Language & Cognitive Development

Piaget and Sensorimotor Development 

Piaget differed from many researchers who studied intelligence and cognitive development in his day. He did not agree that intelligence can be measured by examining the knowledge, information, or facts children acquire. Instead, he viewed intelligence as the processes through which we adapt to our environment. He believed that children, even infants, actively try to make sense of their environments. He argued that differences between children and adults are not based on the fact that children know less than adults. Instead, Infants and children think in different ways than adults do. Piaget thought that children’s ability to understand objects, such as learning that a rattle makes a noise when shaken, was a cognitive skill that develops slowly as a child matures and interacts with the environment.

To learn more about how these processes unfold, Piaget used the clinical method in which he closely observed individual children in great detail over long periods of time in their natural environment. As subjects, he relied on observations of his own children. For example, he would watch his tiny daughter as she tried to get a rattle into her mouth. From these observations he developed his theory of cognitive development, which posits four qualitatively different stages (Piaget, 1954).

Processes of Development: Schema, Assimilation, and Accommodation

In addition to descriptions of different stages, Piaget was also very interested in the processes by which people come to understand the world (and in the process, to understand themselves). He was focused on our understandings of universal physical properties of environments, like time, space, and causality, which he called logic-mathematical thought.

He argued that people make sense of the world by interacting with it. He assumed that all people, even infants, are active, curious, energetic, and intrinsically motivated, and it is through their active attempts to "make things happen" that they learn about natural laws. Piaget held that, as they accumulate experience, infants and children construct models of how the world works, which are partial, incomplete, and not totally accurate. He called these models, schema, which can be thought of as frameworks for organizing information.

As we continue interacting with the world, we keep trying out our mental models, and eventually encounter experiences that contradict them. These contradictions allow us to revise our models so that they can better account for the interactions we are experiencing. As models are revised, they are more adaptive-- meaning that they guide our actions more effectively as we try to reach our goals.

Children develop their models, that is, their schemata, through processes of assimilation and accommodation. When faced with something new, a child is likely to try assimilation, which is fitting the new information into an existing schema. For example, once they have the concept of "doggie," they may call all four-legged animals "doggies." When it becomes clear that the new information can't be assimilated, meaning that it doesn't really fit into the old schema, the child may try accommodation, which is modifying the framework of knowledge to accommodate the new information. For example, a child may learn a new concept to more accurately name the animal; when a child recognizes that a cat is different from a dog, it means the child has accommodated, and now the child has both a doggie schema and a cat schema. Even as adults we continue to try and make sense of new information by determining whether it fits into our old way of thinking (assimilation) or whether we need to modify our thoughts (accommodation).

Piaget also described a process of organization, in which we combine existing schemes into new and more complex ones. By grouping and re-arranging schemas, and connecting them together, we can grow and refine our knowledge structures. Finally, he pointed to the process of disequilibration, where we detect discrepancies or contradictions between the models we are constructing and the experiences we are having in our interactions with the world. These contradictions can produce confusion or frustration, but they are developmentally helpful, because they lead to attempts to readjust actions and models so they are in better alignment, through a process called equilibration. Disequilibration and equilibration can also be applied to models themselves, as we detect that sub-parts of models contradict each other or are not in alignment. Through processes of equilibration we can re-organize models so that they are more internally consistent and coherent.

Cognitive Development during Infancy

Piaget's theories revolutionized the way that developmentalists thought about infants. He was one of the first researchers to argue that infants are intelligent and they are busily constructing their own understandings of the world through their interactions with the environment. According to the Piagetian perspective, infants learn about the world primarily through their senses and motor abilities (Harris, 2005). These basic motor and sensory abilities provide the foundation for the cognitive skills that will emerge during the subsequent stages of cognitive development. The first stage of cognitive development is referred to as the sensorimotor stage and it occurs through six substages. Table 3.5 identifies the ages typically associated with each substage. 

Table 3.5 Infant Ages for the Six Substages of the Sensorimotor Stage

adapted from Lally & Valentine-French, 2019

Substage 1: Reflexes (birth to 1 month). Newborns learn about their world through the use of their reflexes, such as sucking, reaching, and grasping. Eventually the use of these reflexes becomes more deliberate and purposeful. 

Substage 2: Primary Circular Reactions (1 to 4 months). During the next 3 months, infants begin to actively involve their own bodies in some form of repeated activity. An infant may accidentally engage in a behavior, such as making a vocalization, and find it interesting. This interest motivates the infant to try to do it again on purpose and helps the infant learn a new behavior that originally occurred by chance. The behavior is identified as circular because of the repetition, and as primary because it centers on the infant's own body. 

