Ocular dominance and disparity-sensitivity: why there are cells in the visual cortex driven unequally by the two eyes

Summary Tuning curves for stimulus disparity were constructed for units in area 18 and along the 17/18 border of the cat visual cortex (N=248). Units were activated with stimuli moving in the same (in-phase motion) or in the opposite direction (antiphase motion) across the two retinae. Over 70% of the units encountered showed sensitivity to stimulus disparity. A clear relationship was found between disparity-sensitivity and unit ocular dominance (OD). Contrary to what might have been expected, large binocular interactions were correlated with unilateral OD. Units highly sensitive to stimulus disparity generally showed strong dominance by one eye (OD groups 1, 2, 6 and 7), or responded well only to binocular stimulation, and weakly or not at all through each eye separately (“binocular-only”). Units unselective for stimulus disparity were usually driven well through either eye (OD groups 3, 4 and 5). High disparity-sensitivity was due to both strong binocular inhibition and strong binocular facilitation in units of extreme unilateral OD. Nearly all units of OD groups 1 and 7 showed clear binocular interactions, indicating that there are few “truly monocular” cells in the cat visual cortex.