Binocular visual direction is displaced by the slant of surrounding surfaces
56.432, Tuesday, May 14, 2:45 - 6:45 pm, Orchid Ballroom
Tsutomu Kusano1, Koichi Shimono1, Saori Aida1; 1The Graduate School of Marine Science and Technology, Tokyo University of Marine Science and Technology
Relative visual direction between objects in stereoscopic depth is basically determined by the oculocentric direction signals from the two eyes (Mansfield & Legge, 1996). Here we show that spatial context (slant about the horizontal axis of surfaces that surrounds stereoscopic objects) also affects visual judgment of the vertical relative direction between objects. The effect was examined in two experiments in which a stereoscopic half-image was presented to each of the eyes with liquid crystal shutter glasses. The images consisted of two horizontal bars and two random-dot rectangles. When fused, each bar was perceived inside each of the two random-dot rectangle surfaces that had the same horizontal disparity as the bar. The same amount of slant was introduced to both surfaces. In a first experiment, the slant of the surface was achieved by changing the height of an observers head position relative to the monitor. In a second experiment, shear disparity was introduced instead of the change of head position to eliminate cyclovergence induced by gaze elevation. The method of adjustment was used to modify the vertical position of the bar (comparison stimulus) that had zero disparity so that it appeared to be vertically aligned with the other bar (standard stimulus) which had one of five horizontal disparities (-15 arcmin to +15 arcmin in 7.5 arcmin steps). Two experiments showed that 1) when the upper side of each of the two surfaces was farther than the lower side, the standard stimulus was displaced to a lower position as the disparity was increased, and 2) when the lower side of the surfaces was farther than the upper side, the vertical displacement effect was not observed. These results suggest that spatial context should be taken into account to predict the vertical relative direction between binocularly fused stimuli.