Dropping the Other U: An Alternative Approach to U-Shaped Developmental Functions

The aim of this article is to introduce readers to an alternative way of applying U-shaped functions to understand development, especially cognitive development. In classical developmental applications, age is the abscissa; that is, in the fundamental equation B = f(A), some behavioral variable (B) plots as a U-shaped or inverted U-shaped function of chronological age across some age range. Although a U-shaped trend is always a surprising outcome,examples are reasonably thick on the ground—including infant face perception (Cashon & Cohen, 2004), symbolic gestures (Namy, Campbell, & Tomasello, 2004), and motor coordination and language (Gershkoff-Stowe & Thelen, 2004). These nonmonotonic trends are sufficiently numerous that some—notably, Thelen and associates (e.g., Thelen, Schöner, Scheier, & Smith, 2001; Thelen & Smith, 1994)—contend that a theoretical reorientation along dynamical systems lines is in order. There is a second “behavioral U” that figures in adult experimental psychology. It remains largely unknown in developmental work, but we could, I think, employ it to great advantage in research and theory. This article describes the other family of behavioral Us, shows how to apply it in developmental work, and sketches what can be learned from such applications. JOURNAL OF COGNITION AND DEVELOPMENT, 5(1), 81–88 Copyright © 2004, Lawrence Erlbaum Associates, Inc.