Cognitive Development in Infants and Toddlers

What you’ll learn to do: explain cognitive development in infants and toddlers

A toddler building a tower out of colorful blocks

In addition to rapid physical growth, young children also exhibit significant development of their cognitive abilities, particularly in language acquisition and in the ability to think and reason. You already learned a little bit about Piaget’s theory of cognitive development, and in this section, we’ll apply that model to cognitive tasks during infancy and toddlerhood. Piaget described intelligence in infancy as sensorimotor or based on direct, physical contact where infants use senses and motor skills to taste, feel, pound, push, hear, and move in order to experience the world. These basic motor and sensory abilities provide the foundation for the cognitive skills that will emerge during the subsequent stages of cognitive development.

Learning Outcomes

  • Describe each of Piaget’s theories and stages of sensorimotor intelligence
  • Explain learning and memory abilities in infants and toddlers
  • Describe stages of language development during infancy
  • Compare theories of language development in toddlers
  • Explain the procedure, results, and implications of Hamlin and Wynn’s research on moral reasoning in infants

Cognitive Development

Cognitive Development in Children

In order to adapt to the evolving environment around us, humans rely on cognition, both adapting to the environment and also transforming it. In general, all theorists studying cognitive development address three main issues:

  1. The typical course of cognitive development
  2. The unique differences between individuals
  3. The mechanisms of cognitive development (the way genetics and environment combine to generate patterns of change)

Piaget and Sensorimotor Intelligence

Adorable smiling toddler boy.
Figure 1. Toddlers happily explore the world, engaged in purposeful goal-directed behavior.

How do infants connect and make sense of what they are learning? Remember that Piaget believed that we are continuously trying to maintain cognitive equilibrium, or balance, between what we see and what we know (Piaget, 1954). Children have much more of a challenge in maintaining this balance because they are constantly being confronted with new situations, new words, new objects, etc. All this new information needs to be organized, and a framework for organizing information is referred to as a schema. Children develop schemas through the processes of assimilation and accommodation.

For example, 2-year-old Deja learned the schema for dogs because her family has a Poodle. When Deja sees other dogs in her picture books, she says, “Look mommy, dog!” Thus, she has assimilated them into her schema for dogs. One day, Deja sees a sheep for the first time and says, “Look mommy, dog!” Having a basic schema that a dog is an animal with four legs and fur, Deja thinks all furry, four-legged creatures are dogs. When Deja’s mom tells her that the animal she sees is a sheep, not a dog, Deja must accommodate her schema for dogs to include more information based on her new experiences. Deja’s schema for dog was too broad since not all furry, four-legged creatures are dogs. She now modifies her schema for dogs and forms a new one for sheep.

Let’s examine the transition that infants make from responding to the external world reflexively as newborns, to solving problems using mental strategies as two-year-olds. Piaget called this first stage of cognitive development sensorimotor intelligence (the sensorimotor period) because infants learn through their senses and motor skills. He subdivided this period into six substages:

Table 1. Sensorimotor substages.
Stage Age
Stage 1 – Reflexes Birth to 6 weeks
Stage 2 – Primary Circular Reactions 6 weeks to 4 months
Stage 3 – Secondary Circular Reactions 4 months to 8 months
Stage 4 – Coordination of Secondary Circular Reactions 8 months to 12 months
Stage 5 – Tertiary Circular Reactions 12 months to 18 months
Stage 6 – Mental Representation 18 months to 24 months

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Substages of Sensorimotor Intelligence

For an overview of the substages of sensorimotor thought, it helps to group the six substages into pairs. The first two substages involve the infant’s responses to its own body, call primary circular reactions. During the first month first (substage one), the infant’s senses, as well motor reflexes are the foundation of thought.

Substage One: Reflexive Action (Birth through 1st month)

This active learning begins with automatic movements or reflexes (sucking, grasping, staring, listening). A ball comes into contact with an infant’s cheek and is automatically sucked on and licked. But this is also what happens with a sour lemon, much to the infant’s surprise! The baby’s first challenge is to learn to adapt the sucking reflex to bottles or breasts, pacifiers or fingers, each acquiring specific types of tongue movements to latch, suck, breath, and repeat. This adaptation demonstrates that infants have begun to make sense of sensations. Eventually, the use of these reflexes becomes more deliberate and purposeful as they move onto substage two.

Substage Two: First Adaptations to the Environment (1st through 4th months)

Fortunately, within a few days or weeks, the infant begins to discriminate between objects and adjust responses accordingly as reflexes are replaced with voluntary movements. An infant may accidentally engage in a behavior and find it interesting, such as making a vocalization. This interest motivates trying to do it again and helps the infant learn a new behavior that originally occurred by chance. The behavior is identified as circular and primary because it centers on the infant’s own body. At first, most actions have to do with the body, but in months to come, will be directed more toward objects. For example, the infant may have different sucking motions for hunger and others for comfort (i.e. sucking a pacifier differently from a nipple or attempting to hold a bottle to suck it).

The next two substages (3 and 4), involve the infant’s responses to objects and people, called secondary circular reactions. Reactions are no longer confined to the infant’s body and are now interactions between the baby and something else.

