (b) What are some alleles you are certain or
relatively confident you share with other members of
your family? (c) What might be an example of a gene–
environment interaction in your parents’ behavior toward
you? (d) What would be an example of your active selection
of your own environment that might have influenced your
subsequent development? (e) What aspects of your own
environment might have had epigenetic effects on your
gene expression?
2. “Fifty percent of a person’s IQ is due to heredity and fifty
percent to environment.” Discuss what is wrong with this
statement, describing both what heritability estimates mean
and what they do not mean.
3. Relate the developmental processes of synaptogenesis and
synapse elimination to the concepts of experience-expectant
and experience-dependent plasticity.
4. What aspects of brain development do researchers think may
be related to the traits and behaviors of adolescents?
5. Think back over your activities and observations of the past
day or so. What aspects of your environment may relate to
the epidemic of obesity described in this chapter?
6. Consider Figure 3.13, which addresses malnutrition and cog-
nitive development. Imagine an undernourished 6-year-old
child living in the United States. Go through the figure and
generate a specific example of something that might happen
to this child at each point in the diagram. Now do the same
for a 6-year-old living in a poor, war-torn country.

FRENCH SCHOOL (20th century), Learning the Alphabet of Baksheesh (colour litho)

Theories of Cognitive
n Piaget’s Theory
View of Children’s Nature
Central Developmental Issues
The Sensorimotor Stage (Birth to Age 2 Years)
The Preoperational Stage (Ages 2 to 7)
The Concrete Operational Stage (Ages 7 to 12)
The Formal Operational Stage (Age 12 and Beyond)
Piaget’s Legacy
Box 4.1: Applications Educational Applications of
Piaget’s Theory
n Information-Processing Theories
View of Children’s Nature
Central Developmental Issues
Box 4.2: Applications Educational Applications of
Information-Processing Theories
n Sociocultural Theories
View of Children’s Nature
Central Developmental Issues
Box 4.3: Applications Educational Applications of
Sociocultural Theories
n Dynamic-Systems Theories
View of Children’s Nature
Central Development Issues
Box 4.4: Applications Educational Applications of
Dynamic-Systems Theories
n Chapter Summary
chapter 4:

A 7-month-old boy, sitting on his father’s lap, becomes intrigued with the father’s glasses, grabs one side of the frame, and yanks it. The fa-ther says, “Ow!” and his son lets go, but then reaches up and yanks the frame again. The father readjusts the glasses, but his son again grasps them and yanks. How, the father wonders, can he prevent his son from
continuing this annoying routine without causing him to start screaming? Fortu-
nately, the father, a developmental psychologist, soon realizes that Jean Piaget’s the-
ory of cognitive development suggests a simple solution: put the glasses behind his
back. According to Piaget’s theory, removing an object from a young infant’s sight
should lead the infant to act as if the object never existed. The strategy works per-
fectly; after the father puts the glasses behind his back, his son shows no further in-
terest in them and turns his attention elsewhere. The father silently thanks Piaget.
This experience, which one of us actually had, illustrates in a small way how un-
derstanding theories of child development can yield practical benefits. It also illus-
trates three broader advantages of knowing about such theories:
1. Developmental theories provide a framework for understanding important phenom-
ena. Theories help to reveal the significance of what we observe about children,
both in research studies and in everyday life. Someone who witnessed the glasses
incident but who did not know about Piaget’s theory might have found the expe-
rience amusing but insignificant. Seen in terms of Piaget’s theory, however, this
passing event exemplifies a general and profoundly important developmental phe-
nomenon: infants younger than 8 months react to the disappearance of an object
as though they do not understand that the object still exists. In this way, theories
of child development place particular experiences and observations in a
larger context and deepen our understanding of their meaning.
2. Developmental theories raise crucial questions about human nature.
Pia get’s theory about young infants’ reactions to disappearing objects was
based on his informal experiments with infants younger than 8 months.
Piaget would cover one of their favorite objects with a cloth or otherwise
put it out of sight and then wait to see whether the infants tried to re-
trieve the object. They rarely did, leading Piaget to conclude that before
the age of 8 months, infants do not realize that hidden objects still exist.
Other researchers have challenged this explanation. They argue that in-
fants younger than 8 months do in fact understand that hidden objects
continue to exist but lack the memory or problem-solving skills neces-
sary for using that understanding to retrieve hidden objects (Baillargeon,
1993). Despite these disagreements about how best to interpret young
infants’ failure to retrieve hidden objects, researchers agree that Piaget’s
theory raises a crucial question about human nature: Do infants realize
from the first days of life that objects continue to exist when out of sight,
or is this something that they learn later? More significant, do young in-
fants understand that people continue to exist when they cannot be seen?
Do they fear that Mom no longer exists when she disappears from sight?
3. Developmental theories lead to a better understanding of children. Theo-
ries also stimulate new research that may support the theories’ claims,
fail to support them, or require refinements of them, thereby improv-
ing our understanding of children. For example, Piaget’s ideas led
n Nature and Nurture
n The Active Child
n Continuity/Discontinuity
Mechanisms of Change
n The Sociocultural Context
n Research and Children’s
The author whose son loved to grab his
glasses is not the only one who has encoun-
tered this problem. If the mom in this pic-
ture was lucky enough to have read this
textbook, she may have solved the problem
in the same way.

Munakata and her colleagues (1997) to test whether 7-month-olds’ failure to reach
for hidden objects was due to their lacking the motivation or the reaching skill to
retrieve them. To find out, the researchers created a situation similar to Piaget’s
object-permanence experiment, except that they placed the object, an attractive toy,
under a transparent cover rather than under an opaque one. In this situation, in-
fants quickly removed the cover and regained the toy. This finding seemed to sup-
port Piaget’s original interpretation by showing that neither lack of motivation nor
lack of ability to reach for the toy explained the infants’ usual failure to retrieve it.
In contrast, an experiment conducted by Diamond (1985) indicated a need to
revise Piaget’s theory. Using an opaque covering, as Piaget did, Diamond varied the
amount of time between when the toy was hidden and when the infant was allowed
to reach for it. She found that even 6-month-olds could locate the toy if allowed
to reach immediately, that 7-month-olds could wait as long as 2 seconds and still
succeed, that 8-month-olds could wait as long as 4 seconds and still succeed, and
so on. Diamond’s finding indicated that memory for the location of hidden objects,
as well as the understanding that they continue to exist, is crucial to success on the
task. In sum, theories of child development are useful because they provide frame-
works for understanding important phenomena, raise fundamental questions about
human nature, and motivate new research that increases understanding of children.
Because child development is such a complex and varied subject, no single the-
ory accounts for all of it. The most informative current theories focus primarily
on either cognitive development or social development. Providing a good theo-
retical account of development in even one of these areas is an immense challenge,
because each of them spans a huge range of topics. Cognitive development includes
the growth of such diverse capabilities as perception, attention, language, problem
solving, reasoning, memory, conceptual understanding, and intelligence. Social de-
velopment includes the growth of equally diverse areas: emotions, personality, re-
lationships with peers and family members, self-understanding, aggression, and
moral behavior. Given this immense range of developmental domains, it is easy
to understand why no one theory has captured the entirety of child development.
Therefore, we present cognitive and social theories in separate chapters. We
consider theories of cognitive development in this chapter, just before the chapters
on specific areas of cognitive development, and consider theories of social develop-
ment in Chapter 9, just before the chapters on specific areas of social development.
This chapter examines four theoretical perspectives on cognitive develop-
ment that are particularly influential: the Piagetian perspective, the information-
processing perspective, the sociocultural perspective, and the dynamic-systems
perspective. We consider each perspective’s fundamental assump-
tions about children’s nature, the central developmental issues on
which the perspective focuses, and practical examples of the per-
spective’s usefulness for helping children learn.
These four theoretical perspectives are influential in large
part because they provide important insights into the basic de-
velopmental themes described in Chapter 1. Each perspective
addresses all the themes to some extent, but each emphasizes dif-
ferent ones. For example, Piaget’s theory focuses on continuity/
discontinuity and the active child, whereas information-processing
theories focus on mechanisms of change (Table 4.1). Together, the
four perspectives allow a broader appreciation of cognitive devel-
opment than any one of them does alone.
Main Questions Addressed by Theories
of Cognitive Development
Theory Main Questions Addressed
Piagetian Nature–nurture, continuity/discontinuity,
the active child
Information-processing Nature–nurture, how change occurs
Sociocultural Nature–nurture, influence of the
sociocultural context, how change occurs
Dynamic-systems Nature–nurture, the active child, how
change occurs

Piaget’s Theory
Jean Piaget’s studies of cognitive development are a testimony to how much one
person can contribute to a scientific field. Before his work began to appear in the
early 1920s, there was no recognizable field of cognitive development. Nearly a
century later, Piaget’s theory remains the best-known cognitive developmental the-
ory in a field replete with theories. What accounts for its longevity?
One reason is that Piaget’s observations and descriptions vividly convey the
texture of children’s thinking at different ages. Another reason is the exceptional
breadth of the theory. It extends from the first days of infancy through adoles-
cence and examines topics as diverse as conceptualization of time, space, distance,
and number; language use; memory; understanding of other people’s perspectives;
problem solving; and scientific reasoning. Even today, it remains the most encom-
passing theory of cognitive development. A third source of its longevity is that it
offers an intuitively plausible depiction of the interaction of nature and nurture in
cognitive development, as well as of the continuities and discontinuities that char-
acterize intellectual growth.
View of Children’s Nature
Piaget’s fundamental assumption about children was that they are mentally ac-
tive as well as physically active from the moment of birth, and that their activity
greatly contributes to their own development. His approach to understanding
cognitive development is often labeled constructivist, because it depicts children
as constructing knowledge for themselves in response to their experiences. Three
of the most important of children’s constructive processes, according to Piaget,
are generating hypotheses, performing experiments, and drawing conclusions
from their observations. If this description reminds you of scientific problem
solving, you are not alone: the “child as scientist” is the dominant metaphor in
Piaget’s theory. Consider this description of his infant son:
Laurent is lying on his back. . . . He grasps in succession a celluloid swan, a box, etc.,
stretches out his arm and lets them fall. He distinctly varies the position of the fall.
When the object falls in a new position (for example, on his pillow), he lets it fall two
or three more times on the same place, as though to study the spatial relation.
(Piaget, 1952b, pp. 268–269)
In simple activities such as Laurent’s game of “drop the toy
from different places and see what happens,” Piaget per-
ceived the beginning of scientific experimentation.
This example also illustrates a second basic Piagetian as-
sumption: children learn many important lessons on their
own, rather than depending on instruction from adults or
older children. To further illuminate this point, Piaget cited
a friend’s recollection from childhood:
He was seated on the ground in his garden and he was count-
ing pebbles. Now to count these pebbles he put them in a row
and he counted them one, two, three up to 10. Then he fin-
ished counting them and started to count them in the other
direction. He began by the end and once again he found that
he had 10. He found this marvelous. . . . So he put them in a
circle and counted them that way and found 10 once again.
(Piaget, 1964, p. 12)
Jean piaget, whose work has had a profound
influence on developmental psychology, is
seen here interviewing a child to learn about
his thinking.
/ G

This incident also highlights a third basic assumption of Piaget’s: children are
intrinsically motivated to learn and do not need rewards from other people to do
so. When they acquire a new capability, they apply it as often as possible. They also
reflect on the lessons of their experience, because they want to understand them-
selves and everything around them.
Central Developmental Issues
In addition to his view that children actively shape their own development, Piaget
offered important insights regarding the roles of nature and nurture and of conti-
nuities and discontinuities in development.
Nature and Nurture
Piaget believed that nature and nurture interact to produce cognitive development.
In his view, nurture includes not just the nurturing provided by parents and other
caregivers but every experience children encounter. Nature includes children’s ma-
turing brain and body; their ability to perceive, act, and learn from experience; and
their tendency to integrate particular observations into coherent knowledge. As this
description suggests, a vital part of children’s nature is to respond to their nurture.
Sources of Continuity
Piaget depicted development as involving both continuities and discontinuities.
The main sources of continuity are three processes—assimilation, accommodation,
and equilibration—that work together from birth to propel development forward.
Assimilation is the process by which people incorporate incoming information
into concepts they already understand. To illustrate, when one of our children was
2 years old, he saw a man who was bald on top of his head and had long frizzy hair
on the sides. To his father’s great embarrassment, the toddler gleefully shouted,
“Clown! Clown!” (Actually, it sounded more like “Kown! Kown!”) The man appar-
ently looked enough like a “kown” that the boy could assimilate him to his clown
Accommodation is the process by which people improve their current under-
standing in response to new experiences. In the “kown” incident, the boy’s father
explained to his son that the man was not a clown and that even though his hair
looked like a clown’s, he was not wearing a funny costume and was not doing silly
things to make people laugh. With this new information, the boy was able to ac-
commodate his clown concept to the standard one, allowing other men with bald
pates and long side hair to pass by in peace.
Equilibration is the process by which children (indeed, people of all ages) bal-
ance assimilation and accommodation to create stable understanding. Equilibra-
tion includes three phases. First, children are satisfied with their understanding
of a particular phenomenon; Piaget labeled this a state of equilibrium, because the
children do not see any discrepancies between their observations and their under-
standing of the phenomenon. Then, new information leads them to perceive that
their understanding is inadequate. Piaget said that this realization puts children in
a state of disequilibrium; they recognize shortcomings in their understanding of the
phenomenon, but they cannot generate a superior alternative. Finally, they develop
a more sophisticated understanding that eliminates the shortcomings of the old
one, creating a more advanced equilibrium within which a broader range of obser-
vations can be understood.
perhaps toddlers yelling “Kown, kown!” set
Larry, a member of The Three Stooges, on
his career path.
assimilation n the process by which
people translate incoming information
into a form that fits concepts they already
accommodation n the process by which
people adapt current knowledge struc-
tures in response to new experiences
equilibration n the process by which
children (or other people) balance assimi-
lation and accommodation to create
stable understanding

One example of how equilibration works involves the belief—held by most 4- to
7-year-olds in a wide range of cultures (Inagaki & Hatano, 2008)—that animals are
the only living things. This belief seems to stem from the assumption that only ani-
mals can move in ways that help them survive. Sooner or later, children realize that
plants also move in ways that promote their survival (e.g., toward sunlight). This
new information is difficult for them to assimilate to their prior thinking. The re-
sulting disparity between their previous understanding of living things and their new
knowledge about plants creates a state of disequilibrium, in which they are unsure of
what it means to be alive. Later, their thinking accommodates to the new informa-
tion about plants. That is, they realize that both animals and plants move in adaptive
ways and that, because adaptive movement is a key characteristic of living things,
plants as well as animals must be alive (Opfer & Gelman, 2001; Opfer & Siegler,
2004). This realization constitutes a more stable equilibrium, because subsequent
information about plants and animals will not contradict it. Through innumerable
such equilibrations, children acquire knowledge of the world around them.
Sources of Discontinuity
Although Piaget placed some emphasis on continuous aspects of cognitive devel-
opment, the most famous part of his theory concerns discontinuous aspects, which
he depicted as distinct stages of cognitive development. Piaget viewed these stages
as products of the basic human tendency to organize knowledge into coherent
structures. Each stage represents a coherent way of understanding one’s experience,
and each transition between stages represents a discontinuous intellectual leap from
one coherent way of understanding the world to the next, higher one. The follow-
ing are the central properties of Piaget’s stage theory:
1. Qualitative change. Piaget believed that children of different ages think in quali-
tatively different ways. For example, he proposed that children in the early stages
of cognitive development conceive of morality in terms of the consequences of a per-
son’s behavior, whereas children in later stages conceive of it in terms of the person’s
intent. Thus, a 5-year-old would judge someone who accidentally broke a whole jar
of cookies as having been naughtier than someone who deliberately stole a single
cookie; an 8-year-old would reach the opposite conclusion. This difference rep-
resents a qualitative change, because the two children are basing their moral judg-
ments on entirely different criteria.
2. Broad applicability. The type of thinking characteristic of each stage influences
children’s thinking across diverse topics and contexts.
3. Brief transitions. Before entering a new stage, children pass through a brief tran-
sitional period in which they fluctuate between the type of thinking characteristic
of the new, more advanced stage and the type of thinking characteristic of the old,
less advanced one.
4. Invariant sequence. Everyone progresses through the stages in the same order
without skipping any of them.
Piaget hypothesized four stages of cognitive development: the sensorimotor stage,
the preoperational stage, the concrete operational stage, and the formal operational
stage. In each stage, children exhibit new abilities that allow them to understand
the world in qualitatively different ways than they had previously.

1. In the sensorimotor stage (birth to age 2 years), infants’ intelligence is
expressed through their sensory and motor abilities, which they use to per-
ceive and explore the world around them. These abilities allow them to learn
about objects and people and to construct rudimentary forms of fundamental
concepts such as time, space, and causality. Throughout the sensorimotor
period, infants live largely in the here and now: their intelligence is bound to
their immediate perceptions and actions.
2. In the preoperational stage (ages 2 to 7 years), toddlers and preschoolers
become able to represent their experiences in language and mental imagery.
This allows them to remember the experiences for longer periods and to
form more sophisticated concepts. However, as suggested by the term pre-
operational, Piaget’s theory emphasizes young children’s inability to perform
certain mental operations, such as considering multiple dimensions simultane-
ously. This leads to children’s being unable to form certain ideas, such as the
idea that pouring all the water from a short, wide glass into a taller, narrower
glass does not change the total amount of water, even though the column of
water is higher in the second glass. In other words, they do not recognize that
the increased height of the liquid column in the second glass is compensated
for by its narrower width.
3. In the concrete operational stage (ages 7 to 12 years), children can reason
logically about concrete objects and events; for example, they understand
that pouring water from one glass to a taller, narrower one leaves the amount
of water unchanged. However, concrete operational reasoners cannot think
in purely abstract terms or generate systematic scientific experiments to test
their beliefs.
4. In the final stage of cognitive development, the formal operational stage
(age 12 years and beyond), children can think deeply not only about concrete
events but also about abstractions and purely hypothetical situations. They
also can perform systematic scientific experiments and draw appropriate con-
clusions from them, even when the conclusions differ from their prior beliefs.
With this overview of Piaget’s theory, we can consider in greater depth major
changes that take place in each stage.
The Sensorimotor Stage (Birth to Age 2 Years)
One of Piaget’s most profound insights was his realization that the roots of adult
intelligence are present in infants’ earliest behaviors, such as their seemingly aim-
less sucking, flailing, and grasping. He recognized that these behaviors are not
random but instead reflect an early type of intelligence involving sensory and
motor activity. Indeed, many of the clearest examples of the active child theme
come from Piaget’s descriptions of the development of what he called “sensorimo-
tor intelligence.”
Over the course of the first 2 years, infants’ sensorimotor intelligence develops
tremendously. The sheer amount of change may at first seem astonishing. However,
when we consider the immense variety of new experiences that infants encounter
during this period, and the tripling of brain weight between birth and age 3 (with
weight being an index of brain development during this period), the huge increase
in infants’ cognitive abilities is more understandable. The profound developments
that Piaget described as occurring during infancy call attention to a general prin-
ciple: children’s thinking grows especially rapidly in the first few years.
sensorimotor stage n the period (birth
to 2 years) within Piaget’s theory in which
intelligence is expressed through sensory
and motor abilities
preoperational stage n the period
(2 to 7 years) within Piaget’s theory in
which children become able to represent
their experiences in language, mental
imagery, and symbolic thought
concrete operational stage n the
period (7 to 12 years) within Piaget’s
theory in which children become able to
reason logically about concrete objects
and events
formal operational stage n the period
(12 years and beyond) within Piaget’s
theory in which people become able to
think about abstractions and hypothetical

Infants are born with many reflexes. When objects move in front of their eyes,
they visually track them; when objects are placed in their mouths, they suck them;
when objects come into contact with their hands, they grasp them; when they hear
noises, they turn toward them; and so on. Piaget believed that these simple reflexes
and perceptual abilities are the foundation of intelligence.
Even during their first month, infants begin to modify their reflexes to make
them more adaptive. At birth, for example, they suck in a similar way regardless of
what they are sucking. Within a few weeks, however, they adjust their sucking ac-
cording to the object in their mouth. Thus, they suck on a milk-yielding nipple in a
way that enhances the efficiency of their feeding and that is different from the way
they suck on a finger or even a pacifier. As this example illustrates, from the first days
out of the womb, infants accommodate their actions to the parts of the environment
with which they interact.
Over the course of the first few months, infants begin to organize separate re-
flexes into larger behaviors, most of which are centered on their own bodies. For
example, instead of being limited to exercising their grasping and sucking reflexes
separately, they can integrate them: when an object touches their palm, they can
grasp it, bring it to their mouth, and suck on it. Thus, their reflexes serve as build-
ing blocks for more complex behaviors.
In the middle of their first year, infants become increasingly interested in the
world around them—people, animals, toys, and other objects and events beyond
their own bodies. A hallmark of this shift is their repetition of actions on the en-
vironment that produce pleasurable or interesting results. Repeatedly banging a
rattle and squeezing a rubber duck again and again to make it squeak are examples
of favorite activities for many infants at this time.
Piaget (1954) made a striking and controversial claim about a deficiency in in-
fants’ thinking during this period—the one referred to in the chapter-opening an-
ecdote about the father hiding his glasses. The claim was that through the age of
8 months, infants lack object permanence, the knowledge that objects continue
to exist even when they are out of view. This claim was based largely on Piaget’s
observations of his own children, Laurent, Lucienne, and Jacqueline. The follow-
ing account of an experiment with Laurent reflects the type of observation that in-
spired Piaget’s belief about object permanence:
At age 7 months, 28 days, I offer him a little bell behind a cushion. So long as he sees
the little bell, however small it may be, he tries to grasp it. But if the little bell disap-
pears completely he stops all searching. I then resume the experiment using my hand
as a screen. Laurent’s arm is outstretched and about to grasp the little bell at the mo-
ment I make it disappear behind my hand which is open and at a distance of about 15
cm from him. He immediately withdraws his arm, as though the little bell no longer
(Piaget, 1954, p. 39)
Thus, in Piaget’s view, for infants younger than 8 months, the adage “out of
sight, out of mind” is literally true. They are able to mentally represent (think
about) only the objects that they can perceive at the moment.
By the end of the first year, infants search for hidden objects, thus indicating that
they mentally represent the objects’ continuing existence even when they no longer
see them. These initial representations of objects are fragile, however, as reflected
in the A-not-B error. In this error, once 8- to 12-month-olds have reached for and
found a hidden object several times in one place (location A), when they see the
object hidden at a different place (location B) and are prevented from immediately
searching for it, they tend to reach where they initially found the object (location
piaget proposed that when infants suck on
objects, they gain not only pleasure but also
knowledge about the world beyond their
object permanence n the knowledge
that objects continue to exist even when
they are out of view
A-not-B error n the tendency to reach
for a hidden object where it was last
found rather than in the new location
where it was last hidden
deferred imitation n the repetition of
other people’s behavior a substantial time
after it originally occurred

A) (see Figure 4.1). Not until around their first birthday do infants consistently
search first at the object’s current location.
At around 1 year of age, infants begin to actively and avidly explore the po-
tential ways in which objects can be used. The “child as scientist” example pre-
sented earlier, in which Piaget’s son Laurent varied the positions from which he
dropped different objects to see what would happen, provides one instance of this
emerging competency. Similar examples occur in every family with an infant. Few
parents forget their 12- to 18-month-old sitting in a high chair, banging various
objects against the chair’s tray—first a spoon, then a plate, then a cup— seemingly
fascinated by the sounds made by the different objects. Nor do they forget their
infant dropping bathroom articles into the toilet, or pouring a bag of flour on
the kitchen floor, just to see what happens. Piaget regarded such actions as the
beginnings of scientific experimentation (many parents see such behaviors in less
positive terms).
In the last half-year of the sensorimotor stage (ages 18 to 24 months), accord-
ing to Piaget, infants become able to form enduring mental representations. The
first sign of this new capability is deferred imitation, that is, the repetition of other
people’s behavior minutes, hours, or even days after it occurred. Consider Piaget’s
observation of 1-year-old Jacqueline:
Jacqueline had a visit from a little boy . . . who, in the course of the afternoon, got
into a terrible temper. He screamed as he tried to get out of a playpen and pushed it
backward, stamping his feet. . . . The next day, she herself screamed in her playpen and
tried to move it, stamping her foot lightly several times in succession.
(Piaget, 1951, p. 63)
Piaget indicated that Jacqueline had never before thrown such a tantrum. Pre-
sumably, she had watched and remembered her playmate’s behavior, maintained a
representation of it overnight, and imitated it the next day.
FIGURE 4.1 piaget’s A-not-B task A
child looks for and finds a toy under the
cloth where it was hidden (left frame). After
several such experiences, the toy is hidden
in a different location (right frame). The
child continues to look where he found the
toy previously, rather than where it is hidden
now. The child’s ignoring the visible protru-
sion of the toy under the cloth in the right
frame illustrates the strength of the inclina-
tion to look in the previous hiding place.
: B
This toddler’s techniques for applying eye
makeup may not exactly mirror those he
has seen his mother use, but they are close
enough to provide a compelling illustration
of deferred imitation, a skill that children
gain during their second year.

When we consider Piaget’s account of cognitive development during infancy,
several notable trends are evident.
n At first, infants’ activities center on their own bodies; later, their activities
include the world around them.
n Early goals are concrete (shaking a rattle and listening to the sound it makes);
later goals often are more abstract (varying the heights from which objects are
dropped and observing how the effects vary).
n Infants become increasingly able to form mental representations, moving from
“out of sight, out of mind” to remembering a playmate’s actions from a full day
earlier. Such enduring mental representations make possible the next stage,
which Piaget called preoperational thinking.
The Preoperational Stage (Ages 2 to 7)
Piaget viewed the preoperational period as including a mix of striking cognitive
acquisitions and fascinating limitations. Perhaps the foremost acquisition is the
development of symbolic representations; among the most notable weaknesses are
egocentrism and centration.
Development of Symbolic Representations
Have you ever seen preschoolers use two Popsicle sticks to represent a gun or a
playing card to represent an iPhone? Forming such personal symbols is common
among 3- to 5-year-olds. It is one of the ways in which they exercise their emerging
capacity for symbolic representation—the use of one object to stand for another.
Typically, these personal symbols physically resemble the objects they represent.
The Popsicle sticks’ and playing card’s shapes somewhat resemble those of a gun
and iPhone.
As children develop, they rely less on self-generated symbols and more on con-
ventional ones. For example, when 5-year-olds play games involving pirates, they
might wear a patch over one eye and a bandanna over their head because that is the
way pirates are commonly depicted. Heightened symbolic capabilities during the
preoperational period are also evident in the growth of drawing. Children’s draw-
ings between ages 3 and 5 make increasing use of symbolic conventions, such as
representing the leaves of flowers as Vs (Figure 4.2).
Although Piaget noted important growth in children’s thinking during the pre-
operational stage, he found the limitations of this period to be as intriguing and
revealing of preoperational understanding. As noted, one important limitation is
egocentrism, that is, perceiving the world solely from one’s own point of view. An
example of this limitation involves preschoolers’ difficulty in taking other people’s
spatial perspectives. Piaget and Inhelder (1956/1977) demonstrated this difficulty
by having 4-year-olds sit at a table in front of a model of three mountains of dif-
ferent sizes (Figure 4.3). The children were asked to identify which of several
photographs depicted what a doll would see if it were sitting on chairs at various
locations around the table. Solving this problem required children to recognize
that their own perspective was not the only one possible and to imagine what the
view would be from another location. Most 4-year-olds, according to Piaget, can-
not do this.
FIGURE 4.3 piaget’s three-mountains
task When asked to choose the picture that
shows what the doll sitting in the seat across
the table would see, most children younger
than 6 years choose the picture showing
how the scene looks to them, illustrating
their difficulty in separating their own per-
spective from that of others.
FIGURE 4.2 A 4-year-old’s drawing of a
summer day Note the use of simple artistic
conventions, such as the V-shaped leaves on
the flowers.
symbolic representation n the use of
one object to stand for another
egocentrism n the tendency to perceive
the world solely from one’s own point of

The same difficulty in taking other people’s perspectives is seen in quite different
contexts—for example, in communication. As illustrated in Figure 4.4, preschoolers
often talk right past each other, focused only on what they themselves are saying and
seemingly oblivious to their partner’s comments. Preschoolers’ egocentric communi-
cation also is evident when they make statements that require knowledge that they
themselves possess but that their listeners couldn’t be expected to have. For example,
2- and 3-year-olds frequently tell day-care providers and parents things like “He
took it from me,” in situations where the person or object to which the child is re-
ferring is totally unclear. Egocentric thinking is also evident in preschoolers’ expla-
nations of events and behavior. Consider the following interviews with preschoolers
that occurred in the original version of the TV show Kids Say the Darndest Things:
Interviewer: Any brothers or sisters?
Child: I have a brother a week old.
I: What can he do?
C: He can say “Mamma” and “Daddy.”
I: Can he walk?
C: No, he’s too lazy.
Interviewer: Any brothers or sisters?
Child: A 2-months-old brother.
I: How does he behave?
C: He cries all night.
I: Why is that, do you think?
C: He probably thinks he’s missing something on television.
(Linkletter, 1957, p. 6)
Over the course of the preoperational period, egocentric speech becomes less
common. An early sign of progress is children’s verbal quarrels, which become in-
creasingly frequent during this period. The fact that a child’s statements elicit a
playmate’s objection indicates that the playmate is at least paying attention to the
differing perspective that the other child’s comment implies. Children also become
better able to envision spatial perspectives other than their own during the pre-
operational period. We all remain somewhat egocentric throughout our lives, but
most of us do improve.
A related limitation of preschoolers’ thinking is centration, that is, focusing on a
single, perceptually striking feature of an object or event to the exclusion of other
relevant but less striking features. Children’s approaches to balance-scale prob-
lems provide a good example of centration. If presented with a balance scale like
that in Figure 4.5 and asked which side will go down, 5- and 6-year-olds center
on the amount of weight on each side, ignore the distance of the weights from the
fulcrum, and say that whichever side has more weight will go down (Inhelder &
Piaget, 1958).
Another good example of centration comes from Piaget’s research on chil-
dren’s understanding of conservation. The idea of the conservation concept is that
merely changing the appearance or arrangement of objects does not necessarily
change other key properties, such as quantity of material. Three variants of the con-
cept that are commonly studied in 5- to 8-year-olds are conservation of liquid quan-
tity, conservation of solid quantity, and conservation of number (Piaget, 1952a). In
all three cases, the tasks used to measure children’s understanding employ a three-
phase procedure (Figure 4.6). First, as in the figure, children are shown two objects
My dad is a policeman…
I have a real big dog…
He licks my face all the time…
He caught a robber once…
FIGURE 4.4 egocentrism An example
of young children’s egocentric conversations.
FIGURE 4.5 The balance scale When
asked to predict which side of a balance
scale, like the one shown above, would go
down if the arm were allowed to move, 5-
and 6-year-olds almost always center their
attention on the amount of weight and
ignore the distances of the weights from the
fulcrum. Thus, they would predict that the
left side would go down, although it is the
right side that would actually drop.
centration n the tendency to focus on a
single, perceptually striking feature of an
object or event
conservation concept n the idea
that merely changing the appearance of
objects does not necessarily change other
key properties

(e.g., two glasses of orangeade, two clay sausages) that are identical in quantity, or
two sets of objects (e.g., two rows of pennies) that are identical in number. Once
children agree that the dimension of interest (e.g., the amount of orangeade or the
number of pennies) is equal in both items, they observe a second phase in which the
experimenter transforms one object or set of objects in a way that makes it look dif-
ferent but does not change the dimension of interest. Orangeade might be poured
into a taller, narrower, glass; a short, thick clay sausage might be molded into a long,
thin sausage; or one of the two rows of pennies might be spread out. Finally, in the
third phase, children are asked whether the dimension of interest, which they ear-
lier had said was equal for the two objects or sets of objects, is still equal.
The large majority of 4- and 5-year-olds answer “no.” On conservation-
of- liquid-quantity problems, they claim that the taller, narrower glass has more
orangeade; on conservation-of-solid-quantity problems, they claim that the long,
thin sausage has more clay than the short, thick one; and so on. Children of this
age make similar errors in everyday contexts; for example, they often think that if a
child has one fewer cookie than another child, a fair solution is to break one of the
short-changed child’s cookies into two pieces (Miller, 1984).
A variety of weaknesses that Piaget perceived in preoperational thinking con-
tribute to these difficulties with conservation problems. Preoperational thinkers
center their attention on the single, perceptually salient dimension of height or
length, ignoring other relevant dimensions. In addition, their egocentrism leads to
their failing to understand that their own perspective can be misleading—that just
because a tall narrow glass of orangeade or a long thin clay sausage looks as though
“Now watch what I do”
(stretching one piece of clay).
“Now watch what I do”
(pouring contents of one glass).
“Now, do they have the same amount
of clay or a different amount?”
“Do they have the same amount
of clay or a different amount?”
“Now watch what I do”
(spreading one row).
“Is there the same number
or a different number?”
“Do they have the same amount
of orange drink or a different
“Now, do they have the same amount
of orange drink or a different
“Now, is there the same number
or a different number?”
FIGURE 4.6 procedures used to test
conservation of liquid quantity, solid
quantity, and number Most 4- and 5-year-
olds say that the taller liquid column has
more liquid, the longer sausage has more
clay, and the longer row has more objects.

it has more orangeade or clay than a shorter, wider one does not mean that it re-
ally does. Children’s tendency to focus on static states of objects (the appearance
of the objects after the transformation) and to ignore the transformation that was
performed (pouring the orangeade or reshaping the clay) also contributes to their
difficulty in solving conservation problems.
In the next period of cognitive development, the concrete operational stage, chil-
dren largely overcome these and other related limitations.
The Concrete Operational Stage (Ages 7 to 12)
At around age 7, according to Piaget, children begin to reason logically about con-
crete features of the world. Development of the conservation concept exemplifies
this progress. Although few 5-year-olds solve any of the three conservation tasks de-
scribed in the previous section, most 7-year-olds solve all of them. The same progress
in thinking also allows children in the concrete operational stage to solve many other
problems that require attention to multiple dimensions. For example, on the balance-
scale problem, they consider distance from the fulcrum as well as weight of objects.
However, this relatively advanced reasoning is, according to Piaget, limited to
concrete situations. Thinking systematically remains very difficult, as does rea-
soning about hypothetical situations. These limitations are evident in the types
of experiments that concrete operational children perform to solve the pendulum
problem (Inhelder & Piaget, 1958) (Figure 4.7). In this problem, children are pre-
sented a pendulum frame, a set of strings of varying length with a loop at each end,
and a set of metal weights of varying weight, any of which can be attached to any
string. When the loop at one end of the string is attached to a weight, and the loop
at the other end is attached to the frame of the pendulum, the string can be swung.
The task is to perform experiments that indicate which factor or factors influence
the amount of time it takes the pendulum to swing through a complete arc. Is it the
length of the string, the heaviness of the weight, the height from which the weight
is dropped, or some combination of these factors? Think for a minute: How would
you go about solving this problem?
Most concrete operational children begin their experiments believing that the
relative heaviness of the weights being dropped is the most important factor, perhaps
the only important one. This belief is not unreasonable; indeed, most adolescents
and adults share it. What distinguishes the children’s reasoning from that of older
individuals is how they test their belief. Concrete operational reasoners design biased
experiments from which no valid conclusion can be drawn. For example, they might
compare the travel time of a heavy weight on a short string dropped from a high po-
sition to the travel time of a light weight on a long string dropped from a lower posi-
tion. When the first string goes faster, they conclude that, just as they thought, heavy
weights go faster. This premature conclusion, however, reflects their limited ability
to think systematically or to imagine all possible combinations of variables. They
fail to imagine that the faster motion might be related to the length of the string or
the height from which the string was dropped, rather than the weight of the object.
The Formal Operational Stage (Age 12 and Beyond)
Formal operational thinking, which includes the ability to think abstractly and to rea-
son hypothetically, is the pinnacle of the Piagetian stage progression. The difference
between reasoning in this stage and in the previous one is clearly illustrated by for-
mal operational reasoners’ approach to the pendulum problem. Framing the problem
FIGURE 4.7 Inhelder and piaget’s pen-
dulum problem The task is to compare the
motions of longer and shorter strings, with
lighter and heavier weights attached, in
order to determine the influence of weight,
string length, and dropping point on the
time it takes for the pendulum to swing back
and forth. Children younger than 12 usually
perform unsystematic experiments and draw
incorrect conclusions.

