Motor constraints on the development of perception-action matching in infant reaching

Previous studies on reaching and grasping have suggested that infants need considerable experience at both seeing and touching in order to develop responses adapted to the environment. Such an account, however, does not reveal how appropriate perception-action matching emerges from these repeated experiences at seeing and touching. The present research addresses this issue by investigating the dynamics of perceiving and acting in 5- to 9-month-old infants as they saw, reached for, touched, and grasped objects of different sizes and texture. To gain insights into the mechanisms of change that underlie pattern formation, we observed infants' responses as a function of time, as infants reached for and manipulated objects successively. We found that the developmental process by which appropriate perception-action matching emerges is tied to important changes in the motor system. Before 8 months, infants' reaching responses are constrained by systemic motor tendencies that conflict with the process of perceptual-motor mapping. When these motor tendencies disappear, infants are able to use and integrate visual and haptic information to scale their actions to objects. These results are consistent with a dynamic systems approach, which views behavioral changes and their underlying psychological processes as the product of continuous tensions and interactions between the organism's own constraints and the characteristics of the task at hand. (C) 2000 Elsevier Science Inc. All rights reserved.