In this Topic, we discuss the development of cognition and perception in the child. In the first section, we discuss perception, the ability to acquire information about the world. The child’s ability to distinguish different visual and auditory stimuli, as well as stimuli in all the rest of the senses, develops rapidly over the course of the first two years. While some of this development is passive, the majority of it depends on the child’s active exploration of an environment that provides opportunities for diverse kinds of experiences.
Although the meaning of “perception” is fairly well agreed-upon, “cognition” is a term that has been construed in a variety of ways. In modern psychology it is sometimes used to refer to any “information-processing” approach to the study of behavior. This definition is, however, a bit too broad. A clearer and more specific definition might go as follows: cognition is the structure of our representations of the world and the processes we use to manipulate that structure. The study of cognitive development is thus the study of how both our knowledge of the world and our ways of acquiring new knowledge grow over time. Language is obviously an important part of this growth process–so important, in fact, that it is here covered in a separate Topic. While reading this Topic, keep in mind the role language might play in influencing and enabling other cognitive abilities.
In the second section, we discuss one of the most influential theoretical models of cognitive development. Jean Piaget’s model of the stages of cognition, and the observations upon which he founded his model, make him far and away the most important cognitive developmentalist in the history of the field. Piaget distinguished between four stages of development: the sensorimotor stage, the preoperational stage, the concrete-operational stage, and the formal-operational stage. He postulated two processes that drove the child’s development: assimilation and accommodation.
In the third section, we discuss some of the criticisms that have been brought against Piaget’s model and some of the alternatives that have been offered–specifically, information-processing and social accounts of cognitive development.
Finally, we discuss an area of cognitive development that has become an increasingly popular subject of study over the past twenty years: theory of mind. Theory of mind straddles the divide between cognitive and socioemotional development. It is concerned with the development of a child’s recognition of his or her mind and the minds of others, including the child’s ability to understand the existence of false beliefs, the use of deception, and the way that beliefs, desires, and actions are related.
Altricial – The term “altricial” refers to species in which infants are born unable to fend for themselves. It is contrasted with “precocial,” which refers to species, such as horses and other hoofed animals, in which the newborn is immediately able to find food, run from predators, etc.
Accommodation – Accommodation is a process of changing one’s representation of the world to fit the existing evidence. According to Piaget, it is one of the two “functional invariants” that drive development.
Assimilation – Assimilation is the process of changing one’s interpretation of the world to fit one’s representation of it. According to Piaget, it is one of the two “functional invariants” that drive development.
Concrete-Operational Stage – The concrete-operational stage is one of the four stages in Piaget’s developmental theory. It lasts from ages seven to eleven and is characterized by an ability to mentally manipulate representations of real-world (”concrete”) objects.
Formal-Operational Stage – The formal-operational stage is one of the four stages in Piaget’s developmental theory. It starts around age eleven and lasts through adulthood. It is characterized by an ability to mentally manipulate symbols, such as mathematical equations or linguistic sentences, that are not connected to real-world objects.
Object Permanence – Object permanence is the concept that objects continue to exist even when they cannot be seen. The acknowledgment of object permanence starts, according to Piaget, during the preoperational stage.
Preoperational Stage – The preoperational stage is one of the four stages in Piaget’s developmental theory. This stage lasts from ages two to seven. It is characterized by a growing ability to verbalize and symbolize concrete objects, but an inability to perform “operations”–mental manipulations or logical transformations–on them.
Sensorimotor Stage – The sensorimotor stage is one of the four stages in Piaget’s developmental theory. It lasts from birth to age two. It is characterized by the development of internalized representations of concrete objects that grow out of the child’s perceptions of and actions on those objects.
Visual Acuity – Visual acuity refers to the “spatial resolution” of a person’s vision: a person with high visual acuity can distinguish between narrower stripes of different intensities than a person with low visual acuity.
Human beings, unlike many animals, are altricial: they are born with an impoverished set of perceptual and motor skills that make parental care during the first few years of life–and sometimes much longer–essential. Infants are obviously limited in their ability to move in and manipulate their environments, but they also show marked impairments in perception. In this section we will discuss the development of adult-like visual capabilities and the environmental factors that are necessary for it.
1.1 Visual Acuity
At birth, the child is fairly limited in his or her ability to distinguish the combinations of colors and lines that make up the visual world. At a distance of one foot, the infant can distinguish between a gray patch and a striped patch only when the stripes are at least one tenth of any inch thick. (The infant’s acuity is determined using the looking-time measure: if a child looks longer at one of the patches than the other, the child is judged able to distinguish between them.) Over the course of the year, the child’s acuity improves to one eightieth of an inch; much better, but still nowhere as good people who are six years old or older, who generally can distinguish stripes that are one three-hundredth of an inch thick at a distance of one foot.