more abstractly than do children in the concrete operational stage, they see that any
of the variables—weight, string length, and dropping point—might influence the
time it takes for the pendulum to swing through an arc, and that it is therefore neces-
sary to test the effect of each variable systematically. To test the effect of weight, they
compare times to complete an arc for a heavier weight and a lighter weight, attached
to strings of equal length and dropped from the same height. To test the effect of
string length, they compare the travel times of a long and a short string, with equal
weight dropped from the same position. To test the influence of dropping point, they
vary the dropping point of a given weight attached to a given string. Such a
systematic set of experiments allows the formal operational thinker to de-
termine that the only factor that influences the pendulum’s travel time is the
length of the string; neither weight nor dropping point matters.
Piaget believed that unlike the previous three stages, the formal opera-
tional stage is not universal: not all adolescents (or adults) reach it. For those
adolescents who do reach it, however, formal operational thinking greatly
expands and enriches their intellectual universe. Such thinking makes it
possible for them to see the particular reality in which they live as only one
of an infinite number of possible realities. This insight leads them to think
about alternative ways that the world could be and to ponder deep questions
concerning truth, justice, and morality. It no doubt also helps account for
the fact that many people first acquire a taste for science fiction during ado-
lescence. The alternative worlds depicted in science-fiction stories appeal to
adolescents’ emerging capacity to think about the world they know as just
one of many possibilities and to wonder whether a better world is possible.
The attainment of formal operational thinking does not mean that ad-
olescents will always reason in advanced ways, but it does, according to
Piaget, mark the point at which adolescents attain the reasoning powers of
intelligent adults. (Some ways in which Piaget’s theory can be applied to improving
education are discussed in Box 4.1.)
Piaget’s Legacy
Although much of Piaget’s theory was formulated many years ago, it remains a very
influential approach to understanding cognitive development. Some of its strengths
were mentioned earlier. It provides a good overview of children’s thinking at dif-
ferent points in development (Table 4.2). It includes countless fascinating observa-
tions. It offers a plausible and appealing perspective on children’s nature. It surveys
a remarkably broad spectrum of developments and covers the entire age span from
infancy through adolescence.
However, subsequent analyses (Flavell, 1971, 1982; Miller, 2011) have identi-
fied some crucial weaknesses in Piaget’s theory. The following four are particularly
1. The stage model depicts children’s thinking as being more consistent than it is. Accord-
ing to Piaget, once children enter a given stage, their thinking consistently shows
the characteristics of that stage across diverse concepts. Subsequent research, how-
ever, has shown that children’s thinking is far more variable than this depiction sug-
gests. For example, most children succeed on conservation-of-number problems by
age 6, whereas most do not succeed on conservation-of-solid-quantity problems
until age 8 or 9 (Field, 1987). Piaget recognized that such variability exists but un-
derestimated its extent and failed to explain it.
Teenagers’ emerging ability to understand
that their reality is only one of many pos-
sible realities may cause teens to develop a
taste for science fiction.
/ P

BOX 4.1: applications
Piaget’s view of children’s cognitive devel-
opment holds a number of general implica-
tions for how children should be educated
(Case, 1998; Piaget, 1972). Most gener-
ally, it suggests that children’s distinctive
ways of thinking at different ages need to be
considered in deciding how to teach them.
For example, children in the concrete op-
erational stage would not be expected to be
ready to learn purely abstract concepts such
as inertia and equilibrium state, whereas
adolescents in the formal operational stage
would be. Taking into account such general
age-related differences in cognitive level
before deciding when to teach particular
concepts is often labeled a “child-centered
A second implication of Piaget’s approach
is that children learn best by interacting with
the environment, both mentally and physi-
cally. One research demonstration of this
principle involved promoting children’s un-
derstanding of the concept of speed (Levin,
Siegler, & Druyan, 1990). The investigation
focused on problems of a type beloved by
physics teachers: “When a race horse travels
around a circular track, do its right and left
sides move at the same speed?” It appears
obvious that they do, but, in fact, they do
not. The side toward the outside of the track
is covering a slightly greater distance in the
same amount of time as the side toward the
inside and therefore is moving slightly faster.
Levin and her colleagues devised a proce-
dure that allowed children to actively expe-
rience how different parts of a single object
can move at different speeds. They attached
one end of a 7-foot-long metal bar to a pivot
that was mounted on the floor. One by one,
6th-graders and an experimenter took four
walks around the pivot while holding onto the
bar. On two of the walks, the child held the
bar near the pivot and the experimenter held
it at the far end; on the other two walks, they
switched positions (see figure). After each
walk, children were asked whether the inner
or outer part of the bar had moved faster.
The differences in the speeds required
for walking while holding the inner and the
outer parts of the metal bar were so dra-
matic that the children generalized their
new understanding to other problems in-
volving circular motion, such as cars moving
around circular tracks on a computer screen.
In other words, physically experiencing the
concept accomplished what years of formal
science instruction usually fail to do. As
one boy said to the experimenter, “Before,
I hadn’t experienced it. I didn’t think about
it. Now that I have had that experience, I
know that when I was on the outer circle, I
had to walk faster to be at the same place as
you” (Levin et al., 1990). Clearly, relevant
physical activities, accompanied by ques-
tions that call attention to the lessons of the
activities, can foster children’s learning.
The child and adult are holding onto a bar as
they walk around a circle four times. On the
first two trips around, the child holds the bar
near the pivot; on the second two, the child
holds it at its end. The much faster pace
needed to keep up with the bar when holding
onto its end leads the child to realize that the
end was moving faster than the inner portion
(Levin et al., 1990).
piaget’s Stages of Cognitive Development
Stage Approximate Age New Ways of Knowing
Sensorimotor Birth to 2 years Infants know the world through their senses and
through their actions. For example, they learn what
dogs look like and what petting them feels like.
Preoperational 2–7 years Toddlers and young children acquire the ability to
internally represent the world through language and
mental imagery. They also begin to be able to see the
world from other people’s perspectives, not just from
their own.
Concrete operational 7–12 years Children become able to think logically, not just
intuitively. They now can classify objects into precisely
defined categories and understand that events are often
influenced by multiple factors, not just one.
Formal operational 12 years and beyond Adolescents can think systematically and reason about
what might be, as well as what is. This allows them
to understand politics, ethics, and science fiction, as
well as to engage in scientific reasoning.

2. Infants and young children are more cognitively competent than Piaget recognized.
Piaget employed fairly difficult tests to assess most of the concepts he studied. This
led him to miss infants’ and young children’s earliest knowledge of these concepts.
For example, Piaget’s test of object permanence required children to reach for the
hidden object after a delay; Piaget claimed that children do not do this until 8 or
9 months of age. However, alternative tests of object permanence, which analyze
where infants look immediately after the object has disappeared from view, indicate
that by 3 months of age, even these young infants at least suspect that objects con-
tinue to exist (Baillargeon, 1987; 1993).
3. Piaget’s theory understates the contribution of the social world to cognitive devel-
opment. Piaget’s theory focuses on how children come to understand the world
through their own efforts. From the day that children emerge from the womb,
however, they live in an environment of adults and older children who shape their
cognitive development in countless ways. A child’s cognitive development reflects
the contributions of other people, as well as of the broader culture, to a far greater
degree than Piaget’s theory acknowledges.
4. Piaget’s theory is vague about the cognitive processes that give rise to children’s thinking
and about the mechanisms that produce cognitive growth. Piaget’s theory provides any
number of excellent descriptions of children’s thinking. It is less revealing, however,
about the processes that lead children to think in a particular way and that produce
changes in their thinking. Assimilation, accommodation, and equilibration have an
air of plausibility, but how they operate is unclear.
These weaknesses of Piaget’s theory do not negate the magnitude of his achieve-
ment: it remains one of the major intellectual accomplishments of the past century.
However, appreciating the weaknesses as well as the strengths of his theory is nec-
essary for understanding why alternative theories of cognitive development have
become increasingly prominent.
In the remainder of this chapter, we consider the three most prominent alterna-
tive theories: information-processing, sociocultural, and dynamic-systems. Each type
of theory can be seen as an attempt to overcome a major weakness of Piaget’s ap-
proach. Information-processing theories emphasize precise characterizations of
the processes that give rise to children’s thinking and the mechanisms that produce
cognitive growth. Sociocultural theories emphasize the ways in which children’s
interactions with the social world, both with other people and with the products of
their culture, guide cognitive development. Dynamic-systems theories emphasize
infants’ and young children’s developing physical and mental capabilities and how
these capabilities are attained.
Piaget’s theory of cognitive development emphasizes the interaction of nature and nurture,
continuities and discontinuities, and children’s active contribution to their own development.
The continuities of development are produced by assimilation, accommodation, and equili-
bration. Assimilation involves interpreting incoming information to fit current understanding.
Accommodation involves adapting one’s thinking toward being more consistent with new ex-
periences. Equilibration involves balancing assimilation and accommodation in a way that
creates stable understandings.
As depicted by Piaget, the discontinuities of cognitive development involve four discrete
stages: (1) the sensorimotor stage (birth to age 2), in which infants begin to know the world

through the perceptions of their senses and through their motor activities; (2) the preopera-
tional stage (ages 2 to 7), in which children become capable of mental representations but
tend to be egocentric and to focus on a single dimension of an event or problem; (3) the
concrete operational stage (ages 7 to 12), in which children reason logically about concrete
aspects of the environment but have difficulty thinking abstractly; and (4) the formal opera-
tional stage (age 12 and beyond), in which preadolescents and adolescents become capable
of abstract thought.
Among the important strengths of Piaget’s theory are its broad overview of development,
its plausible and attractive perspective on children’s nature, its inclusion of varied tasks and
age groups, and its endlessly fascinating observations. Among the theory’s important weak-
nesses are its overstatement of the consistency of children’s thinking, its underestimation of
infants’ and young children’s cognitive competence, its lack of attention to the contribution
of the social world, and its vagueness regarding cognitive mechanisms.
Information-Processing Theories
Child: Daddy, would you unlock the basement door?
Father: Why?
C: ’Cause I want to ride my bike.
F: Your bike is in the garage.
C: But my socks are in the dryer.
(Klahr, 1978, pp. 181–182)
What reasoning could have produced this 5-year-old’s enigmatic comment, “But
my socks are in the dryer”? David Klahr, an eminent information-processing theo-
rist, formulated the following model of the thought process that led to it:
Top goal: I want to ride my bike.
Bias: I need shoes to ride comfortably.
Fact: I’m barefoot.
Subgoal 1: Get my sneakers.
Fact: The sneakers are in the yard.
Fact: They’re uncomfortable on bare feet.
Subgoal 2: Get my socks.
Fact: The sock drawer was empty this morning.
Inference: The socks probably are in the dryer.
Subgoal 3: Get them from the dryer.
Fact: The dryer is in the basement.
Subgoal 4: Go to the basement.
Fact: It’s quicker to go through the yard entrance.
Fact: The yard entrance is always locked.
Subgoal 5: Unlock the door to the basement.
Fact: Daddies have the keys to everything.
Subgoal 6: Ask Daddy to unlock the door.
Klahr’s analysis of his daughter’s thinking illustrates two notable character-
istics of information-processing theories.1 One is the precise specification of
the processes involved in children’s thinking. Klahr’s approach, for example, used
information-processing theories
n a class of theories that focus on the
structure of the cognitive system and the
mental activities used to deploy attention
and memory to solve problems
1 Here and throughout this section, we use the plural term “information-processing theories” rather than the singular
term “information-processing theory” because information-processing theories consist of a variety of related approaches
rather than a single set of unified ideas. For the same reason, in subsequent sections we refer to “sociocultural theories,”
and “dynamic-systems theories.”

task analysis—that is, the identification of goals the obstacles that prevent their
immediate realization, the prior knowledge and information in the environment
relevant to them, and the potential processing strategies for overcoming the ob-
stacles and attaining the goals.
Such task analysis helps information-processing researchers understand and
predict children’s behavior and allows them to rigorously test precise hypothe-
ses regarding how development occurs. In some cases, it also allows them to for-
mulate computer simulations, a type of mathematical model that expresses ideas
about mental processes in particularly precise ways. For example, Simon and Klahr
(1995) created computer simulations of the knowledge and mental processes that
led young children to fail on conservation problems and of the somewhat different
knowledge and mental processes that allowed older children to succeed on them.
A second distinctive feature of information-processing analysis is an emphasis
on thinking as an activity that occurs over time. Often, a single simple behavior,
such as the initial request of Klahr’s daughter that he open the basement door, re-
flects an extended sequence of rapid mental operations. Information-processing
analyses identify what those mental operations are, the order in which they are ex-
ecuted, and how increasing speed and accuracy of mental operations lead to cogni-
tive growth.
View of Children’s Nature
Information-processing theorists see children’s cognitive growth as occurring con-
tinuously, in small increments that occur at different times on different tasks. This
depiction differs fundamentally from Piaget’s belief that children progress through
qualitatively distinct, broadly applicable stages, separated only by brief transition
The Child as a Limited-Capacity Processing System
In trying to understand differences in children’s thinking at various ages, some
information-processing theorists draw comparisons between the information
processing of computers and that of humans. A computer’s information process-
ing is limited by its hardware and by its software. The hardware limitations relate
to the computer’s memory capacity and its efficiency in executing basic operations.
The software limitations relate to the strategies and information that are available
for performing particular tasks. People’s thinking is limited by the same factors:
memory capacity, speed of thought processes, and availability of useful strategies
and knowledge. In the information-processing view, cognitive development arises
from children’s gradually surmounting their processing limitations through (1) ex-
pansion of the amount of information they can process at one time, (2) increases in
the speed with which they execute thought processes, and (3) acquisition of new
strategies and knowledge.
The Child as Problem Solver
Also central to the view of human nature held by information-processing theories
is the assumption that children are active problem solvers. As suggested by Klahr’s
analysis of his daughter’s behavior, problem solving involves goals, perceived ob-
stacles, and strategies or rules for overcoming the obstacles and attaining the goals.
A description of a younger child’s problem solving reveals the same combination of
goal, obstacle, and strategy:
task analysis n the research technique
of identifying goals, relevant information
in the environment, and potential pro-
cessing strategies for a problem
problem solving n the process of
attaining a goal by using a strategy to
overcome an obstacle

Georgie (a 2-year-old) wants to throw rocks out the kitchen window. The lawn
mower is outside. Dad says that Georgie can’t throw rocks out the window, because
he’ll break the lawnmower with the rocks. Georgie says, “I got an idea.” He goes out-
side, brings in some green peaches that he had been playing with, and says: “They
won’t break the lawnmower.”
(Waters, 1989, p. 7)
In addition to illustrating the typical goal–obstacle–strategy sequence, this ex-
ample highlights another basic tenet of information-processing approaches: chil-
dren’s cognitive flexibility helps them pursue their goals. Even young children show
great ingenuity in surmounting the obstacles imposed by their parents, the physical
environment, and their own lack of knowledge.
Central Developmental Issues
Like all the theories described in this chapter, information-processing theories ex-
amine how nature and nurture work together to produce development. What makes
information-processing theories unique is their emphasis on precise descriptions of
how change occurs. The way in which information-processing theories address the
issues of nature and nurture and how change occurs can be seen particularly clearly
in their accounts of the development of memory and problem solving.
The Development of Memory
Memory is crucial to everything we do. The skills we use on everyday tasks, the
language we employ when writing or speaking, the emotions we feel on a given
occasion—all depend on our memory of past experiences and the knowledge ac-
quired through them. Indeed, without memory of our experiences, we lose our very
identity, a devastating syndrome that has been observed in patients with certain
types of amnesia (Reed & Squire, 1998). Memory plays a role in all cognitive de-
velopmental theories, but it is especially central to information-processing theories.
Most such theories distinguish among working memory, long-term memory, and
executive functions.
Working memory Working memory involves actively attending to, gathering,
maintaining, storing, and processing information. For example, if after reading a
story about birds, a child were asked a question about it, the child would, through
working memory, bring together relevant information from the story, inferences
made from that information, and prior knowledge about birds, and would then
process the information to construct a reasonable answer.
Working memory is limited in both its capacity (the amount of information that
it can store) and in the length of time it can retain information without updating
activities. For example, a child might be able to remember a sequence of five dig-
its but not six, and might be able to remember them for 5 or 10 seconds without
repeating them but not for a longer time. The exact capacity and duration vary
with the task and the type of material being processed, but for a given task and
type of material, both capacity and speed increase with age and relevant experience
(Schneider, 2011).
The basic organization of working-memory subsystems seems to be constant
from early in childhood. However, the capacity and speed of operation of working
memory increase greatly over the course of childhood and adolescence (Cowan
et al., 1999; Gathercole et al., 2004). These changes are believed to occur in part
working memory n memory system
that involves actively attending to, gath-
ering, maintaining, storing, and pro-
cessing information

because of increasing knowledge of the content on which working memory oper-
ates and in part because of maturational changes in the brain (Nelson, Thomas,
& De Haan, 2013; see Figure 4.8).
Long-term memory In contrast to the moment-to-moment nature of working
memory, long-term memory consists of the knowledge that people accumulate
over their lifetime. It includes factual knowledge (e.g., knowing the capitals of dif-
ferent countries or the teams that won the Super Bowl in the past 5 years), con-
ceptual knowledge (e.g., the concepts of justice, mercy, and equality), procedural
knowledge (e.g., knowing how to tie a shoe or play an Xbox game), attitudes (e.g.,
likes and dislikes regarding political parties or anchovies), reasoning strategies (e.g.,
knowing how to take an argument to its logical extreme to show its inadequacy),
and so on. Long-term memory can thus be thought of as the totality of one’s
knowledge, whereas working memory can be regarded as the subset of that knowl-
edge that is being processed at a given time (Cowan, 2005; Ericsson & Kintsch,
In contrast to the severe limits on the capacity and duration of working mem-
ory, long-term memory can retain an unlimited amount of information for unlim-
ited periods. To cite one notable example, research shows that people who studied
Spanish or algebra in high school often retain a substantial amount of what they
learned in the subject 50 years later, despite their not having used the information
in the interim and their having accumulated vast stores of other skills, concepts, and
knowledge in long-term memory over that period (Bahrick, 1987).
executive Functioning Executive functions involve the control of cognition. The
prefrontal cortex (Figure 4.8) plays a particularly important role in this cogni-
tive control. Three major types of executive functions are inhibiting tempting ac-
tions that would be counterproductive; enhancing working memory through use of
long-term memory n information
retained on an enduring basis
Temporal lobe
Primary motor cortex
Frontal lobe
Prefrontal cortex
Parietal lobe
Occipital lobeFIGURE 4.8 All of the major
areas of the cortex shown here
continue maturing after birth.
Brain maturation continues for
a particularly long time in the
prefrontal cortex, an area that is
especially involved in planning,
inhibiting inappropriate behavior,
and adopting new goals in
response to changing situations.

strategies, such as repeating a phone number that would otherwise be forgotten;
and being cognitively flexible, for example, taking someone else’s perspective in an
argument despite its differing from one’s own. As these examples suggest, executive
functioning integrates information from working memory and long-term mem-
ory to accomplish goals (e.g., Diamond, 2013; Miyake & Friedman, 2012; Rose,
Feldman, & Jankowski, 2011).
The ability of executive functions to control thinking and action—enabling
the individual to respond appropriately rather than acting impulsively or doing
what he or she is used to doing—increases greatly during the preschool and early
elementary school years. One aspect of this improvement is children’s increased
cognitive flexibility in shifting goals. For instance, when they are assigned the
task of sorting toys by their color for a long period and then are asked to sort the
same toys by shape, most 3-year-olds have difficulty switching goals, but 5-year-
olds make the switch with ease (Baker, Friedman, & Leslie, 2010; Zelazo et al.,
The ability to inhibit habitual responses occurs slightly later and is evident in
everyday games such as “Simon Says.” Preschoolers have great difficulty inhibiting
the impulse to quickly respond to commands that are not preceded by the critical
phrase in such games, whereas early elementary school children are much better at
inhibiting the impulse to act immediately (Dempster, 1995; Diamond, Kirkham,
& Amso, 2002; Sabbagh et al., 2006). Strategies for controlling working memory
tend to develop a little later, largely in the first few years of elementary school
(Schneider, 2011).
As you might anticipate, the need for strong executive functioning continues to
pose challenges well beyond early childhood. For example, resisting the tempta-
tion to daydream while doing one’s homework, keeping quiet while the teacher is
talking, and inhibiting disrespectful replies to parents or teachers are difficult even
for many adolescents (Bunge & Zelazo, 2006; Munakata, Snyder, & Chat ham,
The quality of executive functioning during early childhood is highly predic-
tive of many important life outcomes years later, including academic achievement
in later grades, enrollment in college, and income and occupational status during
adulthood (Blair & Razza, 2007; Duncan et al., 2007; McClelland & Cameron,
2011; Mischel & Ayduk, 2011; Moffitt et al., 2011). Fortunately, several training
programs for preschoolers have shown considerable promise for improving young
children’s executive functioning (Diamond et al., 2007, 2013; Raver et al., 2009).
In one such training study, disadvantaged preschoolers were randomly as-
signed to classrooms using a curriculum designed to improve executive functioning
(Raver et al., 2011). The intervention involved instructing teachers in strategies—
including stating and implementing clear rules, rewarding positive behaviors, and
redirecting negative behaviors in positive directions—that would help children
inhibit impulses to disrupt classroom activities. By the end of the school year, this
approach had led to improvements in the children’s behavior and self-regulatory
skills. Even more impressive, for the next 3 years, children who had been in the in-
tervention classrooms continued to perform better in math and reading than did
children in a control group (Raver et al., 2011).
explanations of memory development Information-processing theorists try to
explain both the processes that make memory as good as it is at each age and the
limitations that prevent it from being better. These efforts have focused on three
types of capabilities: basic processes, strategies, and content knowledge.

BASIC PROCESSES The simplest and most frequently used mental activities are
known as basic processes. They include associating events with one another, rec-
ognizing objects as familiar, recalling facts and procedures, and generalizing from
one instance to another. Another basic process, which is key to all the others, is
encoding —the representation in memory of specific features of objects
and events. With development, children execute basic processes more ef-
ficiently, enhancing their memory and learning for all kinds of materials.
Most of these basic processes are familiar, and their importance obvi-
ous. However, encoding is probably less familiar. Appreciating its signifi-
cance requires some understanding of the way in which memory works.
People often think of memory as something akin to an unedited video re-
cording of our experiences. Actually, memory is far more selective. People
encode information that draws their attention or that they consider rel-
evant, but they fail to encode a great deal of other information. Informa-
tion that is not encoded is not remembered later. This failure is probably
evident in your own memory of the American flag; although you have
seen it many times, you most likely have not encoded how the stars are
Studies of how children learn to solve balance-scale problems illustrate
the importance of encoding for learning and memory. As discussed on
page 139, most 5-year-olds predict that the side of the scale with more
weight will go down, regardless of the distance of the weights from the ful-
crum. Five-year-olds generally have difficulty learning more advanced ap-
proaches to solving balance-scale problems that take into account distance
as well as weight, because they do not encode information about distance
of the weights from the fulcrum. For example, 5-year-olds are shown a balance
scale with varying arrangements of weights on pegs; the scale is then hidden behind
a barrier, and the children are asked to reproduce the arrangement on an identical
balance scale. Five-year-olds generally reproduce the correct number of weights on
each side but rarely put them the correct distance from the fulcrum (Siegler, 1976).
Teaching them to encode distance by telling them that both weight and distance
are important enables them to learn more advanced balance-scale rules that peers
who were not taught to encode distance have trouble learning (Siegler & Chen,
basic processes n the simplest and
most frequently used mental activities
encoding n the process of representing
in memory information that draws atten-
tion or is considered important
Misencoding common sayings can lead to
memorable confusions.
. R
FIGURE 4.9 Increase with age in speed
of processing on two tasks Note that the
increase is rapid in the early years and more
gradual later. (Data from Kail, 1991)
9 108
Age in years
(a) Mental Rotation
11 12 13 14 15 16 17 18 19 20 21 22
9 108
Age in years
(b) Mental Addition
11 12 13 14 15 16 17 18 19 20 21 22
l r
“Mirror, mirror, on the wall, who’s the fairest of the mall?”
The FAMILY CIrCUS By Bil Keane

Like improved encoding, improved speed of processing plays a key role in the
development of memory and learning. As shown in Figure 4.9, processing speed
increases most rapidly at young ages but continues to increase in adolescence (Kail,
1991, 1997; Luna et al., 2004).
Two biological processes that contribute to faster processing are myelination
and increased connectivity among brain regions (Luna et al., 2004). As discussed
in Chapter 3, from the prenatal period through adolescence, increasing numbers of
axons of neurons become covered with myelin, the fatty insulating substance that
promotes faster and more reliable transmission of electrical impulses in the brain
(Paus, 2009). Myelination enhances executive function, contributing to the ability
to resist distractions (Dempster & Corkill, 1999; Wilson & Kipp, 1998). Greater
connectivity among brain regions also increases processing capacity and speed by
increasing the efficiency of communication among brain areas (Thatcher, 1998).
This growth of long-distance connectivity among brain regions is especially promi-
nent in later childhood and adolescence.
STRATEGIES Information-processing theories point to the acquisition and growth
of strategies as another major source of the development of memory. Between ages
5 and 8 years, children begin to use a number of broadly useful memory strategies,
among them the strategy of rehearsal, the repeating of information multiple times
in order to remember it. The following newspaper item illustrates the usefulness of
rehearsal for remembering information verbatim:
A 9-year-old boy memorized the license plate number of a getaway car following an
armed robbery, a court was told Monday. . . . The boy and his friend . . . looked in the
drug store window and saw a man grab a 14-year-old cashier’s neck. . . . After the
robbery, the boys mentally repeated the license number until they gave it to police.
(Edmonton Journal, Jan. 13, 1981, cited in Kail, 1984)
Had the boys witnessed the same event when they were 5-year-olds, they prob-
ably would not have rehearsed the numbers and would have forgotten the license
number before the police arrived.
Another widely used memory strategy that becomes increasingly prevalent in the
early elementary school years is selective attention, the process of intentionally fo-
cusing on the information that is most relevant to the current
goal. If 7- and 8-year-olds are shown objects from two different
categories (e.g., several toy animals and several household items)
and are told that they later will need to remember the objects in
only one category (e.g., “You’ll need to remember the animals”),
they focus their attention on the objects in the specified category
and remember more of them. In contrast, given the same instruc-
tions, 4-year-olds pay roughly equal attention to the objects in
both categories, which reduces their memory for the objects they
need to remember (DeMarie-Dreblow & Miller, 1988).
CONTENT KNOWLEDGE With age and experience, children’s knowl-
edge about almost everything increases. This increase in knowl-
edge in long-term memory improves recall of new material by
making it easier to integrate new material with existing under-
standing (Pressley & Hilden, 2006). The importance of con-
tent knowledge to memory is illustrated by the fact that when
children know more about a topic than adults do, their memory
for new information about the topic often is superior to the
Through repeated visits to doctors’ offices
and through other experiences that occur
in more or less fixed sequences, children
gain content knowledge that improves their
memory for subsequent, similar events.
. P
rehearsal n the process of repeating
information multiple times to aid memory
of it
selective attention n the process of
intentionally focusing on the information
that is most relevant to the current goal

adults’. For example, when children and adults are provided new information about
children’s TV programs and books, the children generally remember more of the
information than do the adults (Lindberg, 1980, 1991). Similarly, children who
know a lot about soccer learn more from reading new soccer stories than do other
children who are both older and have higher IQs but who know less about soccer
(Schneider, Körkel, & Weinert, 1989).
Prior content knowledge improves memory for new information in several dif-
ferent ways. One is by improving encoding. In tests of memory of various arrange-
ments of chess pieces on a board, child chess experts remember far more than do
adult novices. The reason is that the child experts’ greater knowledge of chess leads
to their encoding higher-level chunks of information that include the positions
of several pieces relative to one another rather than encoding the location of each
piece separately (Chi & Ceci, 1987). Content knowledge also improves memory
by providing useful associations. A child who is knowledgeable about birds knows
that type of beak and type of diet are associated, so remembering either one in-
creases memory for the other ( Johnson & Mervis, 1994). In addition, content
knowledge indicates what is and is not possible and therefore guides memory in
useful directions. For example, when people familiar with baseball are asked to re-
call a particular inning of a game that they watched and they can remember only
two outs in that inning, they recognize that there must have been a third out and
search their memories for it; people who lack baseball knowledge do not (Spilich
et al., 1979).
The Development of Problem Solving
As noted earlier, information-processing theories depict children as active problem
solvers whose use of strategies often allows them to overcome limitations of knowl-
edge and processing capacity. In this section, we present an information-processing
perspective on the development of problem solving—the overlapping-waves theory.
Piaget’s theory depicted children of a given age as using a particular strategy to solve
a particular class of problems. For example, he described 5-year-olds as “solving”
conservation-of-number problems (see Figure 4.6) by choosing the longer row of
objects, and 7-year-olds as solving the same problems by reasoning that if nothing
was added or subtracted, the number of objects must remain the same. According
to overlapping-waves theory, however, children
actually use a variety of approaches to solve this
and other problems (Siegler, 1996). For instance,
examining 5-year-olds’ reasoning on repeated
trials of the conservation-of-number problem
reveals that most children use at least three dif-
ferent strategies (Siegler, 1995). The same child
who on one trial incorrectly reasons that the lon-
ger row must have more objects will on other
trials correctly reason that just spreading a row
does not change the number of objects, and on
yet other trials will count the number of objects
in the two rows to see which has more.
Figure 4.10 presents the typical pattern of de-
velopment envisioned by the overlapping-waves
approach, with strategy 1 representing the sim-
plest strategy, and strategy 5, the most advanced.
Strategy 1
Strategy 4
Strategy 5
Strategy 3
Strategy 2
Younger Older
FIGURE 4.10 The overlapping-waves
model The overlapping-waves model pro-
poses that, at any one age, children use
multiple strategies; that with age and
experience, they rely increasingly on more
advanced strategies (the ones with the
higher numbers); and that development
involves changes in use of existing strategies
as well as discovery of new approaches.
overlapping-waves theory n an infor-
mation-processing approach that empha-
sizes the variability of children’s thinking

At the youngest age depicted, children usually use strategy 1, but they sometimes
use strategy 2 or 4. With age and experience, the strategies that produce more suc-
cessful performances become more prevalent; new strategies also are generated and,
if they are more effective than previous approaches, are used increasingly. Thus, by
the middle of the age range in Figure 4.10, children have added strategies 3 and 5
to the original group and have almost stopped using strategy 1.
This model has been shown to accurately characterize children’s problem solv-
ing in a wide range of contexts, including arithmetic, time-telling, reading, spell-
ing, scientific experimentation, biological understanding, tool use, and recall from
memory (Chen & Siegler, 2000; Kuhn & Franklin, 2006; Lee & Karmiloff-Smith,
2002; Miller & Coyle, 1999).
The overlapping-waves approach specifies several ways in which problem solv-
ing improves over the course of development. Children discover new strategies that
are more effective than their previous ones, they learn to execute both new and old
strategies more efficiently, and they choose strategies that are more appropriate to
the particular situation (Miller & Coyle, 1999; Siegler, 2006).
All these sources of cognitive growth are evident in learning addition. During
kindergarten and the first few years of elementary school, children’s knowledge of
single-digit addition improves greatly. One reason is that children discover new
strategies, such as counting-on (e.g., solving 2 1 9 by thinking “9, 10, 11”). An-
other source of improvement is faster and more accurate execution of all the strate-
gies that children know (e.g., retrieval of answers from memory, counting from one,
and counting-on). A third source of improvement is that children choose among
strategies increasingly adaptively (e.g., using counting-on most often on problems
with a large difference between the addends, such as 2 1 9, and counting from one
on problems such as 7 1 8, which are difficult for them to solve correctly by using
the other strategies they know (Geary, 2006; Siegler, 1987; Sieger & Jenkins, 1989).
(Box 4.2 illustrates how information-processing analyses can improve education.)
planning Problem solving is often more successful if people plan before acting.
Children benefit from planning how to get to friends’ houses, how to get their way
with parents, and how to break bad news to others in ways that are least likely to
trigger angry reactions (Hudson, Sosa, & Schapiro, 1997). Despite the advantages of
planning, however, children, and even adolescents, often fail to plan in situations in
which it would help their problem solving (Berg et al., 1997). The question is why.
Information-processing analyses suggest that one reason planning is difficult for
children is that it requires inhibiting the desire to solve the problem immediately in
favor of first trying to construct the best strategy. Starting to work on an assigned
paper without planning what will be written in the paper is one familiar example.
A second reason planning is difficult for young children is that they tend to be
overly optimistic about their abilities and think that they can solve problems more
effectively than their capabilities actually allow (Bjorklund, 1997; Schneider, 1998).
This overconfidence can lead them to not plan, because they think they will suc-
ceed without doing so. Such overoptimism can lead young children to act rashly.
For instance, 6-year-olds who overestimate their physical abilities have more ac-
cidents than do peers who evaluate their abilities more realistically, presumably
because their confidence leads them not to plan how to avoid potential dangers
(Plumert, 1995).
Over time, maturation of the prefrontal cortex, a part of the brain that is espe-
cially important for planning, along with experiences that reduce overoptimism or
demonstrate the value of planning, lead to increases in the frequency and quality
Young children’s overoptimism sometimes
leads them to engage in dangerous activi-
ties. This particular plan worked out fine,
but not all do.