Substage Three: Repetition (4th through 8th months)

During the next few months, the infant becomes more and more actively engaged in the outside world and takes delight in being able to make things happen by responding to people and objects. Babies try to continue any pleasing event. Repeated motion brings particular interest as the infant is able to bang two lids together or shake a rattle and laugh. Another example might be to clap their hands when a caregiver says “patty-cake.” Any sight of something delightful will trigger efforts for interaction.

Substage Four: New Adaptations and Goal-Directed Behavior (8th through 12th months)

Now the infant becomes more deliberate and purposeful in responding to people and objects and can engage in behaviors that others perform and anticipate upcoming events. Babies may ask for help by fussing, pointing, or reaching up to accomplish tasks, and work hard to get what they want. Perhaps because of continued maturation of the prefrontal cortex, the infant becomes capable of having a thought and carrying out a planned, goal-directed activity such as seeking a toy that has rolled under the couch or indicating that they are hungry. The infant is coordinating both internal and external activities to achieve a planned goal and begins to get a sense of social understanding. Piaget believed that at about 8 months (during substage 4), babies first understood the concept of object permanence, which is the realization that objects or people continue to exist when they are no longer in sight.

The last two stages (5 and 6), called tertiary circular reactions, consist of actions (stage 5) and ideas (stage 6) where infants become more creative in their thinking.

Substage Five: Active Experimentation of “Little Scientists” (12th through 18th months)

The toddler is considered a “little scientist” and begins exploring the world in a trial-and-error manner, using motor skills and planning abilities. For example, the child might throw their ball down the stairs to see what happens or delight in squeezing all of the toothpaste out of the tube. The toddler’s active engagement in experimentation helps them learn about their world. Gravity is learned by pouring water from a cup or pushing bowls from high chairs. The caregiver tries to help the child by picking it up again and placing it on the tray. And what happens? Another experiment! The child pushes it off the tray again causing it to fall and the caregiver to pick it up again! A closer examination of this stage causes us to really appreciate how much learning is going on at this time and how many things we come to take for granted must actually be learned. This is a wonderful and messy time of experimentation and most learning occurs by trial and error.

Watch It

See how even babies think like little scientists in the selected clip from this Ted talk.

Substage Six: Mental Representations (18th month to 2 years of age)

The child is now able to solve problems using mental strategies, to remember something heard days before and repeat it, to engage in pretend play, and to find objects that have been moved even when out of sight. Take, for instance, the child who is upstairs in a room with the door closed, supposedly taking a nap. The doorknob has a safety device on it that makes it impossible for the child to turn the knob. After trying several times to push the door or turn the doorknob, the child carries out a mental strategy to get the door opened – he knocks on the door! Obviously, this is a technique learned from the past experience of hearing a knock on the door and observing someone opening the door. The child is now better equipped with mental strategies for problem-solving. Part of this stage also involves learning to use language. This initial movement from the “hands-on” approach to knowing about the world to the more mental world of stage six marked the transition to preoperational thinking, which you’ll learn more about in a later module.

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Development of Object Permanence

A critical milestone during the sensorimotor period is the development of object permanence. Introduced during substage 4 above, object permanence is the understanding that even if something is out of sight, it continues to exist. The infant is now capable of making attempts to retrieve the object. Piaget thought that, at about 8 months, babies first understand the concept of objective permanence, but some research has suggested that infants seem to be able to recognize that objects have permanence at much younger ages (even as young as 4 months of age). Other researchers, however, are not convinced (Mareschal & Kaufman, 2012).[1] It may be a matter of “grasping vs. mastering” the concept of objective permanence. Overall, we can expect children to grasp the concept that objects continue to exist even when they are not in sight by around 8 months old, but memory may play a factor in their consistency. Because toddlers (i.e., 12–24 months old) have mastered object permanence, they enjoy games like hide-and-seek, and they realize that when someone leaves the room they will come back (Loop, 2013). Toddlers also point to pictures in books and look in appropriate places when you ask them to find objects.

Watch It

Although the styles and cinematography in this video are dated, the information is valuable in understanding how researchers, like Dr. Rene Baillargeon, study object permanence in young infants.

Learning and Memory Abilities in Infants

Memory is central to cognitive development. Our memories form the basis for our sense of self, guide our thoughts and decisions, influence our emotional reactions, and allow us to learn (Bauer, 2008)[2].

It is thought that Piaget underestimated memory ability in infants (Schneider, 2015)[3].

As mentioned when discussing the development of infant senses, within the first few weeks of birth, infants recognize their caregivers by face, voice, and smell. Sensory and caregiver memories are apparent in the first month, motor memories by 3 months, and then, at about 9 months, more complex memories including language (Mullally & Maguire, 2014)[4]. There is agreement that memory is fragile in the first months of life, but that improves with age. Repeated sensations and brain maturation are required in order to process and recall events (Bauer, 2008). Infants remember things that happened weeks and months ago (Mullally & Maguire, 2014), although they most likely will not remember it decades later. From the cognitive perspective, this has been explained by the idea that the lack of linguistic skills of babies and toddlers limit their ability to mentally represent events; thereby, reducing their ability to encode memory. Moreover, even if infants do form such early memories, older children and adults may not be able to access them because they may be employing very different, more linguistically based, retrieval cues than infants used when forming the memory. 