Substage 3: Secondary Circular Reactions (4 to 8 months). The infant begins to interact with objects in the environment. At first the infant interacts with objects (e.g., a crib mobile) accidentally, but then these contacts with the objects are more deliberate and become a repeated activity. The infant becomes more and more actively engaged in the outside world and takes delight in being able to make things happen. Repeated motion and interesting effects bring particular interest as, for example, the infant is able to bang two pot lids together when seated on the kitchen floor. 

Substage 4: Coordination of Secondary Circular Reactions (8 to 12 months). The infant combines these basic reflexes and simple behaviors and uses planning and coordination to achieve a specific goal. Now the infant can imitate behaviors that others perform and anticipate upcoming events. Perhaps because of continued maturation of the prefrontal cortex, the infant becomes capable of having a goal and carrying out planned, goal-directed activity. For example, an infant sees a toy car under the kitchen table and then crawls, reaches, and grabs the toy. The infant is coordinating both internal and external activities to achieve a planned goal. 

Substage 5: Tertiary Circular Reactions (12 to 18 months). The toddler is considered a “little scientist” and begins exploring the world in a trial-and-error manner, using both motor skills and planning abilities. For example, the child might throw her ball down the stairs to see what happens. The toddler’s active engagement in experimentation helps them learn about their world. 

Substage 6: Beginning of Representational Thought (18 to 24 months). The sensorimotor period ends with the appearance of symbolic or representational thought. The toddler now has a basic understanding that objects can be used as symbols. Additionally, the child is able to solve problems using mental strategies, to remember something heard days before and repeat it, and to engage in pretend play. This initial movement from a “hands-on” approach to knowing about the world to the more mental world of substage six marks the transition to preoperational thought. 

Development of Object Permanence. A critical milestone during the sensorimotor period is the development of object permanence. Object permanence is the understanding that even if something is out of sight, it still exists (Bogartz, Shinskey, & Schilling, 2000). According to Piaget, young infants cannot represent objects mentally, so they do not remember one after it has been removed from sight. Piaget studied infants’ reactions when a toy was first shown to them and then hidden under a blanket. Infants who had already developed object permanence would reach for the hidden toy, indicating that they knew it still existed, whereas infants who had not developed object permanence would appear confused.

Piaget emphasizes this behavior because it is an objective way for children to demonstrate how they mentally represent their world. Children have typically acquired this milestone by 8 months. Once toddlers have mastered object permanence, they enjoy games like hide and seek, and they realize that when someone leaves the room they are still in the world. Toddlers also point to pictures in books and look in appropriate places when you ask them to find objects. 

In Piaget’s view, around the same time children develop object permanence, they also begin to exhibit stranger anxiety, which is a fear of unfamiliar people (Crain, 2005). Babies may demonstrate this by crying and turning away from a stranger, by clinging to a caregiver, or by attempting to reach their arms toward familiar faces, such as parents. Stranger anxiety is a normal developmental step, based on the infant's growing ability to distinguish familiar from unfamiliar people, combined with increases in the infant's attachment to familiar people, which leads them to prefer the (familiar) people to whom they are attached. Stranger anxiety varies in its intensity and duration, based on the infant's temperament and social context, but typically abates by about two years of age.

Critiques of Piaget

Piaget revolutionized the way we think about infant intelligence and cognitive development (Ratcliff, 2024), but there have been ongoing investigations and critiques of his theories. Piaget seems to have been accurate about the developmental mechanisms of change (e.g., assimilation, disequilibration) and the sequence of accomplishments that take place during cognitive development. However, developmental psychologists today question the timetables Piaget laid out. Researchers have found that even very young children understand objects and how they work long before they have much experience with them (Baillargeon, 1987; Baillargeon, Li, Gertner, & Wu, 2011). For example, Piaget believed that infants did not fully master object permanence until substage 5 of the sensorimotor period (Thomas, 1979). However, infants seem to be able to recognize that objects have permanence at much younger ages. Diamond (1985) found that infants show earlier knowledge if the waiting period is shorter. At age 6 months, they retrieved the hidden object if their wait for retrieving the object is no longer than 2 seconds, and at 7 months if the wait is no longer than 4 seconds. 

Development of Memory during Infancy

Much has been learned about the development of attention, learning, and memory systems during infancy (Courage & Cowan, 2022; Forest & Amso, 2023). Memory requires the capacity to mentally represent experience, so it should come as no surprise that infant memory is rather fleeting and fragile. As a result, older children and adults experience infantile amnesia, the inability to recall memories from the first few years of life. Several hypotheses have been proposed for this amnesia. From the biological perspective, it has been suggested that infantile amnesia is due to the immaturity of the infant brain, especially those areas that are crucial to the formation of autobiographical memory, such as the hippocampus.

From the cognitive perspective, it has been suggested that babies' and toddlers' lack of  linguistic skill  limits 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 largely photographic or visual memories. Finally, social theorists argue that episodic memories of personal experiences may hinge on an understanding of “self”, something that is clearly lacking in infants and young toddlers. 