BOX 4.2: applications
Children’s knowledge of numbers when they
begin kindergarten predicts their mathemat-
ics achievement years later—in elementary
school, middle school, and even high school
(Duncan et al., 2007; Stevenson & Newman,
1986). It is especially unfortunate, then, that
kindergartners from low-income families lag
far behind middle-income peers in counting,
number recognition, arithmetic, and knowl-
edge of numerical magnitudes (e.g., under-
standing that 7 is less than 9 and that both
are closer to 10 than to 0 on a number line).
What might account for these early differ-
ences in numerical knowledge of children
from different economic backgrounds? An
information-processing analysis suggested
that experience playing numerical board
games such as Chutes and Ladders might
be important. In Chutes and Ladders, play-
ers must move a token across 100 consecu-
tively numbered squares, advancing on each
of their turns by the number of spaces deter-
mined by a spinner. The higher the number
of the square on which a child’s token rests
at any given point in the game, the greater
the number of number names the child
will have spoken and heard, the greater the
distance the child will have moved the token
from the first square, the greater the time
the child will have been playing the game,
and the greater the number of discrete hand
movements with the token the child will
have made. These verbal, spatial, tempo-
ral, and kinesthetic cues provide a broadly
based, multisensory foundation for knowl-
edge of numerical magnitudes, a type of
knowledge that is closely related to math-
ematics achievement test scores (Booth &
Siegler, 2006, 2008; Geary, 2011).
Ramani and Siegler (2008) applied this
information-processing analysis to improving
the numerical understanding of low-income
preschoolers. The researchers randomly as-
signed 4- and 5-year-olds from low-income
families to either an experimental number-
board condition or a control color-board
condition. The number-board condition
was virtually identical to the first row of the
Chutes and Ladders board; it included 10
squares numbered consecutively from left to
right. On each turn, the child spun a dial that
yielded a “1” or a “2” and moved his or her
token the corresponding number of squares
on the board, stating the number on each
square in the process. For example, if a play-
er’s token was on the square with the “4,”
and the player spun a “2,” the player would
say, “5, 6” while moving the token from the
“4” to the “6.” Children in the color-board
condition played the same game, except that
their board had no numbers and the play-
ers would say the name of the color of each
square as they advanced their token. Chil-
dren in both conditions were given a pretest
that examined their knowledge of numbers
before playing the game, and then played
the game for four 15- minute sessions over a
2-week period. At the end of the fourth ses-
sion, the children were given a posttest on
their knowledge of numbers; 9 weeks later,
they were given a follow-up test identical to
the pretest and posttest.
On the posttest, children who played
the number board game showed improved
knowledge of the numbers 1 through 10 on
all four tasks that were presented— counting,
reading of numbers, magnitude comparisons
(e.g., “Which is bigger, 8 or 3?”), and es-
timates of the locations of numbers on a
number line. Significantly, all the gains were
maintained on the follow-up test 9 weeks
later. In contrast, children who played the
color board game showed no improvement in
any aspect of number knowledge. Moreover,
children’s reports of how often they played
Chutes and Ladders and other board games
at home was positively correlated with their
initial knowledge on all four numerical tasks,
and middle-income children reported play-
ing numerical board games (though not video
games) much more often than children from
low-income backgrounds.
Subsequent studies demonstrated that
playing the 1–10 board game also improves
preschoolers’ ability to learn the answers to
arithmetic problems, such as that 2 1 4 5
6 (Siegler & Ramani, 2009). Taken together,
the evidence suggests that numerical board
games represent a quick, effective, and in-
expensive means of improving the numeri-
cal knowledge of low-income children before
they start school.
playing this number board game improves preschoolers’ numerical

of planning, which improves problem solving (Chalmers & Lawrence, 1993). The
improvements in the planning process take a long time, however; even 12-year-
olds leave less distance between themselves and oncoming vehicles than adults do
(Plumert, Kearney, & Cremer, 2004).
Information-processing theories envision children as active learners and problem solvers who
continuously devise means for overcoming their processing limits and reaching their goals.
The capacity and processing speed of working memory and long-term memory influence all
information processing. Executive functioning uses information in working memory and long-
term memory to flexibly shift goals and inhibit impulses to behave in ways that are inappro-
priate in the situation; it also updates the contents of working memory so that new goals can
be pursued effectively. Cognitive growth in general, and development of memory and learning
in particular, are seen as involving increasingly efficient execution of basic processes, con-
struction of more effective strategies, and acquisition of new content knowledge. Overlapping
waves theory indicates that individual children use multiple strategies to solve the same type
of problem, that children choose adaptively among these strategies, and that problem solving
improves through the discovery of more effective strategies, more efficient execution of the
strategies, better choices of when to use the strategies, and improved planning.
Sociocultural Theories
A mother and her 4-year-old daughter, Sadie, assemble a toy, using a diagram to
guide them:
Mother: Now you need another one like this on the other side. Mmmmm . . .
there you go, just like that.
Sadie: Then I need this one to go like this? Hold on, hold on. Let it go. There.
Get that out. Oops.
M: I’ll hold it while you turn it. (Watches Sadie work on toy) Now you make
the end.
S: This one?
M: No, look at the picture. Right here (points to diagram). That piece.
S: Like this?
M: Yeah.
(Gauvain, 2001, p. 32)
This interaction probably strikes you as completely unexceptional—and it is.
From the perspective of sociocultural theories, however, it and thousands of other
everyday interactions like it are of the utmost importance, because they are the en-
gines of development.
One noteworthy characteristic of the event, from the sociocultural perspective, is
that Sadie is learning to assemble the toy in an interpersonal context. Sociocultural
theorists emphasize that much of cognitive development takes place through direct
interactions between children and other people—parents, siblings, teachers, play-
mates, and so on—who want to help children acquire the skills and knowledge val-
ued by their culture. Thus, whereas Piagetian and information-processing theories
emphasize children’s own efforts to understand the world, sociocultural theories em-
phasize the developmental importance of children’s interactions with other people.
The interaction between Sadie and her mother is also noteworthy because it ex-
emplifies guided participation, a process in which more knowledgeable individuals
sociocultural theories n approaches
that emphasize that other people and the
surrounding culture contribute greatly to
children’s development
guided participation n a process in
which more knowledgeable individuals
organize activities in ways that allow less
knowledgeable people to learn

organize activities in ways that allow less knowledgeable people to engage
in them at a higher level than they could manage on their own (Rogoff,
2003). Sadie’s mother, for example, holds one part of the toy so that Sadie
can screw in another part. On her own, Sadie would be unable to screw
the two parts together and therefore could not improve her skill at the
task. Similarly, Sadie’s mother points to the relevant part of the diagram,
enabling Sadie to decide what to do next and also to learn how diagrams
convey information. As this episode illustrates, guided participation often
occurs in situations in which the explicit purpose is to achieve a practi-
cal goal, such as assembling a toy, but in which learning occurs as a by-
product of the goal-directed activity.
A third noteworthy characteristic of the interaction between Sadie
and her mother is that it occurs in a broader cultural context. This con-
text includes not only other people but also the innumerable products of
human ingenuity that sociocultural theorists refer to as cultural tools:
symbol systems, artifacts, skills, values, and so on. In the example of Sadie
and her mother, the relevant symbol systems include the language they
use to convey their thoughts and the diagram they use to guide their as-
sembly efforts; the relevant artifacts include the toy and the printed sheet
on which the diagram appears; the relevant skills include the proficiency
in language that allows them to communicate with each other and the
procedures they use to interpret the diagram; and the values include the
culture’s approval of parents interacting with their children in the way
that Sadie’s mother does and of young girls’ learning mechanical skills. In
the background are an array of broader technological, economic, and historical fac-
tors: the technology needed to manufacture toys and print diagrams, for example;
an economy that allows parents the leisure time for such interactions; and a his-
tory leading up to the symbol systems, artifacts, skills, and values reflected in the
interactions between Sadie and her mother. Thus, sociocultural theories can help
us appreciate the many aspects of culture embodied in even the smallest everyday
View of Children’s Nature
The giant of the sociocultural approach to cognitive development, and in many
ways its originator, was the Russian psychologist Lev Semyonovich Vygotsky. Al-
though Vygotsky and Piaget were contemporaries, much of Vygotsky’s most im-
portant work was largely unknown outside Russia until the 1970s. Its appearance
created a stir, in part because Vygotsky’s view of children’s nature was so different
from Piaget’s.
Vygotsky’s Theory
As noted earlier, Piaget depicted children as little scientists, trying to understand
the world on their own. Vygotsky, in contrast, portrayed them as social learners,
intertwined with other people who are eager to help them gain skills and under-
standing. Whereas Piaget viewed children as intent on mastering physical, math-
ematical, and logical concepts that are the same in all times and places, Vygotsky
viewed them as intent on participating in activities that happen to be prevalent in
their local setting. Whereas Piaget emphasized qualitative changes in thinking,
Vygotsky emphasized continuous, quantitative changes. These Vygotskian views
Through guided participation, parents can
help children not only accomplish imme-
diate goals but also learn skills, such as how
to use written instructions and diagrams to
assemble objects.
/ A
The russian psychologist Lev Vygotsky, the
founder of the sociocultural approach to
child development.

gave rise to the central metaphor of sociocultural theories: children as social learn-
ers, shaped by, and shaping, their cultural contexts.
Vygotsky’s emphasis on children as social learners is evident in his perspective
on the relation between language and thought. Whereas Piaget viewed the two as
largely unrelated, Vygotsky (1934/1962) viewed them as integrally related. In par-
ticular, he believed that thought is internalized speech and that thought originates
in large part in statements that parents and other adults make to children.
To illustrate the process of internalizing speech, Vygotsky described three phases
of its role in the development of children’s ability to regulate their own behavior
and problem solving. At first, children’s behavior is controlled by other people’s
statements (as in the example of Sadie and her mother assembling the toy); then,
children’s behavior is controlled by their own private speech, in which they tell
themselves aloud what to do, much as their parents might have done earlier; and
then, their behavior is controlled by internalized private speech (thought), in which
they silently tell themselves what to do. The transition between the second and
third phases often involves whispers or silent lip movements; in Vygotsky’s terms,
the speech “goes underground” and becomes thought.
Private speech is most prevalent between ages 4 and 6 years, although older chil-
dren and adults also use it on challenging tasks, such as assembling model airplanes
or following complex directions (Winsler et al., 2003). In addition, the progression
from external to internalized speech emerges not only with age but also with experi-
ence; children generate a considerable amount of overt private speech when they first
encounter a challenging task, but the amount lessens as they master it (Berk, 1994).
Children as Teachers and Learners
Contemporary sociocultural theorists, such as Michael Tomasello (2001; 2009), have
extended Vygotsky’s insights. Tomasello proposed that the human species has two
unique characteristics that are crucial to the ability to create complex, rapidly chang-
ing cultures. One of these is the inclination to teach others of the species; the other
is the inclination to attend to and learn from such teaching. In every human society,
adults communicate facts, skills, values, and traditions to their young. This is what
makes culture possible; as Isaac Newton noted, it enables the new generation to
stand on the shoulders of the old and thus to see farther.
The inclination to teach emerges very early: all normal
2-year-olds spontaneously point to and name objects to
call other people’s attention to what they themselves find
interesting. Only humans engage in such rudimentary
teaching behaviors that are not directly tied to survival.
This inclination to teach and to learn from teaching is
what enables children to be socialized into their culture
and to pass that culture on to others.
Children as Products of Their Culture
Sociocultural theorists believe that many of the processes
that produce development, such as guided participation,
are the same in all societies. However, the content that
children learn—the particular symbol systems, artifacts,
skills, and values—vary greatly from culture to culture
and shape thinking accordingly.
cultural tools n the innumerable prod-
ucts of human ingenuity that enhance
private speech n the second phase
of Vygotsky’s internalization-of-thought
process, in which children develop their
self-regulation and problem-solving abili-
ties by telling themselves aloud what to
do, much as their parents did in the first
The inclination to teach and the ability to
learn from teaching are among the most dis-
tinctly human characteristics.
/ G

One example of the impact of culturally specific content comes from a study of
analogical reasoning, a process in which experience with previously encountered
problems is applied to new problems. In the study (Chen, Mo, & Honomichl,
2004), American and Chinese college students were asked to solve two problems.
One problem required a solution analogous to the strategy of leaving a trail of
white pebbles to follow home from the woods in “Hansel and Gretel,” a tale well
known to the American students but unknown to the Chinese. The American
students were far more successful in solving that problem, and many of them al-
luded to the fairy tale even though they had not heard it in many years. The other
problem required a solution analogous to that in a fairy tale that was well known
to the Chinese students but unknown to the Americans. In this case, the Chinese
students were vastly superior in solving the problem, and many alluded to the rel-
evant fairy tale.
Children’s memories of their own experiences also reflect their culture. When
4- to 8-year-olds from China and the United States were asked to describe their
earliest memories, their descriptions differed in ways that reflected their culture’s
attitudes and values (Wang, 2007). Chinese culture prizes and promotes interde-
pendence among people, especially among close relatives. European American cul-
ture, in contrast, prizes and promotes the independence of individuals. Consistent
with these cultural emphases, the Chinese children’s reports of their earliest memo-
ries included more references to other people than did those of American children,
and the American children’s reports included more references to the child’s own
feelings and reactions. Thus, the attitudes and values of a culture, as well as its arti-
facts and technologies, shape the thoughts and memories of people in that culture.
Central Developmental Issues
Vygotsky and contemporary sociocultural theorists have proposed a number of spe-
cific ideas about how change occurs through social interaction. One of these ideas—
guided participation—has already been discussed. In this section, we examine two
related concepts that play prominent roles in sociocultural analyses of change: in-
tersubjectivity and social scaffolding.
As illustrated by this photo of an east
Asian father teaching his children to use
an abacus, the tools available in a culture
shape the learning of children within that
/ C

Sociocultural theorists believe that the foundation of human cog-
nitive development is our ability to establish intersubjectivity, the
mutual understanding that people share during communication
(Gauvain, 2001; Rommetveit, 1985). The idea behind this im-
posing term is both simple and profound: effective communica-
tion requires participants to focus on the same topic, and also on
each other’s reaction to whatever is being communicated. Such a
“meeting of the minds” is indispensable for effective teaching and
The roots of intersubjectivity are evident early in infancy. By age
6 months, infants can learn novel behaviors by observing another
person’s behavior, which requires attending to the same actions as
the person executing the actions (Collie & Hayne, 1999).
This and related developments in early infancy set the stage for
the emergence of a process that is at the heart of intersubjectivity—
joint attention. In this process, infants and their social partners
intentionally focus on a common referent in the external environ-
ment. The emergence of joint attention is evident in numerous
ways. Around their first birthday, infants increasingly look toward
objects that are the targets of their social partners’ gaze, even if
the partner is not acting on the objects, and actively direct a part-
ner’s attention toward objects that they themselves find interesting
(Adamson, Bakeman, & Deckner, 2004; Akhtar & Gernsbacher,
2008; Moore, 2008).
Joint attention greatly increases children’s ability to learn from other people.
One important example involves language learning. When an adult tells a tod-
dler the name of an object, the adult usually looks or points directly at it; children
who are looking at the same object are in a better position to learn what the word
means than ones who are not (Baldwin, 1991). Indeed, the degree of success infants
have in following other people’s gaze predicts their later vocabulary development
(Brooks & Meltzoff, 2008) and their subsequent language development more gen-
erally (Carpenter, Nagell, & Tomasello, 1998).
Intersubjectivity continues to develop well beyond infancy, as children become
increasingly able to take the perspectives of other people. For example, 4-year-olds
are more likely than 3-year-olds to reach agreement with peers on the rules of a
game they are about to play and the roles that each child will assume in the game
(Göncü, 1993). The continuing development of such perspective-taking abilities
also leads to school-aged children’s increasing ability to teach and learn from one
another (Gau vain, 2001).
Social Scaffolding
When putting up tall buildings, construction workers use metal frameworks
called scaffolds, which allow them to work high above the ground. Once a build-
ing’s main structure is in place, it can support further work on its own, thus allow-
ing the scaffolding to be removed. In an analogous fashion, children’s learning is
aided by social scaffolding, in which more competent people provide a tempo-
rary framework that supports children’s thinking at a higher level than children
could manage on their own (Wood, Bruner, & Ross, 1976). Ideally, supplying this
Joint attention, the process through which
social partners focus on the same external
object, underlies the human capacity to
teach and to learn from teaching.
intersubjectivity n the mutual under-
standing that people share during
joint attention n a process in which
social partners intentionally focus on
a common referent in the external
social scaffolding n a process in which
more competent people provide a tempo-
rary framework that supports children’s
thinking at a higher level than children
could manage on their own

framework includes explaining the goal of the task, demonstrating
how the task can be done, and helping the child with the most dif-
ficult parts of the task. This, in fact, is the way parents tend to teach
their children (Pratt et al., 1988; Saxe, Guberman, & Gearhart,
1987; Wood, 1986).
Through the process of social scaffolding, children become capable
of working at a higher level than if they had not received such help.
At first, this higher-level functioning requires extensive support, then
it requires less and less support, and eventually it becomes possible
without any support. The higher the quality of the scaffolding—that
is, the more that instructional efforts are directed at the upper end
of the child’s capabilities—the greater the learning (Conner, Knight,
& Cross, 1997; Gauvain, 2001). The goal of social scaffolding—to
allow children to learn by doing—is the same as that of guided par-
ticipation, but scaffolding tends to involve more explicit instruction
and explanation, whereas guided participation tends to involve adults’
organizing tasks so that children can take increasingly active and re-
sponsible roles in them.
One particularly important way in which parents use scaffold-
ing is in helping children form autobiographical memories, that
is, explicit memories of events that took place at specific times and
places in the individual’s past (Nelson & Fivush, 2004). Autobio-
graphical memories include information about one’s goals, inten-
tions, emotions, and reactions relative to these events. Over time,
these memories become strung together into a more or less coherent narrative
about one’s life.
When discussing past experiences with their young children, some mothers en-
courage them to provide many details about past events and often expand on the
children’s statements. Such a mother might reply to her toddler’s statement “Bird
fly away” by saying, “Yes, the bird flew away because you got close to it and scared
it.” Such statements help children remember their experiences by improving their
encoding of key information (distance from the bird) and their appreciation of the
causal relations among events (Boland, Haden, & Ornstein, 2003; McGuigan &
Salmon, 2004). Other mothers ask fewer questions and rarely elaborate on what
their children say. Children whose mothers use the more elaborative style remem-
ber more about the events than do children whose mothers rarely elaborate (Haden,
Hayne, & Fivush, 1997; Harley & Reese, 1999; Leichtman et al., 2000). (As dis-
cussed in Box 4.3, concepts from sociocultural theories have also proved useful for
improving education in classrooms.)
Sociocultural approaches view children as social learners, shaped by, and shaping, their cul-
tural contexts. These approaches emphasize that children develop in a cultural context of
other people and human inventions, such as symbol systems, artifacts, skills, and values.
Through guided participation, more knowledgeable people help children gain skills in using
these cultural tools; children’s use of the tools, in turn, further transforms their thinking. Cul-
ture is made possible by the human propensity to teach and learn and to establish intersub-
jectivity with other people. Through processes such as social scaffolding and the creation of
communities of learners, older and more skilled individuals help children acquire the skills,
knowledge, and values of their culture.
By providing their children with social scaf-
folding, parents enable them to play with
toys and other objects in more advanced
ways than would otherwise be possible,
which helps the children learn.
/ C
autobiographical memories n memo-
ries of one’s own experiences, including
one’s thoughts and emotions

Dynamic-Systems Theories
Like all biological processes, thinking serves an adaptive purpose: it enables people
and other animals to devise plans for attaining goals. However, attaining goals also
requires the ability to take effective action; without this ability, thinking would be
pointless. For example, what purpose would planning serve for an organism that
could not implement the plans through action (see Figure 4.11)? Despite this in-
herent connection between thinking and acting, however, most theories of cogni-
tive development have ignored the development of the skilled actions that allow
children to realize the fruits of their mental labor.
One increasingly influential exception to this generalization is dynamic-
systems theories, a class of theories that focuses on how change occurs over time
in complex systems. Research that reflects the dynamic-systems perspective indi-
cates that detailed analyses of the development of infants’ basic actions, such as
crawling, walking, reaching, and grasping, yield surprising and impressive insights
into how development occurs. For example, dynamic-systems research has shown
BOX 4.3: applications
For some time, the educational system of
the United States has been criticized for
promoting rote memorization of facts rather
than deep understanding; for promoting
competition rather than cooperation among
students; and for generally failing to create
enthusiasm for learning (National Associa-
tion for the Education of Young Children,
2011; Pellegrino, Chudowsky, & Glaser,
2001). The emphasis of sociocultural theo-
ries on the role of culture in learning im-
plies that one way to improve schooling is to
change the culture of schools. The culture
should be one in which instruction is aimed
at helping children gain deep understand-
ing, in which learning is a cooperative ac-
tivity, and in which learning a little makes
children want to learn more.
One impressive attempt to meet these
goals is Ann Brown’s (1997) community-of-
learners program. Its efforts to build com-
munities of learners have focused on 6- to
12-year-olds, most of them African Amer-
ican children attending inner-city schools
in Boston, Massachusetts, and Oakland,
California. The main curriculum consists of
projects that require research on some large
topic, such as interdependence between
animals and their habitats. The class di-
vides into small groups, each of which fo-
cuses on a particular aspect of the topic.
With the topic of the interdependence be-
tween animals and habitats, for example,
one group might study predator–prey rela-
tions; another, reproductive strategies; an-
other, protection from the elements; and
so on.
At the end of roughly 10 weeks, new
groups are formed, each including one
child from every original group. Children
in the new groups are asked to solve a
problem that encompasses all the aspects
studied by the previous groups, such as
designing an “animal of the future” that
would be particularly well adapted to its
habitat. Because each child’s participation
in the previous group has resulted in the
child’s gaining expertise on the aspect of
the problem studied by that group, and be-
cause no other child in the new group has
that expertise, all of the children’s contri-
butions are essential for the new group to
succeed. Aronson (1978) labeled this tech-
nique the jigsaw approach, because, as in
a jigsaw puzzle, each piece is necessary for
the solution.
A variety of people help foster such com-
munities of learners. Classroom teachers in-
troduce the big ideas of the unit, encourage
children to pool their knowledge to achieve
deeper understanding, push them to provide
evidence for their opinions, and ask them
to summarize what they know and to iden-
tify new learning goals. Outside experts are
at times brought to classrooms to lecture
and answer questions about the topic. Chil-
dren at other schools, who are working on
the same problem, are contacted via email
to see how they are approaching issues that
Communities of learners provide both cog-
nitive and motivational benefits for children.
Participation in such groups helps children
become increasingly adept at construct-
ing high-quality solutions to the problems
they try to solve. It also helps them learn
such general skills as identifying key ques-
tions and comparing alternative solutions to
a problem. Finally, because the children all
depend on one another’s contributions, the
community-of-learners approach encourages
mutual respect and individual responsibility
for the success of the entire group. In short,
the approach creates a culture of learning.
dynamic-systems theories n a class
of theories that focus on how change
occurs over time in complex systems

that improved reaching allows infants to play with objects in more advanced ways,
such as organizing them into categories or interesting configurations (Spencer et
al., 2006; Thelen & Corbetta, 1994). Dynamic-systems research also has shown
that the onset of crawling changes infants’ relationships with family members,
who may be thrilled to see their baby attain an important motor milestone but
also find themselves having to be much more watchful and controlling to avoid
harm to the child and to the objects in the child’s path (Campos, Kermoian, &
Zumbahlen, 1992).
Another contribution of dynamic-systems research has been to demonstrate that
the development of seemingly simple actions is far more complex and interesting
than previously realized. For example, such research has overturned the traditional
belief that physical maturation leads infants to attain motor milestones in stages,
at roughly the same age, in the same way, and in a steady progression. It has shown
instead that individual children acquire skills at different ages and in different
ways, and that their development entails regressions as well as progress (Adolph &
Berger, 2011).
One example of this type of research is a longitudinal study of the develop-
ment of infants’ reaching conducted by Esther Thelen, who, along with her col-
league Linda Smith, was the cofounder of the dynamic-systems approach to
cognitive development. In this particular study, Thelen and colleagues (1993)
repeatedly observed the reaching efforts of four infants during their first year.
Using high-speed motion-capture systems and computer analysis of the infants’
muscle movements, they found that because of individual differences in such
factors as the infants’ physiology, activity level, arousal, motivation, and expe-
rience, each child faced different challenges in his or her attempts to master
reaching. The following observations illustrate some of the complexities these
researchers discovered, including variability in the ages at which infants reach
developmental milestones, their patterns of change, and the differing challenges
they must overcome:
Infants differed dramatically in the ages of the transition (from no reaching to reach-
ing). Whereas Nathan reached first at 12 weeks, Hannah and Justin did not at-
tain this milestone until 20 weeks of age. [In addition,] the infants showed periods
of rapid change, plateaus, and even regressions in performance. . . . There was in
FIGURE 4.11 problem solving often
requires motor skills A major insight of
dynamic-systems theories is that thinking
would be pointless without motor capabili-
ties. In these photos, a 12-month-old is
shown knocking a barrier out of the way
(left frame) and then grasping the edge of a
cloth in order to pull the cloth, string, and
toy toward him (right frame). If the infant
lacked the motor dexterity to grasp the
cloth or the strength to pull in the toy, his
problem-solving processes would have been
, S

Nathan, Justin, and Hannah a rather discontinuous shift to better, less variable per-
formance. . . . Gabriel’s transition to stability was more gradual.
(Thelen & Smith, 1998, pp. 605, 607)
Infants must individually discover the appropriate [reaching] speeds from the back-
ground of their characteristic styles. Gabriel, for example, had to damp down his very
vigorous movements in order to successfully reach, and he did. In contrast, Hannah,
who moved slowly and spent considerable time with her hands flexed near her face,
had to activate her arms more to extend them out in front of her. . . . Reaching is thus
sculpted from ongoing movements of the arms, through a process of modulating what
is in place. . . . As infants become older, their attention becomes more focused, and
their perceptual discrimination improves, and their memories get better, and their
movements become more skilled. A rich, complex, and realistic account of change
must include this dynamic interplay.
(Thelen, 2001, pp. 172, 182)
These descriptions help to convey what is meant by the label “dynamic systems.”
As suggested by the term dynamic, dynamic-systems theories depict development as a
process in which change is the only constant. Whereas some approaches to cognitive
development hypothesize that development entails long periods of relatively stable
stages or ways of thinking separated by relatively brief transition periods, dynamic-
systems theories propose that at all points in development, thought and action change
from moment to moment in response to the current situation, the child’s immediate
past history, and the child’s longer-term history of actions in related situations. Thus,
Thelen and Smith (1998) noted that the development of reaching included regres-
sions as well as improvements, and Thelen (2001) described how differences in Han-
nah’s and Gabriel’s early reaches influenced their later paths to skilled reaching.
As suggested by the second term in the label, dynamic-systems theories depict
each child as a well-integrated system, in which many subsystems—perception, ac-
tion, attention, memory, language, social interaction, and so on—work together to
determine behavior. For example, success on tasks viewed as measures of conceptual
understanding, such as object permanence, is influenced by perception, attention,
motor skills, and a host of other factors (Smith et al., 1999). The assumptions that
development is dynamic and that it functions as an organized system are central to
the theory’s perspective on children’s nature.
View of Children’s Nature
Dynamic-systems theories are the newest of the four types of theories discussed in
this chapter, and their view of children’s nature incorporates influences from each of
the others. Like Piaget’s theory, dynamic-systems theories emphasize children’s in-
nate motivation to explore the environment; like information-processing theories,
they emphasize precise analyses of problem-solving activity; and like sociocultural
theories, they emphasize the formative influence of other people. These similari-
ties to other theories, as well as the differences from them, are evident in dynamic-
systems theories’ emphasis on motivation and the role of action.
Motivators of Development
To a greater extent than any of the other theories except Piaget’s, dynamic- systems
theories emphasize that from infancy onward, children are strongly motivated to
learn about the world around them and to explore and expand their own capabilities

(von Hofsten, 2007). This motivation to explore and learn is clearly apparent in
the fact that children persist in practicing new skills even when they possess well-
practiced skills that are more efficient. Thus, toddlers persist in their first unsteady
efforts to walk, despite the fact that crawling would get them where they want to
go more quickly and without the risk of falling (Adolph & Berger, 2011).
Like sociocultural approaches, but unlike Piagetian theory, dynamic-systems
theories emphasize infants’ interest in the social world as a crucial motivator of de-
velopment. As noted in our discussion of the active child in Chapter 1, even new-
borns prefer attending to the sounds, movements, and features of the human face
over almost any alternative stimuli. By 10 to 12 months of age, infants’ interest in
the social world is readily apparent in the emergence of intersubjectivity (page 159),
as infants look to where the people interacting with them are looking and direct the
attention of others to things they themselves find interesting (Deák, Flom, & Pick,
2000; von Hofsten, Dahlström, & Fredricksson, 2005). Dynamic-systems theo-
rists have emphasized that observing other people, imitating their actions, and at-
tracting their attention are all potent motivators of development (Fischer & Bidell,
2006; von Hofsten, 2007).
The Centrality of Action
Dynamic-systems theories are unique in their pervasive emphasis on how children’s
specific actions shape their development. Piaget’s theory asserts the role of actions
during infancy, but dynamic-systems theories emphasize that actions contribute to
development throughout life. This focus on the developmental role
of action has led to a number of interesting discoveries. For example,
infants’ own reaching for objects helps them infer the goals of other
people’s reaches; infants who can skillfully reach are more likely to
look at the probable target of another person’s reaching just after the
other person’s reach begins (von Hofsten, 2007). Another example of
infants’ learning from actions comes from research in which infants
were outfitted with Velcro mittens that enabled them to “grab” and
explore Velcro-covered objects that they otherwise could not have
picked up. After 2 weeks of grabbing the Velcro-covered objects with
the Velcro-covered mittens, infants showed greater ability to grab
and explore ordinary objects without the mittens than did other in-
fants of the same ages (Needham, Barrett, & Peterman, 2002).
The ways in which children’s actions shape their development
extend well beyond reaching and grasping in infancy. Actions influ-
ence categorization: in one study, encouraging children to move an
object up and down led to their categorizing it as one of a group of
objects that were easiest to move in that way, whereas encouraging
children to move the same object from side to side led them to categorize it as one
of a group of objects that were easiest to move in that way (Smith, 2005). Actions
also affect vocabulary acquisition and generalization (Gershkoff-Stowe, Connell, &
Smith, 2006; Samuelson & Horst, 2008): for example, experimental manipulations
that lead children to state an incorrect name for an object impair the child’s future
attempts to learn the object’s correct name. In addition, actions shape memory, as
demonstrated by research in which children’s past attempts to locate and dig up
objects they had earlier seen being hidden in a sandbox altered their recall of the
objects’ new location after they had seen them being re-hidden. That is, the child’s
new searches tend to be in-between the past and present locations, as if the new
reaching with Velcro-covered mittens for
Velcro-covered objects improved infants’
later ability to grab and explore ordinary
objects without the mittens.

searches involved a compromise between memories of the new hiding place and of
the location where he or she had originally looked (Schutte, Spencer, & Schöner,
2003; Zelazo, Reznick, & Spinazzola, 1998). Thus, just as thinking shapes actions,
actions shape thinking.
Central Development Issues
Two developmental issues that are especially prominent in dynamic-systems theo-
ries are how the cognitive system organizes itself and how it changes.
Dynamic-systems theories view development as a process of self-organization that
involves bringing together and integrating attention, memory, emotions, and ac-
tions as needed to adapt to a continuously changing environment (Spencer et al.,
2006). The organizational process is sometimes called soft assembly, because the
components and their organization change from moment to moment and situation
to situation, rather than being governed by rigid stages that are consistently applied
across time and situations.
The types of research to which this perspective leads are illustrated particularly
well by certain studies of the A-not-B error that 8- to 12-month-olds typically
make in Piaget’s classic object-permanence task. As noted earlier, this error involves
infants’ searching for a toy where they had previously found it (location A), rather
than where they last saw it being hidden (location B). Piaget (1954) explained the
A-not-B error by hypothesizing that before their 1st birthday, infants lack a clear
concept of the permanent existence of objects.
In contrast, viewing the A-not-B error from a dynamic-systems perspective sug-
gested that many factors other than conceptual understanding influence perfor-
mance on the object-permanence task. In particular, Smith and colleagues (1999)
argued that babies’ previous reaching toward location A produces a habit of reach-
ing there, which influences their behavior when the object is subsequently hidden
at location B. On the basis of this premise, the researchers made several predic-
tions that were later borne out. One was that the more often babies had found an
object by reaching to one location, the more likely they would be to reach there
again when the object was hidden at a different location. Also supported was the
prediction that increasing the memory demands of the task by not allowing infants
to search for the object for 3 seconds after it was hidden at the B location would
increase the likelihood of infants’ reaching to location A (Clearfield et al., 2009).
The reasoning here was that the strength of the new memory would fade rapidly
relative to the fading of the habit of reaching to the previous hiding place. The
dynamic-systems perspective also suggested that infants’ attention would influence
their object-permanence performance. Consistent with this view, manipulating
infants’ attention by tapping one of the locations just as the infants were about to
reach usually resulted in their reaching to the tapped location, regardless of where
the object was actually hidden.
In perhaps the most striking test of such predictions, researchers demonstrated
that putting small weights on infants’ wrists after the infants had reached to loca-
tion A but before the object was hidden at location B improved object-permanence
performance (Diedrich et al., 2000). The researchers had reasoned that the addi-
tion of the wrist weights would require the infants to use different muscle tensions
and forces than they had previously used to reach for the object and consequently

would disrupt the infants’ habit of reaching to location A. Thus, rather than pro-
viding a pure measure of conceptual understanding, infants’ performance on the
object-permanence task appears to reflect the combined influence of the strength
of the habit of reaching to location A, the memory demands of the current task,
the infant’s current focus of attention, and the match between the muscular forces
required to reach in the old and new situations.
How Change Occurs
Dynamic-systems theories posit that changes occur through mechanisms of varia-
tion and selection that are analogous to those that produce biological evolution
(Fischer & Biddell, 2006; Steenbeek & Van Geert, 2008). In this context, varia-
tion refers to the use of different behaviors to pursue the same goal. For example, to
descend a ramp, a toddler will sometimes walk, sometimes crawl, sometimes do a
belly slide, sometimes do a sitting slide feet first, and so on (Adolph, 1997; Adolph
& Berger, 2011). Selection involves increasingly frequent choice of behaviors that
are effective in meeting goals and decreasing reliance on less effective behaviors.
For example, when children first learn to walk, they are too optimistic about being
able to walk down ramps, and often fall, but when they gain a few more months of
walking experience, they more accurately judge the steepness of ramps and whether
they can descend them while remaining upright.
BOX 4.4: applications
As noted in Chapter 2, children born prema-
turely with low birth weight are more likely
than other children to encounter develop-
mental difficulties, among them slower emer-
gence and refinement of reaching (Fallang et
al., 2003). These delays in reaching slow
the development of brain areas involved in
reaching (Martin et al., 2004), limiting in-
fants’ ability to explore and learn about ob-
jects (Lobo, Galloway, & Savelsbergh, 2004).
A variety of seemingly reasonable efforts to
improve preterm infants’ reaching, such as
guiding their arms through reaching move-
ments, have yielded discouraging results
(Blauw-Hospers & Hadders-Algra, 2005).
In contrast, a recent intervention based
on dynamic-systems research was quite
successful. This intervention, designed by
Heathcock, Lobo, and Galloway (2008), was
inspired by two findings we have discussed:
(1) the finding by Thelen and colleagues
(1993) that some infants’ slowness to initi-
ate arm activity impedes their development
of reaching, and (2) the finding by Needham
and colleagues (2002) that providing young
infants with experience in reaching for and
grabbing Velcro-patched objects while wear-
ing Velcro-covered mittens improves the
infants’ later ability to reach for and grab
ordinary objects barehanded.
Heathcock, Lobo, and Galloway began
their intervention by requesting that care-
givers of preterm infants in an experimental
group provide the infants with special move-
ment experiences. Specifically, they asked
the caregivers to encourage infants’ arm
movements by (1) tying a bell to the infants’
wrists so that arm movements would make
it ring, presumably motivating further move-
ments, and (2) placing Velcro mittens on
the infants’ hands to allow them to reach for
and grab Velcro-patched toys held in front of
them. The caregivers were asked to do this
at home 5 times per week for 8 weeks.
Caregivers of preterm infants in a control
group were asked to provide their infants
with special social experiences that in-
cluded singing to and talking with the in-
fants on the same intervention schedule as
that of children in the experimental group.
Periodically, the infants in both groups were
brought to the lab to allow project person-
nel to observe their reaching and exploration
under controlled circumstances and during
free play.
As might be expected, the reaching of
preterm infants in both groups improved
over the 8 weeks of the study. However,
the infants in the experimental group im-
proved to a greater degree. They more often
touched toys that were held in front of them,
and more often did so with the inside rather
than the outside part of their hand, as is
needed for grasping objects. Such interven-
tions may also help preterm infants avoid
other types of cognitive and motor impair-
ments that are partially caused by delayed
development of reaching.

chapter summary:
Theories of development are important because they pro-
vide a framework for understanding important phenomena,
raise major issues regarding human nature, and motivate
new research. Four major theories of cognitive development
are Piagetian, information-processing, sociocultural, and
Piaget’s Theory
n Among the reasons for the longevity of Piaget’s theory are that
it vividly conveys the flavor of children’s thinking at different
ages, extends across a broad range of ages and content areas,
and provides many fascinating and surprising observations of
children’s thinking.
n Piaget’s theory is often labeled “constructivist,” because it
depicts children as actively constructing knowledge for them-
selves in response to their experience. The theory posits that
children learn through two processes that are present from
birth—assimilation and accommodation—and that the con-
tribution of these processes is balanced through a third pro-
cess, equilibration. These processes produce continuities
across development.
n Piaget’s theory divides cognitive development into four
broad stages: the sensorimotor stage (birth to age 2), the
preoperational stage (ages 2 to 7), the concrete opera-
tional stage (ages 7 to 12), and the formal operational stage
(age 12 and beyond). These stages reflect discontinuities in
n In the sensorimotor stage, infants’ intelligence is expressed
primarily through motor interactions with the environment.
During this period, infants gain understanding of concepts
such as object permanence and become capable of deferred
Children’s selection among alternative approaches reflects several influences.
Most important is the relative success of each approach in meeting a particular
goal: as children gain experience, they increasingly rely on approaches that pro-
duce desired outcomes. Another important consideration is efficiency: children
increasingly choose approaches that meet goals more quickly or with less effort
than do other approaches. A third consideration is novelty, the lure and challenge
of trying something new. Children sometimes choose new approaches that are
no more efficient, or even less efficient, than an established alternative but that
have the potential to become more efficient. For example, when they first learn
the memory strategy of rehearsal, it does not improve their memory, but they use
it anyway, and eventually it does improve their recall of rehearsed information
(Miller & Seier, 1994). Such a novelty preference tends to be adaptive, because
with practice, a strategy that is initially less efficient than existing approaches
often becomes more efficient (Wittmann et al., 2008). As discussed in Box 4.4,
the insights of dynamic-systems theories have led to useful applications as well
as theoretical progress.
Dynamic-systems theories view children as ever-changing, well-integrated organisms that
combine perception, action, attention, memory, language, and social influences to produce
actions that satisfy goals. From this perspective, children’s actions are shaped by both their
remote and recent history, their current physical capabilities, and their immediate physi-
cal and social environment. The actions, in turn, are viewed as shaping the development
of categorization, conceptual understanding, memory, language, and other capabilities.
Dynamic-systems theories are unique in their emphasis on how children’s actions shape their
development, as well as in the range of developmental influences they consider with regard
to particular capabilities.