Watch It

Watch this Ted talk from Alison Gopnik to hear about more research done on cognition in babies.

Language Development

Given the remarkable complexity of a language, one might expect that mastering a language would be an especially arduous task; indeed, for those of us trying to learn a second language as adults, this might seem to be true. However, young children master language very quickly with relative ease. B. F. Skinner (1957) proposed that language is learned through reinforcement. Noam Chomsky (1965) criticized this behaviorist approach, asserting instead that the mechanisms underlying language acquisition are biologically determined. The use of language develops in the absence of formal instruction and appears to follow a very similar pattern in children from vastly different cultures and backgrounds. It would seem, therefore, that we are born with a biological predisposition to acquire a language (Chomsky, 1965; Fernández & Cairns, 2011). Moreover, it appears that there is a critical period for language acquisition, such that this proficiency at acquiring language is maximal early in life; generally, as people age, the ease with which they acquire and master new languages diminishes (Johnson & Newport, 1989; Lenneberg, 1967; Singleton, 1995).

Children begin to learn about language from a very early age (Table 1). In fact, it appears that this is occurring even before we are born. Newborns show a preference for their mother’s voice and appear to be able to discriminate between the language spoken by their mother and other languages. Babies are also attuned to the languages being used around them and show preferences for videos of faces that are moving in synchrony with the audio of spoken language versus videos that do not synchronize with the audio (Blossom & Morgan, 2006; Pickens, 1994; Spelke & Cortelyou, 1981).

Table 2. Stages of Language and Communication Development
Stage Age Developmental Language and Communication
1 0–3 months Reflexive communication
2 3–8 months Reflexive communication; interest in others
3 8–12 months Intentional communication; sociability
4 12–18 months First words
5 18–24 months Simple sentences of two words
6 2–3 years Sentences of three or more words
7 3–5 years Complex sentences; has conversations

Each language has its own set of phonemes that are used to generate morphemes, words, and so on. Babies can discriminate among the sounds that make up a language (for example, they can tell the difference between the “s” in vision and the “ss” in fission); early on, they can differentiate between the sounds of all human languages, even those that do not occur in the languages that are used in their environments. However, by the time that they are about 1 year old, they can only discriminate among those phonemes that are used in the language or languages in their environments (Jensen, 2011; Werker & Lalonde, 1988; Werker & Tees, 1984).

Watch It

This video explains some of the research surrounding language acquisition in babies, particularly those learning a second language.


Newborn Communication

Wide-eyed baby boy.
Figure 2. Before they develop language, infants communicate using facial expressions.

Do newborns communicate? Certainly, they do. They do not, however, communicate with the use of language. Instead, they communicate their thoughts and needs with body posture (being relaxed or still), gestures, cries, and facial expressions. A person who spends adequate time with an infant can learn which cries indicate pain and which ones indicate hunger, discomfort, or frustration.

Intentional Vocalizations

Infants begin to vocalize and repeat vocalizations within the first couple of months of life. That gurgling, musical vocalization called cooing can serve as a source of entertainment to an infant who has been laid down for a nap or seated in a carrier on a car ride. Cooing serves as practice for vocalization. It also allows the infant to hear the sound of their own voice and try to repeat sounds that are entertaining. Infants also begin to learn the pace and pause of conversation as they alternate their vocalization with that of someone else and then take their turn again when the other person’s vocalization has stopped. Cooing initially involves making vowel sounds like “oooo.” Later, as the baby moves into babbling (see below), consonants are added to vocalizations such as “nananananana.”

Babbling and Gesturing

Between 6 and 9 months, infants begin making even more elaborate vocalizations that include the sounds required for any language. Guttural sounds, clicks, consonants, and vowel sounds stand ready to equip the child with the ability to repeat whatever sounds are characteristic of the language heard. These babies repeat certain syllables (ma-ma-ma, da-da-da, ba-ba-ba), a vocalization called babbling because of the way it sounds. Eventually, these sounds will no longer be used as the infant grows more accustomed to a particular language. Deaf babies also use gestures to communicate wants, reactions, and feelings. Because gesturing seems to be easier than vocalization for some toddlers, sign language is sometimes taught to enhance one’s ability to communicate by making use of the ease of gesturing. The rhythm and pattern of language are used when deaf babies sign just as when hearing babies babble.

At around ten months of age, infants can understand more than they can say. You may have experienced this phenomenon as well if you have ever tried to learn a second language. You may have been able to follow a conversation more easily than to contribute to it.