However, in a series of clever studies Carolyn Rovee-Collier and her colleagues have demonstrated that infants can remember real life events, even if these memories are short-lived. Three-month-old infants were taught that they could make a mobile hung over their crib shake by kicking their legs. The infants were placed in their crib, on their backs. A ribbon was tied to one foot and the other end to the mobile. At first infants made random movements, but then came to realize that by kicking they could make the mobile shake. After two 9-minute sessions with the mobile, the mobile was removed. One week later the mobile was reintroduced to one group of infants and most of the babies immediately started kicking their legs, indicating that they remembered their prior experience with the mobile. A second group of infants was shown the mobile two weeks later, and these babies made only random movements. The memory had faded (Rovee-Collier, 1987; Giles & Rovee-Collier, 2011).

Rovee-Collier and Hayne (1987) found that 3-month-olds could remember the mobile after two weeks if they were shown the mobile and watched it move, even though they were not tied to it. This reminder helped most infants to remember the connection between their kicking and the movement of the mobile. Like many researchers of infant memory, Rovee-Collier (1990) found infant memory to be very context dependent. In other words, the sessions with the mobile and the later retrieval sessions had to be conducted under very similar circumstances or else the babies would not remember their prior experiences with the mobile. For instance, if the first mobile had had yellow blocks with blue letters, but at the later retrieval session the blocks were blue with yellow letters, the babies would not kick. 

Infants older than 6 months of age can retain information for longer periods of time; they also need less reminding to retrieve information in memory. Studies of deferred imitation, that is, the imitation of actions after a time delay, can occur as early as six-months of age (Campanella & Rovee-Collier, 2005), but only if infants are allowed to practice the behavior they were shown. By 12 months of age, infants no longer need to practice the behavior in order to retain the memory for four weeks (Klein & Meltzoff, 1999). 

Language Development

Our vast intelligence also allows us to have language, a system of communication that uses symbols in a regular way to create meaning. Language gives us the ability to communicate our thoughts to others by talking, reading, and writing. There are many components of language, which will be reviewed first, followed by a description of the typical progression of language development during the first two years of life (Bhatia & Ritchie, 2023; Gleason & Ratner, 2022).

Components of Language

Phoneme. A phoneme is the smallest unit of sound that makes a meaningful difference in a language. The word “bit” has three phonemes. In spoken languages, phonemes are produced by the positions and movements of the vocal tract, including our lips, teeth, tongue, vocal cords, and throat, whereas in sign languages phonemes are defined by the shapes and movements of the hands. 

There are hundreds of unique phonemes that can be made by human speakers, but most languages use only a small subset of the possibilities. English contains about 45 phonemes, whereas other languages have as few as 15 and others more than 60. The Hawaiian language contains fewer phonemes as it includes only 5 vowels (a, e, i, o, and u) and 7 consonants (h, k, l, m, n, p, and w). 

Infants are born able to detect all phonemes in all human languages ever spoken, but they lose their ability to do so as they get older. This is called pruning. By 10 months of age a child’s ability to recognize phonemes becomes very similar to that of the adult speakers of the native language, meaning that they are limited by and large to those of their native language(s). Phonemes that were initially differentiated can no longer be distinguished, and so are treated as if they were equivalent (Werker & Tees, 2002). 

Morpheme. Whereas phonemes are the smallest units of sound in language, a morpheme is a string of one or more phonemes that makes up the smallest units of meaning in a language. Some morphemes are prefixes and suffixes used to modify other words. For example, the syllable “re-” as in “rewrite” or “repay” means “to do again,” and the suffix “-est” as in “happiest” or “coolest” means “to the maximum.” 

Semantics. Semantics refers to the set of rules we use to obtain meaning from morphemes. For example, adding “ed” to the end of a verb makes it past tense. 

Syntax. Syntax refers to the set of rules in a language by which we construct sentences. Many languages have their own syntax. The syntax of the English language requires that each sentence have a subject (i.e., a noun or name) and a verb, each of which may be modified by adjectives and adverbs. Some syntaxes make use of the order in which words appear. For example, in English the meaning of the sentence “The man bites the dog” is different from “The dog bites the man.” 

Pragmatics. The social side of language is expressed through pragmatics, or how we communicate effectively and appropriately with others. Examples of pragmatics include turn-taking, staying on topic, volume and tone of voice, and appropriate eye contact. 

Lastly, words do not possess fixed meanings, but change their interpretation as a function of the context in which they are spoken. We use contextual information, the information surrounding language, to help us interpret it. Examples of contextual information include our knowledge and nonverbal expressions, such as facial expressions, postures, and gestures. Misunderstandings can easily arise if people are not attentive to contextual information or if some of it is missing, such as it may be in newspaper headlines or in text messages.

