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The direction of gravitoinertial force (GIF), i.e., the resultant of the gravitational and induced centripetal force vectors, was held constant while the magnitude of force was varied from 1.0-2.0 G to determine its effect upon egocentric visual localization (EVL) of the horizontal. 8 normal and 2 labyrinthine-defective (L-D) men served as Ss. The EVL of the horizontal was found to deviate from the gravitoinertial horizontal as a function of magnitude of the GIF. This magnitude effect tended to increase with the amount of body tilt from its alignment with the resultant force. The increase of GIF in the case of the L-D Ss resulted generally in an apparent rotation of the physical horizontal in a direction of the E then A phenomenon in contrast to the normal Ss who manifested ever increasing amounts of the E phenomenon only. Based upon these findings and the assumption that Ss differed under the experimental conditions primarily in otolithic function, the possible roles of otolithic and nonotolithic gravireceptor cues in visual localization in the absence of empirical visual cues are discussed.

SUMMARY PAGE THE PROBLEMTo determine the separate and combined influences o f otolith and nonotolith sensory inputs on perception of the oculogmvic illusion. By manipulating the visual and gravitoinertial force environments i t was possible to investigate the separate and combined contributions o f 1) field b r c e receptors i n the vestibular organs and 2) nonvestibular proprioceptors stimulated by external contact support, which influenced the visually perceived direction of extrapenonal space.

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