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Holophrasic Speech

Children begin using their first words at about 12 or 13 months of age and may use partial words to convey thoughts at even younger ages. These one-word expressions are referred to as holophrasic speech (holophrase). For example, the child may say “ju” for the word “juice” and use this sound when referring to a bottle. The listener must interpret the meaning of the holophrase. When this is someone who has spent time with the child, interpretation is not too difficult. They know that “ju” means “juice” which means the baby wants some milk! But, someone who has not been around the child will have trouble knowing what is meant. Imagine the parent who exclaims to a friend, “Ezra’s talking all the time now!” The friend hears only “ju da ga” which, the parent explains, means “I want some milk when I go with Daddy.”


A child who learns that a word stands for an object may initially think that the word can be used for only that particular object. Only the family’s Irish Setter is a “doggie.” This is referred to as underextension. More often, however, a child may think that a label applies to all objects that are similar to the original object. In overextension, all animals become “doggies,” for example.

First words and cultural influences

First words for English-speaking children tend to be nouns. The child labels objects such as a cup or a ball. In a verb-friendly language such as Chinese, however, children may learn more verbs. This may also be due to the different emphasis given to objects based on culture. Chinese children may be taught to notice action and relationship between objects while children from the United States may be taught to name an object and its qualities (color, texture, size, etc.). These differences can be seen when comparing interpretations of art by older students from China and the United States.

Vocabulary growth spurt

One-year-olds typically have a vocabulary of about 50 words. But by the time they become toddlers, they have a vocabulary of about 200 words and begin putting those words together in telegraphic speech (short phrases). This language growth spurt is called the naming explosion because many early words are nouns (persons, places, or things).

Two-word sentences and telegraphic speech

Words are soon combined and 18-month-old toddlers can express themselves further by using phrases such as “baby bye-bye” or “doggie pretty.” Words needed to convey messages are used, but the articles and other parts of speech necessary for grammatical correctness are not yet included. These expressions sound like a telegraph (or perhaps a better analogy today would be that they read like a text message) where unnecessary words are not used. “Give baby ball” is used rather than “Give the baby the ball.” Or a text message of “Send money now!” rather than “Dear Mother. I really need some money to take care of my expenses.” You get the idea.

Child-directed speech

Why is a horse a “horsie”? Have you ever wondered why adults tend to use “baby talk” or that sing-song type of intonation and exaggeration used when talking to children? This represents a universal tendency and is known as child-directed speech or motherese or parentese. It involves exaggerating the vowel and consonant sounds, using a high-pitched voice, and delivering the phrase with great facial expression. Why is this done? It may be in order to clearly articulate the sounds of a word so that the child can hear the sounds involved. Or it may be because when this type of speech is used, the infant pays more attention to the speaker and this sets up a pattern of interaction in which the speaker and listener are in tune with one another. When I demonstrate this in class, the students certainly pay attention and look my way. Amazing! It also works in the college classroom!

Watch It

This video examines new research on infant-directed speech.

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Theories of Language Development

How is language learned? Each major theory of language development emphasizes different aspects of language learning: that infants’ brains are genetically attuned to language, that infants must be taught, and that infants’ social impulses foster language learning. The first two theories of language development represent two extremes in the level of interaction required for language to occur (Berk, 2007).

Chomsky and the language acquisition device

This theory posits that infants teach themselves and that language learning is genetically programmed. The view is known as nativism and was advocated by Noam Chomsky, who suggested that infants are equipped with a neurological construct referred to as the language acquisition device (LAD), which makes infants ready for language. The LAD allows children, as their brains develop, to derive the rules of grammar quickly and effectively from the speech they hear every day. Therefore, language develops as long as the infant is exposed to it. No teaching, training, or reinforcement is required for language to develop. Instead, language learning comes from a particular gene, brain maturation, and the overall human impulse to imitate.

Skinner and reinforcement

This theory is the opposite of Chomsky’s theory because it suggests that infants need to be taught language. This idea arises from behaviorism. Learning theorist, B. F. Skinner, suggested that language develops through the use of reinforcement. Sounds, words, gestures, and phrases are encouraged by following the behavior with attention, words of praise, treats, or anything that increases the likelihood that the behavior will be repeated. This repetition strengthens associations, so infants learn the language faster as parents speak to them often. For example, when a baby says “ma-ma,” the mother smiles and repeats the sound while showing the baby attention. So, “ma-ma” is repeated due to this reinforcement.

Social pragmatics

Another language theory emphasizes the child’s active engagement in learning the language out of a need to communicate. Social impulses foster infant language because humans are social beings and we must communicate because we are dependent on each other for survival. The child seeks information, memorizes terms, imitates the speech heard from others, and learns to conceptualize using words as language is acquired. Tomasello &  Herrmann (2010) argue that all human infants, as opposed to chimpanzees, seek to master words and grammar in order to join the social world [5] Many would argue that all three of these theories (Chomsky’s argument for nativism, conditioning, and social pragmatics) are important for fostering the acquisition of language (Berger, 2004).

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Moral Reasoning in Infants

The Foundation of Moral Reasoning in Infants

Young baby, around 6 months old, doing tummy time and looking happily at the camera.
Figure 3. Maybe babies know more than we think they do!

