ABSTRACT
The purpose of this investigation was to examine task constraints on the nonrigid movements of the body during bipedal stance. Nonrigid movements are revealed by patterns of movement that vary across body segments. The central assumption is that such nonrigid movements should be both observable and controllable because they have specific affordances for perception and action (Riccio, 1993, in press; Riccio & Stoffregen, 1988,1991 ). Movement of the head relative to an object of visual regard, for example, can have a greater influence on visual perception than does movement of some other body segment. In addition, head movement can have a greater influence on a task that requires high-acuity vision than on a task that simply requires the maintenance of balance.
