Theme 4: Mechanisms of Developmental Change

As with so many issues, contemporary thinking about developmental change owes a large debt to the ideas of Jean Piaget. Within Piaget’s theory, change occurs through the interaction of assimilation and accommodation. Through assimilation, children interpret new experiences in terms of their existing mental structures; through accommodation, they revise their existing mental structures in accord with the new experiences. Thus, when we hear a truly unfamiliar type of music (for most of us, Javanese 12-tone music would fit this description), we assimilate the sounds to more familiar musical patterns, to the extent we can. At the same time, our understanding accommodates to the experience, so that when we next encounter the unfamiliar music, it will be a little easier to grasp and will feel a little less strange.

A great deal has been learned about developmental mechanisms since Piaget formulated his theory. Some of the advances have come in understanding change at the biological level, others in understanding it at the behavioral level, and still others in understanding it at the level of cognitive processes.

Biological Change Mechanisms

Biological change mechanisms come into play from the moment a sperm unites with an egg. The sperm and the egg each contain half of the DNA that will constitute the child’s genotype throughout life. The genotype contains instructions that specify the rough outline of development, but all particulars are filled in by subsequent interactions between the genotype and the environment.

The way in which the brain forms after conception illustrates the complexity of change at the biological level. The first key process in brain development is neurogenesis, which by the 3rd or 4th week after conception is producing roughly 10,000 brain cells per minute. About 100 days later, the brain contains just about all of the neurons it ever will have. As neurons form, a process of cell migration causes many of them to travel from where they were produced to their long-term location.

Once neurons reach their destination, they undergo a process of differentiation, in which dendrites and axons grow out from the original cell body. Later in the prenatal period, the process of myelination adds an insulating sheath over certain axons, which speeds up the rate of transmission of electrical signals along them. Myelination continues through childhood and into adolescence.

Yet another process, synaptogenesis, involves formation of synapses between the end of axons and the beginning of dendrites that allow neurotransmitters to transmit signals from neuron to neuron. The number of synapses increases rapidly from the prenatal period to early or middle childhood (depending on the particular brain area). By the end of this period of explosive growth, the number of synapses in the area far exceeds the number in the brains of adults. A process of pruning then reduces the number of synapses. The greatest pruning occurs at different times in different brain areas. Those synapses that are frequently used are maintained; those that are not are eliminated (“use it or lose it” at the biological level). The pruning of unused synapses makes information processing more efficient.

The group average pattern of brain activation for each of three increasingly difficult items (from left to right) on a problem-solving task that requires both executive functioning and spatial processing As shown, the amount of activation in this slice of the brain increases with difficulty in the prefrontal cortex (toward the front of the brain, often involved in executive functioning) and in the superior parietal cortex (toward the back of the brain, often involved in spatial processing). (Data from Newman et al., 2003)

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The brain includes a number of areas that are specialized for specific functions. This specialization makes possible rapid and universal development of these functions and thus enhances learning of the relevant type of information. Some of the functions are closely linked to sensory and motor systems. The visual cortex is particularly active in processing sights; the auditory cortex is particularly active in processing sounds; the motor cortex is particularly active in making movements; and so on.

Other brain areas are specialized for functions that are not specific to any one sensory or motor system. The limbic system, located in the lower part of the brain, is particularly prominent in producing emotions. The prefrontal cortex is particularly involved in executive functioning. Some areas toward the back of the right hemisphere are particularly active in processing space, time, and number. All of these areas are involved in numerous other types of processing, and all types of processing involve numerous brain areas, but each of the areas is especially active in processing the type of information associated with it. Thus, biological mechanisms underlie both very specific and very general changes.

Behavioral Change Mechanisms

Behavioral change mechanisms describe responses to environmental contingencies that contribute to development. These learning mechanisms shape behavior from infants’ first days out of the womb onward.

Habituation, Conditioning, Statistical Learning, and Rational Learning

The capacity to habituate to familiar stimuli begins before fetuses leave the womb. By 30 weeks after conception (8 to 10 weeks before the typical time of birth), the central nervous system is sufficiently developed for habituation to occur, as reflected in a fetus’s heart rate initially slowing down (a sign of interest) when a bell is rung next to the mother’s belly and then its returning toward the typical rate as the bell is rung repeatedly. Habituation continues after birth as well, and it is seen in changes in looking patterns as well as in heart-rate patterns. For example, when a picture of a face is shown repeatedly, infants reduce the time they spend looking at it, but they show renewed interest when a different face appears. Habituation motivates babies to seek new stimulation when they have learned from an experience and thus helps them learn more.