Progression of Language Development

An important aspect of cognitive development is language acquisition. The order in which children learn language structures is consistent across children and cultures (Hatch, 1983). Starting before birth, babies begin to develop language and communication skills. At birth, babies recognize their mother’s voice and can discriminate between the language(s) spoken by their mothers and foreign languages, and they show preferences for faces that are moving in synchrony with audible language (Blossom & Morgan, 2006; Pickens et al., 1994; Spelke & Cortelyou, 1981). 

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

Intentional Vocalizations. In terms of producing spoken language, babies begin to coo almost immediately. Cooing is a one-syllable combination of a consonant and a vowel sound (e.g., coo or baa). Interestingly, babies replicate sounds from their own languages. A baby whose parents speak French will coo in a different tone than a baby whose parents speak Spanish or Urdu. These gurgling, musical vocalizations 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, and when the infant hears the sound of their own voice, they may 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 ended. 

At about four to six months of age, 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(s) heard. Eventually, these sounds will no longer be used as the infant grows more accustomed to a particular language or languages. 

Babbling. At about 7 months, infants begin babbling, engaging in intentional vocalizations that lack specific meaning and comprise a consonant-vowel repeated sequence, such as ma-ma-ma, da-da-da. Children babble as practice in creating specific sounds, and by the time they are a 1 year old, their babbling uses primarily the sounds of the language that they are learning (de Boysson-Bardies, Sagart, & Durand, 1984). These vocalizations have a conversational tone that sounds meaningful even though it is not. Babbling also helps children understand the social, communicative function of language. Children who are exposed to sign language babble in sign by making hand movements that represent real language (Petitto & Marentette, 1991). 

Gesturing. Children communicate information through gesturing long before they speak, and there is some evidence that gesture usage predicts subsequent language development (Iverson & Goldin-Meadow, 2005). Deaf babies also use gestures to communicate wants, reactions, and feelings. Because gesturing is easier than vocalization for infants, sign language is sometimes taught to enhance an infant's ability to communicate by making use of the ease of gesturing. The rhythm and pattern of language is used when deaf babies sign, just as it is when hearing babies babble. 

Understanding. By about ten months of age, the infant has developsed receptive language, meaning that they can understand language that is spoken to them. For example, infants shake their head “no” around 6–9 months, and they respond to verbal requests to do things like “wave bye-bye” or “blow a kiss” around 9–12 months. Hence, they 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 contribute to it.

One of the first words that children understand is their own name, usually by about 6 months, followed by commonly used words like “bottle,” “mama,” and “doggie” by 10 to 12 months (Mandel, Jusczyk, & Pisoni, 1995). Children also use contextual information, particularly the cues that parents provide, to help them learn language. Children learn that people are usually referring to things that they are looking at when they are speaking (Baldwin, 1993), and that the speaker’s emotional expressions are related to the content of their speech. 

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. 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, and when this is someone who has spent time with the child, interpretation is not too difficult. But someone who has not been around the child will have trouble knowing what is meant. Imagine the parent who to a friend exclaims, “Ezra’s talking all the time now!” The friend hears only “ju ga da” to which the parent explains means, “I want some milk when I go with Daddy.” 

Language Errors. The early utterances of children contain many errors, for instance, confusing /b/ and /d/, or /c/ and /z/. The words children create are often simplified, in part because they are not yet able to make the more complex sounds of the real language (Dobrich & Scarborough, 1992). Children may say “keekee” for kitty, “nana” for banana, and “vesketti” for spaghetti because it is easier. Often these early words are accompanied by gestures that may be easier to produce than the words themselves. Children’s pronunciations become increasingly accurate between 1 and 3 years, but some problems may persist until school age. 

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, which is referred to as underextension. For example, the word "doggie" refers only to the family’s Irish Setter. More often, however, a child may think that a label applies to all objects that are similar to the original object, which is called overextension. For example, all animals become “doggies”. The first error is often the result of children learning the meaning of a word in a specific context, while the second language error is a function of the child’s smaller vocabulary. 

First Words and Cultural Influences. If the child is using English, first words tend to be nouns. The child labels objects such as cup, ball, or other items that they regularly interact with. 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 relationships 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 (Imai et al., 2008). 

Two-word Sentences and Telegraphic (Text Message) Speech. By the time they become toddlers, children have a vocabulary of about 50-200 words and begin putting those words together in telegraphic speech, such as “baby bye-bye” or “doggie pretty”. Words needed to convey messages are spoken, but the articles and other parts of speech necessary for grammatical correctness are not yet used. These expressions sound like a telegraph, or perhaps a better analogy today would be that they read like a text message. Telegraphic speech/text message speech occurs when unnecessary words are left out. “Give baby ball” is used rather than “Give the baby the ball.” 

