Influence of visual stimulus on the human postural response

Abstract

We investigated the effect of central and peripheral roll rotational visual cues on postural sway and tilt perception. Subjects participated in three test sessions that consisted of three visual stimulus trials: 1) central only; 2) peripheral only1; and 3) both central and peripheral visual stimulus trials. In each session, subjects stood on a force platform with their arms crossed on their chest. Subjects were instructed to maintain upright posture in response to visual stimulus applied by three 19 inch LCD monitors located in front and either side of the subject. Computer-controlled sinusoidal visual stimulus provided randomly ordered roll rotational cues with peak velocity of 13.2 deg/sec over the stimulus frequency ranging from 0.01 Hz to 0.7 Hz. Trials for the stimulus frequency from 0.05 to 0.7 Hz lasted for 3 minutes, while those for lower stimulus frequency such as 0.02 and 0.01 Hz lasted for 5 and 7 minutes, respectively. While maintaining upright posture, subjects performed somatosensory bar task to indicate their perceived roll tilt. Center of pressure trajectories were measured using force platform and analyzed to obtain frequency response function. Results showed that for most of the subjects roll rotational vection started within 20 seconds after onset of visual stimulus, and lasted throughout the trials. Roll tilt perception and center of pressure trajectories were in phase with the stimulus. The magnitude of postural sway decreased as a function of frequency, showing more precipitous decrease for the stimulus frequency over 0.1 Hz. Both tilt perception and postural sway were significantly reduced for central visual stimulus only trials, while no significant change was observed between peripheral only and both central and peripheral visual stimulus trials. The results imply that peripheral vision dominates visually induced postural sway and tilt perception.