[The dependence of the changes in vestibular postural reactions on the information content of visual feedback].

Electrical stimulation of the labyrinth in standing subjects induced the body sway predominantly in the frontal plane. Stabilographic response included both early (latency 120-200 ms) and late (200-500 ms) components. Their magnitudes depended on the visual control condition. Maximal responses were recorded in the eyes-closed condition. The response decreased when subjects maintained erect posture with their eyes closed, when fixing a stable visual target, and when tracking the frontal stabilogram displayed on an oscilloscope screen (visual feedback). In all the conditions the early component decreased by 10-20 percent whereas the late one decreased by 50-70 percent. Visual fixation of a small light stationary relative to the head did not influence the response. On the other hand, information on the direction of the expected body sway given in the visual fixation condition resulted in a considerable and approximately equal decrease of the two components (by 70-80 percent). It is concluded that the early and late components of the vestibulo-motor response are mediated via different mechanisms with specific temporal and functional characteristics.