1.2 What Drives Perceptual Development
What is responsible for this improvement in vision? One answer is that the cones and rods in the retina, the cells that transduce light into neural signals, mature over the course of the first few years. Another, perhaps more important reason is that the brain itself is rapidly developing during that period. As ever- improving visual signals arrive at the primary visual cortex, the cortex itself adapts in order to sensitively and reliably detect differences in those signals. The importance of brain plasticity in the development of visual acuity can be seen in animals that have been deprived of particular types of visual stimulation. Cats, for instance, that have not been exposed to vertical edges during the first few months of life (this can be done by raising them in special environments or with striped blinders) cannot distinguish such edges when they are later exposed to them. Monkeys that have been deprived of vision in one eye during the first few months of life, through the use of sutures or eye patches, fail to develop another important perceptual skill: binocular vision, the ability to perceive depth through the slight differences in retinal stimulation between the two eyes. Perceptual development is obviously largely dependent on the biology of sensory systems, but these examples show that environment has a crucial role to play as well.
Jean Piaget, a Swiss psychologist who began his research in the 1920s and continued through the 1970s, had an enormous impact on the field of cognitive development. Piaget’s theory of development was based on his astute observations of young children in Geneva. Although Piaget’s writings were complex, his conclusions about the nature of development can be summarized in two parts: a set of fixed stages, and a pair of processes that led the child from one stage to the next.
2.1 The Stages
2.1.1 The Sensorimotor Stage (0-2 years)
The sensorimotor stage lasts from birth until about two years of age. During this stage, the child thinks about the world solely by interacting with it. The bundle of reflexes and needs with which the child is born drive it to interact with the world in particular ways and for particular purposes, but the child has little or no independent representations of the world. The child performs what Piaget called “circular reactions”: actions that produce pleasing consequences on the infant’s own body or on aspects of the environment are repeated. These circular reactions form the basis of the child’s later concepts of the world: eventually, the reactions become completely internalized so that the child no longer acts to produce a consequence but simply imagines it instead. The child begins to experiment actively with the world, trying out various reactions to stimuli in systematic and exploratory ways. By the end of the sensorimotor period, the child has a set of basic concepts about time, space, causality, objects, and so forth–the basic building blocks of reality.
2.1.2 The Preoperational Stage (2-7 years)
The preoperational stage lasts roughly from age two to age seven. During this stage, the child acquires a number of abilities that were absent during the sensorimotor stage. Language is, of course, one of them. Another important advance is the recognition of object permanence, the fact that objects continue to exist even when they are out of sight. This is one of the most striking failures of cognition during the sensorimotor period; children at that stage seem to believe that an object that has disappeared behind a screen, for instance, no longer exists. During the preoperational stage, however, children are increasingly able to maintain in mind representations of hidden objects. However, although children have mastered this basic task, they still fail on a variety of tasks that test their ability to apply operations on their representations of the world–thus they are “preoperational.” For instance, children fail to understand that the mass of an object is generally conserved no matter what “operations” are performed on it: a certain amount of milk has the same volume whether it is poured into a wide glass or a narrow glass, and a certain amount of clay has the same mass no matter what shape it takes.
2.1.3 The Concrete-Operational Stage (7-11 years)
It is only in the concrete-operational stage, between the ages of seven and eleven, that children begin to understand that a variety of operations can be conducted on objects in the world that alter the objects’ appearance but leave their basic essence unchanged. During this period, children also become less egocentric than they were in the preoperational stage; they begin to understand that other people do not always share their perspective. However, although children are now able to understand the various operations that can be conducted on real objects, and the kinds of relations that can obtain between them, their cognition is still not entirely adult-like. They have yet to master the use of logical operations on purely logical or verbal statements, an accomplishment that comes in the formal-operational stage.
2.1.4 The Formal-Operational Stage
The formal-operational stage begins around age eleven; by age fifteen, most of the dramatic changes in cognition associated with this stage have taken place. Development over the rest of the life course, according to Piaget, is gradual and incremental. During the formal-operational stage, the adolescent starts to think in a truly logical fashion. When they are faced with problems, adolescents formulate hypotheses about the possible causes and solutions and systematically test those solutions. They are able to conduct purely mathematical or logical operations on symbols, without any references to concrete objects in the world.
2.2 Mechanisms of Development
How is it that children are able to progress from each stage to the next? What are the basic drives or abilities that allow a sensorimotor child to transition to the preoperational stage, or a concrete-operational child to transition to the formal-operational stage? Piaget proposed that there were two invariant mechanisms that drove development: assimilation and accommodation.
“Assimilation” was Piaget’s name for the way in which one construes one’s perceptions to fit one’s conception of the world. Each time we make a judgment about something that we have seen or heard, our judgment is influenced by our assumptions about the way the world works.
“Accommodation” is assimilation’s complement. Just as we often adjust our perceptions to fit our conceptions, we often are forced to adjust our conceptions to fit our perceptions. When assimilation fails–when the world is too dramatically different from what our assumptions tell us it should be–we change our assumptions.
How do assimilation and accommodation work together to drive development? Piaget hypothesized that both processes were involved in every cognitive act performed by the infant. Successful adaptation reflects a balance between accommodation and assimilation such that new experiences are interpreted in the light of one’s views of the world, but one’s views of the world are subject to change when the evidence against them becomes significant. Over the course of development, the child goes through stages of equilibrium, during which the child’s concept of the world is relatively stable and the focus is on assimilation, and stages of disequilibrium, during which the child’s concept of the world is being challenges by new experiences and the emphasis is on accommodation.