n In the preoperational stage, children become able to rep-
resent their experiences in language, mental imagery, and
thought, but because of cognitive limitations such as egocen-
trism and centration, they have difficulty solving many prob-
lems, including Piaget’s various tests of conservation and tasks
related to taking the perspective of others.
n In the concrete operational stage, children become able to
reason logically about concrete objects and events but have dif-
ficulty reasoning in purely abstract terms and in succeeding on
tasks requiring hypothetical thinking, such as the pendulum
n In the formal operational stage, children gain the cognitive
capabilities of hypothetical thinking.
n Four weaknesses of Piaget’s theory are that it depicts children’s
thinking as being more consistent than it is, underestimates
infants’ and young children’s cognitive competence, understates
the contribution of the social world to cognitive development,
and only vaguely describes the mechanisms that give rise to
thinking and cognitive growth.
Information-Processing Theories
n Information-processing theories focus on the specific mental
processes that underlie children’s thinking. Even in infancy,
children are seen as actively pursuing goals, encountering pro-
cessing limits, and devising strategies that allow them to sur-
mount the processing limits and attain the goals.
n The memory system includes working memory, long-term
memory, and executive functioning.
n Working memory is a system for actively attending to, gath-
ering, maintaining, storing, and processing information.
n Long-term memory is the enduring knowledge accumulated
over a lifetime.
n Executive functioning is crucial for controlling thought and
action, develops greatly during the preschool and early ele-
mentary school years, and is related to later academic achieve-
ment and occupational success.
n The development of memory and learning in large part reflects
improvements in basic processes, strategies, and content
n Basic cognitive processes allow infants to learn and remember
from birth onward. Among the most important basic processes
are association, recognition, generalization, and encoding.
n The use of strategies enhances learning and memory beyond
the level that basic processes alone could provide. Rehearsal
and selective attention are two important strategies.
n Increasing content knowledge enhances memory and learning
of all types of information.
n One important contributor to the growth of problem solving is
the development of planning.
Sociocultural Theories
n Starting with Vygotsky’s theory, sociocultural theories have
focused on the way that the social world molds development.
These theories emphasize that development is shaped not only
by interactions with other people and the skills learned from
them, but also by the artifacts with which children interact and
the beliefs, values, and traditions of the larger society.
n Sociocultural theories view humans as differing from other
animals in their propensity to teach and their ability to learn
from teaching.
n Establishing intersubjectivity between people through joint
attention is essential to learning.
n Sociocultural theories describe people as learning through
guided participation and social scaffolding, in which others
who are more knowledgeable support the learner’s efforts.
Dynamic-Systems Theories
n Dynamic-systems theories view change as the one constant
in development. Rather than depicting development as being
organized into long periods of stability and brief periods of
dramatic change, these theories propose that there is no period
in which substantial change is not occurring.
n These theories also view each person as a unified system that,
in order to meet goals, integrates perception, action, catego-
rization, motivation, memory, language, conceptual under-
standing, and knowledge of the physical and social worlds.
n Dynamic-systems theories view development as a self-
organizing process that brings together components as needed
to adapt to a continuously changing environment.
n Attaining goals requires action as well as thought. Thought
shapes action, but action also shapes thought.
n Just as variation and selection produce biological evolution,
they also produce cognitive development.
Critical Thinking Questions
1. Piaget’s theory has been prominent for more than 80 years.
Do you think it will continue to be prominent for the next 20
years as well? Why or why not?
2. Do you think that the term egocentric is a good description of
preschoolers’ overall way of seeing the world? On the basis
of what you learned in this chapter and your own experience,
explain your answer and indicate in what ways preschoolers
are egocentric and in what ways they are not.
3. Information-processing analyses tend to be more specific
about cognitive processes than are analyses generated by

other theories. Do you see this specificity as an advantage or
a disadvantage? Why?
4. Do new behaviors, like new species, grow out of the pro-
cesses of variation and selection, as depicted within dynamic-
systems theories?
5. Imagine that you are trying to help a 6-year-old learn a skill
that you possess. Using the ideas of guided participation
and social scaffolding, describe how you might go about
this task.
6. Dynamic-systems theories reflect influences of each of the
other theories reviewed in this chapter. Which theoretical
influence do you think is strongest: Piagetian, information-
processing, or sociocultural? Explain your reasoning.
Key Terms
A-not-B error, p. 136
accommodation, p. 133
assimilation, p. 133
autobiographical memories, p. 160
basic processes, p. 150
centration, p. 139
concrete operational stage, p. 135
conservation concept, p. 139
cultural tools, p. 156
deferred imitation, p. 137
dynamic-systems theories, p. 161
egocentrism, p. 138
encoding, p. 150
equilibration, p. 133
formal operational stage, p. 135
guided participation, p. 155
information-processing theories, p. 145
intersubjectivity, p. 159
joint attention, p. 159
long-term memory, p. 148
object permanence, p. 136
overlapping-waves theory, p. 152
preoperational stage, p. 135
private speech, p. 157
problem solving, p. 146
rehearsal, p. 151
selective attention, p. 151
sensorimotor stage, p. 135
social scaffolding, p. 159
sociocultural theories, p. 155
symbolic representation, p. 138
task analysis, p. 146
working memory, p. 147

MARY STEVENSON CASSATT, Mother and Child, 1900
, U

chapter 5:
Seeing, Thinking, and
Doing in Infancy
n Perception
Box 5.1: A Closer Look Infants’ Face Perception
Auditory Perception
Box 5.2: A Closer Look Picture Perception
Taste and Smell
Intermodal Perception
n Motor Development
Motor Milestones
Current Views of Motor Development
Box 5.3: A Closer Look “The Case of the
Disappearing Reflex”
The Expanding World of the Infant
Box 5.4: Applications A Recent Secular Change in
Motor Development
Box 5.5: A Closer Look “Gangway—I’m Coming Down”
n Learning
Perceptual Learning
Statistical Learning
Classical Conditioning
Instrumental Conditioning
Observational Learning/Imitation
Rational Learning
n Cognition
Object Knowledge
Physical Knowledge
Social Knowledge
Looking Ahead
n Chapter Summary

Four-month-old Benjamin, perched on the kitchen counter in his infant seat, is watching his parents wash the dinner dishes. What he observes includes two people who move on their own, as well as a variety of glass, ceramic, and metal objects of differing sizes and shapes that move only when picked up and manipulated by the people. Other elements of the scene never move. As
the people go about their task, distinctive sounds emanate from their moving lips,
while different sounds occur as they deposit cutlery, skillets, glasses, and sponges on
the kitchen counter. At one point, Benjamin sees a cup completely disappear from
view when his father places it on the counter behind a cooking pot; it reappears a
moment later when the pot is moved. He also sees objects disappear as they pass
through the suds and into the water, but he never sees one object pass through an-
other. The objects that are placed on the counter stay put, until Benjamin’s father
puts a crystal goblet on the counter with more than half of its base hanging over
the counter’s edge. The crashing sound that follows startles all three people in the
room, and Benjamin is further startled when the two adults begin emitting sharp,
loud sounds toward one another, quite unlike the soft, pleasant sounds they had
been producing before. When Benjamin begins crying in response, the adults rush
to him, patting him and making soft, especially pleasant sounds to him.
This example, to which we will return throughout the chapter, illustrates the enor-
mous amount of information that is available for an infant to observe and learn from
in even the most everyday situations. In learning about the world, Benjamin, like
most infants, avidly explores everything and everyone around him, using every tool
he has: he gathers information by looking and listening, as well as by tasting, smell-
ing, and touching. His explorations will gradually expand as he becomes capable first
of reaching for objects and then of manipulating them, making it possible for him
to discover more about them. When he starts to move around under his own power,
even more of the world will become available to him, including
things his parents would prefer that he not investigate, such as elec-
trical outlets and kitty litter. Never will Benjamin explore so vora-
ciously or learn so rapidly as in the first few years of his young life.
In this chapter, we discuss development in four closely related
areas: perception, action, learning, and cognition. Our discussion
focuses primarily on infancy. One reason for concentrating on this
period is that extremely rapid change occurs in all four areas dur-
ing the first two years of a child’s life. A second reason is the fact
that infant development in these four domains is particularly inter-
twined: the minirevolutions that transform infants’ behavior and
experience in one domain lead to minirevolutions in others. For
example, the dramatic improvements in visual abilities that occur in
their first few months enable infants to see more of the people and
objects around them, thereby greatly increasing the opportunities
they have to learn new information.
A third reason for concentrating on infancy in this chapter is
the fact that the majority of recent research on perceptual and
motor development has been done with infants and young chil-
dren. There is also a large body of fascinating research on learning
and cognition in the first few years. We will review some of this
research here and cover subsequent development in these areas
in later chapters. A final reason for focusing on infants in this
n Nature and Nurture
n The Active Child
n Continuity/Discontinuity
n Mechanisms of Change
n The Sociocultural Context
n Individual Differences
Like Benjamin, this infant will take in a
great deal of perceptual information just
observing his father washing dishes.

chapter is that the methods used to investigate infants’ development in these four
domains are, of necessity, quite different from those that researchers are able to use
to study older children.
Our examination of key developments in infancy will feature several enduring
themes. The active child theme is vividly embodied by infants’ eager exploration of
their environment. Continuity/discontinuity arises repeatedly in research that ad-
dresses the relation between behavior in infancy and subsequent development. In
some sections, the mechanisms of change theme is also prominent, as we explore the
role that variability and selection play in infants’ development. In our discussion
of early motor development, we will examine contributions made by the sociocul-
tural context.
Underlying much of this chapter, of course, is the theme of nature and nurture.
For at least 2,000 years, an often-contentious debate has existed between those
philosophers and scientists who have emphasized innate knowledge in account-
ing for human development and those who have emphasized learning (Spelke &
Newport, 1998). The desire to shed light on this age-old debate is one reason that
an enormous amount of research has been conducted with infants over the past few
decades. As you will see, these discoveries have revealed that infant development is
even more complicated and remarkable than previously suspected.
Parents of new babies cannot help wondering what their children experience—
how much they can see, how well they can hear, whether they connect sight and
sound (as in our opening vignette), and so on. William James, one of the first psy-
chologists, believed that the world of the newborn is a “big blooming, buzzing
confusion.” Because of remarkable advances in the study of early sensation and per-
ception, modern researchers do not share his view. They have demonstrated that in-
fants come into the world with all their sensory systems functioning to some degree
and that subsequent development occurs at a very rapid pace. Sensation refers to
the processing of basic information from the external world by the sensory recep-
tors in the sense organs (eyes, ears, skin, and so forth) and the brain. Perception is
the process of organizing and interpreting sensory information about the objects,
events, and spatial layout of the world around us. In our opening example, sensation
involved light and sound waves activating receptors in Benjamin’s eyes, ears, and
brain; an instance of perception involved, for example, his experiencing the visual
and auditory stimulation provided by the crashing goblet as a single coherent event.
In this section, we devote the most attention to vision, both because of its fun-
damental importance to humans and because so much more research has been
conducted on vision than on the other senses. We will also discuss hearing and, to
a lesser degree, taste, smell, and touch, as well as the coordination between these
multiple sensory modalities. Although these abilities often seem commonplace to
us as adults, they are actually some of the most remarkable achievements attained
during the first year of life.
Humans rely more heavily on vision than most species do: roughly 40% to 50% of
our mature cerebral cortex is involved in visual processing (Kellman & Arterberry,
2006). As recently as a few decades ago, it was generally assumed that newborns’
sensation n the processing of basic
information from the external world by
the sensory receptors in the sense organs
(eyes, ears, skin, etc.) and brain
perception n the process of organizing
and interpreting sensory information

vision was so poor as to be barely functional. However, once researchers started
carefully studying the looking behavior of newborns and young infants, they dis-
covered that this assumption was incorrect. In fact, newborns begin visually explor-
ing the world minutes after leaving the womb. They scan the environment, and
when their gaze encounters a person or object, they pause to look at it. Although
newborns do not see as clearly as adults do, their vision improves extremely rapidly
in their first months. And as you will learn, recent studies have revealed that despite
their immature visual systems, even the youngest infants have some surprisingly
sophisticated visual abilities.
The evidence that enables us to say this so confidently was made possible by
the invention of a variety of ingenious research methods. Because young infants
are unable to understand and respond to instructions, investigations of infant abil-
ities required researchers to devise methods that are quite different from those
used with older children and adults. The first breakthrough was achieved with the
preferential-looking technique, a method for studying visual attention in infants.
In this technique, pioneered by Robert Fantz (1961), two different visual stimuli are
typically displayed on side-by-side screens. If an infant looks longer at one of the two
stimuli, the researcher can infer that the baby is able to discriminate between them
and has a preference for one over the other. Fantz established that newborns, just
like everyone else, would rather look at something than at nothing. When a pattern
of any sort—black and white stripes, newsprint, a bull’s-eye, a schematic face—was
paired with a plain surface, the infants preferred (i.e., looked longer at) the pattern.
Another method that is used to study sensory and perceptual development in
infants is habituation, which you encountered in Chapter 2 as a research tool used
in studying fetal development. This procedure involves repeatedly presenting an
infant with a particular stimulus until the infant’s response to it habituates, that is,
declines. Then a novel stimulus is presented. If the infant’s response increases, the
researcher infers that the baby can discriminate between the old and new stimu-
lus. Despite their simplicity, habituation and preferential-looking procedures have
turned out to be enormously powerful for studying infants’ perception and under-
standing of the world.
Visual Acuity
The preferential-looking method enables researchers (and eye-care professionals)
to assess infants’ visual acuity, that is, to determine how clearly they can see. This
method builds on research showing that infants who can see the difference be-
tween a simple pattern and a solid gray field consistently prefer to
look at the pattern (Figure 5.1). By varying the patterns and as-
sessing infants’ preferences, researchers have learned a great deal
about not only infants’ early visual abilities but also about their
looking preferences. For example, young infants generally pre-
fer to look at patterns of high visual contrast—such as a black-
and-white checkerboard (Banks & Dannemiller, 1987). This is
because young infants have poor contrast sensitivity: they can
detect a pattern only when it is composed of highly contrasting
One reason for this poor contrast sensitivity is the immaturity
of infants’ cones, the light-sensitive neurons that are highly con-
centrated in the fovea (the central region of the retina) and are in-
volved in seeing fine detail and color. In infancy, the cones have a
preferential-looking technique n a
method for studying visual attention in
infants that involves showing infants two
patterns or two objects at a time to see if
the infants have a preference for one over
the other
visual acuity n the sharpness of visual
contrast sensitivity n the ability to
detect differences in light and dark areas
in a visual pattern
cones n the light-sensitive neurons that
are highly concentrated in the fovea (the
central region of the retina)
FIGURE 5.1 testing infants’ visual
acuity paddles like those depicted here
can be used to assess young infants’ visual
acuity. two paddles are shown to the infant
simultaneously, one with stripes and one in
plain gray. If the infant can detect the con-
trast difference between the black and white
stripes, the infant’s gaze should, because
of infants’ preference for a patterned visual
field over a plain one, become oriented
toward the striped paddle. the ophthal-
mologist or researcher presents the infant
a succession of paddles with increasingly
narrow stripes, with increasingly narrow gaps
between them, until the infant can no longer
distinguish between the striped paddle and
the plain gray one. the degree of grating on
the last paddle discriminated provides an
indication of the infant’s visual acuity.

different size and shape and are spaced farther apart than
in adulthood (Kellman & Arterberry, 2006). As a conse-
quence, newborns’ cones catch only 2% of the light strik-
ing the fovea, compared with 65% for adults (Banks &
Shannon, 1993). This is partly why in their first month,
babies have only about 20/120 vision (a level of acuity
that would enable an adult to read the large E at the top
of a standard eye chart). Subsequently, visual acuity de-
velops so rapidly that by 8 months of age, infants’ vision
approaches that of adults, with full adult acuity present
by around 6 years of age (Kellman & Arterberry, 2006).
Another restriction on young infants’ visual experi-
ence is that, for the first month or so, they do not share
adults’ experience of a richly colorful world. At best, they
can distinguish some shades from white (Adams, 1995).
By 2 or 3 months of age, infants’ color vision is simi-
lar to that of adults (Kellman & Arterberry, 2006). Indeed, it is similar to the ex-
tent that 4- and 5-month-olds prefer (look longest at) the same basic colors that
adults rate as most pleasant—red and blue (Bornstein, 1975). They also perceive
the boundaries between colors in more or less the same way as adults do: they re-
spond equivalently to two shades that adults label as the same color (e.g., “blue”),
but they discriminate between two shades that adults refer to with different color
names (e.g., “blue” and “green”) (Bornstein, Kessen, & Weiskopf, 1976).
Visual Scanning
As noted, newborns start visually scanning the environment right away. From the
beginning, they are attracted to moving stimuli. However, they have trouble track-
ing these stimuli because their eye movements are jerky and often do not stay with
whatever they are trying to visually follow. Not until 2 or 3 months of age are in-
fants able to track moving objects smoothly, and then they are able to do so only if
an object is moving slowly (Aslin, 1981). This developmental achievement appears
to be less a function of visual experience than of maturation. Preterm infants, whose
neural and perceptual systems are immature, develop smooth visual tracking later
than full-term infants do (Strand-Brodd et al., 2011).
Another limitation on young infants’ visual experience of the world (and there-
fore on what they can learn) is that their visual scanning is restricted. With a simple
figure like a triangle, infants younger than 2 months old look almost exclusively
at one corner. With more complex shapes, they tend to scan only the outer edges
(Haith, Bergman, & Moore, 1977; Milewski, 1976). Thus, as Figure 5.2 shows,
when 1-month-olds look at a line drawing of a face, they tend to fixate on the
perimeter—on the hairline or chin, where there is relatively high contrast with the
background. By 2 months of age, infants scan much more broadly, enabling them
to pay attention to both overall shape and inner details (see Box 5.1).
Pattern Perception
Accurate visual perception of the world requires more than acuity and systematic
scanning; it also requires analyzing and integrating the separate elements of a visual
display into a coherent pattern. To perceive the face in Figure 5.2, as 2-month-olds
apparently do, they must integrate the separate elements.
the blurred image on the right is roughly
what a 1-month-old infant would perceive.
the infant’s relatively low level of visual
acuity leads some features of the image to
pop out—those with higher contrast (e.g.,
the woman’s eyes and hairline).
: G
/ T
(a) (b)
FIGURE 5.2 Visual scanning the lines
superimposed on these face pictures show
age differences in where two babies fixated
on the images. (a) a 1-month-old looked pri-
marily at the outer contour of the face and
head, with a few fixations of the eyes. (b) a
2-month-old fixated primarily on the internal
features of the face, especially the eyes and
mouth. (From Maurer & Salapatek, 1976)

BOX 5.1: a closer look
A particularly fascinating aspect of infant
perception has to do with the reaction of
human infants to that most social of all
stimuli—the human face. As we have noted,
infants are drawn to faces from birth, lead-
ing researchers to ask what initially attracts
their attention. The answer, it seems, is a
When presented with each of these three pairs of stimuli, newborns look longer at the image in
the left-hand column, revealing a general preference for top-heavy stimuli that contributes to
their preference for human faces (Macchi cassia et al., 2004; Simion et al., 2002). Notice that
this simple preference is all that is needed to result in newborns spending more time looking at
their mother’s face than at anything else. By 3 months of age, however, infants no longer dis-
criminate between the faces in the middle pair of pictures, suggesting that their visual attention
is no longer guided by a general top-heavy bias (Macchi cassia et al., 2006).©
readily discriminate between two human
faces. However, adults and 9-month-olds
have a great deal of difficulty telling the dif-
ference between one monkey face and an-
other (Pascalis, de Haan, & Nelson, 2002).
Surprisingly, 6-month-olds are just as good
at discriminating between monkey faces as
they are at discriminating between human
The researchers concluded that the
9-month-olds and adults rely on a detailed
prototype of the human face to discrimi-
nate between people, but this prototype
does not help them tell the difference be-
tween monkeys. The fact that the 6-month-
olds discriminated among monkey faces
just as well as they discriminated among
human faces suggests that these younger
infants have not yet developed a tightly or-
ganized prototype for human faces. While
6-month-olds are certainly knowledgeable
about faces, they do not yet privilege the
details of human faces over the details of
monkey faces.
Consistent with this account is research
showing effects of experience on face rec-
ognition. In one study, from the age of 6
months to 9 months, infants were shown a
set of pictures of monkey faces on a regu-
lar schedule for 1 to 2 minutes. When they
were tested at 9 months of age, they dem-
onstrated that they had retained their ability
to distinguish between monkey faces, unlike
a control group of 9-month-olds who had not
had the exposure to monkey faces (Pascalis
et al., 2005).
Another type of experience that shapes
infant face perception is exposure to
very general bias toward configurations with
more elements in the upper half than in the
lower half—something that characterizes
all human faces (Macchi Cassia, Turati, &
Simion, 2004; Simion et al., 2002) (see
the images in the first column). Evidence in
support of a general bias to attend to face-
like stimuli comes from studies showing that
newborn humans are equally interested in
human faces and monkey faces—as long as
they are presented right-side up (Di Giorgio
et al., 2012).
From paying lots of attention to faces,
infants very quickly come to recognize and
prefer their own mother’s face. After expo-
sure to Mom over the first few days after
birth, infants look longer at her face than at
the face of another woman, even when con-
trolling for olfactory cues (a necessary step
because, as discussed in Chapter 2, new-
borns are highly attuned to their mother’s
scent) (Bushnell, Sai, & Mullin, 2011). Over
the ensuing months, infants develop a pref-
erence for faces depicting the gender of the
caregiver they see most often, whether fe-
male or male (Quinn, et al., 2002).
With exposure to many different faces
over their first months, infants gradually
develop a well-organized perceptual proto-
type for human faces. The formation of this
detailed face prototype then facilitates dis-
crimination between different faces. Evi-
dence for the formation of a general face
prototype in the first year comes from an in-
triguing study of infants’ and adults’ ability
to discriminate between individual human
faces and individual monkey faces. Adults,
9-month-olds, and 6-month-olds can all

individuals of different races. The other race
effect (ORE) is a well-established finding,
initially observed in adults, in which indi-
viduals find it easier to distinguish between
faces of individuals from their own racial
group than between faces from other ra-
cial groups. It was later determined that the
ORE emerges in infancy. Whereas newborns
show no preference for own-race faces over
other-race faces, 3-month-old White, Afri-
can, and Chinese infants prefer own-race
faces (Kelly, Liu et al., 2007; Kelly et al.,
2005). Over the second half of the first
year, infants’ face processing continues to
become more specialized, as shown by the
emergence of the ORE; by 9 months of age,
infants have more difficulty discriminating
between other-race faces than between own-
race faces (Kelly, Quinn et al., 2007; Kelly
et al., 2009).
What drives these effects is not the infant’s
own race per se but, rather, the features of
individuals in the infant’s immediate envi-
ronment. For example, 3-month-old African
emigrants to Israel who were exposed to both
African and White caregivers showed equal
interest in African and White faces (Bar-Haim
et al., 2006). Further evidence of effects of
visual experience on face perception comes
from a study suggesting that the facial-
scanning abilities of biracial infants—who are
exposed to the facial features characteristic
of two races in the home—are more mature
than those of monoracial infants (Gaither,
Pauker, & Johnson, 2012).
One of the most intriguing aspects of in-
fants’ facial preferences is the fact that,
along with all the rest of us, babies like
a pretty face. From birth, infants look lon-
ger at faces that are judged by adults to
be highly attractive than at faces judged
to be less appealing (Langlois et al.,
1991; Langlois et al., 1987; Rubenstein,
Kalakanis, & Langlois, 1999; Slater et al.,
1998, 2000).
Older infants’ preference for prettiness,
like adults’, also affects their behavior to-
ward real people. This was demonstrated
in a study in which 12-month-olds inter-
acted with a woman whose face was either
very attractive or very unattractive (Langlois,
Roggman, & Rieser-Danner, 1990). The first
key feature of this study was that the attrac-
tive woman and the unattractive woman were
one and the same! This duality of appearance
was achieved through the use of extremely
natural-looking professional masks that were
applied before the woman interacted with
the infants. On a given day, the young woman
who would test the babies emerged from her
makeup session looking either fabulous or
not so fabulous, depending on which mask
she was wearing. The masks conformed to
what adults judge to be a very attractive face
and a relatively unattractive one.
When interacting with the woman, in-
fant participants behaved differently as a
function of which mask she was wearing.
They were more positive, became more in-
volved in play, and were less likely to with-
draw when she was wearing the attractive
mask than when she had on the unattract-
ive one. This study was particularly well
designed because the young woman never
knew on any given day which mask she had
on. Thus, the children’s behavior could not
have been cued by her behavior; it could
only have been due to her pretty or homely
Do the photographs of the men show the same person or different people? how
about the two monkey photos? as an adult human, you no doubt can tell the two
men apart quite easily, but you may still not be sure whether the two monkey
photos are of different individuals. (they are.)

A striking demonstration of integrative pattern perception in infancy comes
from research using the stimulus shown in Figure 5.3. When you look at it, you
no doubt perceive a square, even though no square actually exists. This perception
of subjective contour results from your active integration of the separate elements
in the stimulus into a single pattern. If you simply looked at the individual shapes
in turn, no square would pop out. Like you, 7-month-olds perceive the subjective
square in Figure 5.3 (Bertenthal, Campos, & Haith, 1980), indicating that they
integrate the separate elements to perceive the whole. Even newborns can do so if
motion cues are added to the display, such as arranging it so that the illusory square
appears to move back and forth (Valenza & Bulf, 2007).
Infants are also able to perceive coherence among moving elements. In research
by Bertenthal and his colleagues (Bertenthal, 1993; Bertenthal, Proffitt, & Kramer,
1987), infants watched a film of moving points of light. Adults who watch this
film immediately and confidently identify what they see as a person walking; the
moving lights appear to be (and are) attached to the major joints and head of an
adult. Five-month-olds apparently see the same thing; they look longer at the
point-light displays that suggest human movement than at ones that do not. As
with the research on newborns’ response to the illusory square in Figure 5.3, recent
studies have confirmed that even newborns show a preference for a moving-lights
depiction of biological motion over one of nonbiological motion (Bardi, Regolin,
& Simion, 2011). Taken together, these results suggest that despite their limited
acuity and lack of visual experience, newborns are already attentive to the configu-
rations of elements in their visual world.
Object Perception
One of the most remarkable things about our perception of objects in the world
around us is how stable the world appears to be. When a person approaches or moves
away from us, or slowly turns in a circle, our retinal image of the person changes in
size and shape, but we do not have the impression that the person changes in size
and shape. Instead, we perceive a constant shape and size, a phenomenon known
as perceptual constancy. For a good demonstration of size constancy, look in the
mirror and notice that the image of your face seems to be the normal size of a face.
Then steam up the mirror and trace the outline of your face on the mirror. You will
find that the outline is actually a great deal smaller than your face. But because of
perceptual constancy, you perceive the image in the mirror as being the same size as
any other adult face.
The origin of perceptual constancy was a traditional component
in the debates between empiricists and nativists. Briefly, empiricists
maintain that all knowledge arises from experience, whereas nativists
hold that certain aspects of knowledge are, in fact, innate, or hard-
wired. Thus, empiricists argue that our perception of the constant
size and shape of objects develops as a function of spatially experi-
encing our environment, whereas nativists argue that this perceptual
regularity stems from inherent properties of the nervous system.
The nativist view is supported by evidence of perceptual con-
stancy in newborns and very young infants. In a study of size con-
stancy (Slater, Mattock, & Brown, 1990), newborns were repeatedly
shown either a large or a small cube at varying distances. While the
cube’s actual size remained the same, the size of the retinal image
projected by the cube changed from one trial to the next (see Fig-
ure 5.4). The question was whether the newborns would perceive
FIGURE 5.3 Subjective contour When
you look at this figure, you no doubt see a
square—what is called a subjective contour,
because it does not actually exist on the
page. Seven-month-olds also detect the illu-
sory square. (From Bertenthal et al., 1980)
perceptual constancy n the percep-
tion of objects as being of constant size,
shape, color, etc., in spite of physical dif-
ferences in the retinal image of the object
FIGURE 5.4 If this infant looks longer at
the larger but farther-away cube, researchers
will conclude that the child has size

these events as multiple presentations of the same object or as presentations of simi-
lar objects of different sizes.
To answer this question, the researchers subsequently presented the newborns
with the original cube and a second one that was identical except that it was twice
as large. The crucial factor was that the second cube was located twice as far away
as the original one, so it produced the same-size retinal image as the original. The
infants looked longer at the new cube, indicating that they saw it as different in size
from the original one. This, in turn, revealed that they had perceived the multiple
presentations of the original cube as a single object of a constant size, even though
its retinal size varied. Thus, visual experience is not necessary for size constancy
(Granrud, 1987; Slater & Morison, 1985).
Another crucial perceptual ability is object segregation, the perception of the
boundaries between objects. To appreciate the importance of this ability, look around
and try to imagine that you are seeing the scene and the objects in it for the first
time. How can you tell where one object ends and another begins? If the objects are
separated by a gap, the boundaries between the objects are obvious. But what if there
are no visible gaps? Suppose, for example, that as baby Benjamin watches his par-
ents washing dishes, he sees a cup sitting on a saucer. An adult would perceive this
arrangement as two distinct objects, but will Benjamin? Lacking experience with
china, Benjamin may be unsure: the difference in shape suggests two objects, but the
common texture suggests only one. Now suppose that Ben’s mother picks up the cup
to dip it in the suds, leaving the saucer on the table. Will he still be uncertain? No,
because even infants treat the independent motion of cup and saucer (or any objects)
as a signal that they are separate entities. Is this knowledge innate, or do infants ac-
quire it from observing everyday events in their environment?
The importance of motion as a cue indicating the boundaries between objects
was initially demonstrated in a classic experiment by Kellman and Spelke (1983).
First, 4-month-olds were presented with the display shown in Figure 5.5a. This
display could be perceived either as two pieces of a rod moving on each end of a
block of wood or as a single rod moving back and forth behind the block. Impor-
tantly, adults perceive displays of this type the latter way. After habituating to the
display, the infants were shown the two test displays in Figure 5.5b: a whole rod
and a rod broken into two pieces. The investigators reasoned that if the infants, like
adults, assumed that there was a single intact rod moving behind the block during
habituation, they would look longer at the broken rod because that display would
be relatively novel. And that is exactly what the babies did.
What caused the infants to perceive the two rod segments presented during ha-
bituation as parts of a unitary object? The answer is common movement, that is, the
fact that the two segments always moved together in the same direction and at the
same speed. Four-month-olds who saw a display that was the same as the one in
Figure 5.5a, except that the rod was stationary, looked equally long at the two test
displays. In other words, in the absence of common movement, the display was
Common movement is such a powerful cue that it leads infants to perceive
disparate elements moving together as parts of a unitary object. It does not mat-
ter if the two parts of the object moving behind the block differ in color, texture,
and shape, nor does it make much difference how they move (side to side, up and
down, and so forth) (Kellman & Spelke, 1983; Kellman, Spelke, & Short, 1986).
For infants, common motion may have this effect, in part, because it draws their
attention to the relevant aspects of the scene—the moving pieces rather than the
block (S. P. Johnson et al., 2008). Strikingly, however, even this seemingly very
basic feature of visual perception must be learned. Newborn infants, tested using
FIGURE 5.5 Object segregation Infants
who see the combination of elements in (a)
perceive two separate objects, a rod moving
behind a block. after habituating to the dis-
play, they look longer at two rod segments
than at a single rod (b), indicating that they
find the single rod familiar but the two seg-
ments novel. If they first see a display with
no movement, they look equally long at the
two test displays. this result reveals the
importance of movement for object segrega-
tion. (From Kellman & Spelke, 1983)
object segregation n the identification
of separate objects in a visual array

displays similar to those described above and shown in Figure 5.5, do not appear
to make use of common motion as a cue to object identity (Slater et al., 1990,
1996). Only at 2 months of age do infants show any evidence that they use com-
mon motion to interpret the occluded rod as a single object (S. P. Johnson & Aslin,
1995). Thus, as powerful a cue as common motion may be, infants must develop
the ability to exploit it.
As they get older, infants use additional sources of information for object seg-
regation, including their general knowledge about the world (Needham, 1997;
Needham & Baillargeon, 1997). Look at the displays shown in Figure 5.6. The
differences in color, shape, and texture between the box and the tube in Figure
5.6a suggest that there are two separate objects, although you cannot really be sure.
However, your knowledge that objects cannot float in midair tells you that Figure
5.6b has to be a single object; that is, the tube must be attached to the box.
Like you, 8-month-olds interpret these two displays differently. When they see
a hand reach in and pull on the tube in Figure 5.6a, they look longer (presumably
they are more surprised) if the box and tube move together than if the tube comes
apart from the box, indicating that they perceive the display as two separate objects.
However, the opposite pattern occurs in Figure 5.6b: now the infants look longer if
the tube alone moves, indicating that they perceive a single object. Follow-up stud-
ies using the displays in Figure 5.6 with younger infants suggest that younger in-
fants (4½-month-olds) exhibit the adultlike interpretation of these displays, but only
when they have been familiarized previously with the box or the tube ( Needham &
Baillargeon, 1998). Thus, it appears that experience with specific objects helps in-
fants to understand their physical properties. We will return to this idea later in this
chapter when we discuss the implications of motor development for infants’ knowl-
edge about objects (particularly with respect to reaching, on page 192).
Depth Perception
To navigate through our environment, we need to know where we are with respect
to the objects and landmarks around us. We use many sorts of depth and distance
cues to tell us whether we can reach the coffee cup on our desk or whether the ap-
proaching car is far enough away that we can safely cross in front of it. From the
beginning, infants are sensitive to some of these cues, and they rapidly become
sensitive to the rest.
One cue that infants are sensitive to very early on is optical expansion, in which
the visual image of an object increases in size as the object comes toward us, oc-
cluding more and more of the background. When an image of an approaching ob-
ject expands symmetrically, we know that the object is headed right for us, and a
sensible response is to duck. Babies cannot duck, but they can blink. Timing this
(a) (b)
FIGURE 5.6 Knowledge and object
segregation (a) It is impossible to know
for sure whether what you see here is one
object or two. (b) Because of your knowledge
about gravity and support, you can be sure
that this figure is a single (albeit very odd)
object. (From Needham, 1997)
optical expansion n a depth cue in
which an object occludes increasingly
more of the background, indicating that
the object is approaching

blinking response is critical; if infants blink too soon or too late, they risk having
the oncoming object hit their open eye. If you think about it, though, it’s not at all
obvious how infants would know how to correctly time a blink. Doing so requires
infants to rapidly exploit information present in the visual image looming before
them, including how rapidly the image is expanding and amount of the visual field
taken up by the image. Rather remarkably, infants as young as 1 month blink de-
fensively at an expanding image that appears to be an object heading toward them
(Ball & Tronick, 1971; Náñez & Yonas, 1994; Yonas, 1981). Preterm infants show a
delayed developmental pattern of blinks to looming objects, suggesting that matu-
ration, and not solely postnatal visual experience, is crucial for this developmental
achievement (Kayed, Farstad, & van der Meer, 2008).
Another depth cue that emerges early is due to the simple fact that we have two
eyes. Because of the distance between them, the retinal image of an object at any
instant is never quite the same in both eyes. Consequently, the eyes never send quite
the same signal to the brain—a phenomenon known as binocular disparity. The
closer the object we are looking at, the greater the disparity between the two images;
the farther away the object, the less the disparity. In a process known as stereopsis,
the visual cortex computes the degree of disparity between the eyes’ differing neu-
ral signals and produces the perception of depth. This form of depth perception
emerges quite suddenly at around 4 months of age and is generally complete within
a few weeks (Held, Birch, & Gwiazda, 1980), presumably due to maturation of the
visual cortex.
At around 6 or 7 months of age, infants begin to become sensitive to a variety of
monocular depth cues (so called because they denote depth even if only one eye is
open) (Yonas, Elieff, & Arterberry, 2002). These cues are also known as pictorial
cues, because they can be used to portray depth in pictures. Three of them, includ-
ing relative size, are presented in Figure 5.7.
FIGURE 5.7 pictorial cues this renais-
sance painting contains multiple examples
of pictorial cues. One is interposition—
nearer objects occlude ones farther away.
the convergence of lines in the distance is
another. to appreciate the effectiveness of a
third cue—relative size—compare the actual
size of the man on the steps in the fore-
ground to the actual size of the woman in
the blue dress.EM
, 1
, M
, R
binocular disparity n the difference
between the retinal image of an object in
each eye that results in two slightly dif-
ferent signals being sent to the brain
stereopsis n the process by which
the visual cortex combines the differing
neural signals caused by binocular dis-
parity, resulting in the perception of
monocular depth (or pictorial) cues
n the perceptual cues of depth (such as
relative size and interposition) that can be
perceived by one eye alone

