Why Should Cognitive Developmental Psychology Remember that Individuals Are Different?

Abstract

This article is a plea to cognitive developmental psychology to show a genuine and durable interest in individual variability, be it inter- or intraindividual. Individual differences have indeed often been relegated to domains of application whereas intraindividual variability has been considered as measurement noise. Moreover, interindividual differences are most frequently considered only as quantitative variations around a same norm (e.g., are individuals faster or slower in their development/aging?). In contrast, it is here argued that individual variability constitutes an important fundamental phenomenon, which would help us better understand processes underlying cognition as well as cognitive development. Also, one should look for qualitative differences, that is, for differences in the way individuals develop or age. Illustrations are provided of erroneous or only partial conclusions that were reached because of an over reliance on cross-sectional, univariate experimental designs.

Notes

¹ Note that cognitive aging researchers have granted a larger status to individual variability than child developmentalists. Likewise, individual differences have been assigned a larger role in the personality domain than in the cognitive one.

² Piaget wrote, in his concluding comments of the CTB/McGraw-Hill Conference on Ordinal Scales of Cognitive Development (Piaget, 1971, p. 211) and addressing the issue of using the concept of developmental stage for diagnostic purposes: “We are dealing with a problem of differential psychology, of psychology of the individual. … This, I must confess, is a problem I have unfortunately never studied, because I have no interest whatsoever in the individual. I am very interested in general mechanisms, intelligence and cognitive functions, but what makes one individual different from another seems to me—and I am speaking personally and to my great regret- far less instructive as regards the study of the human mind in general.” [underlined added].

³ This type of intraindividual variability is probably also close to the concept of differentiation. Note, incidentally, that the hypothesis of differentiation-dedifferentiation (Baltes, Lindenberger, & Staudinger, 2006) has received little empirical support and was advanced on the basis of correlations, that is, between-individual differences. It is out of the scope of this article to discuss this hypothesis (see Mella et al., under revision).

⁴ Needless to say that the paper was not accepted in that journal, but this is not the point here.

Additional information

Funding

This article was made possible by a number of grants received from the Swiss National Science Foundation, in particular grants 100014_120510 and 100014_135410.