CONCEPT I: The Process of Development

Developmental psychology is the branch of psychology that attempts to explain the regular patterns of growth and change that occur during the human life cycle. Developmental psychologists generally ask two closely related questions: How do people change as they grow older and why do these changes occur in the ways they do?

Development is sequential; present change builds on previous development. However, individuals vary widely in the age at which certain behaviors develop. The concept of sequence emphasizes that development is not random and that it is predictable.

Any developmental event is the product of heredity and environment. Heredity refers to the inherited set of developmental instructions transmitted to us from our parents by the genes we are born with. Environment includes the external surroundings, social and cultural influences, and internal biological factors. Behavior genetics is the field of study that tries to determine the relative contribution of environmental and hereditary differences to human thought and behavior.

Heredity traits are established at conception when a male sperm penetrates the female egg. Both the sperm and the egg are produced by a cell division process called meiosis. Each sperm and each egg cell contains twenty-three chromosomes. At conception, the two sets of twenty-three chromosomes pair up to make the normal human complement of forty-six chromosomes, arranged in twenty-three pairs.

These chromosomes carry the genes, which are the basic units of the hereditary mechanism. A gene is a small portion of a DNA (deoxyribonucleic acid) molecule containing a code for the development and maintenance of a living organism. Genetic instructions can be modified by inadequate nutrition, various drugs such as thalidomide, and emotional deprivation. Drugs like thalidomide, which when taken during pregnancy can cause deformation of the baby's limbs, and alcohol that are known to cause abnormalities in fetuses are called teratogens. As an example, if a woman abuses alcohol during pregnancy, her baby may be born with fetal alcohol syndrome, a condition associated with certain physical deformities and mental retardation. Teratogens are usually most harmful early in pregnancy. Almost all genetic traits, at least to some extent, are susceptible to environmental influences. Even the retardation produced by Down's syndrome can be reduced by environmental enrichment. All human traits are influenced by both genes and environment.

CONCEPT II: The Competency of the Human Infant

Although newborns seem totally dependent on their environment, they are actually capable of a rather impressive set of skills. For example, they can see objects at close range, even though their vision is about 20/300. From birth, they show a preference for novel stimuli, and they will imitate an adult facial expression.

Babies are able to differentiate similar sounds such as b and p, they can distinguish among smells, and they can coordinate their auditory and visual processes. Research on the sensory capabilities of newborns generally involves the repeated presentation of one stimulus, then a shift to a new stimulus. Results show that a baby becomes less interested in the repeated stimulus, a kind of learning called habituation, but regains interest when the new stimulus is presented.

Newborns are equipped with several crucial reflexes. The rooting reflex, in which a baby turns its head toward anything that touches its cheek, allows the baby to locate a nipple for feeding. The grasping reflex, in which the newborn will firmly grasp an object placed in its hand, may be a remnant from our evolutionary past. These reflexes usually disappear by four months of age, and immature reflexes or reflexes which last too long can be signs of neurological problems.

Several changes in the brain allow this development: dendrites grow, many new synapses form, and myelin sheaths develop to help speed neural conduction. Also, the volume of nerve cell bodies increases and more glial cells grow, thereby tripling the size of the brain cortex from birth to four years of age.

Newborns are capable of learning from birth. Experimental observation leads one to believe that infants derive pleasure from solving problems. Research indicates that infants can remember over longer periods of time than was previously thought. However, adults have great difficulty in remembering events from their own infancy, a phenomenon called infantile amnesia. Several theories have been advanced to explain this memory failure. Freud believed we store these memories but can't retrieve them in adulthood because of their sexual nature. Other researchers believe our retrieval failure results from our lack of appropriate retrieval cues or from the fact that early memories are not processed with language and are therefore not stored. Others think that brain changes that accompany growth disrupt these early memories.

CONCEPT III: Cognitive Development in Infancy and Childhood

Jean Piaget proposed the most influential stage (qualitative) theory of cognitive development. He believed that intellectual development progresses through four major stages: the sensorimotor period (birth to two years), the preoperational period (the preschool years), the concrete-operational period (the elementary school years), and the formal-operational period (adolescence through adulthood). Three processes interact to advance the individual from one stage to another. Assimilation occurs when new information is incorporated into preexisting schemas. Accommodation is the process of changing thinking to adapt to new information. Information and schemas must be in a state of balance, called equilibration. Accommodation and equilibration move the individual from one stage to the next.

The information processing approach argues that development is the increasing of the capacity to process information. This view describes the quantitative rather than the qualitative difference from one age to another. Whereas Piaget's qualitative differences imply that children of different ages perceive the world in quite different ways, information-processing theory suggests that children's thinking gradually improves.

According to Piaget, during the sensorimotor period, infants learn to act in the world but they do not appear to be able to think about their behavior until they develop the understanding that objects exist apart from their experience. Early in this period, infants do not understand that objects and people have a permanent existence. Instead they act as if objects cease to exist when the objects are removed from their presence. The development of object permanence is gradual: at four months a baby will reach for a partially hidden object; between four and eight months, it will visually track an object being placed behind a screen; between eight and twelve months, it will search for a hidden object. Only in the last period of the sensorimotor stage will a baby follow the placement of an object from one location to another to another. Not all psychologists agree with Piaget's explanation. Some prefer to consider the development of object permanence as the result of improving memory capabilities. Research has demonstrated that the concept of object permanence may develop at earlier ages than Piaget has concluded.