In one of the earliest studies of infants’
sensitivity to monocular depth cues, Yonas,
Cleaves, and Pettersen (1978) capitalized on
the fact that infants will reach toward which-
ever of two objects is nearer. The investigators
put a patch over one eye of 5- and 7-month-
olds (so binocular depth information would
not be available) and presented them with
a trapezoidal window with one side consid-
erably longer than the other (Figure 5.8).
(When viewed by an adult with one eye
closed, the window appears to be a standard
rectangular window sitting at an angle with
one side closer to the viewer.) The 7-month-
olds (but not the younger babies) reached toward the longer side, indicating that
they, as you would, perceived it as being nearer, providing evidence that they used
relative size as a cue to depth. (Box 5.2 reviews research on infants’ perception of
Auditory Perception
Another rich source of infants’ information about the world is sound. As we dis-
cussed in Chapter 2, fetuses can hear sufficiently well to learn basic features of their
auditory environment (their mother’s heartbeat, the rhythmic patterns of her native
language, and so forth). At birth, the human auditory system is well developed rela-
tive to the visual system. That said, although the inner ear structures appear to be
mature and adultlike, the conduction of sound through the outer parts of the ear is
inefficient (Keefe et al., 1993). Over the course of infancy, there are vast improve-
ments in sound conduction from the outer and middle ear to the inner ear. Simi-
larly, over the first year, auditory pathways in the brain mature significantly. Taken
together, these developments in the ear and in the brain greatly improve the infant’s
ability to respond to, and learn from, sound.
Other factors add to infants’ auditory improvement. One example involves
auditory localization, the perception of the spatial location of a sound source.
When they hear a sound, newborns tend to turn toward it. However, newborns
and young infants are far worse at determining the spatial location of a sound than
older infants and toddlers are. To localize a sound, listeners rely on differences in
the sounds that arrive at both of their ears: a sound played to their right will ar-
rive at their right ear before reaching their left ear, and will be louder at their right
ear than at their left ear, thereby signaling the direction the sound is coming from.
Young infants may have more difficulty using this information because their heads
are small, and thus the differences in timing and loudness in information arriv-
ing at each ear are smaller for infants than for toddlers and children with larger
heads. Another reason that this information may be difficult for infants to use is
that the development of an auditory spatial map (that is, a mental representation
of how sounds are organized in physical space—right versus left, up versus down)
requires multimodal experiences, through which infants become able to integrate
information from what they hear with information from what they see and touch.
The development of an auditory spatial map must therefore await the improve-
ments in visual and motor skills that emerge later in infancy (Saffran, Werker, &
Werner, 2006).
FIGURE 5.8 Monocular depth cues
this 7-month-old infant is using the mon-
ocular depth cue of relative size. Wearing
an eye patch to take away binocular depth
information, he is reaching to the longer
side of a trapezoidal window. this behavior
indicates that the baby sees it as the nearer,
and hence more readily reachable, side of
a regular rectangular window. (Yonas et al.,
: A
auditory localization n perception of
the location in space of a sound source

A special case of perceptual development
concerns pictures. Paintings, drawings, and
photographs are ubiquitous in modern soci-
eties, and we acquire an enormous amount
of information through them. When can in-
fants perceive and understand these impor-
tant cultural artifacts?
Even young infants perceive pictures in
much the same way that you do. In a classic
study, Hochberg and Brooks (1962) raised
their own infant son with no exposure to
pictures at all: no art or family photos; no
picture books; no patterns on sheets, cloth-
ing, or toys. They even removed the labels
from canned foods. Nevertheless, when
tested at 18 months, the child readily iden-
tified people and objects in photographs
and line drawings. Later research estab-
lished that infants as young as 5 months
old can recognize people and objects in
photographs and drawings of them (e.g.,
DeLoache, Strauss, & Maynard, 1979;
Dirks & Gibson, 1977), and even newborns
can recognize two-dimensional versions of
three-dimensional objects (Slater, Morison,
& Rose, 1984).
Despite their precocious perception of
pictures, infants do not understand their
nature. The four babies shown here—two
from the United States and two from a rural
village in West Africa—are all manually ex-
ploring depicted objects. Although these
9-month-old babies can perceive the differ-
ence between pictures and objects, they do
not yet understand what two-dimensionality
means; hence, they attempt to treat pic-
tured objects as if they were real objects—
with an inevitable lack of success. By 19
months of age and after substantial expe-
rience with pictures, American infants no
longer manually investigate pictures, ap-
parently having learned that pictures are
to look at and talk about, but not to feel,
pick up, or eat (DeLoache et al., 1998;
Pierroutsakos & DeLoache, 2003). In short,
they have come to understand the sym-
bolic nature of pictures and appreciate that
a depicted object stands for a real object
(Preissler & Carey, 2003).
Whereas most Western infants live in en-
vironments filled with pictured objects, in-
fants in other cultures often lack experience
with such images. Fascinating cross-cultural
research suggests that, in fact, infants who
grow up in homes and communities with-
out pictured objects do not show the same
trajectory of understanding that pictures
are representations of real objects. In one
study, Canadian toddlers and preschool-
ers outstripped their peers from rural India
and Peru in their ability to match line draw-
ings of objects to toy objects (Callaghan et
al., 2011). Similarly, toddlers from rural
Tanzania, who had no prior exposure to pic-
tures, had greater difficulty than did North
American toddlers in generalizing the names
of objects in color photographs to the ob-
jects themselves (Walker, Walker, & Ganea,
2013). These studies suggest that under-
standing the relationship between 2D im-
ages and 3D objects requires experience
with pictorial media.
BOX 5.2: a closer look
: C
, 1
these 9-month-old infants—two from the
United States and two from West africa—are
responding to pictures of objects as if they
were real objects. they do not yet know the
true nature of pictures. (From DeLoache et
al., 1998)

Infants are adept at perceiving patterns in the streams of sound they hear. They
are remarkably proficient, for example, at detecting subtle differences in the sounds
of human speech, an ability we will review in detail in our discussion of language
development in Chapter 6. Here we will focus on another realm in which infants
display an impressive degree of auditory sensitivity—music.
Music Perception
Infants are sensitive to music, as shown by the fact that caregivers around the world
sing while caring for their infants (Trehub & Schellenberg, 1995). In the United
States, for example, 60% of parents sing or play music to their children every day
(Custodero, Britto, & Brooks-Gunn, 2003).
When adults sing to their infants, they do so in a characteristic fashion which,
like the infant-directed speech register we will discuss in Chapter 6 (pages 223–
224), tends to be slower and higher-pitched, and to suggest more positive af-
fect, than does singing directed toward adult listeners. Perhaps because of these
characteristics, infants prefer infant-directed singing over adult-directed singing
(Masataka, 1999; Trainor, 1996). Indeed, infant-directed singing even appears to
trump infant-directed speech as a preferred stimulus, as suggested by a study in
which 6-month-olds were more attentive to videos of their own mother singing
than to videos of her speaking (Nakata & Trehub, 2004).
Beyond their interest in music, infants are also able to remember what they
hear, recognizing musical excerpts several weeks after first being exposed to them
(Saffran, Loman, & Robertson, 2000; Trainor, Wu, & Tsang, 2004; Volkova,
Trehub, & Schellenberg, 2006). These memories are surprisingly detailed, and in-
clude aspects of the pitch, timbre, and tempo of the original performances. For ex-
ample, when 7-month-olds were tested on songs that they had heard in a particular
key two weeks earlier, they listened longer when the same songs were sung in a new
key than when they were sung in the original key (Volkova et al., 2006). This indi-
cates that infants not only discriminated between performances of the same song in
two different keys but also continued to remember the original key of the song two
weeks after they had last heard it sung.
In many ways, infant music perception is adultlike. One well-studied example is
the preference for consonant intervals (e.g., octaves, or perfect fifths like the open-
ing notes of the ABCs song) over dissonant intervals (e.g., augmented fourths like
the opening of “Maria” from the musical West Side Story, or minor seconds like the
theme from the film Jaws). From Pythagoras to Galileo to the present day, many
scientists and scholars have argued that consonant tones are inherently pleasing
to human ears, whereas dissonant tones are unpleasant (Schellenberg & Trehub,
1996; Trehub & Schellenberg, 1995). To see if infants agree, researchers employ a
simple but reliable procedure. They draw infants’ attention toward an audio speaker
by using a visually interesting stimulus (e.g., a flashing light) and then play music
through the speaker. The length of time infants look at the speaker (actually, at the
visual stimulus located in the same position as the speaker) is taken as a measure of
their interest in, or preference for, the music emanating from the speaker.
Studies have shown that infants pay more attention to a consonant version of a
piece of music, whether a folk song or a minuet, than to a dissonant one (Trainor
& Heinmiller, 1998; Zentner & Kagan, 1996, 1998). A study by Masataka revealed
that even 2-day-old infants show this pattern of preference (Masataka, 2006). This
study is particularly notable in that it was conducted with hearing infants whose
mothers were deaf, making it unlikely that the infants would have had prenatal

exposure to singing. These results suggest that preferences for consonant music as
opposed to dissonant music are not due to musical experience. Indeed, other spe-
cies (including chicks, macaque monkeys, and chimps) also show preferences for
consonant music, supporting the view that preferences for consonance over disso-
nance are unrelated to musical experience (e.g., Chiandetti & Vallortigara, 2011;
Sugimoto et al., 2010).
In certain other aspects of music perception, infants diverge markedly from
adult listeners. One of the most interesting differences is in the area of melodic
perception, in which infants can make perceptual discriminations that adults can-
not. In one set of studies, 8-month-old infants and adults listened to a brief repeat-
ing melody that was consistent with the harmonic conventions of Western music.
Then, in a series of test trials, they heard the melody again—but with one note
changed. On some trials, the changed note was in the same key as the melody; on
others, it fell outside the key. Both infants and adults noticed changes that violated
the key of the melody, but only the infants noticed the changes that stayed within
the key of the melody (Trainor & Trehub, 1992). Does this mean that infants are
more musically attuned than adults? Probably not. What appeared to be a height-
ened musical sensitivity in the infant participants was more likely a reflection of
their relative lack of implicit knowledge about Western music. Because it takes
years to acquire culture-specific familiarity with musical key structures, the within-
key and out-of-key changes were equally salient to the infant listeners (Trainor &
Trehub, 1994). For adults, years of hearing music makes it very difficult to detect
note changes that stay within a key.
In a similar way, infants are also more “sensitive” to aspects of musical rhythm than
adults are. Musical systems vary in the complexity of their rhythmic patterning; the
rhythms of Western music, for example, are relatively simple compared with those
of some cultures in Africa, India, and Europe. Hannon and Trehub (2005a, 2005b)
tested adults and 6-month-olds on their ability to detect meter-disrupting changes
in simple rhythms versus complex rhythms. Notably, some of the adults lived in the
Balkans, where the local music contains complex rhythmic patterns, and others lived
in North America, where popular music is characterized by simpler rhythmic pat-
terns. The results revealed that all groups detected changes in the simple rhythms,
but only the North American infants and the Balkan adults detected changes in
the complex rhythms. Thus, North American 6-month-olds outperformed North
American adults on this task. A follow-up study asked whether North American
12-month-olds and adults could be trained to detect such changes in the complex
rhythms. After 2 weeks of exposure to the Balkan rhythms, the 12-month-olds were
able to detect changes in complex rhythms, but the adults still failed to do so.
These examples from the musical domain suggest that, with experience, there
is a process of perceptual narrowing. Infants, who are relatively inexperienced with
music, can detect differences between musical stimuli that adults cannot. Develop-
mental changes in which experience fine-tunes the perceptual system are observed
across numerous domains. Indeed, you saw this process of perceptual narrowing in
our discussion of face perception in Box 5.1, and you will see the same pattern of
development when we examine intermodal aspects of speech perception (page 187)
and, quite prominently, when we take up language acquisition in Chapter 6. Across
all these examples and in other domains, experience leads the young learner to
begin to “lose” the ability to make distinctions that he or she could make at earlier
points in development. In each case, this perceptual narrowing permits the devel-
oping child to become especially attuned to patterns in biological and social stimuli
that are important in their environment.

Taste and Smell
As you learned in Chapter 2 (page 53), sensitivity to taste and smell develops be-
fore birth, and newborns prefer sweet flavors. Preferences for smells are also present
very early in life. Newborns prefer the smell of the natural food source for human
infants—breast milk (Marlier & Schaal, 2005). Smell plays a powerful role in how
a variety of infant mammals learn to recognize their mothers. It probably does the
same for humans, as shown by studies in which infants chose between the scent of
their own mother and that of another woman. A pad that an infant’s mother had
worn next to her breast was placed on one side of the infant’s head and a pad worn
by a different woman was placed on the other side. Two-week-old infants turned
more often and spent more time oriented to the pad infused with their mother’s
unique scent (MacFarlane, 1975; Porter et al., 1992).
Another important way that infants learn about the environ-
ment is through active touch, initially through their mouth and
tongue, and later with their hands and fingers. Oral exploration
dominates for the first few months, as infants mouth and suck
on their own fingers and toes, as well as virtually any object they
come into contact with. (This is why it is so important to keep
small, swallowable objects away from babies.) Through their ar-
dent oral exploration, babies presumably learn about their own
bodies (or at least the parts they can get their mouths on), as well
as about the texture, taste, and other properties of the objects
they encounter.
From around the age of 4 months, as infants gain greater con-
trol over their hand and arm movements, manual exploration
increases and gradually takes precedence over oral exploration.
Infants actively rub, finger, probe, and bang objects, and their ac-
tions become increasingly specific to the properties of the objects.
For example, they tend to rub textured objects and bang rigid
ones. Increasing manual control facilitates visual exploration in
that infants can hold interesting objects in order to examine them
more closely, rotating the objects to view them from different
angles and transferring them from hand to hand to get a better
view (Bushnell & Boudreau, 1991; Lockman & McHale, 1989;
Rochat, 1989; Ruff, 1986).
Intermodal Perception
Most events that both adults and infants experience involve simultaneous stimula-
tion through multiple sensory modalities. In the crystal-goblet-falling-on-tile-floor
event witnessed by Benjamin, the shattering glass provided both visual and audi-
tory stimulation. Through the phenomenon of intermodal perception, the com-
bining of information from two or more sensory systems, Ben’s parents perceived
the auditory and visual stimulation as a unitary, coherent event. It is likely that
4-month-old Ben did, too.
According to Piaget (1954), information from different sensory modalities is ini-
tially separate, and only after some months do infants become capable of forming
Initially, every object that a baby can pick
up gets directed to his or her mouth for oral
exploration—whether or not it will fit. Later,
infants are more inclined to explore objects
visually, thereby showing an interest in the
object itself.
intermodal perception n the com-
bining of information from two or more
sensory systems

associations between how things look and how they sound, taste, feel, and so on.
However, it has become abundantly clear that from very early on, infants inte-
grate information from different senses. Research has shown, for example, that very
young infants link their oral and visual experiences. In studies with newborns (Kaye
& Bower, 1994) and 1-month-olds (Meltzoff & Borton, 1979), infants sucked on
a pacifier that they were prevented from seeing. They were then shown a picture of
the pacifier that had been in their mouth and a picture of a novel pacifier of a dif-
ferent shape or texture. The infants looked longer at the pacifier they had sucked
on. Thus, these infants could visually recognize an object they had experienced only
through oral exploration.
When infants become capable of exploring objects manually, they readily inte-
grate their visual and tactile experience. In one study, for example, 4-month-olds
were allowed to hold and feel, but not see, a pair of rings that were connected by
either a rigid bar or a string. When the babies were shown both types of rings,
they recognized the ones they had previously explored with their hands (Streri &
Spelke, 1988).
Researchers have also discovered that infants possess a variety of forms of
auditory–visual intermodal perception. In studies of this mode of perception, in-
fants simultaneously view two different videos, side by side, while listening to a
soundtrack that is synchronized with one of the videos but not the other. If an infant
responds more to the video that goes with the soundtrack, it is taken as evidence
that the infant detects the common structure in the auditory and visual information.
In a classic study using this procedure, Spelke (1976) showed 4-month-olds two
videos, one of a person playing peekaboo and the other of a hand beating a drum-
stick against a block. The infants responded more to the film that matched the
sounds they were hearing. When they heard a voice saying “Peekaboo,” they looked
more at the person, but when they heard a beating sound, they looked longer at the
hand. In subsequent studies, infants showed finer discriminations. For example,
4-month-olds responded more to a film of a “hopping” toy animal in which the
sounds of impact coincided with the animal’s landing on a surface than they did to
a film in which the impact sounds occurred while the animal was in midair (Spelke,
1979). At this age, infants can also draw more abstract connections between sights
and sounds. For example, 3- to 4-month-olds look longer at visual displays in
which dimensions in each modality are congruent, such as a ball rising and falling
at the same rate as a whistle rising and falling in pitch (Walker et al., 2010).
Similar studies have found that infants are especially sensitive to the relation
between human faces and voices. Between 5 and 7 months of age, infants notice
the connection between emotional expressions in faces and voices (Soken & Pick,
1992; Walker-Andrews, 1997). When infants hear a happy voice, they look longer
at a smiling face, and they look longer at an angry face when they hear an angry
voice. Infants are also attuned to the match between faces producing speech and
the sounds of speech. When 4-month-olds are shown side-by-side films of a per-
son talking while they are listening to a soundtrack that matches one of the films,
they look longer at the face whose lip movements are synchronized with the speech
they hear (Spelke & Cortelyou, 1980; Walker-Andrews, 1997). Four-month-olds
even detect the relation between specific speech sounds, such as “a” and “i,” and the
specific lip movements associated with them (Kuhl & Meltzoff, 1982, 1984).
However, the processes of perceptual narrowing that we have noted elsewhere
also occur in intermodal perception. Young infants can detect correspondences
between speech sounds and facial movements for nonnative speech sounds (those
not present in their native language), but older infants cannot (Pons et al., 2009).
a setup like this one enables researchers to
study auditory–visual intermodal perception.
the two monitors display different films, one
of which is coordinated with a soundtrack.
the video camera records the infant’s
looking toward the two screens.
Child on mother’s lap
Hidden speaker

Similarly, young infants can detect the correspondence between monkey fa-
cial movements and monkey vocalizations, but older infants are unable to do so
(Lewkowicz & Ghazanfar, 2006). Experience thus fine-tunes the types of inter-
modal correspondences that infants detect.
Infants can do more than detect relationships between information across mo-
dalities: they can use information in one modality to interpret ambiguous infor-
mation in another modality. In an ingenious series of experiments, 7-month-olds
listened to a musical rhythm that was ambiguous and could be interpreted in either
duple or triple time (Phillips-Silver & Trainor, 2005). While infants were listening,
they were bounced up and down at a rate matching either a duple- or triple-time
interpretation of the ambiguous rhythm. When tested, infants preferred to listen to
the version of the rhythm that fit the pattern in which they were bouncing. These
results indicate that infants readily integrate vestibular information with auditory
information: how infants were bounced altered how infants interpreted what they
were hearing.
Using a variety of special techniques, developmental psychologists have discovered an enor-
mous amount about perceptual development in infancy. They have documented rapid de-
velopment of basic visual abilities from birth over the next few months, discovering that by
approximately 8 months of age infants’ visual acuity, scanning patterns, and color perception
are similar to those of adults. Some forms of depth perception are present at birth, whereas
others develop in the ensuing months. By 5 to 7 months of age, infants actively integrate
separate elements of visual displays to perceive coherent patterns. They use many sources of
information, including movement and their knowledge of their surroundings, for object seg-
regation. Faces are of particular interest to infant perceivers.
Research on auditory perception has shown that right from birth, babies turn toward
sounds they hear. They are quite sensitive to music and display some of the same musical
preferences adults do, such as a preference for consonance over dissonance. Infants also
show perceptual abilities for music that exceed those of adults, whose auditory processing
has been shaped by years of musical listening. Smell and touch both play an important role in
infants’ interaction with the world around them. The crucial ability to link what they perceive
in separate modalities to experience unitary, coherent events is present in a simple form at
birth, but more complex associations develop gradually.
There is much in recent research to encourage anyone of a nativist persuasion: neonates
show remarkable perceptual abilities that cannot be due to experience, even prenatal expe-
rience. At the same time, most perceptual skills also show development over time, much of
which clearly involves learning. Infants gradually become more adultlike in their perceptual
abilities through perceptual narrowing: as expertise increases (via learning) within and across
modalities, infants lose the ability to distinguish between less familiar sights and sounds,
becoming increasingly attuned to their native environment.
Motor Development
As you learned in Chapter 2, human movement starts well before birth, as the
fetus floats weightlessly in amniotic fluid. After birth, the newborn’s movements
are jerky and relatively uncoordinated, in part because of physical and neurological
immaturity and in part because the baby is experiencing the full effects of gravity
for the first time. As you will see in this section, the story of how the uncoordinated
newborn, a prisoner of gravity, becomes a competent toddler confidently exploring
the environment is remarkably complicated.

Newborns start off with some tightly organized patterns of action known as neona-
tal reflexes. Some reflexes, such as withdrawal from a painful stimulus, have clear
adaptive value; others have no known adaptive significance. In the grasping reflex,
newborns close their fingers around anything that presses against the palm of their
hand. When stroked on the cheek near their mouth, infants exhibit the rooting
reflex, turning their head in the direction of the touch and opening their mouth.
Thus, when their cheek comes into contact with their mother’s breast, they turn
toward the breast, opening their mouth as they do. Oral contact with the nipple
then sets off a sucking reflex, followed by the swallowing reflex, both of which in-
crease the baby’s chance of getting nourishment and ultimately of surviving. These
reflexes are not fully automatic; for example, a rooting reflex is more likely to occur
when an infant is hungry.
No benefit is known to be associated with other reflexes, such as the tonic neck
reflex: when an infant’s head turns or is turned to one side, the arm on that side of
the body extends, while the arm and knee on the other side flex. It is thought that
the tonic neck reflex involves an effort by the baby to get and keep its hand in view
(von Hofsten, 2004).
Neonatal reflexes: (a) Grasping
(c) Sucking
(b) rooting
(d) tonic neck reflex
/ P
/ R
/ T
reflexes n innate, fixed patterns of
action that occur in response to particular

The presence of strong reflexes at birth is a sign that the newborn’s central ner-
vous system is in good shape. Reflexes that are either unusually weak or unusu-
ally vigorous may signal brain damage. Most of the neonatal reflexes disappear on
a regular schedule, although some—including coughing, sneezing, blinking, and
withdrawing from pain—remain throughout life. Persistence of a neonatal reflex
beyond the point at which it is expected to disappear can indicate a neurological
Motor Milestones
Infants progress quickly in acquiring the basic movement patterns of our species,
shown in Figure 5.9. As you will see, the achievement of each of the major “motor
milestones” of infancy, especially walking, constitutes a major advance, and provides
new ways for infants to interact with the world.
The average ages that Figure 5.9 gives for the development of each of these
important motor skills are based on research with Western, primarily North
American, infants. There are, of course, tremendous individual differences in the
ages at which these milestones are achieved. Of particular interest is the fact that
the degree to which motor skills are encouraged varies from one culture to another,
and such variation can affect the course of motor development. Indeed, some cul-
tures actively discourage early locomotion. In modern urban China, for example,
infants are typically placed on beds and surrounded by thick pillows to keep them
from crawling on the dirty floor (Campos et al., 2000). These restrictions make it
difficult for infants to develop the muscle strength required to support their upper
trunk, which is necessary for crawling. Among the Aché, a nomadic people who
Age (in months)
f m
Prone, lifts head
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Prone, chest up, uses arms for support
Rolls over
Supports some weight with legs
Sits without support
Stands with support
Pulls self to stand
Walks using furniture for support
Stands alone easily
Walks alone easily
FIGURE 5.9 the major milestones
of motor development in infancy the
average age and range of ages for achieve-
ment of each milestone are shown. Note
that these age norms are based on research
with healthy, well-nourished North american

live in the rain forest of Paraguay, infants spend almost all of their first 3 years of
life being carried by their mothers or kept very close to her because of safety con-
cerns. These infants thus get relatively little opportunity early on to exercise their
locomotor skills (Kaplan & Dove, 1987).
In direct contrast, the Kipsigis people in rural Kenya actively encourage the
motor development of their infants; for example, they help their babies practice sit-
ting by propping them up in shallow holes dug in the ground to support their backs
(Super, 1976). Other groups, in West Africa and the West Indies, institute an ag-
gressive program of massage, manipulation, and stimulation designed to facilitate
their infants’ motor development (A. Gottlieb, 2004; Hopkins &
Westra, 1988).
These widely varying cultural practices can affect infants’ devel-
opment. Researchers have documented somewhat slower motor de-
velopment in Aché and Chinese infants compared with the norms
shown in Figure 5.9; Kipsigis babies and the infants who undergo
exercise regimes, on the other hand, are advanced in their motor-
skill development compared with North American infants. Even as-
pects of infant life that we take for granted in our own culture have
an effect on motor development. In a recent study, researchers asked
whether diapers—a relatively recent cultural invention—have an im-
pact on walking behavior (Cole, Lingeman, & Adolph, 2012; see
Figure 5.10). The researchers found that the same infants exhib-
ited more mature walking behavior when tested naked than when
tested diapered, despite the fact that these infants—all residents of
New York City—were accustomed to wearing diapers and had rarely
walked naked. These data beautifully demonstrate that cultural prac-
tices that are undertaken in one domain (toileting) can have unfore-
seen consequences in another domain (walking behavior).
Current Views of Motor Development
Impressed by the orderly acquisition of skills reflected in Figure 5.9, two early pio-
neers in the study of motor development, Arnold Gesell and Myrtle McGraw, con-
cluded that infants’ motor development is governed by brain maturation (Gesell &
Thompson, 1938; McGraw, 1943). In contrast, current theorists, many of whom
take a dynamic-systems approach (see Chapter 4, pages 161–167), emphasize that
early motor development results from a confluence of numerous factors that include
developing neural mechanisms, increases in infants’ strength, posture control, bal-
ance, and perceptual skills, as well as changes in body proportions and motivation
(Bertenthal & Clifton, 1998; Lockman & Thelen, 1993; von Hofsten, 2004). (Box
5.3 offers a detailed account of a program of research exemplifying this approach.)
Think for a moment about how each of these factors plays a part in infants’
gradual transition from newborns unable even to lift their head to toddlers who
walk independently, holding their upper body erect while coordinating the move-
ment of their legs that have grown strong enough to support their weight. Every
milestone in this transition is fueled by what infants can perceive of the external
world and their motivation to experience more of it. The vital role of motivation is
especially clear in infants’ determined efforts to attempt to walk when they can get
around much more efficiently by crawling. Most parents—and many researchers—
have the impression that infants derive pleasure from pushing the envelope of their
motor skills.
FIGURE 5.10 these images depict the
footprint paths for a single infant partici-
pant who was tested walking naked, wearing
lightweight disposable diapers, and wearing
bulkier cloth diapers. the most mature
walking behavior was seen in the left-most
path, in the absence of diapers (cole et al.,
Naked Diposable Cloth
: C

The Expanding World of the Infant
Infants’ mastery of each of the milestones shown in Figure 5.9 greatly expands their
world: there is more to see when they can sit up, more to explore when they can
reach for things themselves, and even more to discover when they can move about
on their own. In this section, we consider some of the ways that motor development
affects infants’ experience of the world.
The development of reaching sets off a minirevolution in the infant’s life: “once
infants can reach for and grasp objects, they no longer have to wait for the world
to come to them” (Bertenthal & Clifton, 1998). However, reaching takes time to
develop. That is because, as discussed in Chapter 4, this seemingly simple behav-
ior actually involves a complex interaction of multiple, independent components,
BOX 5.3: a closer look
One of the primary proponents of the
dynamic-systems point of view we dis-
cussed in Chapter 4 was Esther Thelen.
Early research by Thelen and her col-
leagues provides an excellent example of
this approach to investigating motor de-
velopment, as well as a good example of
how to formulate hypotheses and test them
in general. In one study, they held infants
under the arms and submerged them waist-
deep in water. As you read the following
paragraphs, see how soon you can figure
out the rationale for this somewhat strange-
sounding, but, in fact, extremely informa-
tive, experiment.
This particular study was one in a series
of investigations of what Thelen (1995) re-
ferred to as “the case of the disappearing
reflex.” The reflex in question, the stepping
reflex, can be elicited by holding a newborn
under the arms so that his or her feet touch
a surface; the baby will reflexively perform
stepping motions, lifting first one leg and
then the other in a coordinated pattern as
in walking. The reflex typically disappears
at around 2 months of age. It was long as-
sumed that the stepping reflex disappears
from the infant’s motor repertoire as a result
of cortical maturation.
However, the results of a classic study
by Zelazo, Zelazo, and Kolb (1972) were
inconsistent with this view. In that research,
2-month-old infants were given extra prac-
tice exercising their stepping reflex; as a
result, the infants continued to show the
reflex long after it would otherwise have
disappeared. Other research also showed
persistence of the stepping pattern long be-
yond 2 months of age. For one thing, the
rhythmical kicking that babies engage in
when they are lying down on their back in-
volves the same pattern of alternating leg
movement as stepping does. However, un-
like stepping, kicking continues through-
out infancy (Thelen & Fisher, 1982). For
another, when 7-month-olds (who neither
walk nor typically show the stepping reflex)
are supported on a moving treadmill, they
step smartly (Thelen, 1986). If the step-
ping reflex can be prolonged or elicited long
after it is supposedly scheduled to disap-
pear, cortical maturation cannot account
for its vanishing. Why then does it normally
A clue was provided by the observation
that chubbier babies generally begin walk-
ing (and crawling) somewhat later than do
slimmer ones. Thelen reasoned that in-
fants’ very rapid weight gain in the first few
weeks after birth may cause their legs to get
heavier faster than they get stronger. More
strength is needed to step while upright
than to kick while lying down, and more
is needed to lift a fat leg than a thin one.
Thus, Thelen hypothesized that the solution
to the mystery might have more to do with
brawn than with brains.
Thelen and her colleagues conducted
two elegant experiments to test this hy-
pothesis (Thelen, Fisher, & Ridley- Johnson,
1984). In one, the researchers put weights
on the ankles of very young infants who
still had a stepping reflex. The amount
of weight was roughly equivalent to the
amount of fat typically gained in the first
few months. When the weight was added,
the babies suddenly stopped stepping. In
the second study, older infants who no
longer showed a stepping reflex were sus-
pended waist-deep in a tank of water. As
predicted, the babies resumed stepping
when the buoyancy of the water supported
their weight. Thus, the scientific detective
work of these investigators established that
the normal disappearance of the stepping
reflex is not caused by cortical maturation,
as previously assumed. Rather, the move-
ment pattern (and its neural basis) remains
but is masked by the changing ratio of leg
weight to strength. Only by considering
multiple variables simultaneously was it
possible to solve the mystery of the disap-
pearing reflex.
stepping reflex n a neonatal reflex in
which an infant lifts first one leg and then
the other in a coordinated pattern like

including muscle development, postural control, development of various perceptual
and motor skills, and so on.
Initially, infants are limited to prereaching movements—clumsy swiping to-
ward the general vicinity of objects they see (von Hofsten, 1982). At around 3 to 4
months of age, they begin successfully reaching for objects, although their move-
ments are initially somewhat jerky and poorly controlled, and their grabs fail more
often than not.
Earlier, we noted that infants’ achievements in motor development pave the way
for new experiences and opportunities to learn. A particularly compelling example
comes from studies (described in Chapter 4) in which prereaching infants were
given Velcro-patched mittens and Velcro-patched toys that allowed them to pick
up objects (Needham, Barrett, & Peterman, 2002). The manual exploration of ob-
jects made possible by these “sticky mittens” led to the infants’ increased interest in
objects and the earlier emergence of their ability to reach independently for them.
Interestingly, a related study found that the effects of the “sticky mittens” interven-
tion extended beyond objects (Libertus & Needham, 2011). Improved ability to
interact with objects gives infants additional opportunities to learn about the social
world—namely, how people interact with objects. Such improvement also provides
infants with new ways to interact with caregivers through shared play with objects.
Together, these factors serve to increase infants’ interest in social partners.
At around 7 months, as infants gain the ability to sit independently, their reach-
ing becomes quite stable, and the trajectory of their reaches is consistently smooth
and straight to the target (Spencer et al., 2000; Thelen et al., 1993; von Hofsten,
1979, 1991). The achievement of stable sitting and reaching enables infants to en-
large their sphere of action, because they can now lean forward to capture objects
previously out of reach (Bertenthal & Clifton, 1998; Rochat & Goubet, 1995).
These increased opportunities for object exploration have ramifications for visual
perception. For example, consider the difficulty of perceiving 3D objects as whole
objects. By their very nature, the front portions of 3D objects block perception of
their back portions. Nevertheless, even without X-ray vision, adults readily fill in
the nonvisible portions of 3D objects and perceive them as solid volumes. It turns
out that having more experience manipulating objects helps infants to become bet-
ter at this process of 3D object completion. Infants with better sitting and manual
skills are better at perceiving complete 3D objects from a limited view than are
infants with weaker sitting and manual skills (Soska, Adolph, & Johnson, 2010).
These sources of evidence suggest that there is a great deal of interaction between
visual development and motor development. At the same time, infants can perform
quite well on some motor tasks in the absence of vision by using auditory or vestibu-
lar cues instead. For example, vision is not necessary for accurate reaching: infants
in a completely dark room can successfully nab an invisible object that is making a
sound (Clifton et al., 1991). In addition, when reaching for objects they can see, in-
fants rarely reach for ones that are too distant, suggesting that they have some sense
of how long their arms are (Bertenthal & Clifton, 1998).
With age and practice, infants’ reaching shows increasingly clear signs of
anticipation; for example, when reaching toward a large object, infants open
their fingers widely and adjust their hand to the orientation of the desired ob-
ject (Lockman, Ashmead, & Bushnell, 1984; Newell et al., 1989). Furthermore,
like an outfielder catching a fly ball, infants can make contact with a moving
object by anticipating its trajectory and aiming their reach slightly ahead of it
(Robin, Berthier, & Clifton, 1996; von Hofsten et al., 1998). Most impressive,
10-month-olds’ approach to an object is affected by what they intend to do after
prereaching movements n clumsy
swiping movements by young infants
toward the general vicinity of objects
they see

they get their hands on it. Like adults, they reach faster for an object that they
plan to throw than for one they plan to use in a more precise fashion (Claxton,
Keen, & McCarty, 2003). However, as Figure 5.11 illustrates, infants’ anticipa-
tion skills remain quite limited for some time.
At around 8 months of age, infants become capable for the first time in their lives
of self- locomotion, that is, of moving around in the environment on their own. No
longer limited to being only where someone else carries or puts them, their world
must seem vastly larger to them.
Infants’ first success at moving forward under their own power typically takes
the form of crawling. (Box 5.4 describes a recent increase in variability in the
Van Gogh’s painting First Steps may have
been inspired by the joy that most parents
feel at seeing their baby walk alone for the
first time and the joy the baby feels taking
those first steps. TH
/ A
FIGURE 5.11 this right-handed
14-month-old—a participant in research
by rachel Keen and colleagues—is having
a hard time getting the applesauce he has
been offered into his mouth. as the photo
on the left shows, he has been presented
the spoon with its handle to his left, but he
has grabbed it with his dominant right hand,
which makes it extremely difficult to keep
the spoon upright on its way to his mouth. a
spill ensued.
self-locomotion n the ability to move
oneself around in the environment