Infant-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 infant-directed speech. It involves using a high-pitched voice, exaggerating the vowel and consonant sounds, and delivering the phrase with great facial expression (Clark, 2009). Why is this done?

Infants are frequently more attuned to the tone of voice of the person speaking than to the content of the words themselves and are aware of the target of speech. Werker, Pegg, and McLeod (1994) found that infants listened longer to a woman who was speaking to a baby than to a woman who was speaking to another adult. Adults may use this form of speech in order to clearly articulate the sounds of a word so that the child can hear the sounds involved. It may also 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. 

Theories of Language Development

As you know, researchers generally agree that development is a product of both nature and nurture. Hence, it is not surprising that scholars of language acquisition believe that it is based partially on inborn human characteristics and partially on learning via our interactions with our linguistic environment (Gleitman & Newport, 1995; Stork & Widdowson, 1974). However, psychological theories of language learning differ in terms of the relative importance they place on nature and nurture. First to be discussed is evidence for neurobiological factors, including nativist theories, and research on brain areas and critical periods. Next, evidence for that environmental factors is outlined, based on learning theory and social pragmatics. 

Nativism. The linguist Noam Chomsky is a proponent of the nature approach to language, arguing that human brains contain a language acquisition device (LAD) that includes a universal grammar that underlies all human language (Chomsky, 1965, 1972).

According to this approach, each of the many languages spoken around the world (there are between 6,000 and 8,000) is an individual example of the same underlying set of procedures that are hardwired into human brains. Chomsky’s account proposes that children are born with a knowledge of general rules of syntax that determine how sentences are constructed. Language develops as long as the infant is exposed to it. Contrary to learning theory (described below), Chomsky argued that no teaching, training, or reinforcement is required for language to develop. 

Chomsky differentiates between the deep structure of an idea; that is, how the idea is represented in the fundamental universal grammar that is common to all languages, and the surface structure of the idea or how it is expressed in any one language. Once we hear or say a thought (via surface structure), we generally forget exactly how it was expressed. For example, at the end of a lecture, you can typically remember a lot of the deep structure (i.e., the meaning of the ideas expressed by the instructor), but you cannot reproduce the surface structure (the exact words that the instructor used to communicate the ideas). 

Although there is general agreement among psychologists that babies are neurophysiologically prepared to learn language, there is still debate about Chomsky’s idea that there is a universal grammar that can account for all language learning. For example, Evans and Levinson (2009) surveyed the world’s languages and found that none of the presumed underlying features of the language acquisition device were entirely universal. In their search they found languages that did not have noun or verb phrases, that did not have tenses (e.g., past, present, future), and even some that did not have nouns or verbs at all, even though a basic assumption of a universal grammar is that all languages should share these features. 

Brain Areas for Language. For the 90% of people who are right-handed, language is stored and controlled by the left cerebral cortex, although for some left-handers this pattern is reversed. These differences can easily be seen in the results of neuroimaging studies that show that listening to and producing language creates greater activity in the left hemisphere than in the right. Broca’s area, an area in front of the left hemisphere near the motor cortex, is responsible for language production (Figure 3.28). This area was first localized in the 1860s by the French physician Paul Broca, who studied patients with lesions in various parts of the brain. Wernicke’s area, an area of the brain next to the auditory cortex, is responsible for language comprehension.

Is there a critical period for learning language? Psychologists believe there is a critical period, a time during which learning can easily occur, for language. This critical period appears to be between infancy and puberty (Lenneberg, 1967; Penfield & Roberts, 1959), but isolating the exact timeline has been difficult. Children who are not exposed to language during these years are at risk for ever being able to grasp the grammatical and communication nuances of language.

A test for the notion of critical periods for language can be found in studies of children with hearing loss. Several studies show that the earlier children are diagnosed with hearing impairment and receive treatment, the better the child’s long-term language development. For instance, Stika et al. (2015) reported that when children’s hearing loss was identified during newborn screening, and subsequently addressed, the majority showed normal language development when later tested at 12-18 months. Fitzpatrick, Crawford, Ni, and Durieux-Smith (2011) reported that early language intervention in children who were moderately to severely hard of hearing, demonstrated normal outcomes in language proficiency by 4 to 5 years of age. Tomblin et al. (2015) reported that children who were fit with hearing aids by 6 months of age showed good levels of language development by age 2.

Those whose hearing was not corrected until after 18 months showed lower language performance, even in the early preschool years. However, this study did reveal that those whose hearing was corrected by toddlerhood had greatly improved language skills by age 6. The research with hearing impaired children reveals that this critical period for language development is not exclusive to infancy, and that the brain is still receptive to language development in early childhood. Fortunately, it is has become routine to screen hearing in newborns, because when hearing loss is not treated early, it can delay spoken language, literacy, and impact children’s social skills (Moeller & Tomblin, 2015; Rescorla, 2019). 