The work of Lawrence Kohlberg was an important start to modern research on moral development and reasoning. However, Kohlberg relied on a specific method: he presented moral dilemmas and asked children and adults to explain what they would do and—more importantly—why they would act in that particular way. Kohlberg found that children tended to make choices based on avoiding punishment and gaining praise. But children are at a disadvantage compared to adults when they must rely on language to convey their inner thoughts and emotional reactions, so what they say may not adequately capture the complexity of their thinking.

Starting in the 1980s, developmental psychologists created new methods for studying the thought processes of children and infants long before they acquire language. One particularly effective method is to present children with puppet shows to grab their attention and then record nonverbal behaviors, such as looking and choosing, to identify children’s preferences or interests.

A research group at Yale University has been using the puppet show technique to study moral thinking of children for much of the past decade. What they have discovered has given us a glimpse of surprisingly complex thought processes that may serve as the foundation of moral reasoning.

EXPERIMENT 1: Do children prefer givers or takers?

In 2011, J. Kiley Hamlin and Karen Wynn put on puppet shows for very young children: 5-month-old infants. The infants watch a puppet bouncing a ball. We’ll call this puppet the “bouncer puppet.” Two other puppets stand at the back of the stage, one to left and the other to the right. After a few bounces, the ball gets away from the bouncer puppet and rolls to the side of the stage toward one of the other puppets. This puppet grabs the ball. The bouncer puppet turns toward the ball and opens its arms as if asking for the ball back.

This is where the puppet show gets interesting (for a young infant, anyway!).  Sometimes, the puppet with the ball rolls it back to the bouncer puppet. This is the “giver puppet” condition. Other times, the infant sees a different ending. As the bouncer puppet opens its arms to ask for the ball, the puppet with the ball turns and runs away with it. This is the “taker puppet” condition. Although the giver and taker puppets are two copies of the same animal doll, they are easily distinguished because they are wearing different colored shirts, and color is a quality that infants easily distinguish and remember. It looks like this:

Each infant sees both conditions: the giver condition and the taker condition. Just after the end of the second puppet show (i.e., the second condition), a new researcher, who doesn’t know which puppet was the giver and which was the taker, sits in front of the infant with the giver puppet in one hand and the taker puppet in the other. The 5-month-old infants are allowed to reach for a puppet. The one the child reaches out to touch is considered the preferred puppet.

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Remember that Lawrence Kohlberg thought that children at this age—and, in fact, through 9 years of age—are primarily motivated to avoid punishment and seek rewards. Neither Kohlberg nor Carol Gilligan nor Jean Piaget was likely to predict that infants would develop preferences based on the type of behavior shown by other individuals.

Work It Out

The puppet show is over and the experimenter is holding the two dolls—the giver puppet and the taker puppet—in front of the infant. The reaching behavior of the infant is being videotaped for later analysis.

What do you think? Make a prediction about the results of this study—which should reflect your own theory of an infant’s ability to judge and care about the types of behavior others display. Do you think infants will choose the taker or the giver puppet? Do you expect the results to be significant?

INSTRUCTIONS: Adjust the pink bar on the left to show the percentage of infants who reached for the giver puppet. The yellow bar on the right will automatically adjust to make the total (sum of both bars) equal 100%.

[reveal-answer q=”291461″]Show Answer[/reveal-answer]
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Here are the results from Experiment 1:

Results from experiment 1 show the giver bar at 83% and the taker bar at 17%.
Figure 4. Results from Experiment 1.

Experiment 1 suggests that 5-month-old infants are not just passive observers. They notice what others do and, if we are interpreting the results of experiments like this one correctly, they distinguish helpful behaviors (“prosocial behaviors”) from behaviors that hurt others (“antisocial behaviors”). But they do more that that. They are attracted to those who are acting in a prosocial way, and they reject those who act in an antisocial way.

These researchers also tested infants who were only 3-months old. These infants were so immature that they did not yet have good control of their arms, so the experimenter could not use “reaching for one of the puppets” as the dependent variable, as they did with the 5-month-olds. Three-month-old infants can control where they look quite well, and previous research has indicated that very young infants will look longer at objects they want. The researchers showed these very young infants the same puppet shows that were described above and then, during the choice phase, they recorded which puppet (giver or taker) the 3-month-olds looked at longer. The results were very similar to those found with the 5-month-olds. A strong majority of younger infants (92%) looked longer at the giver puppet than the taker puppet.

But this isn’t the end of the story…

EXPERIMENT 2: Do infants judge others based on their behavior?

In the research world, the early attempts to study something, when the researchers work to develop a solid and reliable research procedure, is often the most challenging time. Once the researcher works through initial problems and issues and begins to get consistent results, they can gain a deeper understanding by adding new variables or testing different groups of subjects (e.g., older children or children with some interesting psychological characteristics).

The study you just read about is an example of a simple, basic study. The researchers found that infants preferred puppets that help another puppet (the puppet in the giver condition) over puppets that are not nice to another puppet (the puppet in the taker condition). A common sense interpretation of this simple result is that infants like nice behavior and they dislike hurtful behavior. And perhaps that is as complicated as an 8-month-old infant’s thoughts can be. But maybe not.

