From Embryo to Ethics

The Harmful Effects of Television on Young Children

PIAGET’S MODEL OF COGNITIVE DEVELOPMENT

How does human knowledge develop? Swiss psychologist Jean Piaget devoted his entire life to this question. His studies, spread out over nearly 60 years, laid the foundations for the vast research field of genetic epistemology, which attempts to understand how our modes of thinking evolve over the course of our lives.

Trained in biology and philosophy, Piaget drew on concepts from both these disciplines to study the development of young children—an ideal setting for observing thoughts as they are being formed. He concluded very early on that cognitive development is the product of complex interactions between the maturation of the nervous system and that of language, and that this maturation depends on children’s social and physical interactions with the world around them.

According to Piaget, it is by acting on their environment that children develop their first rational constructs. Initially, these cognitive structures, or thought schemas, as Piaget also called them, are completely different from an adult’s, but gradually, they are internalized and become more and more abstract.

Piaget’s theory of cognitive development distinguishes four primary cognitive structures that correspond to four stages of development. These stages are in turn divided into distinct substages during which specific cognitive abilities emerge.

	The first stage of development, beginning at birth and continuing until about age 2, is the sensorimotor stage. In this stage, children’s contact with the world around them depends entirely on the movements that they make and the sensations that they experience. Whenever they encounter a new object, they shake it, throw it, or put it in their mouth, so that they gradually come to understand its characteristics through trial and error. Around the middle of this stage (about age 1), children first understand the concept of object permanence—that an object continues to exist even when it moves beyond their field of vision.
	The second stage is the preoperational stage. It begins around age 2 and ends around age 6 or 7. During this stage, which is marked by the acquisition of language, among other things, children become able to think in symbolic terms, to form ideas from words and symbols. Children also begin to understand spatial and numerical concepts and the distinction between past and future. But they remain highly focused on the present and on concrete physical situations and have difficulty in dealing with abstract concepts. Children’s thinking is also very egocentric at this stage; a child this age often assumes that other people see situations from his or her viewpoint.
	Third comes the concrete operations stage, from age 6 or 7 to age 11 or 12. Having absorbed more and more experience of the world, children now become able to imagine events that occur outside their own lives. They also begin to conceptualize and to create sequences of logical reasoning, though this reasoning still depends on a direct relationship to concrete things. Children also acquire a certain capacity for abstraction. Hence they can begin to study disciplines such as mathematics, in which they can solve problems with numbers and reverse previously performed operations, but only ones that involve observable phenomena. At this stage, it is still only the exceptional child who can solve problems with multiple variables by breaking them down systematically.
	Lastly, what Piaget called the formal operations stage begins at age 11 or 12. The new capabilities developed in this stage, such as the abilities to reason hypothetically and deductively and to establish abstract relationships, are generally mastered around age 15. By the end of this stage, adolescents, like adults, can use formal, abstract logic. They can also begin to think about probabilities and about moral issues such as justice.

BEYOND PIAGET’S MODEL

Piaget’s idea that all children go through fixed, sequential stages of development has been the target of much criticism. According to Russian psychologist Lev Vygotsky, the development of human beings is too complex to be defined by such stages. Vygotsky, and others after him, accorded far more importance than Piaget did to the social and environmental influences on cognitive development.

To Piaget, the primary motivation for the process of human cognitive development came from inside the individual. His most famous metaphor for describing this idea was that children are “lone scientists” who experiment with and explore the world. In contrast, for Vygotsky, the metaphor that best describes the primary source of development is that children are “little apprentices” who receive the help and support that they need from their teachers in learning situations. Thus, for Vygotsky, the development of cognition comes more from outside the individual than from inside.

There is indeed no question that human children are affected by the cultures in which they grow up, and even more strongly affected by their family environments. Children internalize these social influences through their interactions with the adults who guide them in their problem-solving efforts.

Contrary to what Piaget posited with his stages of development, Vygotsky’s followers see a difference between what children can accomplish on their own and what they can do with the help of an adult. Vygotsky used the term “zone of proximal development” to denote the distance at any given time between what a child actually knows and what the child can learn under the supervision of an adult or through contact with other children.

According to Vygotsky, because the culture (in the large sense) that surrounds a child is thus a determining factor in that child’s development, if one studies the development of this child in isolation, as Piaget does, one cannot adequately represent the process by which children actually acquire knowledge.

It follows that language is the most effective means that adults have at their disposal to convey knowledge to children. As learning progresses, children’s language itself becomes a learning tool that they internalize and use “in their heads ” to think about the world.

However, these interactions with other people, so essential for the child’s development, require an emotional equilibrium and self-esteem that other researchers have placed at the centre of their conception of how the mind develops.

CRITICAL PERIODS IN COGNITIVE DEVELOPMENT

The wide variations in human personalities and behaviours are the result of the uniqueness of the brain of every individual. This distinctiveness develops initially through the first steps in connecting the brain’s circuits, in which intrinsic mechanisms lay down the neural pathways that are the source of a wide range of instinctive behaviours, for purposes such as seeking food, defending oneself against enemies, and mating.

But the construction of the nervous system in animals, including humans, is also influenced by experience. People’s interactions with the environment produce certain patterns of neural activity that shape the circuits of the brain. Influences from the outside world are especially important early in life, during certain limited time intervals called critical periods.

Critical periods are a general phenomenon that is associated with a number of different sensory systems. Though the most comprehensive studies have dealt with the visual systems of mammals (follow the Experiment Module link to the left), critical periods have also been identified in the development of the auditory, olfactory, and somesthetic systems (see sidebar).

Some critical periods can be very short—for example, the critical period for imprinting in birds. But critical periods for the development of complex behaviours such as human language can be longer and less sharply defined.

Unlike animals, whose cries of alarm are inborn, humans need prolonged post-natal experience before they can produce and decode the sounds that are the basis for language. Children can learn a language only if they are exposed to the words of this language during a limited, critical period before puberty (see sidebar). Similar conditions of exposure or non-exposure outside this critical period, later in adult life, will have little effect on language acquisition. In addition, the phonetic structure of the particular language that someone hears during the first few years of life will permanently affect the way that person perceives and produces speech.

During the first few months of life, infants do not have any inborn predispositions for the characteristic phonemes of any particular language. Hence they can perceive and discriminate all the sounds of any human language. But eventually, people lose this ability. For example, adult native speakers of Japanese cannot reliably distinguish the English “R”and “L” sounds, probably because this phonetic distinction does not occur in Japanese.

Studies have been conducted to determine up to what age Japanese babies can still discriminate between these two sounds. In these studies, discrimination was measured by an increase in the frequency with which the babies engaged in sucking behaviour or turned their heads away when presented with one of these sounds after they had habituated to the other. It was found that at 4 months of age, Japanese babies could distinguish the “R” and “L” sounds just as well as 4-month-olds who were growing up in English-speaking families. But around 6 months of age, the two sets of babies showed preferences for the phonemes of their mother tongues. By the time they were 1 year old, the babies no longer responded at all to the phonetic elements of a language other than their own.

Up to age 7 or 8, however, children can still learn to speak a second language fluently, with no grammatical errors and no accent, which indicates that the ability to perceive some phonetic contrasts does last longer than just the first year of life.