Learning Theory. Perhaps the most straightforward explanation of language development is that it occurs through the principles of learning, including association and reinforcement (Skinner, 1953). Additionally, Bandura (1977) described the importance of observation and imitation of others in learning language.

There must be at least some truth to the idea that language is learned through environmental interactions or nurture. Why? Because children always learn the language that they hear spoken around them rather than some other language. Also supporting this idea is the gradual improvement in language skills over time. It seems that children modify their language through imitation and reinforcement, such as parental praise and being understood. For example, when a two-year-old child asks for juice, he might say, “me juice,” to which his mother might respond by giving him a cup of apple juice.

However, language cannot be entirely learned by imitation and reinforcement. Children learn words too fast for them to be learned through reinforcement. Between the ages of 18 months and 5 years, children learn up to 10 new words every day (Anglin, 1993). More importantly, language is not merely imitative; it is actually more generative. Language is not a predefined set of phrases or sentences that we choose when we need them, but rather a system of rules and procedures that allows us to create an infinite number of statements expressing thoughts and ideas, including those that have never been articulated before. When a child says that she “swimmed” in the pool, for instance, she is not imitating anyone; she is showing generativity. No adult speaker of English would ever say “swimmed,” yet it is easily generated from the normal system of English language production.

Other evidence that refutes the idea that all language is learned through imitation and reinforcement comes from the observation that children tare able to learn languages better than they ever hear them. Deaf children whose parents do not communicate using ASL very well nevertheless are able to learn it perfectly on their own and may even make up their own language if they need to (Goldin-Meadow & Mylander, 1998).

For example, a group of deaf children in a school in Nicaragua, whose teachers could not sign, invented a way to communicate through self-generated signs (Senghas, Senghas, & Pyers, 2005). The development of this new Nicaraguan Sign Language has continued and evolved as new generations of students have come to the school and started using the language. Although the original system was not a standard language, it is becoming closer and closer every year, showing the emergence of a new language in modern times. 

Social Pragmatics. Another view emphasizes the very social nature of human language. Language from this view is not only a cognitive skill, but also a social one. Language is a tool humans use to communicate, connect to, share with, influence, and inform others. Most of all, language comes out of a need to cooperate. The social nature of language has been demonstrated by a number of studies showing that children use several pre-linguistic skills (such as pointing and other gestures) to communicate not only their own needs, but what others may need. For example, a small child watching their mother search for an object may point to the object to help their mother find it.

Eighteen-month to 30-month-olds have been shown to make linguistic repairs when it is clear that the other person does not understand them (Grosse, Behne, Carpenter & Tomasello, 2010). Grosse et al. (2010) found that even when the child was given the desired object, if there had been any misunderstanding along the way (such as a delay in being handed the object, or the experimenter calling the object by the wrong name), children will make linguistic repairs. This would suggest that children are using language not only as a means of achieving some material goal, but also to make themselves understood in the mind of another person. 

Supplemental Materials

Planful Problem-solving during Late Infancy

To give you a sense of what infants' cognitive capacities allow them to do, here are some video clips of planful problem-solving at 8 months and about a year old:

How do I get off this bed?

How can I stack these blocks?

How do I get into the zoo?

How do we both get on the bed?

Language Development

For a Bio-ecological perspective on understanding language development, have a look at Rowe and Weisleder (2020). They provide a review describing how different features and components of context, together, shape language development.

Note also a recent review (Gowenlock et al., 2024) and meta-analysis (Madigan et al., 2020) examining how screen use is associated with language skills and development.

Motor Development

Motor development occurs in an orderly sequence as infants move from reflexive reactions (e.g., sucking and rooting) to more advanced and intentional motor functioning (Adolph & Hospodar, 2024; Boonzaaijer et al., 2021). As mentioned during the prenatal section, development occurs according to the Cephalocaudal (from head to tail) and Proximodistal (from the midline outward) principles. For instance, babies first learn to hold their heads up, then to sit with assistance, then to sit unassisted, followed later by crawling, pulling up, cruising or walking while holding on to something, and then unassisted walking (Eisenberg, Murkoff, & Hathaway, 1989).

As motor skills develop, there are certain developmental milestones that young children should achieve. For each milestone there is an average age, as well as a range of ages in which the milestone should be reached. An example of a developmental milestone is a baby holding up its head. Babies on average are able to hold up their heads at 6 weeks, and 90% of babies achieve this between 3 weeks and 4 months old.

On average, most babies sit alone at 7 months. Sitting involves both coordination and muscle strength, and 90% of babies achieve this milestone between 5 and 9 months old. If the child is displaying delays on several milestones, that is reason for concern, and the parent or caregiver should check in with the child’s pediatrician. Once developmental delays are identified, they can be addressed through early intervention.