Dr. Hamlin and her colleagues wondered if infants might consider more factors when judging an event. Adults generally prefer situations where good things happen to someone rather than something harmful. However, when adults see someone do something bad, they may find satisfaction in seeing that person punished by having something bad happen to him or her. In a nutshell: good things should happen to good people and bad things should happen to bad people. This is what is called “just world” thinking, where people get what they deserve.

In the study we will call Experiment 2, Hamlin’s team tested 8-month-old infants and repeated the procedures from Experiment 1 with a major addition. In Experiment 1 (described above), the puppet bouncing the ball was a neutral character, neither good nor bad. In Experiment 2, the infants saw 2 different shows. First, they saw the bouncer puppet either helping or hindering another puppet. Then, they watched the same ball-bouncing puppet show. Here is what happened:

  • Puppet Show #1:  A puppet is trying to open a box, but cannot quite succeed. Two puppets stand in the background. For some infants, as the first puppet struggles to open the box, one of the puppets in the back comes forward and helps to open the box. This is the helper puppet. For other children, as the first puppet struggles, a puppet comes from the back and jumps on the box, slamming it shut. This is the hinderer puppet. Each infant sees only a helper or a hinderer—not both. Here is a video showing the helper puppet situation:

  • Puppet Show #2: Just after the infants have watched the first show, the second puppet show begins. This is the show that you read about in Experiment 1. The only thing that is new is that the bouncer puppet, the one that loses the ball, is either the helper puppet from Puppet Show #1 or the hinderer puppet from Puppet Show #1. Each infant sees this puppet lose the ball to a giver, who returns the ball, and to a taker, who runs off with the ball.

This video demonstrates show #2.  The elephant in the yellow shirt from the first show is now bouncing a ball. After dropping the ball, the moose in the green shirt gives it back to him, while the moose in the red shirt takes it away.



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So far we have concluded that even young babies prefer the “nice” puppet and show a preference for a puppet who helps another puppet. But this only happened when the bouncer puppet was the helper from the first puppet show. What if, instead of the nice elephant in the yellow shirt bouncing the ball, the elephant in the red shirt (the one who jumped on the duck’s box, remember?) was the one bouncing the ball? Imagine the same scenario: the mean elephant in the red shirt is bouncing the ball, he drops it, and the moose in the green shirt gives it to him or the moose in the red shirt takes it away.

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Bar graph showing the percentage of eight month olds who prefer the giver puppet or the taker puppet. The blue bars show that 75% of babies preferred the giver when giving to the helper bouncer, while 25% chose the taker. If the hinderer were bouncing the ball, the red graphs show that only 19% chose the giver, and 81% chose the taker.
Figure 5. This bar graph shows the results of Experiment 2 for 8-month-old infants. The blue bars show the preferences for the infants who saw the helper from the first show as the bouncer in the second. Bar A is taller than Bar B, showing the greater choice of the giver than the taker puppet. The red bars show the reverse effect. The babies strongly preferred the taker (Bar C) to the giver (Bar D) when the puppet bouncing the ball had been the hinderer, who jumped on the box in the first show.

So now things are getting interesting, right? Do 8-month old infants understand the concepts of revenge or justice? We must always be careful when labeling behaviors of children (or animals) with characteristics we use for human adults. In the description above, we have talked of “nice puppets” and “mean puppets” and used other loaded terms. It is tempting to interpret the choices of the 8-month-olds as a kind of revenge motive: the bad guy gets its just desserts (the hinderer puppet has its ball stolen) and the good guy gets its just reward (the helper puppet is itself helped by the giver). Maybe that is what is going on, but we encourage you to consider these very sophisticated types of thinking as merely one hypothesis. Remember the facts—what did the puppets do and what choices did the infants make?—without committing yourself to the adult-level interpretation.

The researchers believe that this type of thinking, which is remarkably sophisticated, takes some cognitive development. They tested 5-month-olds using the same procedures, and the results with these younger infants were different. The 5-month-olds showed an overwhelming preference for the giver puppets, regardless of who was bouncing the ball. Maybe it is too complex for them to understand that the bouncer puppet in the second show was the same puppet from the first show. Or perhaps their memory processes are too fragile to hold onto information for that length of time. Maybe the revenge motive is too advanced. Or maybe something else is going on. What is clear is that 5-month-olds and 8-month-olds respond differently to the situations tested in the second experiment.

EXPERIMENT 3: Do infants judge others based on their preferences?

Across the first two experiments, infants appear to prefer puppets (and, by extension, maybe people, as well) that are helpful over those that are not helpful. Experiment 2 complicated our story a bit, but it still appears that prosocial behavior is attractive to infants and antisocial behavior is unattractive. But another experiment, again using the bouncing ball show, suggests that infants as young as 8-months of age may have some other motives that are less altruistic than the first two experiments indicate.

In a study by Hamlin, Mahanjan, Liberman, and Wynn from 2013, 9-month-old infants watched the bouncing ball show, but with a new twist.

At the beginning of the experiment—Phase 1—the infants were given a choice between graham crackers and green beans. The experimenters determined which food the infant preferred.

