POSTURAL RESPONSES TO STATIONARY AND MOVING SCENES AS A FUNCTION OF DISTANCE TO THE SCENE

Amplitude of postural sway in fore-after direction was investigated as a function of suggested distance between the observer and a stationary or moving scene. These experiments were done with a set-up in which movements of the observer were fed back real-time to a graphics workstation to modify the video image projected on the screen. The results show that sway amplitude for a stationary scene increases with increasing distance. Sway amplitude in response to a scene moving along the line of sight with constant amplitude did not depend on distance. Both of these results can be explained by assuming a threshold for visual motion perception and by assuming that observers move so as to minimize retinal slip.