Motor skills refer to our ability to move our bodies and manipulate objects. Gross motor skills focus on large muscle groups that control our head, torso, arms and legs and involve larger movements (e.g., balancing, running, and jumping). These skills begin to develop first. Examples in infancy include moving to bring the chin up when lying on the stomach, moving the chest up, and rocking back and forth on hands and knees.

But it also includes exploring an object with one’s feet as many babies do as early as 8 weeks of age if seated in a carrier or other device that frees the hips. This may be easier than reaching for an object with the hands, which requires much more practice (Berk, 2007). Sometimes an infant will try to move toward an object while crawling and surprisingly move backward because of the greater amount of strength in the arms than in the legs.

Fine motor skills focus on the muscles in our fingers, toes, and eyes, and enable coordination of small actions (e.g., grasping a cup, turning over a toy, and using a spoon). Newborns cannot grasp objects voluntarily but do wave their arms toward objects of interest. At about 4 months of age, the infant is able to reach for an object, first with both arms and within a few weeks, with only one arm. At this age grasping an object involves the use of the fingers and palm, but no thumbs. This is known as the Palmer Grasp.

The use of the thumb comes at about 9 months of age when the infant is able to grasp an object using the forefinger and thumb. Now the infant uses a Pincer Grasp, and this ability greatly enhances the ability to control and manipulate an object. Infants take great delight in this newfound ability. They may spend hours picking up small objects from the floor and placing them in containers. By 9 months, an infant can also watch a moving object, reach for it as it approaches, and grab it. 

Development of Sensory Capacities

Throughout much of history, the newborn was considered a passive, disorganized being who possessed minimal abilities. William James, an early psychologist, had described the newborn’s world as “a blooming, buzzing confusion” (Shaffer, 1985). However, current research techniques have demonstrated just how developed the newborn is with especially organized sensory and perceptual abilities.

Vision. The womb is a dark environment void of visual stimulation. Consequently, vision is one of the most poorly developed senses at birth, and time is needed to build neural pathways between the eyes and the brain (American Optometric Association [AOA], 2019). Newborns typically cannot see further than 8 to 10 inches away from their faces (AOA, 2019). An 8-week old’s vision is 20/300. This means an object 20 feet away from an infant has the same clarity as an object 300 feet away from an adult with normal vision. By 3-months visual acuity has sharpened to 20/200, which would allow them the see the letter E at the top of a standard eye chart (Hamer, 2016). As a result, the world initially looks blurry to young infants (Johnson & deHaan, 2015).

Why is visual acuity so poor in the infant? The fovea, which is the central field of vision in the retina and allows us to see sharp detail, is not fully developed at birth, and does not start to reach adult levels of development until 15 months (Li & Ding, 2017). Even by 4 years of age some of the sensory neurons (cones) of the fovea are still not fully grown. Can babies see color? Young infants can perceive color, but the colors need to be very pure forms of basic colors, such as vivid red or green rather than weaker pastel shades. Most studies report that babies can see the full spectrum of colors by about five months of age (AOA, 2019).

Newborn infants prefer and orient to face-like stimuli more than they do other patterned stimuli (Farroni et al., 2005). They also prefer images of faces that are upright and not scrambled (Chien, 2011). Infants quickly learn to distinguish the face of their mother from faces of other women (Bartrip, Morton, & De Schonen, 2001). When viewing a person’s face, one-month olds fixate on the outer edges of the face rather than the eyes, nose, or mouth, but two-month olds gaze more at the inner features, especially the eyes (Hainline, 1978). Researchers have examined the development of attention and tracking in the visual system and have found the following for young infants:

• One-month-olds have difficulty disengaging their attention and can spend several minutes fixedly gazing at a stimulus (Johnson & deHaan, 2015).
• Aslin (1981) found that when tracking an object visually, the eye movements of newborns and one-month olds are not smooth but saccadic, that is step-like jerky movements. Aslin also found that eye movements lag behind an object’s motion. This means young infants do not anticipate the trajectory of the object. By two months of age, their eye movements are becoming smoother, but they still lag behind the motion of the object and will not achieve the capacity to anticipate its movement until about three to four months of age (Johnson & deHaan, 2015).
• Newborns also orient more to the visual field toward the side of the head, than to the visual field on either side of the nose (Lewis, Maurer, & Milewski, 1979). By two to three months, stimuli in both fields are now attended to equally (Johnson & deHaan, 2015).

Binocular Vision, which requires input from both eyes, is evident around the third month and continues to develop during the first six months (Atkinson & Braddick, 2003). At that point infants can perceive depth perception in pictures as well (Sen, Yonas, & Knill, 2001). Infants who have experience crawling and exploring will pay greater attention to visual cues of depth and modify their actions accordingly (Berk, 2007).