Then, in Phase 2, the infants watched a puppet make the same choice. For half of the infants, the puppet chose the same food that they preferred, saying “Mmmm, yum! I like ___(graham crackers or green beans)!” and saying “Eww, yuck! I don’t like _____ (graham crackers or green beans!”  This was called the SIMILAR condition because the puppet was similar to the child in its food preference. For the other half of the infants, the puppet chose the other food, choosing graham crackers if the infant preferred green beans and preferring green beans if the infant liked graham crackers. This was the DISSIMILAR condition.

Why did the experimenters do this? They wanted to know if young children form in-groups and out-groups by perceiving some people as being like them and other people as being unlike them. The experimenters noted in their research introduction that we (adults) are influenced by our perception that others are similar to us or not like us. We tend to project positive qualities—being trustworthy, intelligent, kind—on people we perceive as similar to ourselves, and people we see as unlike us are seen as having negative qualities—being relatively untrustworthy, unintelligent, and unkind.[6]

Of course, there is a big difference between claiming that adults use similarity to make judgments about others and saying that infants less than a year of age do the same thing. However, the researchers note that some recent research has suggested that infants less than a year old are more likely to develop peer friendships with other infants who “share their own food, clothing, or toy preferences” compared to those who don’t.

So, back to the experiment. In Phase 3, the infants either saw a similar puppet (one that chose the food the baby preferred) or a dissimilar puppet (one that chose the food the baby did not prefer) bouncing the ball. As in the other experiments, the ball got away from the bouncer and rolled to the back of the stage. In one instance, the giver puppet returned the ball and, in the other instance, the taker puppet ran away with the ball. Finally, in Phase 4, the 9-month-old baby was shown the giver and taker puppet and the experimenters recorded which of the two puppets the baby preferred (reached out to touch). This video shows the dog in the light blue shirt giving the ball back to the red bunny that preferred graham crackers.

Here is a summary of the four phases in Experiment 3:

  • Phase 1: The infant chooses graham crackers or green beans.
  • Phase 2: The bouncer puppets choose graham crackers or green beans.
    • Similar condition: The bouncer chooses the same food that the infant chose.
    • Dissimilar condition: The bouncer chooses the food that the infant did not choose.
  • Phase 3: This is the same bouncing ball experiment that you have been reading about.
    • Remember that each child sees both the Giver and Taker shows.
  • Phase 4: This is the same choice—Giver or Taker—that was the final phase in the other two experiments

Try It

Work It Out

Now make predictions for the results. Here is a matrix picture of the design of the experiment:

INSTRUCTIONS: Adjust bars A and C to make your predictions. Bar A represents the “nice” puppet who gave the ball to the bouncer puppet that liked the same food as the child, while bar B represents the “mean” puppet who took the ball away from the bouncer puppet who liked the same food as the child. Bar C represents the “nice” puppet who gave the ball back to the puppet who did not like the same food as the child, and bar D represents the puppet who took the ball away from the puppet who did not like the same food.

As before, move the bars on the left to indicate the percentage of infants preferring the giver puppet in the similar condition (purple bars) and in the dissimilar condition (green bars). The bars on the right will adjust to make the total in each of the similarity conditions equal 100%.

After you have recorded your predictions, click the “Show Answer” link to see the results from the experiment.

[reveal-answer q=”291462″]Show Answer[/reveal-answer]
[hidden-answer a=”291462″]
Here are the results from Experiment 3:

Results from experiment 3 show the giver bar at 75% and the taker bar at 25% for the Similar situation and the give bar at 19% and the taker bar at 81% for the Dissimilar situation.
Figure 6. Results from Experiment 3.

These results are similar to those for the 8-month-olds in the previous experiment. But remember that, in this experiment, the variable that distinguishes the two bouncer puppets was a food choice, not the prosocial or antisocial behavior in Experiment 2. If we take the results from Experiments 2 and 3 together, the results here suggest that the similar puppet is being treated as if it is nice or good. Puppets that treat this similar puppet in a nice way are preferred. Conversely, the dissimilar puppets are treated as if they have done something negative and puppets that treat these dissimilar puppets badly are preferred.


The experimenters also tested an older group of babies that were 14-months-old. The results for these older babies were consistent with the 9-month-old and, if anything, the effects were stronger. Their results showed that all infants preferred when the giver puppet was nice to the puppet that was similar to them and all infants preferred when puppets were mean to the puppet that was dissimilar to them.

Bar graphs depicting the results of the experiment with 14 month olds and how 100% of children preferred the giver with the similar puppet or the taker with the dissimilar puppet.
Figure 7. These bar graphs show the results of the experiment when 14-month olds were tested. One hundred percent of the children chose the puppet that gave the ball back to the puppet that was similar to them, and 100% of children chose the puppet that took the ball away from the puppet that had a different preference than they did.


This exercise started with a reminder that Lawrence Kohlberg found that children went through a long developmental process in their moral reasoning. Based on children’s reasoning aloud about moral dilemmas, Kohlberg concluded that children younger than about 8 or 9 years of age make moral decisions based on avoiding punishment and receiving praise. Neither his research nor that of most others in the 1970s and 1980s suggested that young children would use multiple sources of information and judgments about the meaning of behaviors in their thinking about what sorts of behaviors are better or worse.

