[VEPs induced by binocular disparity stimulus of the retinal nasotemporal overlap]

The human visual evoked potentials (VEPs) elicited by retinal disparity stimulation of the nasotemporal overlap area of the fundus, where ipsilaterally and contralaterally projecting retinal ganglion cells intermingle, were recorded bilaterally at the cortical hemispheres, and the contribution of the nasotemporal overlap to the mechanism of stereopsis was studied. The stimulus was a slit of a stereogram or correlogram applied to the center of the fovea of the right eye, or 3 degrees or 6 degrees nasal or temporal to the fovea. The negative waves of the VEPs evoked by the stereogram were located at O1 and O2. The VEP amplitudes evoked by the stereogram markedly exceeded those by the correlogram. In comparing the VEP amplitude of O1 with that of O2, when the slit of the stereogram hit the nasal side of the nasotemporal overlap O1 exceeded O2, and on the temporal side, this was reversed. The difference between the amplitudes at O1 and O2 was significant at 3 degrees from the fovea. These results showed electrophysiologically that the width of the nasotemporal overlap in the human retina is more or less 4 degrees and that the activity from the overlap area converges to disparity selective neurons in the visual cortex, suggesting that the overlap area is the region where cues to depth perception are obtained in the front-posterior plane of the fixation point.