Optokinetic-Graviceptive Interaction in Different Head Positions

Abstract

With increasing lateral tilt of the head (0°, 30°, 45°, 60°) the apparent vertical (AV) is progressively inclined in the same direction. Simultaneously, the variance of settings of a test edge increases, consistent with the theory of a progressive decline in the effectiveness of the statolith organs. The AV can also be influenced by moving visual scenes rotating around the observer's line of sight. It has been argued that visual motion information, which also results in apparent body tilt, contributes to the central computation of orientation of the gravitational vector. If with lateral head tilt graviceptive sensory input is less accurate and less powerful the visual influence should become more potent. Indeed, displacements of AV induced by exclusive visual stimulation with the head erect are moderate but increase progressively with larger head tilt angles. The potentiation of the net visual effect on AV in an inclined head position is maximal if the visual stimulus is moving opposite to the head tilt. The demonstrated visual-graviceptive interaction seems to have functional implications for postural orientation.