Intro to Developmental Psychology

Developmental psychology is the study of the human mind across the life span. Unlike other areas of psychology--personality, cognitive, social--developmental psychology is explicitly concerned with how the rules of human behavior change over time. All of the methods used in psychology can be, and are, applied to the study of development. These range from neurobiological studies of the brain's growth to studies of the effect of social context on a child's future behavior.

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Terms List and Analysis

Cross-Sectional Study - A study in which separate groups of subjects at different ages are compared. For example, a study in which the performance of a group of three-year-olds on a language comprehension test is compared to the performance of a difference group of four-year-olds.

Experimental Study -A study in which one variable is manipulated (the independent variable) and its effect on another variable (the dependent variable) is observed.

Incremental Theory -A developmental theory that postulates that development proceeds in a series of steps or a gradual increase in capabilities. For example, information-processing theories.

Longitudinal Study -A study in which changes over time in the performance of a single group of subjects is studied. For example, a study in which the same group of children is studied at age three and a year later at age four.

Observational Study -A study in which the variables of interest are observed, rather than manipulated. Harder to interpret than an experimental study because other, unmeasured factors, may be the cause of any observed relationship between the variables of interest.

Stage Theory -A developmental theory that postulates that development proceeds in a sequence of qualitatively different stages. For example, Piaget's theory of cognitive development.

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Methods

In order to study human development, researchers face a set of problems that often overlaps with that of researchers of other areas but which also includes problems specific to development. Foremost among those is the fact that developmental psychology is the study of behavioral change over long periods of time. Furthermore, researchers often cannot, for ethical reasons, experimentally manipulate the variables that interest them (such as parenting style), so they are forced to conduct observational studies rather than experimental ones. Finally, the study of pre- linguistic infants poses special problems for determining those infants' abilities.

1.1 Cross-sectional and Longitudinal Studies
Two major types of studies are conducted in developmental psychology: longitudinal studies and cross-sectional studies. Cross- sectional studies are by far the most common. In these studies, different groups of children or adults are studied at a single time and the results compared across groups. For instance, a researcher could address the question of whether sentence comprehension improves between the ages of three and four years of age by testing a group of three-year-olds and a group of four-year-olds and comparing their performance. This approach has some pitfalls. Among them is the fact that, since performance is being tested in two separate groups, it is hard to determine the cause of any difference in performance that might be found. There may be hidden differences between the two groups, aside from their age, that are the real cause of the behavioral differences.

Longitudinal studies avoid some of these pitfalls at the cost of a much greater investment of time and effort. In a longitudinal study, the performance of a single population is followed across time periods spanning from weeks or months to many years. For instance, the question about sentence comprehension described above could be addressed by testing a group of three-year-olds and then, a year later, bringing the same children back into the laboratory to perform the same test. This has the advantage of controlling for some of the potentially confounding factors mentioned above for the simple reason that each child can be directly compared with himself or herself at an earlier age. It is, however, often very difficult, for practical reasons, to implement longitudinal studies: subjects may move to different geographical areas or decide that they are no longer interested in participating.

1.2 Observational and Experimental Studies
In addition to the division between cross- sectional and longitudinal studies, two further divisions can be made in the kinds of studies carried out by developmental psychologists. Ideally, researchers like to carry out studies in which the variable of interest can be directly controlled. An example of such an experimental study would be a test of the effects of visual contrast on depth perception; in such a study, contrast could be changed by the experimenter in a systematic fashion and differences in subjects' performance could be directly measured. However, many of the variables that interest developmental psychologists cannot, for ethical reasons, be directly manipulated. A researcher who was interested in the effect of maternal care on emotional development could not in good conscience randomly assign one group of infants to a "care" condition and another group to a "no care" condition. Instead, the researcher must conduct an observational study. In the example of maternal care, measures of maternal care in a randomly-selected group of mothers could be collected and correlated with measures of their children's performance on psychological tests. Although the conclusions that can be drawn from such a study are weaker than those that can be drawn from experimental studies, they are sometimes the developmental psychologist's only resort.