From their first days in the outside world, infants also can learn through classical conditioning. If an initially neutral stimulus is repeatedly presented just before an unconditioned stimulus, it comes to elicit a similar response to that elicited by the unconditioned stimulus. Recall Little Albert, who, after repeatedly seeing a harmless white rat and then hearing a frightening loud noise immediately after, came to fear the white rat (and also came to fear doctors and nurses wearing white lab coats).

The fact that an infant would become afraid not only of the white rat but also of people with white coats illustrates the functioning of another key learning ability that is present from infancy: generalization. Although infants’ learning tends to be less general than that of older children, it is never completely literal. Infants generalize the lessons of their past experience to new situations that differ at least in a few details from the original ones.

Like older children, infants also learn through instrumental conditioning; behaviors that are rewarded become more frequent, and behaviors that do not lead to rewards become less frequent. Even young infants appear highly motivated to learn in this way: 2-month-olds express joy and interest while learning a contingency relation, and they often cry and express anger when a learned response no longer produces the expected results.

Yet another mechanism that allows infants to acquire information rapidly is statistical learning. From birth onward, infants quickly learn the likelihood that one sight or sound will follow another. Because many events, including the sounds within words and certain daily activities, occur in predictable orders, statistical learning helps infants anticipate other people’s actions and generate similar sequences of behavior themselves.

Closely related to statistical learning is rational learning, which involves integrating the learner’s prior beliefs and biases with what actually occurs in the environment. When, for example, infants observe an adult pulling balls of two different colors out of a box, seemingly at random, and the ratio of the colors of those balls deviates greatly from that of all the balls in the box, the infants’ looking times suggest that they are surprised. Together with habituation and classical, instrumental, and statistical learning, such rational learning allows infants to acquire knowledge of the world from the first days following birth.

Social Learning

Children (and adults) learn a great deal from observing and interacting with other people. This social learning pervades our lives to such an extent that it is difficult to think of it as a specific learning capability. However, when we compare humans with other animals, even close relatives such as chimpanzees and other apes, the omnipresence of social learning in people’s lives becomes apparent. Humans are far more skillful than any other animal in learning what others are trying to teach them; they also are far more inclined to teach others what they know. Among the crucial contributors to this social learning are imitation, social referencing, language, and guided participation.

Imitation starts in infancy.

JUDITH KRAMER/THE IMAGE WORKS

The first discernible form of social learning is imitation. At first, the imitation seems limited to behaviors that infants sometimes produce on their own, such as sticking out their tongue. However, by age 6 months, infants begin to imitate novel behaviors that they never make spontaneously. By 15 months, toddlers not only learn novel behaviors but can remember them and continue to produce them for at least a week. This imitation is not just “monkey see, monkey do.” When children of this age see a model try to do something but fail, they imitate what the model was trying to do rather than what the model actually did.

Using tools to build and repair things is a common context for social scaffolding, in which the older and more experienced person helps the younger and less experienced person to operate at a higher level than would otherwise be possible, as well as to meet goals and acquire skills.

INSADCO PHOTOGRAPHY/ALAMY

Social learning influences socioemotional development as well as acquisition of knowledge. When an unfamiliar person enters the room, 12-month-olds look to their mother for guidance. If the mother’s face or voice shows fear, the baby tends to stay close to her; if the mother smiles, the baby is more likely to approach the stranger. Similarly, in the laboratory, a baby of this age will cross the visual cliff if the mother smiles but not if she looks worried.

Social learning also shapes children’s standards and values. From the second year of life, toddlers internalize their parents’ values and standards and use them to guide and evaluate their own conduct. Later in development, peers, teachers, and other adults also influence children’s standards and values through the process of social learning. Peers, in particular, play a steadily increasing role over the course of childhood and adolescence.

Imitation is not the only mechanism of social learning. Another is social scaffolding. In this change mechanism, an older and more knowledgeable person provides a learner with an overview of a given task, demonstrates how to do the most difficult parts, provides help with the difficult parts if necessary, and offers suggestions to the learner on how to proceed. Such scaffolding allows a beginner to do more than he or she could without help. Then, as the learner masters the basics of the task, the scaffolder transfers more and more responsibility to the learner until the learner is doing the entire task. Thus, adults and children collaborate to produce social learning.

Cognitive Change Mechanisms

Many of the most compelling analyses of developmental change are at the level of cognitive processes. Both general and specific information-processing mechanisms play important roles.

General Information-Processing Mechanisms

Four categories of information-processing mechanisms are especially general and pervasive: basic processes, strategies, metacognition, and content knowledge.

Basic processes are the simplest, most broadly applicable, and earliest-developing general information-processing mechanisms. They overlap considerably with behavioral learning processes and include associating events with each other, recognizing objects as familiar, recalling facts and procedures, encoding key features of events, and generalizing from one instance to another. Changes with age occur in the speed and efficiency of these basic processes, but all of the basic processes are present from infancy onward. These basic processes provide a foundation that allows infants to learn about the world from their very first days.