onset of crawling.) Many (perhaps most) infants begin by belly crawling or using
other idiosyncratic patterns of self-propulsion, one of which researchers refer to
as the “inchworm belly-flop” style (Adolph, Vereijken, & Denny, 1998). Most
belly crawlers then shift to hands-and-knees crawling, which is less effortful and
faster. Other styles of crawling also have colorful names: bear crawls, crab crawls,
spider crawls, commando crawls, and bum shuffles (Adolph & Robinson, 2013).
The broader point is that infants are remarkably good at finding ways to get
around prior to their being able to walk.
When infants first begin walking independently, at around 11 to 12 months,
they keep their feet relatively wide apart, which increases their base of support;
they flex slightly at the hip and knee, thereby lowering their center of gravity;
they keep their hands in the air to facilitate balance; and they have both feet on
the ground 60% of the time (as opposed to only 20% for adults) (Bertenthal &
Clifton, 1998). As they grow stronger and gain experience, their steps become
longer, straighter, and more consistent. Practice is vital to infants’ gradual mas-
tery over their initially weak muscles and precarious balance (Adolph, Vereikjen,
& Shrout, 2003). And practice they do: Adolph and colleagues (2012) found that
their sample of 12- to 19-month-olds in New York City averaged 2,368 steps
(and 17 falls) per hour!
The everyday life of the newly mobile crawler or walker is replete with chal-
lenges to locomotion—slippery floors, spongy carpets, paths cluttered with objects
and obstacles, stairs, sloping lawns, and so on. Infants must constantly evaluate
whether their developing skills are adequate to enable them to travel from one
point to another. Eleanor Gibson and her colleagues found that infants adjust
their mode of locomotion according to their perception of the properties of the
surface they want to traverse (Gibson et al., 1987; Gibson & Schmuckler, 1989).
For example, an infant who had promptly walked across a rigid plywood walkway
would prudently revert to crawling in order to get across a water bed. Box 5.5
summarizes a program of research on the early development of locomotion and
In the late 1990s, pediatricians noticed a
surprising increase in the number of visits
they received from parents worried because
their infants either began crawling quite
late or never crawled at all. Many babies
had simply gone from sitting to walking.
The cause for this genuine secular
change in motor development seems to be
traceable to the campaign, described in
Box 2.4 (page 61), to get parents to put
their babies to sleep on their backs (Davis
et al., 1998). As we discussed in Chapter
2, this public health effort has been very
successful in changing parents’ behavior
and has resulted in a remarkable reduction
in the incidence of sudden infant death
syndrome. However, it appears that regu-
larly lying on their backs makes infants less
likely to turn over on schedule. One source
of this effect may be motivational: the bet-
ter view of the environment that they have
on their backs may lessen infants’ motiva-
tion to roll over onto their stomachs, where
the view is quite restricted. But, spending
less time on their tummies, the babies have
less opportunity to discover that they can
propel themselves forward by squirming.
With less practice pushing themselves up
from lying on their stomachs, the infants’
arm strength may develop somewhat more
In any event, the research is reassuring:
when observed at 18 months, there was no
developmental difference between infants
who had crawled on schedule and those
who had not.
BOX 5.4: applications

other forms of motor behavior in infancy, focusing specifically on the integration
of perception and locomotion.
The challenge that young children experience in integrating perceptual in-
formation in the planning and execution of actions sometimes results in quite
surprising behaviors, especially when children fail to meet the challenge. A par-
ticularly dramatic example of failure in the integration of perception and action is
provided by scale errors (Brownell, Zerwas, & Ramani, 2007; DeLoache, Uttal,
The interdependence of different develop-
mental domains is beautifully illustrated
by a rich and fascinating series of experi-
ments conducted over five decades. This
work started with a landmark study by El-
eanor Gibson and Richard Walk (1960) that
addressed the question of whether infants
can perceive depth. It has culminated in
research linking depth perception, locomo-
tion, cognitive abilities, emotion, and the so-
cial context of development.
To answer the depth-perception question,
Gibson and Walk used an apparatus known
as the “visual cliff.” As the photo shows,
the visual cliff consists of a thick sheet of
plexiglass that can support the weight of an
infant or toddler. A platform across the mid-
dle divides the apparatus into two sides. A
checked pattern right under the glass on one
side makes it look like a solid, safe surface.
On the other side, the same pattern is far
beneath the glass, and the contrast in the
apparent size of the checks makes it look
as though there is a dangerous drop-off—a
“cliff”—between the two sides.
Gibson and Walk reported that 6- to
14-month-old infants would readily cross
the shallow side of the visual cliff. They
would not, however, cross the deep side,
even when a parent was beckoning to them
to come across it. The infants were appar-
ently unwilling to venture over what looked
like a precipice—strong evidence that they
perceived and understood the significance
of the depth cue of relative size.
Karen Adolph, who had been a student
of Gibson, has conducted extensive re-
search on the relation between perception
and action in infancy. Adolph and her col-
leagues have discovered surprising discon-
tinuities in infants’ learning what they can
and cannot accomplish with their develop-
ing locomotor and postural skills (Adolph,
1997, 2000; Adolph, Eppler, & Gibson,
1993; Adolph et al., 2003; Eppler, Adolph,
& Weiner, 1996). This research exempli-
fies our theme of mechanisms of change, in
which variation and selection produce de-
velopmental change.
As a way of studying the relation between
early motor abilities and judgment, the in-
vestigators asked parents to try to entice
their infants to lean over or crawl across
gaps of varying widths in an elevated surface
or to crawl or walk down sloping walkways
that varied in how steep they were. Some
of these tasks were possible for a given in-
fant; the baby would have no trouble, for
example, negotiating a slope of a particular
steepness. Others, however, were impossi-
ble for that infant. Would the babies identify
which tasks were which? (An experimenter
always hovered nearby to catch any infant
who misjudged his or her prowess.)
The photos on the next page show how
infants behaved on slopes when beckoned
by an adult (usually their mother). In their
first weeks of crawling, infants (averaging
around 8½ months in age) unhesitatingly
and competently went down shallow slopes.
Confronted with slopes that were too steep
to crawl down, the babies typically paused
for a moment, but then launched themselves
headfirst anyway (requiring the experimenter
to catch hold of them). With more weeks of
crawling practice, the babies got better at
judging when a slope was simply too steep
and should be avoided. They also improved
at devising strategies to get down somewhat
steep slopes, such as turning around and
cautiously inching backward down the slope.
BOX 5.5: a closer look
are close to being able to make it down a
relatively steep walkway can be rather eas-
ily discouraged from trying to do so by their
mother telling them, “No! Stop!” Con-
versely, enthusiastic encouragement from
a parent can lead an inexperienced crawler
or walker to attempt a currently too-steep
slope. Thus, the child uses both perceptual
and social information in deciding what to
do. In this case, the information is obtained
through social referencing, the child’s use of
another person’s emotional response to an
uncertain situation to decide how to behave
(see Chapter 10, page 417).
A key finding of Adolph’s research is that
infants have to learn from experience what
they can and cannot do with respect to each
new motor skill that they master. Just like
the new crawlers and walkers who literally
this infant is refusing to cross the deep side
of the visual cliff, even though his mother
is calling and beckoning to him from the
other side. CO
. C

, B
scale error n the attempt by a young
child to perform an action on a miniature
object that is impossible due to the large
discrepancy in the relative sizes of the
child and the object

However, when the infants started walking,
they again misjudged which slopes they could
get down using their new mode of locomotion
and tried to walk down slopes that were too
steep for them. In other words, they failed to
transfer what they had learned about crawl-
ing down slopes to walking down them. Thus,
infants apparently have to learn through ex-
perience how to integrate perceptual infor-
mation with each new motor behavior they
develop. With experience comes increased
flexibility, allowing access to multiple strat-
egies for solving previously intractable
problems, including laboratory-created chal-
lenges such as descending impossibly steep
slopes or crossing narrow bridges with wobbly
handrails (Adolph & Robinson, 2013).
Infants’ decisions in such situations also
depend on social information. Infants who
are close to being able to make it down a
relatively steep walkway can be rather eas-
ily discouraged from trying to do so by their
mother telling them, “No! Stop!” Con-
versely, enthusiastic encouragement from
a parent can lead an inexperienced crawler
or walker to attempt a currently too-steep
slope. Thus, the child uses both perceptual
and social information in deciding what to
do. In this case, the information is obtained
through social referencing, the child’s use of
another person’s emotional response to an
uncertain situation to decide how to behave
(see Chapter 10, page 417).
A key finding of Adolph’s research is that
infants have to learn from experience what
they can and cannot do with respect to each
new motor skill that they master. Just like
the new crawlers and walkers who literally
plunge ahead when put atop a sloping
walkway, an infant who has just developed
the ability to sit will lean too far out over
a gap in a platform in an attempt to snag
an out-of-reach toy and would fall over the
edge if not for the ever-present reseacher–
catcher. And, like the experienced crawlers
and walkers who pause to make a prudent
judgment about whether or not to try a
descent, an infant who has been capable
of sitting unsupported for some time can
judge whether the gap is too wide to lean
across and will stay put if it appears to be
so. These highly consistent findings across
a variety of motor skills have made a very
important contribution to our understanding
of how infants learn to interact successfully
with their environment.
Integrating perceptual information with new motor skills. researcher
Karen adolph will need to rescue the newly crawling young infant
on the left, who does not realize that this slope is too steep for her
current level of crawling expertise. In contrast, the experienced walker
on the right is judiciously deciding that the slope is too steep for him
to walk down.
: C
& Rosengren, 2004; Ware et al., 2006). In this kind of error, very young children
try to do something with a miniature replica object that is far too small for the
action to be at all possible. Toddlers will attempt, in all seriousness, to sit in a tiny,
dollhouse-sized chair or to get into a small toy car (see Figure 5.12). In commit-
ting a scale error, the child momentarily fails to take into account the relation
between his or her own body and the size of the target object. These errors are
hypothesized to result from a failure to integrate visual information represented

in two different areas of the brain in the service of action. With development, the
incidence of scale errors diminishes, although even adults make a variety of action
errors (e.g., putting a cup of water into the cupboard instead of the microwave or
trying to squeeze into a too tight pair of pants).
Typically developing infants display a similar sequence of milestones in the development of
motor behavior, starting with a common set of neonatal reflexes. Although the timing of these
milestones may differ across infants, and is affected by cultural differences, their order rarely
varies. Researchers emphasize the pervasive interconnectedness between infants’ motor be-
havior, perception, and motivation, as well as the many ways that infants’ experience of the
world changes as motor skills improve. In the development of self-locomotion (crawling, walk-
ing), infants adopt a variety of different movement patterns and strategies to get around and
to cope with different environmental challenges. With experience, infants begin to develop
the crucial ability to make accurate judgments about what actions they are and are not ca-
pable of performing.
Who do you think learned more today—you or a 10-month-old infant? We’d bet
on the baby, just because there is so much that is new to an infant. Think back to
baby Benjamin in the kitchen with his parents. A wealth of learning opportunities
was embedded in that everyday scene. Benjamin was, for example, gaining experi-
ence with some of the differences between animate and inanimate entities, with the
particular sights and sounds that occur together in events, with the consequences of
objects’ losing support (including the effect of this event on his parents’ emotional
state), and so on. He also experienced consequences of his own behavior, such as
his parents’ response to his crying.
In this section, we review seven different types of learning by which infants
profit from their experience and acquire knowledge of the world. Some of the
questions that developmental psychologists have addressed with respect to infants’
learning include at what age the different forms of learning appear and in what
ways learning in infancy is related to later cognitive abilities. Another important
question concerns the extent to which infants find some things easier or more dif-
ficult to learn. The learning abilities described below are implicated in developmen-
tal achievements across every domain of human functioning, from visual perception
to social skills. It is thus impossible to think about development without consid-
ering the nature of the learning mechanisms that support developmental change.
FIGURE 5.12 Scale errors these three
children are making scale errors, treating a
miniature object as if it were a much larger
one. the girl on the left has just fallen off
the toy slide she was trying to go down; the
boy in the middle is persistently trying to
get into a very small car; and the boy on
the right is attempting to sit in a miniature
chair. (From DeLoache et al., 2004)

The simplest form of learning is recognizing
something that has been experienced before. As
we discussed in Chapter 2 and again earlier in
this chapter, babies—like everybody else—tend
to respond relatively less to stimuli they have
previously experienced, and relatively more to
novel stimuli (see Figure 5.13). The occurrence
of habituation in response to repeated stimula-
tion reveals that learning has taken place; the
infant has formed a memory representation of
the repeated, and now familiar, stimulus. Habit-
uation is highly adaptive: diminished attention
to what is familiar enables infants to pay atten-
tion to, and learn about, what is new.
The speed with which an infant habituates
is believed to reflect the general efficiency of
the infant’s processing of information. Related
measures of attention, including duration of
looking and degree of novelty preference, also
indicate speed and efficiency of processing. A
substantial and surprising degree of continu-
ity has been found between these measures in
infancy and general cognitive ability later in
life. Infants who habituate relatively rapidly,
who take relatively short looks at visual stim-
uli, and/or who show a greater preference for
novelty tend to have higher IQs when tested
as much as 18 years later (Colombo et al.,
2004; Rose & Feldman, 1997). Thus, habitua-
tion, one of the earliest and simplest forms of
human learning, is fundamental to basic cog-
nitive development.
Perceptual Learning
From their first moments of life, infants actively search for order and regularity
in the world around them, and they learn a great deal from simply paying close
attention to the objects and events they perceive. According to Eleanor Gibson
(1988), the key process in perceptual learning is differentiation—extracting from
the events in the environment the relation between those elements that are con-
stant. For example, infants learn the association between tone of voice and facial
expression because, in their experience, a pleasant, happy, or eagerly excited tone of
voice occurs with a smiling face—not a frowning one—and a harsh, angry tone of
voice occurs with a frowning face—not a smiling one.
A particularly important part of perceptual learning is the infant’s discovery of
affordances—that is, the possibilities for action offered, or afforded, by objects and
situations (Gibson, 1988). They discover, for example, that small objects—but not
large ones—afford the possibility of being picked up, that liquid affords the possibil-
ity of being poured and spilled, that chairs of a certain size afford the possibility of
FIGURE 5.13 habituation this 3-month-old pro-
vides a vivid demonstration of habituation. She is
seated in front of a screen on which photographs
are displayed. at the first appearance of a photo of
a face, her eyes widen and she stares intently at it.
With three more presentations of the same picture,
her interest wanes and a yawn appears. By its fifth
appearance, other things are attracting the baby’s
attention, and by the sixth even her dress is more
interesting. When a new face finally appears, her
interest in something novel is evident. (From Maurer
& Maurer, 1988)
: C
differentiation n the extraction from the
constantly changing stimulation in the
environment of those elements that are
invariant, or stable
affordances n the possibilities for
action offered by objects and situations

being sat on, and so forth. Infants discover affordances
by figuring out the relations between their own bodies
and abilities and the things around them. As we dis-
cussed earlier, for example, infants learn that solid, flat
surfaces afford stable walking, whereas squishy, slick, or
steeply sloping ones do not (e.g., Adolph, 2008).
Perceptual learning underlies the development of
some, but not all, aspects of intermodal perception. As
we noted previously, learning is not required to detect
an event involving sight and sound as unitary; thus,
baby Benjamin naturally perceives a single, coherent
event the first time he sees and hears a crystal goblet
crashing on the floor. However, one does have to learn
what particular sights and sounds go together, so only
through experience does Ben know that a particular
tinkling sound means a glass is being broken. As you
have seen, young infants are sensitive early on to the synchrony of lip movements
and vocal sounds, but they have to learn to relate the unique sight of their mother’s
face with the unique sound of her voice, which they accomplish by 3½ months of
age (Spelke & Owsley, 1979). The necessity for perceptual learning is especially
clear with regard to events that involve arbitrary relations, such as an association
between the color of a cup and the taste of the food inside. The fact that 7-month-
olds can be taught color–taste associations in the lab (Reardon & Bushnell, 1988)
would come as no surprise to those parents whose infants clamp their mouths shut
at the sight of a spoon conveying anything green.
Statistical Learning
A related type of learning also involves simply picking up information from the en-
vironment, specifically, detecting statistically predictable patterns (Aslin, Saffran, &
Newport, 1998; Kirkham, Slemmer, & Johnson, 2002; Saffran, Aslin, & Newport,
1996). Our natural environment contains a high degree of regularity and redun-
dancy; certain events occur in a predictable order, certain objects appear at the same
time and place, and so on. A common example for a baby is the regularity with
which the sound of Mom’s voice is followed by the appearance of her face.
From quite early on, infants are highly sensitive to the regularity with which
one event follows another. In one study, 2- to 8-month-olds were habituated to six
simple visual shapes that were presented one after another with specified levels of
probability (Kirkham et al., 2002). For example, three pairs of colored shapes al-
ways occurred together in the same order (e.g., a square was always followed by a
cross), but the next stimulus could be any of three different shapes (e.g., a cross was
followed by a circle, triangle, or square equally often). Thus, the probability that
the cross would follow the square was 100%, but the probability that the circle (or
triangle or square) would follow the cross was 33%. In a test, the order of appear-
ance of one or more of the shapes was changed. The infants looked longer when
the structure inherent in the initial set was violated (e.g., square followed by circle).
Statistical learning abilities have been measured across numerous domains, in-
cluding music, action, and speech (Roseberry et al., 2011; Saffran & Griepentrog,
2001; Saffran et al., 1996). Even newborn infants track statistical regularities in
these domains, suggesting that statistical learning mechanisms are available at birth
if not before (Bulf, Johnson, & Valenza, 2011; Kudo et al., 2011; Teinonen et al.,
the objects surrounding this baby offer a
variety of affordances. Some can be picked
up, but others are too big for the infant’s
small hands or too heavy for her limited
strength. the rattle makes noise when
shaken, the piano, when banged. Small
objects can be inserted into the yellow con-
tainer, but larger ones won’t fit. the stuffed
toy can be enjoyably cuddled, but not the
telephone. through interacting with the
world around them, infants discover these
and many other types of affordances.

2009). Finally, statistical learning has been proposed to be of vital importance in
language learning, as we will discuss in Chapter 6.
Several recent studies suggest that infants prefer to attend to certain types of sta-
tistical patterns over others. In particular, they appear to prefer patterns that have
some variability over patterns that are very simple (perfectly predictable) or very
complex (random) (Gerken, Balcomb, & Minton, 2011; Kidd et al., 2012). This
“Goldilocks effect”—avoiding patterns that are either too easy or too hard, while
continuing to focus on those that are just right, given the infant’s learning abilities—
suggests that infants allocate attention differently to different learning problems,
preferentially attending to those patterns that are the most informative.
Classical Conditioning
Another type of learning, classical conditioning, was first discovered by Ivan
Pavlov in his famous research with dogs (who learned an association between the
sound of a bell and the arrival of food and gradually came to salivate at the sound
of the bell alone). Classical conditioning plays a role in infants’ everyday learning
about the relations between environmental events that have relevance for them.
Consider young babies’ mealtimes, which occur frequently and have a predictable
structure. A breast or bottle contacts the infant’s mouth, eliciting the sucking reflex.
The sucking causes milk to flow into the infant’s mouth, and the infant experiences
the pleasurable sensations of a delicious taste and the satisfaction of hunger. Learn-
ing is revealed when an infant’s sucking motions begin to occur at the mere sight
of the bottle or breast.
In terms of classical conditioning, the nipple in the infant’s mouth is an
unconditioned stimulus (UCS) that reliably elicits a reflexive, unlearned
response—in this case, the sucking reflex—the unconditioned response (UCR).
Learning, or conditioning, occurs when an initially neutral stimulus—the breast
or bottle, which is the conditioned stimulus (CS)—repeatedly occurs just before
the unconditioned stimulus (the baby sees the breast or bottle before receiving the
nipple). Gradually, the originally reflexive response becomes a learned behavior, or
conditioned response (CR), triggered by exposure to the CS (anticipatory sucking
movements now begin as soon as the baby sees the breast or bottle). In other words,
the sight of the bottle or breast has become a signal of what will follow. Gradually,
the infant may also come to associate caregivers with the entire sequence, including
the pleasurable feelings that result from feeding. If so, these feelings could eventu-
ally be evoked simply by the presence of a caregiver. It is thought that many emo-
tional responses are initially learned through classical conditioning.
Instrumental Conditioning
A key form of learning for infants (and everyone else) is learning the consequences
of one’s own behavior. In everyday life, infants learn that shaking a rattle produces
an interesting sound, that cooing at Dad gets him to coo back, and that explor-
ing the dirt in a potted plant leads to a parental reprimand. This kind of learn-
ing, referred to as instrumental conditioning (or operant conditioning), involves
learning the relationship between one’s own behavior and the reward or punish-
ment it results in. Most research on instrumental conditioning in infants involves
positive reinforcement, that is, a reward that reliably follows a behavior and in-
creases the likelihood that the behavior will be repeated. Such research features
a contingency relation between the infant’s behavior and the reward: if the infant
classical conditioning n a form of
learning that consists of associating an
initially neutral stimulus with a stimulus
that always evokes a particular reflexive
unconditioned stimulus (UCS) n in
classical conditioning, a stimulus that
evokes a reflexive response
unconditioned response (UCR) n
in classical conditioning, a reflexive
response that is elicited by the uncondi-
tioned stimulus
conditioned stimulus (CS) n in clas-
sical conditioning, the neutral stimulus
that is repeatedly paired with the uncon-
ditioned stimulus
conditioned response (CR) n in clas-
sical conditioning, the originally reflexive
response that comes to be elicited by the
conditioned stimulus
instrumental (or operant) condi-
tioning n learning the relation between
one’s own behavior and the consequences
that result from it
positive reinforcement n a reward that
reliably follows a behavior and increases
the likelihood that the behavior will be

makes the target response, then he or she receives the reinforcement.
Table 5.1 shows a few examples of the great variety of ingenious situa-
tions that researchers have engineered in order to examine instrumental
learning in infants.
Carolyn Rovee-Collier (1997) developed an instrumental-
conditioning procedure for studying learning and memory in young
infants. In this method, experimenters tie a ribbon around a baby’s
ankle and connect it to a mobile hanging above the infant’s crib (Fig-
ure 5.14). In the course of naturally kicking their legs, infants as
young as 2 months of age quickly learn the relation between their leg
movements and the enjoyable sight of the jiggling mobile. They then
quite deliberately and often joyfully increase their rate of foot kick-
ing. The interesting mobile movement thus serves as reinforcement
for the kicking. An additional feature of this procedure is that the
intensity of the reward—the amount of movement of the mobile—
depends on the intensity of the baby’s behavior. This task has been
used extensively to investigate age-related changes in how long, and
under what circumstances, infants continue to remember that kick-
ing will activate the mobile (e.g., Rovee-Collier, 1999). Among the
findings: (1) 3-month-olds remember the kicking response for about
1 week, whereas 6-month-olds remember it for 2 weeks; (2) infants
younger than about 6 months of age remember the kicking response
only when the test mobile is identical to the training mobile, whereas
older infants remember it with novel mobiles.
Infants’ intense motivation to explore and master their environ-
ment, which we have emphasized in our active child theme, shows up
in instrumental-learning situations: infants work hard at learning to
predict and control their experience, and once control has been estab-
lished, they dislike losing it. Infants as young as 2 months old display
facial expressions of joy and interest while learning a contingency rela-
tion, and display expressions of anger when a learned response no lon-
ger produces the expected results (Lewis, Alessandri, & Sullivan, 1990;
Sullivan, Lewis, & Alessandri, 1992). In one study, for example, seven
out of eight newborns cried when they failed to receive the sweet liq-
uid they had learned would follow a head-turn response (Blass, 1990).
Infants may also learn that there are situations over which they have no con-
trol. For example, infants of depressed mothers tend to smile less and show lower
levels of positive affect than do infants whose mothers are not depressed. In part,
this may be because infants of depressed mothers learn that their smiling is rarely
rewarded by their preoccupied parent (Campbell, Cohn, & Meyers, 1995). More
generally, through contingency situations, whether in a lab or an everyday setting,
infants learn more than just the particular contingency relations to which they are
exposed. They also learn about the relation between themselves and the world and
the extent to which they can have an impact on it.
Observational Learning/Imitation
A particularly potent source of infants’ learning is their observation of other peo-
ple’s behaviors. Parents, who are often amused and sometimes embarrassed by their
toddler’s reproduction of their own behavior, are well aware that their offspring
learn a great deal through simple observation.
Studying Instrumental conditioning in Infants
Age Group Learned Response Reinforcement
Newborns Head turn to side Drink of sucrose water
3 weeks Sucking pattern Interesting visual display
5–12 weeks Sucking pattern Keep a movie in focus
6 months Push a lever Cause a toy train to
move along a track
Source: Bruner, 1973; Hartshorn & Rovee-Collier, 1997; Siqueland & DeLucia,
1969; Siqueland & Lipsitt, 1966
FIGURE 5.14 contingency this young
infant learned within minutes that kicking
her leg would cause the mobile to move in
an interesting way; she learned the con-
tingency between her own behavior and an
external event.

The ability to imitate the behavior of other people appears to be present very
early in life, albeit in an extremely limited form. Meltzoff and Moore (1977, 1983)
found that after newborns watch an adult model slowly and repeatedly stick out his
or her tongue, they often stick out their own tongue. By the age of 6 months, infant
imitation is quite robust. Six-month-old infants not only imitate tongue protru-
sion, but they also attempt to poke their tongue out to the side when that is what
they have seen an adult do (Meltzoff & Moore, 1994). From this age on, the scope
of infant imitation expands. Infants begin to imitate novel, and sometimes quite
strange, actions they have seen performed on objects. In one such study, infants ob-
served an experimenter performing unusual behaviors with objects, such as leaning
over from the waist to touch his or her forehead to a box, causing the box to light
up. The infants were later presented with the same objects the experimenter had
acted on. Infants as young as 6 to 9 months imitated some of the novel actions they
witnessed, even after a delay of 24 hours (Barr, Dowden, & Hayne, 1996; Bauer,
2002; Hayne, Barr, & Herbert, 2003; Meltzoff, 1988b). Fourteen-month-olds imi-
tated such actions a full week after first seeing them (Meltzoff, 1988a).
In choosing to imitate a model, infants seem to analyze the reason for the per-
son’s behavior. If infants see a model lean over and touch a box with her forehead,
they later do the same. If, however, the model remarks that she’s cold and tightly
clutches a shawl around her body as she leans over and touches a box with her
forehead, infants reach out and touch the box with their hand instead of their
head (Gergely, Bekkering, & Kiraly, 2002). They apparently reason that the model
wanted to touch the box and would have done so in a standard way if her hands
had been free. Their imitation is thus based on their analysis of the person’s inten-
tions. In general, infants are flexible in learning through imitation: as in the case of
touching the box, they can copy either the specific behavior through which a model
achieves a goal, or they can employ different behaviors to achieve the same goal the
model achieved (Buttelmann et al., 2008).
Further evidence of infants’ attention to intention comes from research in which
18-month-olds observed an adult attempting, but failing, to pull apart a small
dumbbell toy (Meltzoff, 1995a). The adult pulled on the two ends, but his hand
“slipped off,” and the dumbbell remained in one piece (Figure 5.15a). When the
infants were subsequently given the toy, they pulled the two ends apart, imitating
what the adult had intended to do, not what he had actually done. This research
also established that infants’ imitative actions are limited to human acts. A differ-
ent group of 18-month-olds watched a mechanical device with pincers grasp the
two ends of the dumbbell. The pincers either pulled apart the dumbbell or slipped
off the ends (Figure 5.15b). Regardless of what the infants had seen the mechani-
cal device do, they rarely attempted to pull apart the dumbbell themselves. Thus,
infants attempt to reproduce the behavior and intentions of other people, but not
of inanimate objects.
FIGURE 5.15 Imitating intentions
(a) When 18-month-olds see a person
ap parently try, but fail, to pull the ends off
a dumbbell, they imitate pulling the ends
off—the action the person intended to do,
not what the person actually did. (b) they
do not imitate a mechanical device at all.
(From Meltzoff, 1995a)

Babies are by no means restricted to learning from the behavior of live adult
models. Infants as young as 15 months of age imitate actions they have seen an
adult perform on a video screen (Barr & Hayne, 1999; Meltzoff, 1988a). Peers
can also serve as models for young toddlers, as demonstrated by a study in which
well-trained 14-month-old “expert peers” performed novel actions (e.g., pushing a
button hidden inside a box to sound a buzzer) for their age-mates, either at their
preschool or in a laboratory (Hanna & Meltzoff, 1993). When the observer chil-
dren were tested in their own homes 48 hours later, they imitated what they had
seen the child model do earlier.
Current research is focused on the neural underpinnings of imitative learning.
One area that has received a good deal of attention as a potential locus for imita-
tion involves the so-called mirror neuron system, which was first identified in the
ventral premotor cortex in nonhuman primates (e.g., Gallese et al., 1996; Rizzolatti
& Craighero, 2004). In research with macaque monkeys, this system becomes ac-
tivated when the monkey engages in an action; it also is activated when the ma-
caque merely observes another monkey (or a human) engage in an action, as though
the macaque itself were engaging in the same action—hence, the name “mirror”
neuron system. (Mirror neurons were discovered when neuroscientists who were
monitoring the brain activity of a monkey noticed that when the monkey hap-
pened to see a lab assistant raising an ice cream cone to his mouth, neurons in the
monkey’s premotor cortex began firing as though the monkey were about to eat
the ice cream cone.)
The degree to which the same system is present in humans, as well as what be-
havioral domains it might affect, if any at all, is an area of hot debate. Researchers
have, however, begun to discover patterns of infant brain activity that are consis-
tent with the hypothesis that mirror neurons are present—namely, patterns of neu-
ral firing when infants are observing an action that is similar to those they display
when they are performing the same action (Marshall & Meltzoff, 2011). Future
studies using neuroscientific techniques should be informative about the roots of
imitation, identifying what infants are actually encoding as they observe the actions
of others, and how that perceptual information is transformed into self-action.
Rational Learning
As adults, we have many beliefs about the world, and we are usually surprised when
the world violates our expectations based on those beliefs. We can then adjust our
expectations based on the new information we have just received. For example, you
can infer from prior meals at your favorite Chinese restaurant that it will be serving
Chinese food the next time you go there, and your expectations would be violated if
the restaurant turned out to be serving Mexican food on your next visit. You would
then, however, update your expectations about the nature of the cuisine at this es-
tablishment. Indeed, scientific reasoning is based on precisely this sort of inference
from prior data—for example, using data drawn from a sample of a particular pop-
ulation to make predictions about that population. Infants, too, can use prior expe-
rience to generate expectations about what will happen next. This is called rational
learning because it involves integrating the learner’s prior beliefs and biases with
what actually occurs in the environment (Xu & Kushnir, 2013).
In an elegant study, Xu & Garcia (2008) demonstrated that 8-month-olds could
make predictions about simple events. Infants were shown a box containing 75
ping-pong balls; 70 were red and 5 were white. The infants then observed an ex-
perimenter close her eyes (to suggest a random selection) and draw 5 balls from the
rational learning n the ability to use
prior experiences to predict what will
occur in the future

box—either 4 red and 1 white or 4 white and 1 red—and put them on display. (The
experimenter was actually drawing preselected “random samples” from a hidden
compartment in the box.) The infants looked longer at the display with the 4 white
balls, indicating that they were surprised that the experimenter drew mostly white
balls from a box that was mostly filled with red balls. (Later in this chapter, we will
further discuss the use of so-called violation-of-expectation paradigms, which use
infants’ “surprise” at unexpected outcomes to draw inferences about their expecta-
tions.) It is important to note that the infants showed no such surprise when it was
clear that the displayed balls did not come from the box (as when the experimenter
took them from her pocket) or when they could see that the red balls were stuck to
the box and could not be removed (Denison & Xu, 2010; Teglas et al., 2007; Teglas
et al., 2011; Xu & Denison, 2009). Infants as young as 6 months of age appear to
be sensitive to the distribution of elements (here, colors) as a source of information
upon which to base future expectations (Denison, Reed, & Xu, 2013). Similar find-
ings are emerging across a number of domains, all suggesting that infants generate
inferences about the future based on prior data, in tasks ranging from word learn-
ing to social interactions, and that infants can use new experiences to adjust these
inferences (e.g., Schulz, 2012; Xu & Kushnir, 2013).
Infants begin learning about the world immediately. They habituate to repeatedly encoun-
tered stimuli, form expectancies for repeated event sequences, and learn associations be-
tween particular sights and sounds that regularly occur together. Classical conditioning,
which has been demonstrated in newborn and older infants, is believed to be especially im-
portant in the learning of emotional reactions. Infants are highly sensitive to a wide range of
contingency relations between their own behavior and what follows it. A particularly powerful
form of learning for older infants is observational learning: from 6 months of age on, infants
learn many new behaviors simply by watching what other people do. Although an enormous
amount of learning goes on during the infancy period, some associations or relations are eas-
ier for babies to learn than others are. In observational learning, for example, intentionality
is a key factor. Finally, infants are able to use their accumulated experience to make rational
predictions about the future.
Clearly, infants are capable of learning in a variety of ways. But do they actually
think? This is a question that has intrigued parents and developmental psycholo-
gists alike. Baby Benjamin’s parents have no doubt looked with wonderment at
their child, asking themselves, “What is he thinking? Is he thinking?” Developmen-
tal scientists have been working diligently to find out to what extent infants engage
in cognition (knowledge, thought, reasoning). The resulting explosion of fascinat-
ing research has established that infants’ cognitive abilities are much more impres-
sive than previously believed, although the nature and origin of these impressive
skills is a matter of considerable debate. Theorists of cognitive development vary
with respect to the relative roles they attribute to nature and nurture, especially
in terms of whether development is guided by innate knowledge structures and
special-purpose learning mechanisms or by general learning mechanisms relevant
to experiences in all domains.
So once again, the primary debate is between nativists and empiricists. Some na-
tivists argue that infants possess innate knowledge in a few domains of particular

importance (Carey & Spelke, 1994; Gelman, 2002; Gelman & Williams, 1998;
Scholl & Leslie, 1999; Spelke, 2000; Spelke & Kinzler, 2007). As you will see in
Chapter 7, for example, these nativists maintain that infants are born with some
knowledge about the physical world, such as the fact that two objects cannot oc-
cupy the same space, and that physical objects move only if something sets them in
motion. They also propose that infants possess rudimentary understandings in the
domains of biology and psychology. Other nativists emphasize specialized learning
mechanisms that enable infants to acquire this kind of knowledge rapidly and ef-
ficiently (Baillargeon, 2004; Baillargeon, Kotovsky, & Needham, 1995). According
to empiricists, infants’ mental representations of the physical world are gradually
acquired and strengthened through the general learning mechanisms that function
across multiple domains (Munakata et al., 1997). The details of this debate are exam-
ined in detail in Chapter 7 with respect to conceptual development. In the following
sections, we examine findings regarding infants’ cognitive abilities and limitations,
explanations for which both nativists and empiricists are working to pin down.
Object Knowledge
A large part of what we know about infant cognition has come from research on the
development of knowledge about objects, research originally inspired by Piaget’s
theory of sensorimotor intelligence. As you learned in Chapter 4, Piaget believed
that young infants’ understanding of the world is severely limited by an inability to
mentally represent and think about anything that they cannot currently see, hear,
touch, and so on. His tests of object permanence led him to infer that when an infant
fails to search for an object—even a favorite toy—that has disappeared from sight,
it is because the object has also disappeared from the infant’s mind.
A substantial body of research has provided strong support for Piaget’s original
observation that young infants do not manually search for hidden objects. How-
ever, as noted in Chapter 4, skepticism gradually arose about his explanation of this
fascinating phenomenon, and an overwhelming body of evidence has established
that young infants are in fact able to mentally represent and think about the exis-
tence of objects and events that are currently out of sight.
The simplest evidence for young infants’ ability to represent an object that has
vanished from sight is the fact that they will reach for objects in the dark, that is, they
reach for objects they cannot see. When young infants are shown an attractive object
and the room is then plunged into darkness, causing the object (and everything else)
to disappear from view, most babies reach to where they last saw the object, indicat-
ing that they expect it to still be there (Perris & Clifton, 1988; Stack et al., 1989).
Young infants even seem to be able to think about some characteristics of invis-
ible objects, such as their size (Clifton et al., 1991). When 6-month-olds sitting in
the dark heard the sound of a familiar large object, they reached toward it with both
hands (just as they had in the light); but they reached with only one hand when the
sound they heard was that of a familiar small object.
The majority of the evidence that young infants can represent and think about
invisible objects comes from research using the violation-of-expectancy proce-
dure. The logic of this procedure is similar to that of the visual-preference method
we discussed earlier (page 174). The basic assumption is that if infants observe an
event that violates something they know about the world, they will be surprised or
at least interested. Thus, an event that is impossible or inconsistent with respect to
the infant’s knowledge should evoke a greater response (such as longer looking or
a change in heart rate) than does a possible or consistent event.
violation-of-expectancy n a procedure
used to study infant cognition in which
infants are shown an event that should
evoke surprise or interest if it violates
something the infant knows or assumes
to be true

