Binocular neurons in V1 of awake monkeys are selective for absolute, not relative, disparity

Most neurophysiological accounts of disparity selectivity in neurons of the primary visual cortex (V1) imply that they are selective for absolute reti nal disparities, By contrast, a number of psychophysical observations indic ate that relative disparities play a more important role in depth perceptio n, During recordings from disparity selective neurons in area V1 of awake b ehaving monkeys, we used a disparity feedback loop (Rashbass and Westheimer , 1961) to add controlled amounts of absolute disparity to a display contai ning both absolute and relative disparities. This manipulation changed the absolute disparity of all the visible features in the display but left unch anged the relative disparities signalled by these features. The addition of absolute disparities produced clear changes in the neural responses to unc hanged external stimuli, which were well predicted by the measured change i n absolute disparity: in 45/53 cases, the neuron maintained a consistent fi ring pattern with respect to absolute disparity so that the manipulation cr eated no significant change in the absolute disparity preferred by the neur on. No neuron in V1 maintained a consistent relationship with relative disp arity. We conclude that the relative disparity signals used in primate dept h perception are constructed outside area V1.