ANTEROPOSTERIOR DYNAMIC BALANCE REACTIONS INDUCED BY CIRCULAR TRANSLATION OF THE VISUAL-FIELD

The anteroposterior sway of subjects under conditions of spontaneous d ynamic balance on a wobbly platform was measured during visual stimula tion by a visual target executing a circular trajectory in the frontal plane. The target was either a component of the whole moving visual s cene or moving on a stationary background. With the former stimulation , obtained through the use of rotating prismatic glasses, every point of the visual Field appeared to describe a circular trajectory around its real position so that the whole visual field appeared to be circul arly translated, undistorted, inducing binocular pursuit movement. Und er these conditions, stereotyped anteroposterior dynamic balance react ions synchronous with the position of the stimulus were elicited. The latter stimulation consisted of pursuing a luminous target describing a trajectory similar to that of the fixation point seen through the ro tating prisms on the same, this time stable, visual background. Althou gh pursuit eye movements were comparable, as demonstrated by electro-o culographic recordings, no stereotyped equilibration reaction was indu ced. It is concluded that the translatory motion of the background ima ge on the retina in the latter experiments contributed to the body's s tability as well as to the: perception of a stable environment.