The violation-of-expectancy technique was first used in a classic series of stud-
ies designed by Renée Baillargeon and her colleagues ( Baillargeon, Spelke, &
Wasserman, 1985) to see if infants too young to search for an invisible object might
nevertheless have a mental representation of its existence. In some of these studies,
infants were first habituated to the sight of a solid screen rotating back and forth
through a 180-degree arc (Figure 5.16). Then a box was placed in the screen’s path,
and the infants saw two test events. In one, the possible event, the screen rotated
upward, occluding the box as it did so, and stopped when it contacted the box. In
the impossible event, the screen continued to rotate a full 180 degrees, appearing to
pass through the space occupied by the box (which the experimenter had surrepti-
tiously removed).
Infants as young as 3½ months of age looked longer at the impossible event than
at the possible one. The researchers reasoned that the full rotation of the screen (to
which the infants had previously been habituated) would be more interesting or
surprising than the partial rotation only if the infants expected the screen to stop
when it reached the box. And the only reason for them to have had that expecta-
tion was if they thought the box was still present—that is, if they mentally repre-
sented an object they could no longer see. The results also indicate that the infants
expected the box to remain in place and did not expect the screen to be able to pass
through it.
Other studies have shown that young infants’ behavior in this situation is in-
fluenced by some of the characteristics of the occluded objects, including height
(Baillargeon, 1987a; Baillargeon, 1987b). They expect the screen to stop sooner
for a taller object than for a shorter one. Thus, research using two very different
assessments—reaching in the dark and visual attention—provides converging evi-
dence that infants who do not yet search for hidden objects nevertheless can rep-
resent their continued existence and some of their properties.
Physical Knowledge
Infants’ knowledge about the physical world is not limited to what they know and
are learning about objects. Other research has examined what they know about
physical phenomena, such as gravity. Even in the first year of life, infants seem to
appreciate that objects do not float in midair, that an object that is inadequately
supported will fall, that a nonround object placed on a stable surface will stay put,
and so forth. For example, in a series of studies in which infants observed a ball
being released on a slope, 7-month-olds (but not 5-month-olds) looked longer
when the ball moved up the slope than when it moved down, indicating that they
had expected the ball to go down (Kim & Spelke, 1992). Similarly, they looked
longer at an object that traveled more slowly as it rolled down a slope than at one
that picked up speed.
Infants also gradually come to understand under what conditions one object
can support another. Figure 5.17 summarizes infants’ reactions to simple support
problems involving boxes and a platform (Baillargeon, Needham, & DeVos, 1992;
Needham & Baillargeon, 1993). At 3 months of age, infants are surprised (they
look longer) if a box that is released in midair remains suspended (as in Figure
5.17a), rather than falling. However, as long as there is any contact at all between
the box and the platform (as in Figure 5.17b and 5.17c), these young infants do
not react when the box remains stationary. By approximately 5 months of age, they
appreciate the relevance of the type of contact involved in support. They now know
that the box will be stable only if it is released on top of the platform, so they would
FIGURE 5.16 possible versus impos-
sible events In a classic series of tests of
object permanence, renée Baillargeon first
habituated young infants to the sight of a
screen rotating through 180 degrees. then
a box was placed in the path of the screen.
In the possible event, the screen rotated
up, occluding the box, and stopped when
it reached the top of the box. In the impos-
sible event, the screen rotated up, occluding
the box, but then continued on through
180 degrees, appearing to pass through the
space where the box was. Infants looked
longer at the impossible event, showing that
they mentally represented the presence of
the invisible box. (From Baillargeon, 1987a)

be surprised by the display in Figure 5.17b. Roughly a month later,
they recognize the importance of the amount of contact, and hence
they look longer when the box in Figure 5.17c stays put with only a
small portion of its bottom surface on the platform. Shortly after their
1st birthday, infants also take into account the shape of the object and
hence are surprised if an asymmetrical object like that shown in Figure
5.17d remains stable.
Infants presumably develop this progressively refined understand-
ing of support relations between objects as a result of experience.
They observe innumerable occasions of adults placing objects on sur-
faces, and once in a while, as in the crashing crystal observed by baby
Benjamin, they see the consequences of inadequate support. And, of
course, they collect additional data through their own manipulation
of objects, including lots more evidence than their parents would like
about what happens when a milk cup is deposited on the very edge
of a high-chair tray.
Social Knowledge
In addition to acquiring knowledge about the physical world, infants
need to learn about the social world—about people and their behav-
ior. An important aspect of social knowledge that emerges relatively
early is the understanding that the behavior of others is purposive and
goal-directed. In research by Amanda Woodward (1998), 6-month-
old infants saw a hand repeatedly reach toward one of two objects sit-
ting side by side in a display (see Figure 5.18). Then the position of the
two objects was reversed, and the hand reached again. The question
was whether the infants interpreted the reaching behavior as directed
toward a particular object. They did, as shown by their looking longer
when the hand went to the new object (in the old place) than when it
reached for the old object it had reached to before. Thus, the infants
apparently interpreted the reaching behavior as directed toward a par-
ticular object. However, this was true only for a human hand; another
group of infants did not react the same way when a mechanical claw
did the reaching. (This study may remind you of the one by Meltzoff
[1995b] in which older infants imitated the actions of a human but
not of a mechanical device.) Shown the same training event (Figure
5.18a), slightly older infants (11-month-olds) were able to correctly
predict what the human hand would do next, moving their eyes to
the goal object in the test display before the hand actually moved to the goal object
(Cannon & Woodward, 2012). Again, though, they did not have the same expecta-
tions for the claw as they had for the human hand.
Other research by Sommerville, Woodward, and Needham (2005) established
that infants’ understanding of the goal-directed nature of another’s actions is re-
lated to their own experience achieving a goal. Three-month-olds, who were not
yet able to pick up objects on their own, were fitted with Velcro “sticky mittens”
(like those described earlier in this chapter and in Chapter 4) that enabled them
to capture Velcro-patched toys. Their brief experience successfully “picking up”
objects enabled them to interpret the goal-directed reaching of others in the pro-
cedure in Figure 5.18 a few months earlier than they would otherwise have been
able to do.
(a) 3 months
Initial concept:
Contact/No contact
(b) 5 months
Type of contact
(c) 6.5 months
Amount of contact
(d) 12.5 months
Shape of the box
Violation detected
at each stage
FIGURE 5.17 Infants’ developing
understanding of support relations Young
infants appreciate that an object cannot
float in midair, but only gradually do they
come to understand under what conditions
one object can be supported by another.
(adapted from Baillargeon, 1998)

Further understanding of intentionality is revealed by studies showing that older
infants even attribute intentions and goals to inanimate entities if the objects seem
to “behave” like humans. In research by Susan Johnson, 12- and 15-month-olds
were introduced to a faceless, eyeless blob that “vocalized” and moved in response
to what the infant or experimenter did, thus simulating a normal human interac-
tion ( Johnson, 2003; Johnson, Slaughter, & Carey, 1998) (see Figure 5.19). Subse-
quently, when the blob turned in one direction, the infants looked in that direction.
Thus, they seemed to be following the blob’s “gaze,” just as they would do with a
human partner, assuming that the person had turned to look at something. They
did not behave this way when the blob’s initial behavior was not contingently re-
lated to their own.
FIGURE 5.18 Infants were habituated to the
event shown in (a), a hand repeatedly reaching for
a ball on one side of a display. When tested later
with displays (b), (c), and (d), infants who saw the
hand reach for the other object looked longer than
did those who saw it reach for the ball (regardless of
the ball’s position). the pattern of results indicates
that the babies interpreted the original reaching as
object-directed. (adapted from Woodward, 1998)
(b) (c) (d)
FIGURE 5.19 When this amorphous
blobby object “responds” contingently to
infants, they tend to attribute intention to it.CO

Older infants even interpret quite abstract displays in terms of intention and
goal-directed action (Csibra et al., 1999, 2003; Gergely et al., 2002). For ex-
ample, 12-month-olds saw a computer animation of a ball repeatedly “jumping”
over a barrier toward a ball on the other side. Adults interpret this display as the
jumping ball’s “wanting” to get to the other ball. So, apparently, did the infants.
When the barrier was removed, the infants looked longer when they saw the ball
continue to jump, just as it had done before, than when they saw it move straight
to the second ball.
Even younger infants seem to attribute intention with respect to simple dis-
plays involving small objects. In a study that used a ball, a cube, and a pyramid, all
with “googly” eyes attached, 10-month-olds watched as the ball—the “climber”—
repeatedly “attempted” to climb up a hill, each time falling back to the bottom
(Hamlin, Wynn, & Bloom, 2007; see Figure 5.20). Then the climber was alter-
nately bumped up the hill by the pyramid or pushed back down by the cube. On
the subsequent test event, the infants observed the climber alternately approach
the “helper” triangle or the “hinderer” cube. The infants looked longer when the
climber approached the “hinderer,” indicating by their surprise not only their
understanding of the “intentions” of all three objects but also their understand-
ing of what the “climber’s” response to the “helper” and “hinderer” might be ex-
pected to be.
Infants go beyond attributing intentions to others based on their actions: they
exhibit preferences for particular individuals and objects based on the individu-
als’ and objects’ actions. Earlier in this chapter, we described research focused
on infants’ visual preferences (Box 5.1). Infants also exhibit social preferences,
as evidenced by their desire to engage with some individuals over others. In
one of the first studies to demonstrate early social preferences (Kinzler, Dup-
oux, & Spelke, 2007), U.S. and French 10-month-olds saw alternating life-sized
video projections of two individuals speaking to them, one in English and one
in French. They then saw another life-sized video of the same two individuals
standing side by side behind a table, both holding an identical plush toy. Silently
and simultaneously, they smiled at the infant, then at the toy, then at the infant
again, and then leaned forward, holding the toys out as though giving them to
the infant. The moment the toys disappeared from view on the screen, they ap-
peared (through researchers’ magic) on a table in front of the infant, creating
the impression that they had come directly from the individuals in the video.
The infants’ responses suggested a social preference for the individual who had
spoken their native language: English-learning infants chose the toy offered by
, W
, &
, 2
/ R
FIGURE 5.20 Viewers of the “climber”
event described above—infants and adults
alike—readily interpret it in terms of inten-
tional action. First they see the ball as
“trying” to move up a hill, but then rolling
back down, thereby “failing” to achieve its
goal of reaching the top. On some trials,
after the ball starts to roll back down, a tri-
angle appears below the ball and seems to
“push” it upward, “helping” it get to the
top. On other trials, a cube appears in front
of the ball and “hinders” it by seeming to
“push” it down the hill.

the English speaker, whereas French-learning infants chose the toy offered by
the French speaker. Crucially, because the toy was offered in silence, these social
preferences were attributable to a preference for the individual who shared the
infant’s language, not for the language itself.
Similar findings emerged in a food-choice paradigm, in which infants were more
likely to choose a food offered by a speaker of their language than by a speaker of an-
other language (Shutts et al., 2009). Indeed, even objects similar to those depicted
in Figure 5.20 evoke social preferences (Hamlin et al., 2007). In a variation of the
“climber” procedure described above when infants as young as 6 months were pre-
sented with the objects they had just observed bumping the “climber” object up the
hill or pushing it down the hill, they tended to choose the “helper” object. The social
preferences exhibited in studies like these can be quite nuanced. In one recent study
that used puppets rather than objects, 5-month-olds uniformly preferred characters
who were positive toward “helpers,” whereas 8-month-olds preferred characters who
were positive toward “helpers” and negative toward “hinderers” (Hamlin et al., 2011).
These and related studies indicate that well before their 1st birthday, infants
have already learned a great deal about how humans behave and how their behavior
is related to their intentions and goals. Infants and young children can also draw
inferences about other people’s knowledge states. For example, 15-month-olds can
make inferences about what a person will do based on their knowledge of what the
person knows (Onishi & Baillargeon, 2005). In a visual-attention version of the
false-belief task (discussed in Chapter 4), infants seem to keep track of what in-
formation an adult has about the location of an object. If the object is moved to a
new location while an infant—but not the adult—witnesses the move, the infant
expects the adult to subsequently search for the object in its original location. That
is, the infant expects the adult to search where he or she should believe the toy to be,
rather than in the location where the infant knows it actually is. This interpreta-
tion is based on the fact that the infants looked longer when the adult searched the
object’s current location than they did when the adult searched its original loca-
tion. Thus, this study indicates that 15-month-olds assume that a person’s behavior
will be based on what the person believes to be true, even if the infant knows that
the belief is false. This result suggests that there may be very early precursors of a
theory of mind.
Looking Ahead
The intense activity focused on cognition in infancy has produced a wealth of fas-
cinating findings. This new information has not, however, resolved the basic issues
about how cognition develops in infancy. The evidence we have reviewed reveals a
remarkable constellation of abilities and deficits. Infants can be both surprisingly
smart and surprisingly clueless (Keen, 2003; Kloos & Keen, 2005). They can infer
the existence of an unseen object but cannot retrieve it. They appreciate that objects
cannot float in midair but think that any kind and amount of contact at all provides
sufficient support. The challenge for theorists is to account for both competence
and incompetence in infants’ thinking.
Building on the insights and observations of Piaget, and using an array of extremely clever
methods, modern researchers have made a host of fascinating discoveries about the cogni-
tive processes of infants. They have demonstrated that infants mentally represent not only

the existence of hidden objects but also characteristics such as the object’s size, height,
and noise-making properties. Infants’ understanding of the physical world grows steadily, as
shown by their appreciation of support relations and their increasing ability to solve everyday
problems. At the same time, their understanding of the social world also increases, as shown,
for example, by their interpretation of and preferences concerning the behavior of actors, both
human and animated.
chapter summary:
n The human visual system is relatively immature at birth; young
infants have poor acuity, low contrast sensitivity, and minimal
color vision. Modern research has demonstrated, however,
that newborns begin visually scanning the world minutes after
birth and that very young infants show preferences for strongly
contrasted patterns, for the same colors that adults prefer, and,
especially, for human faces.
n Some visual abilities, including perception of constant size
and shape, are present at birth; others develop rapidly over
the first year. Binocular vision emerges quite suddenly at
around 4 months of age, and the ability to identify object
boundaries—object segregation—is also present at that age.
By 7 months, infants are sensitive to a variety of monocular,
or pictorial, depth cues; and pattern perception has developed
to the point that infants can perceive illusory (subjective)
contours, as adults do.
n The auditory system is comparatively well developed at birth,
and newborns will turn their heads to localize a sound. Young
infants’ remarkable proficiency at perceiving pattern in audi-
tory stimulation underlies their sensitivity to musical structure.
n Infants are sensitive to smell from birth. They learn to identify
their mother in part by her unique scent.
n Through active touching, using both mouth and hands, infants
explore and learn about themselves and their environment.
n Research on the phenomenon of intermodal perception has
revealed that from very early on, infants integrate information
from different senses, linking their visual with their auditory,
olfactory, and tactile experiences.
Motor Development
n Motor development, or the development of action, proceeds
rapidly in infancy through a series of “motor milestones,”
starting with the reflexes displayed by newborn babies. Recent
research has demonstrated that the regular pattern of develop-
ment results from the confluence of many factors, including
the development of strength, posture control, balance, and per-
ceptual skills. Some aspects of motor development vary across
cultures as a result of different cultural practices.
n Each new motor achievement, from reaching to self-
locomotion, expands the infant’s experience of the world but
also presents new challenges. Infants adopt a variety of strate-
gies to move around in the world successfully and safely. In the
process, they make a variety of surprising mistakes.
n Various kinds of learning are present in infancy. Infants habit-
uate to repeated stimuli and form expectancies about recur-
rent regularities in events. Through active exploration, they
engage in perceptual learning. They also learn through classical
conditioning, which involves forming associations between
natural and neutral stimuli as well as through instrumental
conditioning, which involves learning about the contingency
between one’s own behavior and some outcome. They can also
make use of prior experiences to generate expectations about
the future.
n From the second half of the first year on, observational
learning—watching and imitating the behavior of other
people—is an increasingly important source of information.
Infants’ assessment of the intention of a model affects what
they imitate.
n Powerful new research techniques—most notably the
violation-of-expectancy procedure—have established that
infants display impressive cognitive abilities. Much of this
work on mental representation and thinking was originally
inspired by Piaget’s concept of object permanence. But it has
been revealed that, contrary to Piaget’s belief, young infants
can mentally represent invisible objects and even reason about
observed events.
n Other research, focused on infants’ developing knowledge of
the physical world, has demonstrated their understanding of
some of the effects of gravity. It takes babies several months to
work out the conditions under which one object can provide
stable support for another.
n What infants know about people is a very active area of
research. One clear finding is that infants pay particular atten-
tion to the intentions of others.

n Although many fascinating phenomena have been dis-
covered in the area of infant cognition, basic issues about
cognitive development remain unresolved. Theorists are
sharply divided on how to account for the abilities, on the
one hand, and the deficiencies, on the other hand, in infants’
Critical Thinking Questions
1. The major theme throughout this chapter was nature and
nurture. Consider the following research findings discussed
in the chapter: infants’ preference for consonance (versus
dissonance) in music, their preference for faces that adults
consider attractive, and their ability to represent the exis-
tence and even the height of an occluded object. To what
extent do you think these preferences and abilities rest on
innate factors, and to what extent might they be the result of
2. As you have seen from this chapter, researchers have learned
a substantial amount about infants in the recent past. Were
you surprised at some of what has been learned? Describe
to a friend something from each of the main sections of the
chapter that you would never have suspected an infant could
do or would know. Similarly, tell your friend a few things that
you were surprised to learn infants do not know or that they
fail to do.
3. Studying infants’ perceptual and cognitive abilities is espe-
cially tricky given their limited abilities to respond in a
study—they can’t respond verbally or even with a reliable
reach or point. Consider some of the methods described in
this chapter (preferential looking, conditioning, habitua-
tion, violation of expectation, imitation, and so on). Can you
match each method up with a study described in the chapter?
What kinds of questions are best suited to each method?
4. Explain why researchers did the following things, each of
which seems somewhat odd if one does not know the ratio-
nale behind it. What hypotheses were they trying to test?
(a) Suspended infants in water up to their waists
(b) Put a patch over one eye and showed infants a misshapen
(c) “Hid” a toy under a transparent container
(d) Pretended to be unable to pull the end off a dumbbell
Key Terms
affordances, p. 199
auditory localization, p. 182
binocular disparity, p. 181
classical conditioning, p. 201
conditioned response (CR), p. 201
conditioned stimulus (CS), p. 201
cones, p. 174
contrast sensitivity, p. 174
differentiation, p. 199
instrumental (or operant) conditioning, p. 201
intermodal perception, p. 186
monocular depth (or pictorial) cues, p. 181
object segregation, p. 179
optical expansion, p. 180
perception, p. 173
perceptual constancy, p. 178
positive reinforcement, p. 201
preferential-looking technique, p. 174
prereaching movements, p. 193
rational learning, p. 204
reflexes, p. 189
scale error, p. 196
self-locomotion, p. 194
sensation, p. 173
stepping reflex, p. 192
stereopsis, p. 181
unconditioned response (UCR), p. 201
unconditioned stimulus (UCS), p. 201
violation-of-expectancy, p. 206
visual acuity, p. 174

NICOLA BEALING, Lucas Talking to a Dog, 2006 (oil on board)

Development of
Language and Symbol Use
n Language Development
The Components of Language
What Is Required for Language?
Box 6.1: Applications Two Languages Are Better
Than One
The Process of Language Acquisition
Box 6.2: Individual Differences The Role of Family and
School Context in Early Language Development
Box 6.3: Applications iBabies: Technology and
Language Learning
Theoretical Issues in Language Development
Box 6.4: A Closer Look “I Just Can’t Talk Without My
Hands”: What Gestures Tell Us About Language
Box 6.5: Individual Differences Developmental
Language Disorders
n Nonlinguistic Symbols and Development
Using Symbols as Information
n Chapter Summary
chapter 6:

n Nature and Nurture
n The Active Child
n The Sociocultural Context
n Individual Differences
“Woof.” (used at age 11 months to refer to neighbor’s dog)
“Hot.” (used at age 14 months to refer to stove, matches, candles, light reflecting off
shiny surfaces, and so forth)
“Read me.” (used at age 21 months to ask mother to read a story)
“Why I don’t have a dog?” (27 months of age)
“If you give me some candy, I’ll be your best friend. I’ll be your two best friends.” (48
months of age)
“Granna, we went to Cagoshin [Chicago].” (65 months of age)
“It was, like, ya’ know, totally awesome, dude.” (192 months of age)
These utterances were produced by one boy during the process of his becoming a native English speaker (Clore, 1981). Each one reflects the capacity that most sets humans apart from other species: the creative and flexible use of symbols, which include language and many kinds of non-linguistic symbols (print, numbers, pictures, models, maps, and so forth).
We use symbols (1) to represent our thoughts, feelings, and knowledge, and (2) to
communicate our thoughts, feelings, and knowledge to other people. Our ability to
use symbols vastly expands our cognitive and communicative power. It frees us from
the present, enabling us to learn from the generations of people who preceded us and
to contemplate the future. Becoming symbol-minded is a crucial developmental task
for children around the world (DeLoache, 2005).
In this chapter, we will focus primarily on the acquisition of
the preeminent symbol system: language. We will then discuss
children’s understanding and creation of nonlinguistic symbols,
such as pictures and models.
The dominant theme in this chapter will once again be the
relative contributions of nature and nurture. A related issue con-
cerns the extent to which language acquisition is made possi-
ble by abilities that are specialized for language learning versus
general- purpose mechanisms that support all sorts of learning.
The sociocultural context is another prominent theme and fea-
tures research that examines differences in language acquisition
across cultures and communities. This comparative work often
provides evidence that is crucial to various theories of language
A third recurring theme is individual differences. For any given
language milestone, some children will achieve it much earlier,
and some much later, than others. The active child theme also
puts in repeated appearances. Infants and young children pay
close attention to language and a wide variety of other symbols, and they work hard
at figuring out how to use them to communicate.
Language Development
What is the average kindergartener almost as good at as you are? Not much, with
one important exception: using language. By 5 years of age, most children have
mastered the basic structure of their native language or languages (the possibility
of bilingualism is to be assumed whenever we refer to “native language”), whether
spoken or manually signed. Although their vocabulary and powers of expression are
These children are intent on mastering one
of the many important symbol systems in
the modern world.
/ A
symbols n systems for representing our
thoughts, feelings, and knowledge and for
communicating them to other people

less sophisticated than yours, their sentences are as grammatically correct as those
produced by the average college student. This is a remarkable achievement.
Language use requires comprehension, which refers to understanding what oth-
ers say (or sign or write), and production, which refers to actually speaking (or sign-
ing or writing). As we have observed for other areas of development, infants’ and
young children’s ability to understand precedes their ability to produce. Children un-
derstand words and linguistic structures that other people use months or even years
before they include them in their own utterances. This is, of course, not unique to
young children; you no doubt understand many words that you never actually use.
In our discussion, we will be concerned with the developmental processes involved
in both comprehension and production, as well as the relation between them.
The Components of Language
How do languages work? Despite the fact that there are thousands of human
languages, they share overarching similarities. All human languages are similarly
complex, with different pieces combined at different levels to form a hierarchy:
sounds are combined to form words, words are combined to form sentences, and
sentences are combined to form stories, conversations, and other kinds of narra-
tives. Children must acquire all of these facets of their native language. The enor-
mous benefit that emerges from this combinatorial process is generativity; by
using the finite set of words in our vocabulary, we can generate an infinite number
of sentences, expressing an infinite number of ideas.
However, the generative power of language carries a cost for young language
learners: they must deal with its complexity. To appreciate the challenge presented
to children learning their first language, imagine yourself as a stranger in a strange
land. Someone walks up to you and says, “Jusczyk daxly blickets Nthlakapmx.” You
would have absolutely no idea what this person had just said. Why?
First, you would probably have difficulty perceiving some of the phonemes that
make up what the speaker is uttering. Phonemes are the units of sound in speech; a
change in phoneme changes the meaning of a word. For example, “rake” and “lake”
differ by only one phoneme (/r/ versus /l/), but the two words have quite different
meanings to English speakers. Different languages employ different sets of pho-
nemes; English uses just 45 of the roughly 200 sounds found across the world’s lan-
guages. The phonemes that distinguish meaning in any one language overlap with,
but also differ from, those in other languages. For example, the sounds /r/ and /l/
are a single phoneme in Japanese, and do not carry different meanings. Further-
more, combinations of sounds that are common in one language may never occur
in others. When you read the stranger’s utterance in the preceding paragraph, you
probably had no idea how to pronounce the word Nthlakapmx, because some of
its sound combinations do not occur in English (though they do occur in other
languages). Thus, the first step in children’s language learning is phonological
development: the mastery of the sound system of their language.
Another reason you would not know what the stranger had said to you, even if
you could have perceived the sounds being uttered, is that you would have had no
idea what the sounds mean. The smallest units of meaning are called morphemes.
Morphemes, alone or in combination, constitute words. The word dog, for example,
contains one morpheme. The word dogs contains two morphemes, one designating
a familiar furry entity (dog) and the second indicating the plural (-s). Thus, the sec-
ond component in language acquisition is semantic development, that is, learning
the system for expressing meaning in a language, including word learning.
comprehension n with regard to lan-
guage, understanding what others say (or
sign or write)
production n with regard to language,
speaking (or writing or signing) to others
generativity n refers to the idea that
through the use of the finite set of words
and morphemes in humans’ vocabulary,
we can put together an infinite number of
sentences and express an infinite number
of ideas
phonemes n the elementary units
of meaningful sound used to produce
phonological development n the
acquisition of knowledge about the sound
system of a language
morphemes n the smallest units of
meaning in a language, composed of one
or more phonemes
semantic development n the learning
of the system for expressing meaning in a
language, including word learning

However, even if you were told the meaning of each individual word the
stranger had used, you would still not understand the utterance unless you knew
how words are put together in the stranger’s language. To express an idea of any
complexity, we combine words into sentences, but only certain combinations are
allowed in any given language. Syntax refers to the permissible combinations of
words from different categories (nouns, verbs, adjectives, etc.). In English, for ex-
ample, the order in which words can appear in a sentence is crucial: “Lila ate the
lobster” does not mean the same thing as “The lobster ate Lila.” Other languages
indicate which noun did the eating and which noun was eaten by adding mor-
phemes like suffixes to the nouns. For example, a Russian noun ending in “a” is
likely to refer to the entity doing the eating, while the same noun ending in “u”
is likely to refer to the thing that was eaten. The third component in language
learning, then, is syntactic development, that is, learning how words and mor-
phemes are combined.
Finally, a full understanding of the interaction with the stranger would necessi-
tate having some knowledge of the cultural rules and contextual variations for using
language. In some societies, for example, it would be quite bizarre to be addressed
by a stranger in the first place, whereas in others it would be commonplace. You
would also need to know how to go beyond the speaker’s specific words to under-
stand what the speaker was really trying to communicate—to use factors such as
the context and the speaker’s emotional tone to read between the lines and to learn
how to hold a conversation. Acquiring an understanding of how language is typi-
cally used is referred to as pragmatic development.
Our example of the bewilderment one experiences when listening to an unfa-
miliar language is useful for delineating the components of language use. However,
when we, as adults, hear someone speaking an unfamiliar language, we already
know what a language is. We know that the sounds the person is uttering constitute
words, that words are combined to form sentences, that only certain combinations
are acceptable, and so on. In other words, in contrast with
young language learners, adults have considerable meta­
linguistic knowledge—that is, knowledge about language
and its properties.
Thus, learning language involves phonological, seman-
tic, syntactic, and pragmatic development, as well as meta-
linguistic knowledge. The same factors are involved in
learning a sign language, in which the basic linguistic el-
ements are gestures rather than sounds. There are more
than 200 languages, including American Sign Language
(ASL), that are based on gestures, both manual and facial.
They are true languages and are as different from one an-
other as spoken languages are. The course of acquisition of
a sign language is remarkably similar to that of a spoken
What Is Required for Language?
What does it take to be able to learn a language in the first place? Full-fledged
language is achieved only by humans, so, obviously, one requirement is the human
brain. But a single human, isolated from all sources of linguistic experience, could
never learn a language; hearing (or seeing) language is a crucial ingredient for suc-
cessful language development.
By the age of 5, children are capable of gen-
erating totally novel sentences that are cor-
rect in terms of the phonology, semantics,
and syntax of their native language. They
are also able to make appropriate pragmatic
inferences regarding the content of their
partner’s utterances.
syntax n rules in a language that specify
how words from different categories
(nouns, verbs, adjectives, and so on) can
be combined
syntactic development n the learning
of the syntax of a language
pragmatic development n the acqui-
sition of knowledge about how language
is used
metalinguistic knowledge n an under-
standing of the properties and function
of language—that is, an understanding of
language as language

A Human Brain
The key to full-fledged language development lies in the human brain. Language
is a species-specific behavior: only humans acquire language in the normal course of
development. Furthermore, it is species-universal: language learning is achieved by
typically developing infants across the globe.
In contrast, no other animals naturally develop anything approaching the com-
plexity or generativity of human language, even though they can communicate with
one another. For example, birds claim territorial rights by singing (Marler, 1970),
and vervet monkeys can reveal the presence and identity of predators through spe-
cific calls (Seyfarth & Cheney, 1993).
Researchers have had limited success in training nonhuman primates to use
complex communicative systems. One early effort was an ambitious project in
which a dedicated couple raised a chimpanzee (Vicki) with their own children
(Hayes & Hayes, 1951). Although Vicki learned to comprehend some words and
phrases, she produced virtually no recognizable words. Subsequent researchers
attempted to teach nonhuman primates sign language. Washoe, a chimpanzee,
and Koko, a gorilla, became famous for their ability to communicate with their
human trainers and caretakers using manual signs (Gardner & Gardner, 1969;
Patterson & Linden, 1981). Washoe could label a variety of objects and could
make requests (“more fruit,” “please tickle”). The general consensus is that, how-
ever impressive Washoe’s and Koko’s “utterances” were, they do not qualify as
language, because they contained little evidence of syntactic structure (Terrace et
al., 1979; Wallman, 1992).
The most successful sign-learning nonhuman is Kanzi, a great ape of the bonobo
species. Kanzi’s sign-learning began when he observed researchers trying to teach
his mother to communicate with them by using a lexigram board, a panel composed
of a few graphic symbols representing specific objects and actions (“give,” “eat,” “ba-
nana,” “hug,” and so forth) (Savage-Rumbaugh et al., 1993). Kanzi’s mother never
caught on, but Kanzi did, and over the years his lexigram vocabulary increased from
6 words to more than 350. He is now very adept at using his lexigram board to
answer questions, to make requests, and even to offer comments. He often com-
bines signs, but whether they can be considered syntactically structured sentences
is not clear.
There are also several well-documented cases of nonprimate animals that have
learned to respond to spoken language. Kaminski, Call, and Fischer (2004) found
that Rico, a border collie, knew more than 200 words and could learn and remem-
ber new words using the same kinds of processes that toddlers use
(see pages 236–237). Alex, an African Grey parrot, learned to pro-
duce and understand basic English utterances, although his skills
remained at a toddler level (Pepperberg, 1999).
Whatever the ultimate decision regarding the extent to which
trained nonhuman animals should be credited with language, sev-
eral things are clear. Even their most basic linguistic achievements
come only after a great deal of concentrated human effort, whereas
human children master the rudiments of their language with little
explicit teaching. Furthermore, while the most advanced nonhu-
man communicators do combine symbols, their utterances show
limited evidence of syntactic structure, which is a defining feature
of language (Tomasello, 1994). In short, only the human brain
acquires a communicative system with the complexity, structure,
and generativity of language. Correspondingly, we humans are
Kanzi, a bonobo chimpanzee, and his care-
takers communicate with one another by
using a specially designed set of symbols
that stand for a wide variety of objects,
people, and actions.
This photo shows rico demonstrating his
language comprehension by fetching spe-
cific toys on request.
/ C

notoriously poor at learning the communicative systems of other species (Harry
Potter’s ability to speak Parseltongue with snakes aside). There is an excellent
match between the brains of animals of different species and their respective com-
municative systems.
Brain–language relations A vast amount of research has examined the relation-
ship between language and brain function. It is clear that language processing in-
volves a substantial degree of functional localization. At the broadest level, there are
hemispheric differences in language functioning that we discussed to some extent
in Chapter 3. For the 90% of people who are right-handed, language is primarily
represented and controlled by the left hemisphere.
Left-hemisphere specialization appears to emerge very early in life. Studies
using neuroimaging techniques have demonstrated that newborns and 3-month-
olds show greater activity in the left hemisphere when exposed to normal speech
than when exposed to reversed speech or silence (Bortfeld, Fava, & Boas, 2009;
Dehaene-Lambertz, Dehaene, & Hertz-Pannier, 2002; Pena et al., 2003). In addi-
tion, EEG studies show that infants exhibit greater left-hemisphere activity when
listening to speech but greater right-hemisphere activity when listening to non-
speech sounds (Molfese & Betz, 1988). An exception to this pattern of lateraliza-
tion occurs in the detection of pitch in speech, which in infants, as in adults, tends
to involve the right hemisphere (Homae et al., 2006).
Although it is evident that the left hemisphere predominantly processes speech
from birth, the reasons for this are not yet known. One possibility is that the left
hemisphere is innately predisposed to process language but not other auditory
stimuli. Another possibility is that speech is localized to the left hemisphere be-
cause of its acoustic properties. In this view, the auditory cortex in the left hemi-
sphere is tuned to detect small differences in timing, whereas the auditory cortex in
the right hemisphere is tuned to detect small differences in pitch (e.g., Zatorre et
al., 1992; Zatorre & Belin, 2001; Zatorre, Belin, & Penhune, 2002). Because speech
turns on small differences in timing (as you will see when we discuss voice onset
time, page 225), it may be a more natural fit for the left hemisphere.
critical period for language development If you were to survey your classmates
who have studied another language, we predict you would discover that those who
learned a foreign language in adolescence found the task to be much more chal-
lenging than did those who learned the foreign language in early childhood. A
considerable body of evidence suggests that, in fact, the early years constitute a crit­
ical period during which language develops readily. After this period (which ends
sometime between age 5 and puberty), language acquisition is much more difficult
and ultimately less successful.
Relevant to this hypothesis, there are several reports of children who barely de-
veloped language at all after being deprived of early linguistic experience. The most
famous case in modern times is Genie, who was discovered in appalling conditions
in Los Angeles in 1970. From the age of approximately 18 months until she was
rescued at age 13, Genie’s parents kept her tied up and locked alone in a room.
During her imprisonment, no one spoke to her; when her father brought her food,
he growled at her like an animal. At the time of her rescue, Genie’s development
was stunted—physically, motorically, and emotionally—and she could barely speak.
With intensive training, she made some progress, but her language ability never
developed much beyond the level of a toddler’s: “Father take piece wood. Hit. Cry”
(Curtiss, 1977, 1989; Rymer, 1993).
critical period for language n the
time during which language develops
readily and after which (sometime
between age 5 and puberty) language
acquisition is much more difficult and
ultimately less successful

Does this extraordinary case support the critical-period hypothesis?
Possibly, but it is difficult to know for sure. Genie’s failure to develop
full, rich, language after her discovery might have resulted as much
from the bizarre and inhumane treatment she suffered as from linguistic
Other areas of research provide much stronger evidence for the
critical- period hypothesis. As noted in Chapter 3, adults, who are well
beyond the critical period, are more likely to suffer permanent language
impairment from brain damage than are children, presumably because
other areas of the young brain (but not the older brain) are able to take
over language functions (see M. H. Johnson, 1998). Moreover, adults
who learned a second language after puberty use different neural mecha-
nisms to process that language than do adults who learned their second
language from infancy (e.g., Kim et al., 1997; Pakulak & Neville, 2011).
These results strongly suggest that the neural circuitry supporting lan-
guage learning operates differently (and better) during the early years.
In an important behavioral study, Johnson and Newport (1989) tested the En-
glish proficiency of Chinese and Korean immigrants to the United States who had
begun learning English either as children or as adults. The results, shown in Figure
6.1, reveal that knowledge of key aspects of English grammar was related to the age
at which these individuals began learning English, but not to the length of their
exposure to the language. The most proficient were those who had begun learning
English before the age of 7.
A similar pattern has been described for first-language acquisition in the Deaf
community: individuals who acquired ASL as a first language when they were chil-
dren become more proficient signers than do individuals who acquired ASL as a
first language as teens or adults (Newport, 1990). Johnson and Newport also ob-
served a great deal of variability among “late learners”—those who were acquiring
a second language, or a sign language as their first formal language, at puberty or
beyond. As in the findings we predicted for your survey of classmates, some indi-
viduals achieved nativelike skills, whereas the language outcomes for others were
quite poor. For reasons that are still unknown, some individuals continue to be tal-
ented language learners even after puberty, while most do not.
Newport (1990) proposed an intriguing hypothesis to explain these results and,
more generally, to explain why children are usually better language learners than
adults. According to her “less is more” hypothesis, perceptual and memory limita-
tions cause young children to extract and store smaller chunks of the language than
adults do. Because the crucial building blocks of language (the meaning-carrying
morphemes) tend to be quite small, young learners’ limited cognitive abilities may
actually facilitate the task of analyzing and learning language.
The evidence for a critical period in language acquisition has some very clear
practical implications. For one thing, deaf children should be exposed to sign lan-
guage as early as possible. For another, foreign-language exposure at school, dis-
cussed in Box 6.1, should begin in the early grades in order to maximize children’s
opportunity to achieve native-level skills in a second language.
A Human Environment
Possession of a human brain is not enough for language to develop. Children must
also be exposed to other people using language—any language, signed or spoken.
Adequate experience hearing others talk is readily available in the environment
Native 8–10 11–15 17–39 3–7
Age (in years) at arrival
FIGURE 6.1 Test of critical-period
hypothesis performance on a test of
en glish grammar by adults originally from
Korea and china was directly related to the
age at which they came to the United States
and were first exposed to english. The
scores of adults who emigrated before the
age of 7 were indistinguishable from those
of native speakers of english. (adapted from