Hearing. The infant’s sense of hearing is very keen at birth, and the ability to hear is evidenced as soon as the seventh month of prenatal development. Newborns prefer their mother’s voices over another female even if speaking the same material (DeCasper & Fifer, 1980).

Additionally, they will register in utero specific information heard from their mother’s voice. DeCasper and Spence (1986) tested 16 infants (average age of 55.8 hours) whose mothers had previously read to them prenatally. The mothers read several passages to their fetuses, including the first 28 paragraphs of the Cat in the Hat, beginning when they were 7 months pregnant. The fetuses had been exposed to the stories an average of 67 times or 3.5 hours. When the experimental infants were tested, the target stories (previously heard) were more reinforcing than the novel story as measured by their rate of sucking. However, for control infants, the target stories were not more reinforcing than the novel story indicating that the experimental infants had heard them before.

An infant can distinguish between very similar sounds as early as one month after birth and can distinguish between a familiar and non-familiar voice even earlier. Infants are especially sensitive to the frequencies of sounds in human speech and prefer the exaggeration of infant-directed speech, which will be discussed later. Additionally, infants are innately ready to respond to the sounds of any language, but between six and nine months they show preference for listening to their native language (Jusczyk, Cutler, & Redanz, 1993). Their ability to distinguish the sounds that are not in the language around them diminishes rapidly (Cheour-Luhtanen, et al., 1995).

Touch and Pain. Immediately after birth, a newborn is sensitive to touch and temperature, and is also highly sensitive to pain, responding with crying and cardiovascular responses (Balaban & Reisenauer, 2013). Newborns who are circumcised, which is the surgical removal of the foreskin of the penis, without anesthesia experience pain as demonstrated by increased blood pressure, increased heart rate, decreased oxygen in the blood, and a surge of stress hormones (United States National Library of Medicine, 2016). Research has demonstrated that infants who were circumcised without anesthesia experienced more pain and fear during routine childhood vaccines. Fortunately, today many local pain killers are currently used during circumcision.

Taste and Smell. Studies of taste and smell demonstrate that babies respond with different facial expressions, suggesting that certain preferences are innate. Newborns can distinguish between sour, bitter, sweet, and salty flavors and show a preference for sweet flavors.

Newborns also prefer the smell of their mothers. An infant only 6 days old is significantly more likely to turn toward its own mother’s breast pad than to the breast pad of another baby’s mother (Porter, Makin, Davis, & Christensen, 1992). And within hours of birth an infant also shows a preference for the face of its own mother (Bushnell, 2001; Bushnell, Sai, & Mullin, 1989).

Intermodality. Infants seem to be born with the ability to perceive the world in an intermodal way; that is, through stimulation from more than one sensory modality. For example, infants who sucked on a pacifier with either a smooth or textured surface preferred to look at a corresponding (smooth or textured) visual model of the pacifier. By 4 months, infants can match lip movements with speech sounds and can match other audiovisual events. Sensory processes are certainly affected by the infant's developing motor abilities (Boonzaaijer et al., 2021; Hyvärinen, Walthes, Jacob, Nottingham Chapin, & Leonhardt, 2014). Reaching, crawling, and other actions allow the infant to see, touch, and organize their experiences in new ways.

How Do We Know What We Know about Infant Development?

What kind of research methods and studies allow us to make conclusions about what infants see, hear, smell, taste, think, and remember? Increasingly, habituation procedures, that is measuring decreased responsiveness to a stimulus after repeated presentations, have been used to evaluate infants in studies of the development of perceptual and memory skills. Phelps (2005) describes a habituation procedure used when measuring the rate of the sucking reflex. Researchers first measure the initial baseline rate of sucking to a pacifier equipped with transducers that measure muscle contractions. Next, a novel auditory stimulus is presented, such as a human voice uttering a speech sound such as “da.” The rate of sucking will typically increase with the new sound, but then decreases to baseline levels as “da” is repeatedly presented, showing habituation. It is as if the novelty catches infant attention and interest, but then over time, the infant becomes accustomed to the sound and gets bored. If the sound “ma” is then presented, the rate of sucking would again increase, demonstrating that the infant can discriminate between these two stimuli. If they thought that the sounds were identical, then they would continue to be bored.

Additionally, the speed or efficiency with which infants show habituation has been shown to predict outcomes in behaviors, such as language acquisition and verbal and nonverbal intelligence. Infants who show difficulty during habituation, or habituate at slower than normal rates, have been found to be at an increased risk for significant developmental delays. Infants with Down syndrome, teratogen-exposed infants, malnourished infants, and premature infants have all been studied. Researchers have found that at the age of 16 months, high-risk infants show rates of habituation comparable to newborn infants (Phelps, 2005).

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OER Attribution: “Lifespan Development: A Psychological Perspective, Second Edition” by Martha Lally and Suzanne Valentine-French is licensed under a CC-BY-NC-SA-3.0