Strategies also contribute to many types of development. Toddlers, for example, form strategies for achieving such goals as obtaining a toy that is out of reach or descending a steep surface; preschoolers form strategies for counting and solving arithmetic problems; school-age children form strategies for playing games and getting along with others; and so on. Often, children acquire multiple strategies for solving a single kind of problem—for example, strategies for approaching unfamiliar children on a playground or for solving arithmetic problems. Knowing multiple strategies allows children to adapt to the demands of different problems and situations.

Exceptional content knowledge can outweigh all of adults’ usual intellectual advantages over children. On the day this photograph was taken, this 8-year-old boy became the youngest person ever to defeat a chess grandmaster (the ranking awarded to the greatest chess players in the world).

TOPHAM/THE IMAGE WORKS

Metacognition is a third type of cognitive process that contributes to development in large ways. For instance, increasing use of memory strategies stems in large part from children’s increasing realization that they are unlikely to remember large amounts of material verbatim without using such strategies. Among the most important applications of metacognition is adaptive choice among alternative strategies, for example in deciding whether rereading is necessary to understand text, whether to count or state a retrieved answer to solve an arithmetic problem, and whether to write an outline before beginning an essay. The cognitive control involved in executive functioning, such as inhibiting tempting but counterproductive actions, being cognitively flexible, and considering other people’s perspectives, is another crucial type of metacognition.

Content knowledge is a fourth pervasive contributor to cognitive change. The more children know about any topic—whether it be chess, soccer, dinosaurs, or language—the better able they are to learn and remember new information about it. Knowledge also facilitates learning of unfamiliar content by allowing children to draw analogies between the new content and content that is familiar to them.

Domain-Specific Learning Mechanisms

Infants acquire some complex competencies surprisingly rapidly, including basic perception and understanding of the physical world, language comprehension and production, interpretation of emotions, and attachment to caregivers. What seems to unite the varied capabilities that children acquire especially rapidly is their apparent evolutionary importance. Virtually everyone quickly and easily acquires abilities that are important to survival.

A number of theorists have posited that the nearly universal, rapid learning in these domains is produced by domain-specific learning mechanisms that operate on everyday experience to produce accurate conclusions about the world in domains of evolutionary importance. For example, even infants in their first year seem to expect bigger moving objects to produce stronger effects than smaller moving objects. Similarly, toddlers’ word learning seems to be aided by the whole-object assumption (the idea that words used to label objects refer to the whole object rather than to a part of it) and the mutual exclusivity assumption (the idea that each object has a single name). These assumptions are usually correct for the words that young children hear, thus helping them learn what the words mean.

Children’s informal theories about the main types of entities in the world—inanimate objects, people, and other living things—also facilitate their learning about them. The value of learning rapidly about the properties of people, other living things, and inanimate objects is clear; saying “More juice” to another person, for example, is considerably more likely to yield the desired outcome than is saying the same words to the family dog. Crucial in children’s informal theories, as in scientists’ formal ones, are causal relations that explain a large number of observations in terms of a few basic unobservable processes.

Possessing basic understanding of key concepts—such as inertia and solidity for inanimate objects; goal-directed movement and growth for living things; and intentions, beliefs, and desires for people—helps children act appropriately in new situations. For example, when preschoolers meet an unfamiliar child, they assume that the child will have intentions, beliefs, and desires—an assumption that helps them understand the other child’s actions and react appropriately to them. These assumptions about other people’s minds aid the social understanding of children in all societies. Thus, both general and domain-specific cognitive learning mechanisms help children understand the world around them.

Change Mechanisms Work Together

Although it is often easiest to discuss different change mechanisms separately, it is crucial to remember that biological, cognitive, and behavioral mechanisms all reflect interactions between the person and the environment and that all types of mechanisms work together to produce change. For instance, consider effortful attention. The development of this capability reflects a combination of biological and environmental factors. On the biological side, genes influence the production of neurotransmitters that affect children’s ability to concentrate and ignore distractions. Effortful attention also relies on the development of connections between two parts of the brain—the anterior cingulate, which is active in attention to goals, and the limbic area, which is active in emotional reactions. On the environmental side, the development of effortful attention can be influenced by the quality of parenting a child receives—though this is true primarily for children with a particular genotype. For children with one form of a relevant gene, quality of parenting influences the development of effortful attention, whereas for children with another form of the gene, quality of parenting has little effect on its development. Specific experiences can also be influential; for example, playing specially designed computer games increases the activity of the anterior cingulate and thus the ability to sustain attention on both experimental tasks and intelligence tests. In short, varied types of mechanisms work together to produce development of even a single capability.