The topic of bilingualism, the ability to use
two languages, has attracted substantial at-
tention in recent years as increasing num-
bers of children are developing bilingually.
Indeed, almost half the children in the
world are regularly exposed to more than
one language, often at home with parents
who speak different languages. Remark-
ably, despite the fact that bilingual children
have twice as much to learn as monolingual
children, they show little confusion and lan-
guage delay. In fact, there is evidence to
suggest that being bilingual improves as-
pects of cognitive functioning in childhood
and beyond.
Bilingual learning can begin in the womb.
Newborns prenatally exposed to just their
native language prefer it over other lan-
guages, whereas newborns whose mothers
spoke two languages during pregnancy pre-
fer both languages equally (Byers- Heinlein,
Burns, & Werker, 2010). Bilingual infants
are able to discriminate the speech sounds
of their two languages at roughly the same
pace that monolingual infants distinguish
the sounds of their one language (e.g.,
Albareda-Castellot, Pons, & Sebastián-
Gallés, 2011; Sundara, Polka, & Molnar,
2008). How might this be, given that bilin-
gual infants have twice as much to learn?
One possibility is that bilinguals’ attention
to speech cues is heightened relative to that
of monolinguals. For example, bilingual in-
fants are better than monolingual infants at
using purely visual information (a silent talk-
ing face) to discriminate between unfamiliar
languages (Sebastián-Gallés et al., 2012).
For the most part, children who are ac-
quiring two languages do not seem to con-
fuse them; indeed, they appear to build
two separate linguistic systems. When lan-
guage mixing does occur, it usually reflects
a gap of knowledge in one language that the
child is trying to fill in with the other, rather
than a confusing of the two language sys-
tems (e.g., Deuchar & Quay, 1999; Paradis,
Nicoladis, & Genesee, 2000).
Children developing bilingually may ap-
pear to lag behind slightly in each of their
languages because their vocabulary is dis-
tributed across two languages (Oller &
Pearson, 2002). That is, a bilingual child
may know how to express some concepts in
one language but not the other. However,
both the course and the rate of language de-
velopment are generally very similar for bi-
lingual and monolingual children (Genesee
& Nicoladis, 2006). And as we have noted,
there are cognitive benefits to bilingual-
ism: children who are competent in two
languages perform better on a variety of
measures of executive function and cogni-
tive control than do monolingual children
(Bialystok & Craik, 2010; Costa, Hernandez,
& Sebastián- Gallés, 2008). Recent results
reveal similar effects for bilingual toddlers
(Poulin-Dubois et al., 2011). Even bilin-
gual infants appear to show greater cogni-
tive flexibility in learning tasks (Kovács &
Mehler, 2009a, b). The link between bilin-
gualism and improved cognitive flexibility
likely lies in the fact that bilingual individu-
als have had to learn to rapidly switch be-
tween languages, both in comprehension
and production.
More difficult issues arise with respect to
second-language learning in the school set-
ting. Some countries with large but distinct
language communities, like Canada, have
embraced bilingual education. Others, in-
cluding the United States, have not. The de-
bate over bilingual education in the United
States is tied up with a host of political,
ethnic, and racial issues. One side of this
debate advocates total immersion, in which
children are communicated with and taught
exclusively in English, the goal being to
help them become proficient in English as
quickly as possible. The other side recom-
mends an approach that initially provides
children with instruction in basic subjects
in their native language and gradually in-
creases the amount of instruction provided
in English (Castro et al., 2011).
In support of the latter view, there is evi-
dence that (1) children often fail to master
basic subject matter when it is taught in a
language they do not fully understand; and
(2) when both languages are integrated in
the classroom, children learn the second lan-
guage more readily, participate more actively,
and are less frustrated and bored (August &
Hakuta, 1998; Crawford, 1997; Hakuta,
1999). This approach also helps prevent sit-
uations where children might become less
proficient in their original language as a re-
sult of being taught a second one in school.
BOX 6.1: applications
The issue of bilingualism in the classroom has
been a topic of intense debate in the United
States and other parts of the world. how-
ever, research conducted by ellen Bialystok
in canada, where a substantial proportion of
the population is bilingual, reveals a variety of
benefits of proficiency in multiple languages.

of almost all children around the world. Much of the speech directed to infants
occurs in the context of daily routines—during thousands of mealtimes, diaper
changes, baths, and bedtimes, as well as in countless games like peekaboo and nurs-
ery rhymes like the “Itsy Bitsy Spider.”
Infants identify speech as something important very early. When given the choice,
newborns prefer listening to speech rather than to artificial sounds (Vouloumanos
et al., 2010). Intriguingly, newborns also prefer nonhuman primate (rhesus ma-
caque) vocalizations to nonspeech sounds, and show no preference for speech over
macaque vocalizations until 3 months of age (Vouloumanos et al., 2010). These re-
sults suggest that infants’ auditory preferences are fine-tuned through experience
with human language during their earliest months.
Infant-directed speech Imagine yourself on a bus listening
to a stranger who is seated behind you and speaking to some-
one. Could you guess whether the stranger was addressing an
infant or an adult? We have no doubt that you could, even if the
stranger was speaking an unfamiliar language. The reason is that
in virtually all cultures, adults adopt a distinctive mode of speech
when talking to babies and very young children. This special way
of speaking was originally dubbed “motherese” (Newport, Glei-
tman, & Gleitman, 1977). The current term, infant­directed
speech (IDS), recognizes the fact that this style of speech is used
by both males and females, including parents and nonparents
alike. Indeed, even young children adopt it when talking to ba-
bies (Shatz & Gelman, 1973).
emotional tone. It is speech suffused with affection—“the sweet music of the spe-
cies,” as Darwin (1877) put it. Another obvious characteristic of IDS is exaggeration.
When people speak to babies, their speech is slower, and their voice is often higher
pitched, than when they speak to adults, and they swoop abruptly from high pitches
to low pitches and back again. Even their vowels are clearer (Kuhl et al., 1997). All
this exaggerated speech is accompanied by exaggerated facial expressions. Many of
these characteristics have been noted in adults speaking such languages as Arabic,
French, Italian, Japanese, Mandarin Chinese, and Spanish (see de Boysson-Bardies,
1996/1999), as well as in deaf mothers signing to their infants (Masataka, 1992).
Beyond expressing emotional tone, caregivers can use various pitch patterns
of IDS to communicate important information to infants even when infants
don’t know the meaning of the words uttered. For example, a word uttered with
sharply falling intonation tells the baby that their caregiver disapproves of some-
thing, whereas a cooed warm sound indicates approval. These pitch patterns
serve the same function in language communities ranging from English and
Italian to Japanese (Fernald et al., 1989). Interestingly, infants exhibit appropri-
ate facial emotion when listening to these pitch patterns, even when the lan-
guage is unfamiliar (Fernald, 1993).
IDS also seems to aid infants’ language development. To begin with, it draws in-
fants’ attention to speech itself. Indeed, infants prefer IDS to adult-directed speech
(Cooper & Aslin, 1994; Pegg, Werker, & McLeod, 1992), even when it is in a lan-
guage other than their own. For example, both Chinese and American infants lis-
tened longer to a recording of a Cantonese-speaking woman talking to a baby in
IDS than to the same woman speaking normally to an adult friend (Werker, Pegg, &
McLeod, 1994). Some studies suggest that infants’ preference for IDS may emerge
The infant-directed talk used by this father
grabs and holds his baby’s attention.
bilingualism n the ability to use two
infant-directed speech (IDS) n the
distinctive mode of speech that adults
adopt when talking to babies and very
young children

because it is “happy speech”; when speakers’ affect is held constant, the pref-
erence disappears (Singh, Morgan, & Best, 2002). Perhaps because they pay
greater attention to IDS, infants learn and recognize words better when the
words are presented in IDS than when they are presented in adult-directed
speech (Ma et al., 2011; Singh et al., 2009; Thiessen, Hill, & Saffran, 2005).
Although IDS is very common throughout the world, it is not universal.
In some cultures, such as the Kwara’ae of the Solomon Islands, the Ifaluk of
Micronesia, and the Kaluli of Papua New Guinea, it is believed that because
infants cannot understand what is said to them, there is no reason for caregiv-
ers to speak to them (Le, 2000; Schieffelin & Ochs, 1987; Watson-Gegeo, &
Gegeo, 1986). For example, young Kaluli infants are carried facing outward
so that they can engage with other members of the group (but not with their
caregiver), and if they are spoken to by older siblings, the mother will speak
for them (Schieffelin & Ochs, 1987). Thus, even if they are not addressed
directly by their caregivers, these infants are still immersed in language.
That infants begin life equipped with the two basic necessities for acquir-
ing language—a human brain and a human environment—is, of course, only
the beginning of the story. Of all the things we learn as humans, languages
are arguably the most complex; so complex, in fact, that scientists have yet
to be able to program computer systems to acquire a human language. The
overwhelming complexity of language is further reflected in the difficulty
most people have in learning a new language after puberty. How, then, do
infants and young children manage to acquire their native language with such as-
tounding success? We turn now to the many steps through which that remarkable
accomplishment proceeds.
The Process of Language Acquisition
Acquiring a language involves listening and speaking (or watching and signing)
and requires both comprehending what other people communicate and producing
intelligible speech (or signs). Infants start out paying attention to what people say
or sign, and they know a great deal about language long before their first linguistic
Speech Perception
The first step in language learning is figuring out the sounds of one’s native lan-
guage. As you saw in Chapter 2, the task usually begins in the womb, as fetuses
develop a preference for their mother’s voice and the language they hear her speak.
The basis for this very early learning is prosody, the characteristic rhythmic and
intonation patterns with which a language is spoken. Differences in prosody are in
large part responsible for why languages—from Japanese to French to Swahili—
sound so different from one another.
Speech perception also involves distinguishing among the speech sounds that
make a difference in a given language. To learn English, for example, one must dis-
tinguish between bat and pat, dill and kill, Ben and bed. As you will see next, young
infants do not have to learn to hear these differences: they perceive many speech
sounds in very much the same way that adults do.
categorical perception of speech sounds Both adults and infants perceive
speech sounds as belonging to discrete categories. This phenomenon, referred to
as categorical perception, has been established by studying people’s response to
around the world, parents in some cultures
talk directly to their babies, whereas parents
in other cultures do not. almost everywhere,
adults and older children use some form of
“baby talk” to address infants.
prosody n the characteristic rhythm,
tempo, cadence, melody, intonational pat-
terns, and so forth with which a language
is spoken
categorical perception n the percep-
tion of speech sounds as belonging to dis-
crete categories

speech sounds. In this research, a speech synthesizer is used to gradually and con-
tinuously change one speech sound, such as /b/, into a related one, such as /p/. These
two phonemes are on an acoustic continuum; they are produced in exactly the same
way, except for one crucial difference—the length of time between when air passes
through the lips and when the vocal cords start vibrating. This lag, referred to as
voice onset time (VOT), is shorter for /b/ (less than 25 milliseconds [ms]) than
for /p/ (greater than 25 ms). (Try saying “ba” and “pa” alternately several times, with
your hand on your throat, and you will likely experience this difference in VOT.)
To study the perception of VOT, researchers create recordings of speech sounds
that vary along this VOT continuum, so that each successive sound is slightly dif-
ferent from the one before, with /b/ gradually changing into /p/. What is surprising
is that adult listeners do not perceive this continuously changing series of sounds
(Figure 6.2). Instead, they hear /b/ repeated several times and then hear an abrupt
switch to /p/. All the sounds in this continuum that have a VOT of less than 25 ms
are perceived as /b/, and all those that have a VOT greater than 25 ms are perceived
as /p/. Thus, adults automatically divide the continuous signal into two discontinu-
ous categories—/b/ and /p/. This perception of a continuum as two categories is a
very useful perceptual ability because it allows one to pay attention to sound differ-
ences that are meaningful in one’s native language, such as, in English, the difference
between /b/ and /p/, while allowing meaningless differences, such as the difference
between a /b/ with a 10 ms VOT versus a /b/ with a 20 ms VOT, to be ignored.
Young infants draw the same sharp distinctions between speech sounds. This re-
markable fact was established using the habituation technique familiar to you from
previous chapters. In the original, classic study (one of the 100 most frequently
cited studies in psychology), 1- and 4-month-olds sucked on a pacifier hooked up
to a computer (Eimas et al., 1971). The harder they sucked, the more often they’d
hear repetitions of a single speech sound. After hearing the same sound repeatedly,
the babies gradually sucked less enthusiastically (habituation). Then a new sound
was played. If the infants’ sucking rate increased in response to the new sound, the
researchers inferred that the infants discriminated the new sound from the old one
The crucial factor in this study was the relation between the new and old
sounds—specifically, whether they were from the same or different phonemic cat-
egories. For one group of infants, the new sound was from a different category;
–10 10 20 30 40 50 60 70 0 –50 –40 –30 –20
Voice onset time (ms)

/ba/ FIGURE 6.2 categorical perception
of speech sounds by adults When adults
listen to a tape of artificial speech sounds
that gradually change from one sound to
another, such as /ba/ to /pa/ or vice versa,
they suddenly switch from perceiving one
sound to perceiving the other. (adapted from
voice onset time (VOT) n the length
of time between when air passes through
the lips and when the vocal cords start

thus, after habituation to a series of sounds that adults
perceive as /b/, sucking now produced a sound that adults
identify as /p/. For the second group, the new sound was
within the same category as the old one (i.e., adults per-
ceive them both as /b/). A critical feature of the study is
that for both groups, the new and old sounds differed
equally in terms of VOT.
As Figure 6.3 shows, after habituating to /b/, the in-
fants increased their rate of sucking when the new sound
came from a different phonemic category (/p/ instead
of /b/). Habituation continued, however, when the new
sound was within the same category as the original one.
Since this classic study, researchers have established that
infants show categorical perception of numerous speech
sounds (Aslin, Jusczyk, & Pisoni, 1998).
A fascinating outcome of this research is the discovery
that young infants actually make more distinctions than
adults do. This rather surprising phenomenon occurs because any given language
uses only a subset of the large variety of phonemic categories that exist. As noted
earlier, the sounds /r/ and /l/ make a difference in English, but not in Japanese.
Similarly, speakers of Arabic, but not of English, perceive a difference between the
/k/ sounds in “keep” and “cool.” Adults simply do not perceive differences in speech
sounds that are not important in their native language, which partly accounts for
why it is so difficult for adults to become fluent in a second language.
In contrast, infants can distinguish between phonemic contrasts made in all
the languages of the world—about 600 consonants and 200 vowels. For example,
Kikuyu infants in Africa are just as good as American babies at discriminating
English contrasts not found in Kikuyu (Streeter, 1976). Studies done with infants
from English-speaking homes have shown that they can discriminate non-English
distinctions made in languages ranging from German and Spanish to Thai, Hindi,
and Zulu ( Jusczyk, 1997).
This research reveals an ability that is innate, in the sense that it is present at
birth, and experience-independent, because infants can discriminate between speech
sounds they have never heard before. Being born able to distinguish speech sounds
of any language is enormously helpful to infants, priming them to start learning
whichever of the world’s languages they hear around them. Indeed, the crucial role
of early speech perception is reflected in a positive correlation between infants’
speech-perception skills and their later language skills. Babies who were better at
detecting differences between speech sounds at 6 months scored higher on measures
of vocabulary and grammar at 13 to 24 months of age (Tsao, Liu, & Kuhl, 2004).
Developmental changes in speech perception During the last months of their
first year, infants increasingly home in on the speech sounds of their native lan-
guage, and by 12 months of age, they have “lost” the ability to perceive the speech
sounds that are not part of it. In other words, their speech perception has become
adultlike. This shift was first demonstrated by Werker and her colleagues (Werker,
1989; Werker & Lalonde, 1988; Werker & Tees, 1984), who studied infants rang-
ing in age from 6 to 12 months. The infants, all from English-speaking homes, were
tested on their ability to discriminate speech contrasts that are not used in English
but that are important in two other languages—Hindi and Nthlakapmx (a language
spoken by indigenous First Nations people in the Canadian Pacific Northwest).
Time (min)

4 3 2 1 1 2 3 4 5 B
4 3 2 1 1 2 3 4 5 B
VOT = 20 VOT = 60 VOT = 80 VOT = 40
(a) (b) (c) (d)
FIGURE 6.3 categorical perception of
speech sounds by infants Infants aged
1 to 4 months were habituated to a tape
of artificial speech sounds. (a) One group
repeatedly heard a /ba/ sound with a VOT of
20, and they gradually habituated to it. (b)
When the sound changed to /pa/, with a VOT
of 40, they dishabituated, indicating that
they perceived the difference between the
two sounds, just as adults do. (c) a different
group was habituated to a /pa/ sound with a
VOT of 60. (d) When the sound changed to
another /pa/ with a VOT of 80, the infants
remained habituated, suggesting that, like
adults, they did not discriminate between
these two sounds. (adapted from eimas et

The researchers used a simple conditioning procedure, shown in Figure 6.4. The
infants learned that if they turned their head toward the sound source when they
heard a change in the sounds they were listening to, they would be rewarded by an
interesting visual display. If the infants turned their heads in the correct direction
immediately following a sound change, the researchers inferred that they had de-
tected the change.
Figure 6.5 shows that at 6 to 8 months of age, English-learning infants readily
discriminated between the sounds they heard; they could tell one Hindi syllable
from another, and they could also distinguish between two sounds in Nthlakapmx.
At 10 to 12 months of age, however, the infants no longer perceived the differences
they had detected a few months before. Two Hindi syllables that had previously
sounded different to them now sounded the same. Other research indicates that a
similar change occurs slightly earlier for the discrimination of vowels (Kuhl et al.,
1992; Polka & Werker, 1994). Interestingly, this perceptual narrowing does not ap-
pear to be an entirely passive process. Kuhl, Tsao, and Liu (2003) found that infants
learned more about the phonetic structure of Mandarin from a live interaction with
a Mandarin speaker than from watching a videotape of one.
Is this process of perceptual narrowing limited to speech? To answer this ques-
tion, a recent study asked whether this narrowing process also occurs in ASL
(Palmer et al., 2012). The researchers began by determining whether infants who
had never been exposed to ASL were able to discriminate between highly simi-
lar ASL signs that are differentiated by the shape of the hand. They found that
4-month-olds could, in fact, discriminate between the signs. However, by 14
months of age, only infants who were learning ASL were able to detect the dif-
ference between the hand shapes; those who were not learning ASL had lost their
ability to make this perceptual discrimination. Perceptual narrowing is thus not
limited to speech. Indeed, this narrowing process may be quite broad; recall the dis-
cussion of perceptual narrowing in the domains of face perception (page 185) and
musical rhythm (page 184) discussed in Chapter 5.
Thus, after the age of 8 months or so, infants begin to specialize in their dis-
crimination of speech sounds, retaining their sensitivity to sounds in the native lan-
guage they hear every day, while becoming increasingly less sensitive to nonnative
FIGURE 6.4 Speech perception This infant is participating in a study of speech perception in
the laboratory of Janet Werker. The baby has learned to turn his head to the sound source whenever he
hears a change from one sound to another. a correct head turn is rewarded by an exciting visual dis-
play, as well as by the applause and praise of the experimenter. To make sure that neither the mother
nor the experimenter can influence the child’s behavior, they are both wearing headphones that prevent
, J
. (

, 7
. R

, J
. P
, A
6–8 8–10
Age (in months)
FIGURE 6.5 percent of infants able
to discriminate foreign-language speech
sounds Infants’ ability to discriminate
between speech sounds that are not in their
native language declines between 6 and
12 months of age. Most 6-month-olds from
english-speaking families readily discrimi-
nate between syllables in hindi (blue bars)
and Nthlakapmx (green bars), but most 10-
to 12-month-olds do not. (adapted from

speech sounds. Indeed, becoming a native listener is one of the greatest accom-
plishments of the infant’s first year of postnatal life.
Word Segmentation
As infants begin to tune into the speech sounds of their language, they also begin to
discover another crucial feature of the speech surrounding them: words. This is no
easy feat. Unlike the words typed on this page, there are no spaces between words
in speech, even in IDS. What this means is that most utterances infants hear are
strings of words without pauses between them, like “Lookattheprettybaby! Haveyou
everseensuchaprettybabybefore?” They then have to figure out where the words start
and end. Remarkably, they begin the process of word segmentation during the
second half of the first year.
In the first demonstration of infant word segmentation, Jusczyk & Aslin (1995)
used a head-turn procedure designed to assess infants’ auditory preferences. In this
study, 7-month-olds first listened to passages of speech in which a particular word
was repeated from sentence to sentence—for example, “The cup was bright and
shiny. A clown drank from the red cup. His cup was filled with milk.” After listening
to these sentences several times, infants were tested using the head-turn preference
procedure to see whether they recognized the words repeated in the sentences. In
this method, flashing lights mounted near two loudspeakers located on either side
of an infant are used to draw the infant’s attention to one side or the other. As soon
as the infant turns to look at the light, an auditory stimulus is played through the
speaker, and it continues as long as the infant is looking in that direction. The length
of time the infant spends looking at the light—and hence listening to the sound—
provides a measure of the degree to which the infant is attracted to that sound.
Infants in this study were tested on repetitions of words that had been presented
in the sentences (such as cup) or words that had not (such as bike). The researchers
found that infants listened longer to words that they had heard in the passages of
fluent speech, as compared with words that never occurred in the passages. This
result indicates that the infants were able to pull the words out of the stream of
speech—a task so difficult that even sophisticated speech-recognition software
often fails at it.
How do infants find words in pause-free speech? They appear to be remark-
ably good at picking up regularities in their native language that help them to find
word boundaries. One example is stress patterning, an element of prosody. In En-
glish, the first syllable in two-syllable words is much more likely to be stressed than
the second syllable (as in “English,” “often,” and “second”). By 8 months of age,
English-learning infants expect stressed syllables to begin words and can use this
information to pull words out of fluent speech (Curtin, Mintz, & Christiansen,
2005; Johnson & Jusczyk, 2001; Jusczyk, Houston, & Newsome, 1999; Thiessen
& Saffran, 2003).
Another regularity to which infants are surprisingly sensitive concerns the
distributional properties of the speech they hear. In every language, certain sounds
are more likely to appear together than are others. Sensitivity to such regularities
in the speech stream was demonstrated in a series of statistical-learning experi-
ments in which babies learned new words based purely on regularities in how often
a given sound followed another (Aslin, Saffran, & Newport, 1998; Saffran, Aslin,
& Newport, 1996). The infants listened to a 2-minute recording of four different
three-syllable “words” (e.g., tupiro, golabu, bidaku, padoti) repeated in random order
with no pauses between the “words.” Then, on a series of test trials, the babies were
word segmentation n the process of
discovering where words begin and end in
fluent speech
distributional properties n the phe-
nomenon that in any language, certain
sounds are more likely to appear together
than are others

presented with the “words” they had heard (e.g., bidaku, padoti) and with sequences
that were not words (such as syllable sequences that spanned a word boundary—
for example, kupado, made up from the end of bidaku and the beginning of padoti).
Using the same kind of preferential listening test described for the Juscyzk &
Aslin (1995) study on the previous page, the researchers found that infants dis-
criminated between the words and the sequences that were not words. To do so,
the babies must have registered that certain syllables often occurred together in the
sample of speech they heard. For example, “bi” was always followed by “da” and “da”
was always followed by “ku,” whereas “ku” could be followed by “tu,” “go,” or “pa.”
Thus, the infants used recurrent sound patterns to fish words out of the passing
stream of speech. This ability to learn from distributional properties extends to real
languages as well; English-learning infants, for example, can track similar statistical
patterns when listening to Italian IDS (Pelucchi, Hay, & Saffran, 2009).
Identifying these regularities in speech sounds supports the learning of words.
After repeatedly hearing novel “words” such as timay and dobu embedded in a long
stream of speech sounds, 17-month-olds readily learned those sounds as labels for
objects (Graf Estes et al., 2007). Similarly, after hearing Italian words like mela and
bici embedded in fluent Italian speech, 17-month-olds who had no prior exposure
to Italian readily mapped those labels to objects (Hay et al., 2011). Having already
learned the sound sequences that made up the words apparently made it easier for
the infants to associate the words with their referents.
Probably the most salient regularity for infants is their own name. Infants as
young as 4½ months will listen longer to repetitions of their own name than to
repetitions of a different but similar name (Mandel, Jusczyk, & Pisoni, 1995). Just
a few weeks later, they can pick their own name out of background conversations
(Newman, 2005). This ability helps them to find new words in the speech stream.
After hearing “It’s Jerry’s cup!” a number of times, 6-month-old Jerry is more likely
to learn the word cup than if he had not heard it right after his name (Bortfeld et
al., 2005). Over time, infants recognize more and more familiar words, making it
easier to pluck new ones out of the speech that they hear.
Infants are exceptional in their ability to identify patterns in the speech sur-
rounding them. They start out with the ability to make crucial distinctions among
speech sounds but then narrow their focus to the sounds and sound patterns that
make a difference in their native language. This process lays the groundwork for
their becoming not just native listeners but also native speakers.
Preparation for Production
In their first months, babies are getting ready to talk. The repertoire of sounds
they can produce is initially extremely limited. They cry, sneeze, sigh, burp, and
smack their lips, but their vocal tract is not sufficiently developed to allow them to
produce anything like real speech sounds. Then, at around 6 to 8 weeks of age, in-
fants begin to coo—producing long, drawn-out vowel sounds, such as “ooohh” or
“aaahh.” Young infants entertain themselves with vocal gymnastics, switching from
low grunts to high-pitched cries, from soft murmurs to loud shouts. They click,
smack, blow raspberries, squeal, all with apparent fascination and delight. Through
this practice, infants gain motor control over their vocalizations.
While their sound repertoire is expanding, infants become increasingly aware
that their vocalizations elicit responses from others, and they begin to engage in
dialogues of reciprocal ooohing and aaahing, cooing and gooing with their parents.
With improvement in their motor control of vocalization, they imitate the sounds
how quickly could you pick out a word from
a stream of speech like the one shown here?
It takes 8-month-old infants only 2 minutes
of listening.

of their “conversational” partners, even producing higher-pitched sounds when in-
teracting with their mothers and lower-pitched sounds when interacting with their
fathers (de Boysson-Bardies, 1996/1999).
Babbling Sometime between 6 and 10 months of age, but on average at around 7
months, a major milestone occurs: babies begin to babble. Standard babbling involves
producing syllables made up of a consonant followed by a vowel (“pa,” “ba,” “ma”) that
are repeated in strings (“papapa”). Contrary to the long-held belief that infants babble
a wide range of sounds from their own and other languages ( Jakobson, 1941/1968),
research has revealed that babies actually babble a fairly limited set of sounds, some of
which are not part of their native language (de Boysson-Bardies, 1996/1999).
Native language exposure is a key component in the development of babbling.
Although congenitally deaf infants produce vocalizations similar to those of hear-
ing babies until around 5 or 6 months of age, their vocal babbling occurs very late
and is quite limited (Oller & Eilers, 1988). However, some congenitally deaf ba-
bies do “babble” right on schedule—those who are regularly exposed to sign lan-
guage. Infants exposed to ASL babble manually. They produce repetitive hand
movements that are components of full ASL signs, just as vocally babbled sounds
are repeated components of spoken words (Petitto & Marentette, 1991). Thus, like
infants learning a spoken language, infants learning signed languages seem to ex-
periment with the elements that are combined to make meaningful words in their
native language (Figure 6.6).
As their babbling becomes more varied, it gradually takes on the sounds, rhythm,
and intonational patterns of the language infants hear daily. In a simple but clever
experiment, French adults listened to the babbling of a French 8-month-old and an
8-month-old from either an Arabic- or Cantonese-speaking family. When asked to
identify which baby was the French one in each pair, the adults chose correctly 70%
of the time (de Boysson-Bardies, Sagart, & Durand, 1984). Thus, before infants
utter their first meaningful words, they are, in a sense, native speakers of a language.
early interactions Before we turn to the next big step in language production—
uttering recognizable words—it is important to consider the social context that
promotes language development in most societies. Even before infants start speak-
ing, they display the beginnings of communicative competence: the ability to com-
municate intentionally with another person.
The first indication of communicative competence is turn-taking. In a conversa-
tion, mature participants alternate between speaking and listening. Jerome Bruner
and his colleagues (Bruner, 1977; Ratner & Bruner, 1978) have proposed that learn-
ing to take turns in social interactions is facilitated by parent–infant games, such as
peekaboo and “give and take,” in which caregiver and baby take turns giving and
receiving objects. In these “dialogues,” the infant has the opportunity to alternate
between an active and a passive role, as in a conversation in which one alternates
between speaking and listening. These early interactions give infants practice in bi-
directional communication, providing infants with a scaffold to learn how to use
language to converse with others. Indeed, recent research suggests that caregivers’
babbling n repetitive consonant–vowel
sequences (“bababa . . .”) or hand move-
ments (for learners of signed languages)
produced during the early phases of lan-
guage development
FIGURE 6.6 Manual babbling Babies who are exposed to the sign
language of their deaf parents babble with their hands. a subset of
their hand movements differs from those of infants exposed to spoken
language, and corresponds to the rhythmic patterning of adult signs.
. L

responses to infant babbling may serve a similar function.
When an adult labels an object for an infant just after the in-
fant babbles, the infant’s learning of the label is more greatly
enhanced than when the labeling occurs in the absence of
babbling (Goldstein et al., 2010). The results of this study
suggest that babbling may serve as a signal to the caregiver
that the infant is attentive and ready to learn. This early
back-and-forth may also provide infants with practice in
conversational turn-taking.
As discussed in Chapter 4, successful communication also
requires intersubjectivity, in which two interacting partners
share a mutual understanding. The foundation of intersub-
jectivity is joint attention, which, early on, is established by
the parent’s following the baby’s lead, looking at and com-
menting on whatever the infant is looking at. By 12 months
of age, infants have begun to understand the communicative
nature of pointing, with many also being capable of mean-
ingful pointing themselves (Behne et al., 2012).
We have thus seen that infants spend a good deal of time
getting ready to talk. Through babbling, they gain some initial level of control over
the production of sounds that are necessary to produce recognizable words. As
they do so, they already begin to sound like their parents. Through early interac-
tions with their parents, they develop interactive routines similar to those required
in the use of language for communication. We will now turn our attention to the
processes that lead to infants’ first real linguistic productions: words.
First Words
When babies first begin to segment words from fluent speech, they are
simply recognizing familiar patterns of sounds without attaching any
meaning to them. But then, in a major revolution, they begin to recognize
that words have meaning.
The problem of reference The first step for infants in acquiring the
meanings of words is to address the problem of reference, that is, to start
associating words and meaning. Figuring out which of the multitude of
possible referents is the right one for a particular word is, as the philoso-
pher Willard Quine (1960) pointed out, a very complex problem. If a child
hears someone say “bunny” in the presence of a rabbit, how does the child
know whether this new word refers to the rabbit itself, to its fuzzy tail, to
the whiskers on the right side of its nose, or to the twitching of its nose?
That the problem of reference is a real problem is illustrated by the case
of a toddler who thought “Phew!” was a greeting, because it was the first
thing her mother said on entering the child’s room every morning (Ferrier, 1978).
Early Word Recognition
Infants begin associating highly familiar words with their highly familiar referents
surprisingly early on. When 6-month-olds hear either “Mommy” or “Daddy,” they
look toward the appropriate person (Tincoff & Jusczyk, 1999). Infants gradually
come to understand the meaning of less frequently heard words, with the pace of
their vocabulary-building varying greatly from one child to another. Remarkably,
This toddler is pointing to get her father to
share her attention—to achieve intersubjec-
tivity. Once the father identifies the focus of
his daughter’s attention, he may even decide
to add it to the shopping basket.
a classic problem posed by philosopher
Willard Quine was how someone who does
not know the word rabbit could figure out
exactly what it refers to. This mother may be
helping her son learn a new word by labeling
the referent while it is the focus of her son’s
/ D
reference n in language and speech, the
associating of words and meaning

parents are often unaware of just how many words their infants rec-
ognize. Using a computer monitor, Bergelson and Swingley (2012)
showed infants pairs of pictures of common foods and body parts
and tracked the infants’ eye gaze when one of the pictures was
named. They found that even 6-month-olds looked to the correct
picture significantly more often than would be expected by chance,
demonstrating that they recognized the names of these items. Strik-
ingly, most of their parents reported that the infants did not know
the meanings of these words. So not only do infants understand far
more words than they can produce; they also understand far more
words than even their caregivers realize.
One of the remarkable features of infants’ early word recognition
is how rapidly they understand what they are hearing. To illumi-
nate the age-related dynamics of this understanding, Fernald and
her colleagues presented infants with images depicting pairs of fa-
miliar objects, such as a dog and a baby, and observed how quickly the infants moved
their eyes to the correct object after hearing its label used (e.g., “Where’s the baby?”).
The researchers found that whereas 15-month-olds waited until they had heard the
whole word to look at the target object, 24-month-olds looked at the correct ob-
ject after hearing only the first part of its label, just as adults do (Fernald et al., 1998;
Fernald, Perfors, & Marchman, 2006; Fernald, Swingley, & Pinto, 2001). Older in-
fants can also use context to help them recognize words. For example, those who are
learning a language that has a grammatical gender system (like Spanish or French)
can use the gender of the article preceding the noun (la versus el in Spanish; la versus
le in French) to speed their recognition of the noun itself (Lew-Williams & Fernald,
2007; Van Heugten & Shi, 2009). Other visual-fixation research has shown that older
infants can even recognize familiar words when they are mispronounced (e.g., “vaby”
for “baby,” “gall” for “ball,” “tog” for “dog,” etc.), though their recognition is slower
than when they hear the words pronounced correctly (Swingley & Aslin, 2000).
early word production Gradually, infants begin to say some of the words they un-
derstand, with most producing their first words between 10 and 15 months of age.
The words a child is able to say are referred to as the child’s productive vocabulary.
What counts as an infant’s “first word”? It can be any specific utterance con-
sistently used to refer to something or to express something. Even with this loose
criterion, identification of an infant’s earliest few words can be problematic. For
one thing, doting parents often misconstrue their child’s babbling as words. For
another, early words may differ from their corresponding adult forms. For exam-
ple, Woof was one of the first words spoken by the boy whose linguistic progress
was illustrated at the beginning of this chapter. It was used to refer to the dog next
door—both to excitedly name the animal when it appeared in the neighbors’ yard
and to wistfully request the dog’s presence when it was absent.
Infants’ early word productions are limited by their ability to pronounce words
clearly enough that an adult can recognize them. To make life easier for themselves,
infants adopt a variety of simplification strategies (Gerken, 1994). For example,
they leave out the difficult bits of words, turning banana into “nana,” or they sub-
stitute easier sounds for hard-to-say ones—“bubba” for brother, “wabbit” for rab-
bit. Sometimes they reorder parts of words to put an easier sound at the beginning
of the word, as in the common “pasketti” (for spaghetti) or the more idiosyncratic
“Cagoshin” (the way the child quoted at the beginning of the chapter continued for
several years to say Chicago).
When this infant hears the word mouth,
will she look at the picture of the mouth or
at the picture of the apple? The speed and
accuracy of her looks in response to words
provide a useful measure of her vocabulary

Once children start talking, what do they talk about? The early productive vo-
cabularies of children in the United States include names for people, objects, and
events from the child’s everyday life (Clark, 1979; K. Nelson, 1973). Children
name their parents, siblings, pets, and themselves, as well as other personally im-
portant objects such as cookies, juice, and balls. Frequent events and routines are
also labeled—“up,” “bye-bye,” “night-night.” Important modifiers are also used—
“mine,” “hot,” “all gone.” Table 6.1 reveals substantial cross-linguistic similarities
in the content of the first 10 words of children in the United States, Hong Kong,
and Beijing. As the table shows, many of infants’ first words in the three societies
referred to specific people or were sound effects (Tardif et al., 2008).
In the early productive vocabularies of children learning English, nouns predomi-
nate. One reason may be that because nouns label entities—whereas verbs represent
relations among entities—the meanings of nouns are easier to pick up from observa-
tion than are the meanings of verbs (Gentner, 1982). Similarly, words that are easier
to picture—that are more imageable—are easier for infants and toddlers to learn
(McDonough et al., 2011). Another reason is that middle-class American mothers
(the group most frequently studied) engage in frequent bouts of object-labeling for
their infants—“Look, there’s a turtle! Do you see