1.3 Performance and Ability
A final methodological issue needs to be addressed before we discuss the kinds of theories that figure in developmental psychology. In all of psychology, but particularly in developmental psychology, researchers must confront the issue of the extent to which their measures of a subject's performance actually reflect that subject's ability. In the study of pre-linguistic infants, the issue is particularly striking since many researchers are specifically concerned with cognitive structures whose existence is usually determined linguistically. For instance, researchers have been interested in how infants develop a sense of the basic laws of physics--e.g., that two things cannot occupy the same space at the same time--but for a long time they were stymied in their efforts to study this by infants' inability to report on what they knew. Some solutions to this problem are discussed in more detail in the section on cognitive development.

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Theories in Developmental Psychology

 

There is currently no overarching theory of developmental psychology, but there are several approaches to which researchers more or less adhere. One useful way of categorizing these theoretical approaches is based on the way each theory parses the developmental trajectory. Some theories, called stage theories, divide the life span into qualitatively different segments. Others, called incremental theories or continuous theories, suggest that the sweeping changes seen across the life span are the result of incremental advances in a person's abilities.

2.1 Stage Theories
The most influential stage theory--in fact, the most influential theory in developmental psychology, period--was introduced by Jean Piaget in books and papers written in the 1920s and the decades after. Piaget suggested that children went through four stages of development through their childhood, during which qualitatively different rules applied to their behavior and growth. Although there were some similarities between the stages and some rules of behavior that applied throughout the life course, Piaget argued that the best way to understand development was by focusing on the qualitative differences between each stage and the processes involved in moving from one stage to the next. Although stage theories are less popular now than when Piaget introduced his, they still hold some sway over developmental psychologists' explanations of behavior. However, most psychologists now tend more toward some version of incremental theory, described below, than they do towards stage theories.

2.2 Incremental/Continuous Theories 
Incremental or continuous theories of development argue that behavior across the life span cannot be divided into qualitatively different stages, although behavior does qualitatively change as we grow older. These changes are, rather, due to basic principles of growth and development that lead to new developments as the child and adult interact with the world. Changes are gradual, not sudden, and they typically involve small, incremental changes in the individual's understanding of the world and his or her behavior towards it. The information-processing account is one prominent example of an incremental theory. According to this theory, children's improvements in performance and acquisition of new skills are dependent on some basic cognitive factor, such as working memory capacity. As working memory capacity increases, the child is able to acquire qualitatively new skills and abilities.

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Sources of Developmental Change

 

The issue of "why" lies behind every developmental study or theory. Whether one studies development observationally or experimentally, cross-sectionally or longitudinally, within a stage-based or an incremental theoretical framework, the central question remains: What is the source of development change? The answer to this question has important consequences not only for our understanding of development but also for the kinds of strategies we should pursue to solve real-world problems.

3.1 Genes 
The structures of our bodies and brains are largely determined by the kinds of genes we have. Thus it is tempting to look to genes as the source of the changes in those structures, and in the behaviors they cause, over the course of the life span. Few would deny that genes have a large role to play in the increases in height, weight, strength, and other physical attributes that we see during childhood. More controversial, but quite prevalent, is the conclusion that mental abilities are similarly influenced by genes.

3.2 Environment 
In contrast to gene-based explanations, many have argued that the environment is the primary cause of developmental change. Support for this claim comes from the wide range of studies that show that experience in the world is crucial for any kind of development, and that differences in the environment can have enormous consequences for the direction of development. Perhaps the most important part of the environment is the social environment: the people with whom the child interacts on a daily basis.

3.3 The Interactionist Approach 
Between the extremes of genetic and environmental approaches to development is a middle ground: the interactionist approach. According to this approach, development arises from a combination of genetic and environmental factors. Throughout the life course, genetics obviously have an important role to play in influencing behavior; however, the exact effect they have depends on one's current environment and past experiences. The biology of genes are also strongly influenced by behavior; for instance, stress hormones and many other brain chemicals whose levels are influenced by the environment can cause changes in the expression of genes in the brain and even in the
growth of different parts of the brain.