Visual guidance of passing under a barrier

Abstract

The theory of affordances proposes that organisms control their actions according to the fit between the organism and the environment. This study set out to examine the proposal that actions are attuned to environmental demands on the basis of body-scaled information and how modifications to such actor-environment synergies might be influenced by speed of locomotion and locomotor ability. The paradigm task was walking and running under a barrier set at different heights. The subject groups comprised normal adults, nursery school children, cerebral palsied children, and infants with less than 6 weeks' independent walking experience. A body-scaled critical point, at which they began to duck under the barrier, was observed for all but the infant subjects. In addition, the nursery school children were found to be more cautious in their behaviour than adults both when walking and running. The cerebral palsied children compensated for their poorer ability to control vertical position in space by allowing an even greater safety margin when passing under the barrier. The results provide support for an affordance theory of perception, in which body size, speed of locomotion and level of motor control are considered important properties of the actor-environment fit. ©1997 John Wiley & Sons, Ltd.