Although Piaget’s research has been incredibly influential in the field of cognitive development, it has fallen out of favor in the past twenty to thirty years, in part because of advances in technique that have illustrated a different set of abilities in children than that observed by Piaget and in part because of several principled criticisms of his theory. Some of the features of the theory that have been criticized are 1) the lack of evidence for qualitatively different stages, 2) Piaget’s focus on the physical environment to the exclusion of the social environment, and 3) the theory’s vagueness about the mechanisms of developmental change. Two approaches that attempt to integrate new evidence and provide models that are not vulnerable to those criticisms–the information-processing approach and Vygotsky’s social learning approach– are described below.
3.1 Information-Processing Accounts of Cognitive Development
Whereas Piaget’s account of development postulates distinct stages, information-processing accounts almost uniformly postulate incremental advances in cognitive abilities over the course of development. Working memory, for instance, has been shown to increase gradually over the course of childhood: over the short term, a four-year-old can remember about four letters, an eleven-year-old can remember about six, and an adult can remember seven or eight. These increases in basic cognitive resources may be the driving force behind many of the advances that Piaget though were due to the dual processes of assimilation and accommodation. With increased working memory, the child’s ability to hold images, words, and operations in mind increases. This increase may, in combination with various skills and acquired knowledge, be enough to account for development.
3.2 Vygotsky’s Sociocultural Account of Development
Although the information-processing account avoids the pitfalls of an overly stage-based theory, it does not rectify Piaget’s failure to account for the effect of the child’s social environment on cognitive development. Lev Vygotsky, a Russian psychologist who wrote on development in the 1920s and 1930s, offered a sociocultural perspective on development that continues to influence research today. Vygotsky argued that the most important environment for a child was not, as Piaget had suggested, the child’s physical surroundings, but rather the social context within which the child developed. Within every human society, older siblings, peers, or parents act as models for the child. The child jointly participates in a variety of activities, at first playing only an observational role but taking on greater and greater responsibility as the child’s experience grows. Vygotsky’s theory explicitly takes into account the effect of culture and society on development.
“Theory of mind” describes an area of research that focuses on the child’s ability to understand mental concepts such as belief, desire, the difference between appearance and reality, and the existence of other minds. The field has flourished in the past twenty years for at least two reasons: it is of great theoretical interest and it has taken advantage of relatively recent developments in methods for studying infant cognition. The theoretical interest lies in the fact that theory of mind research explores the development of our na ve concepts about mind in the same way that Piaget’s theory explores the development of our na ve concepts about the physical world. Theory of mind research has shown that young children make just as many systematic mistakes in the mental arena as they do in the physical. The methodologies that have helped advance theory of mind research are those that allow researchers to probe the cognition of infants who cannot yet speak. The most important of these methods is the looking-time paradigm, in which the amount of time a child looks at an image is used to judge whether that image is “surprising” given the child’s representation of the world. More concrete examples are given below.
4.1 False Belief, Metacognition, and the Appearance- Reality Distinction
The false-belief paradigm is the classic example of pre-preschool children’s failures in theory of mind. The experiment, stripped down to its essentials, is as follows: a child is shown two dolls, two boxes (one red and one green), and a marble, all of which are in a single miniature scene. One doll puts the marble in the green box, so that it is hidden, and then departs. While the first doll is gone, the second doll removes the marble from the green box and puts it in the red box. The first doll then returns, and the child is asked: Where will the first doll look for the marble? Children before the age of four will typically say that the doll will look in the red box, where the marble actually is. They seem to have a hard time understanding that the doll might have a false belief, one that does not correspond to reality. After the age of four, children begin to give the correct response: the doll will look in the green box, where it had last seen the marble.
This inability to comprehend the idea of false belief extends to other paradigms as well. In one study, children are shown a box of pencils. When asked what they think is inside the box, most children understandably respond “pencils.” The box is then opened and the child is shown the box’s actual contents: candy. The child is then asked to imagine what someone who had seen the closed box would think was inside. Before the age of four, most children will respond “candy,” failing to recognize that people sometimes believe falsely. In fact, when asked what they themselves thought was in the box when they first saw it, children often report that they thought the box contained candy–even though just moments before they had reported thinking it contained pencils. This shows that children have impairments in metacognition, the ability to think about and remember their own thoughts.
A further demonstration of this failure to distinguish between appearance and reality is given by the “filter experiment.” In this experiment, the child is shown a white piece of paper and a transparent blue screen. The child correctly indicates that the paper is white and the filter is blue, but when the paper is placed behind the filter the child is unable to make the distinction between the paper’s appearance–now blue–and its intrinsic, or “real,” color.
The studies mentioned above describe impairments in theory of mind that have almost completely disappeared, in most children, by the time of puberty. Some children, however, are severely impaired on these tasks throughout their lives. Children with autism, for example, are often as intelligent as children with other forms of mental retardation when measured by standard IQ tests, but they are much worse at the false belief, appearance-reality, and metacognitive tasks described above. Some have argued that this failure in theory of mind lies at the root of autistic deficits in language, communication, and empathy.