If Dr. Hamlin and her colleagues are right, then infants are much more sophisticated and complex in their thinking about the world than these earlier researchers thought. In Dr. Hamlin’s view, infants like good things to happen to good puppets and people, and bad things to happen to bad puppets and people. Experiment 3 suggests that they make judgments about more than helping and harming behavior. They prefer others who are like them (green beans vs. graham crackers) and they don’t mind if others who are not like them have unpleasant experiences.

The research we have been reviewing is just part of an impressive set of research on infant thinking. The ideas that the researchers have developed are intriguing and they are consistent with the modern view of the infant as an active, creative thinker. At the same time, remember that science doesn’t rest on an early set of explanations based on a small set of complicated experiments. Science pushes beyond what we currently know and believe. This starts with curiosity on your part. Are the experimenters correct in interpreting reaching behavior as showing a preference or is something else going on? Do infants really prefer prosocial behaviors to antisocial behaviors, or is there some other explanation for their preferences? How else could we test the moral judgments of infants without using puppet shows? The next generation of creative scientists will push beyond what we know now, with new research methods and new ideas about the mind.

We’ll give Dr. Hamlin the last word. Here is part of her conclusion section from an article that summarizes some of the research we have been studying: “In sum, recent developmental research supports the claim that at least some aspects of human morality are innate…Indeed, these early tendencies are far from shallow, mechanical predispositions to behave well or knee-jerk reactions to particular states of the world. Infant moral inclinations are sophisticated, flexible, and surprisingly consistent with adults’ moral inclinations, incorporating aspects of moral goodness, evaluation, and retaliation.“ (Hamlin, 2013, p. 191)



accommodation: when we restructure or modify what we already know so that new information can fit in better
assimilation: when we modify or change new information to fit into our schemas (what we already know)
babbling: an infant’s repetition of certain syllables, such as ba-ba-ba, that begins when babies are between 6 and 9 months old
holophrase: a single word that is used to express a complete, meaningful thought
infantile or childhood amnesia: the idea that people forget everything that happened to them before the age of 3
language acquisition device (LAD): Chomsky’s term for the hypothesized mental structure that enables humans to learn the language, including the basic aspects of grammar, vocabulary, and intonation
morpheme: the smallest unit of language that conveys some type of meaning
naming explosion: a sudden increase in an infant’s vocabulary, especially in the number of nouns, that begins at about 18 months of age
object permanence: the realization that objects (including people) still exist even if they can no longer be seen, touched, or heard
phoneme: a basic sound unit of a given language
primary circular reactions: the first two stages of Piaget’s sensorimotor intelligence which involve the infant’s responses to its own body
schema: a set of linked mental representations of the world, which we use both to understand and to respond to situations
secondary circular reactions: stages 3 and 4 of Piaget’s sensorimotor intelligence which involves the infant’s responses to objects and people
sensorimotor intelligence: Piaget’s term for the way infants think (by using their senses and motor skills) during the first stage of cognitive development
tertiary circular reactions: consist of actions (stage 5) and ideas (stage 6) where infants become more creative in their thinking


  1. Mareshcal, D. & Kauffman, J. (2012). Object Permanence in infancy: Revisiting Baillargeon's drawbridge study. In Alan M. Slaster & Paul C. Quinn (Eds.), Developmental Psychology: Revisiting the classic studies. Thousand Oaks, CA: Sage.
  2. Bauer PJ, Pathman T. Memory and Early Brain Development. In: Tremblay RE, Boivin M, Peters RDeV, eds. Paus T, topic ed. Encyclopedia on Early Childhood Development [online]. Published December 2008. Accessed March 2, 2019.
  3. Schneider, Wolfgang. (2015). This belief came in part from findings that adults rarely recall personal events from before the age of 3 years (a phenomenon known as infantile or childhood amnesia). However, research with infants and young children has made it clear that they can and do form memories of events. Memory development from early childhood through emerging adulthood. Switzerland: Spring International. doi: 10.1007/978-3-319-09611-7.
  4. Mullally, Sinead L. & Maguire, Eleanor. A. (2014). Learning to remember: The early ontogeny of episodic memory. Developmental Cognitive Neuroscience, 9(13), 12-29. doi: 10.1016/j.dcn.2013.12.006
  5. Tomasello, M. & Hermann, E. (2010). Ape and human cognition. Current Directions in Psychological Science, 19(1), 3-8.
  6. The experimenters support these claims by citing the following studies: (1) DeBruine, L.M. Facial resemblance enhances trust: Proceedings of the Royal Society of London B, 2002, 269: 1307-1312. (2) Brewer, M.B. In-group bias in the minimal intergroup situation: A cognitive-motivational analysis. Psychological Bulletin, 1979, 86: 307-324. (3) Doise, W., Cspely, G., Dann, and others. An experimental investigation into the formation of intergroup representation. European Journal of Social Psychology, 1972, 2: 202-204.


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