Abstract
INTRODUCTION. One of the most fascinating phenomena in stereopsis is the profound hysteresis reported by Fender and Julesz (1967), in which the depth percept with increasing disparity persisted long past the point of depth recovery with decreasing disparity. To control retinal disparity without vergence eye movements, they stabilized the stimuli on the retinas with an eye tracker. We now report that stereo hysteresis can be observed simply by rotating the binocular stereogram image. As the image rotates, the horizontal disparities rotate to become vertical, then horizontal with inverted sign, then vertical again before returning to the original orientation. The depth shows an interesting popout effect, almost as though the depth was rapidly switching on and off, despite the inherently sinusoidal change in the horizontal disparity vector. METHODS. This stimulus was set up electronically in a circular format so that the random-dot field could be dynamically replaced, eliminating any cue to cyclorotation. Noise density was proportional eccentricity to fade the stimulus near the zero-disparity fixation target, allowing us to verify that fixation was held accurately at zero disparity. RESULTS AND DISCUSSION. For both the invariant and the dynamic noise, profound hysteresis of many seconds delay was found in eight observers for both the onset and offset of the perceived depth surface. This hysteresis was far longer than the <1000 ms reaction time to respond to changes in disparity. A similar hysteresis was obtained for depth popout from vertical disparity modulation of a fixed horizontal disparity. Conversely, sinusoidal modulation of the horizontal disparity to match the horizontal vector component of the disparity rotation did not show the popout effect, which thus seems to be a function of the interaction between horizontal and vertical disparities and is attributable to the time course of surface interpolation processes for the perceived depth structure.
Meeting abstract presented at VSS 2012