The preschool years (the preoperational period) are most importantly characterized by representational thought, the ability to think about objects not immediately present. A preschooler's thought differs from an older child's in that it is egocentric (the child is unable to understand a situation from another person's perspective).

Older children (concrete-operational stage) can think in logical ways that preschoolers cannot and can perform concrete operations, or mental transformations. During this stage they learn conservation, the ability to recognize that certain features of things remain unchanged even when other features change. Piaget suggested that this learning reflects a qualitative change in cognition, but more recent work which shows that even young children can conserve numbers if verbal instructions do not confuse them challenges this view. Recent work by Gelman suggests that the child's inability to interpret the task may confuse the kinds of responses being given to the conservation problem.

Robbie Case has proposed a theory that integrates Piaget's perspective and the information processing perspective. Case argues that as age increases, the efficiency of use of short-term memory storage space (the memory capacity available to think about problems) also increases. Movement from one stage to another requires the acquisition of new executive control structures (the child's current ways of representing the world and strategies for problem solving). Executive controls can advance in one area before others depending on how efficient storage space is and how complex the new control structure is.

All normal children go through a series of stages in the development of spoken language, regardless of their culture. There are, however, individual variations in the rate of progress through the stages. From the earliest weeks of life, newborns develop distinguishable patterns of crying. By age three months they can coo; by six or seven months they can babble. Babbling does not seem to be directly related to adult speech, since it can contain sounds from all languages and since there are no differences between normal and deaf babies in the way they babble. Intonation (pitch pattern) and gesturing are also important in prespeech communication.

Children speak their first words at about the end of their first year. These words all focus on present objects and events. At this stage, children often commit errors of overextension (applying a category label to objects that don't fit the category, such as calling all four-legged animals doggie) and underextension (failing to include all category members in the category label, such as not calling a German shepherd a doggie). Through the processes of overextension and underextension, a child learns the mental representations used in a language.

Around age two, children begin putting words together in sentences, the first being two-word combinations. This telegraphic speech is characterized by elimination of descriptors and connectors; it focuses on nouns and action verbs. Even this early speech is highly structured. The emergence of this early speech depends on the attainment of a certain level of neurological maturation, particularly in the rapid increase in the number of neural synapses that occurs at about age one-and-one-half.

Between ages two and five, vocabulary increases dramatically, complex grammatical rules are mastered, and the child's ability to communicate moves beyond the immediate situation. Grammatical rules are acquired in sequential steps. Young children often commit errors of overregularization, in which they extend rules to instances in which the rules do not apply. Children also begin to learn about pragmatics, the study of how social context influences the use of language.

The nativist theories of language acquisition claim that language development is controlled by genetically programmed neural circuits. Noam Chomsky, for example, argues that the human brain contains a language acquisition device (LAD) which automatically analyzes the components of speech a child hears. The patterns of acquiring negation, the age of language mastery, and the speed of acquisition are similar enough across languages to support the nativist view.

Learning theories emphasize the crucial element of experience, and point out that no child learns language without exposure to language. Although most parents feel that their children learn language through imitation and reinforcement, research indicates that parents reinforce meaning rather than grammar. Consequently, most psychologists believe that language acquisition is highly creative, although reinforcement and imitation probably have some effect.

Younger children use fewer deliberate strategies for memory storage and retrieval than do older children. However, when required to use memory cues, younger children can utilize a strategy, thereby indicating that better memory may be the result of learning more efficient storage and retrieval strategies. Also, familiarity with material being remembered improves recall, and older children's better memories may be partially the result of being more familiar with the material being stored.

Preschoolers tend to overestimate their abilities to remember. Metacognition (the ability to monitor one's own thoughts) emerges in middle childhood, giving older children a much more realistic appraisal of capabilities.

CONCEPT IV: Cognitive Development in Adolescence and Adulthood

Formal operational intelligence expands the child's cognitive abilities to include systematic (scientific) testing of hypotheses, and hypothetical and abstract thinking. Piaget suggested that formal operational thought developed at adolescence, although not all adolescents and adults use this ability all of the time. In fact, research has shown that many adults may be capable of formal thinking only in their areas of expertise. Information-processing theorists believe that the improvement in logical and hypothetical thinking which accompanies adolescence is the result of their having acquired better information-processing skills, such as better memory storage and retrieval strategies and metacognition.

Maccoby and Jacklin reported in 1974 that boys tended to perform better at mathematical and spatial abilities tasks and girls did better at certain verbal tasks. Careful analysis of their data, however, shows that there are no sex differences on most tasks, and that, when one sex did show an advantage, it was small in absolute terms. Also, these performance differences have been shrinking in recent years, indicating that cultural factors probably are involved. The big exception is that the performance gap still favors boys at the highest levels of performance on tests of mathematics, but this is to be expected since boys' scores fall slightly above girls' at all levels. These sex differences might result from differences in hormones and brain development or may come from social and cultural expectations. In any case, the differences are small enough that they do not allow us to predict the performance of an individual based on that person's sex alone.

Cognitive development does not stop with the formal operations stage at adolescence. Early adulthood (age twenty to forty) is a time of peak intellectual accomplishment, especially on tasks involving memory, speed, or intellectual flexibility. Middle adulthood (age forty to sixty) is accompanied by even better verbal skills and reasoning ability as well as increases in IQ. Only on tasks involving hand-eye coordination do middle adults perform less well than when they were younger. Although aging does produce some decline in long-term memory functions, the decline is usually small and probably is related to slower processing speeds. Short-term memory is unaffected. Of course, the effects of aging vary a great deal from person to person and result from both biological (hereditary) and environmental factors.