Developmental psychology is the branch of psychology that studies intraindividual changes and interindividual changes within those intraindividual changes. Its task, as La Bouvie has pointed out, is “not only description but also explication of age-related changes in behaviour in terms of antecedent-consequent relationships.”
Some developmental psychologists study developmental change covering the life span from conception to death. By so doing, they attempt to give a complete picture of growth and decline. Others cover only a segment of the life span – childhood, adulthood, or old age. In this book an attempt will be made to cover all segments and show the important developmental changes at different periods during the entire life span.
In the early years, as Siegel has explained, “developmental psychology was preoccupied with ages and stages. Investigators sought to learn the typical age at which various stages of development occurred”. The areas in which research was mainly concentrated were those considered significant for human evolutional adaptation. For the most part, research studies were concentrated on preschool and school-age children and on adolescents. Only later did research extend downward, first to birth and then to conception, and later upward, to adulthood, old age, and finally to middle age.
There are two major reasons for the uneven emphasis of developmental psychology. First, the study of a particular period in the developmental pattern has been greatly influenced by the desire to solve some practical problem or problems associated with that period. Research in the area of middle age, for example, is an outgrowth of the realization that good adjustments in the latter years of life depend on how well on has adjusted to the physical and psychological changes that normally occur in the middle years.
Because the focus of interest in developmental psychology has changed over the years, there are gaps in our knowledge of the different developmental phenomena characteristic of the different periods. These gaps are also due in part to difficulties in studying the different patterns of behaviour characteristic of a given period, especially difficulties in getting representative samplings of subjects of a given age and in finding a suitable method for the study of behaviour patterns.
The second reason for the uneven emphasis is that it is harder to study people at some stages of life than at others. Getting middle-aged and elderly subjects, for example, is far more difficult than getting preschool or school-age children or even adolescents.
Today, developmental psychologists have six major objectives: (1) to find out what are the common and characteristic age changes in appearance, in behaviour, in interests, and in goals from one developmental period to another; (2) to find out when these changes occur; (3) to find out what causes them; (4) to find out how they influence behaviour; (5) to find out whether they can or cannot be predicted; and (6) to find out whether they are individual or universal.
Meaning of Developmental Changes
The term development means a progressive series of changes that occur as a result of maturation and experience. As Van den Daele has pointed out, “development implies qualitative change”. This means that development does not consist merely of adding inches to one’s height or of improving one’s ability. Instead, it is a complex process of integrating many structures and functions.
Two essentially antagonistic processes in development take place simultaneously throughout life – growth, or evolution, and atrophy, or involution. Both begin at conception and end at death. In the early years growth predominates, even though atrophic changes occur as early as embryonic life. In the latter part of life, atrophy predominates, though growth does not stop; hair continues to grow, and cells continue to be replaced. With aging, some parts of the body and mind change more than others.
The human being is never static. From conception to death, change is constantly taking place in physical and psychological capacities. As Piaget has explained, structures are “far from being static and given from the start.” Instead, a maturing organism undergoes continued and progressive changes in response to experiential conditions, and these result in a complex network of interaction.
Even though development is continuous, as Bower has pointed out, in the sense that it is a cyclic process with competences developing, then disappearing, only to appear at a later age, it is not continuous in the sense that it increases constantly but rather in a series of waves with whole segments of development reoccurring repetitively. For example, as Bower has explained, newborns walk, if held, and then this ability disappears only to reappear at eight or ten months of age. He goes on to explain that the “various explanations of repetitive processes in development thus seem to differ depending on the specific repetition to be explained. What all the explanations have in common, however, is that they preserve the assumption that psychologic growth, in spite of its apparent reversals, is a continuous and additive process”. When regression to an earlier stage occurs, there is usually a cause for it, as in the regression to awkwardness that occurs with the rapid growth at puberty.
Often the pattern of change resembles a bell-shaped curve, rising abruptly at the start and then flattening out during the middle years, only to decline slowly or abruptly in old age. It is important to recognize that at no time can this pattern be represented by a straight line, though plateau periods of short or long duration may occur in the development of different capacities.
