Abstract
A stimulus flashed immediately before a saccade is perceived as mislocalized in the direction of the eye movement. This perisaccadic-positional shift varies with the time from the flash to the saccade onset (TSO:). We have shown that this shift is also strongly affected by the stimulus luminance for a single flash: the shift is larger with low than high luminance. We also found an interaction between flashes presented asynchronously to the same eye in which a flash with a longer TSO is shifted more than a second flash with a shorter TSO. The results suggest a low-level mechanism in which the visual system combines eye position information with a persistent neural representation of the retinal image (temporal impulse response) to estimate the visual direction during saccadic eye movements. These results also provided the foundation for studies of a head-centric disparity mechanism in which asynchronous dichoptic foveal flashes presented before a saccade produced different amounts of perisaccadic shift in each eye and resulted in the depth percept from the head-centric disparity of the zero retinal disparity stimulus. This head-centric disparity also cancelled a retinal disparity of opposite sign, illustrating an interaction between the retinal and headcentric disparity estimates. This is the first experimental evidence that demonstrates a head-centric disparity mechanism for stereopsis in human.