Neurons in the Primary

1.1 Introduction Neurons sensitive to binocular disparity have been found in the visual cortex of many mammals and in the visual wulst of the owl, and are thought to play a signiicant role in stereopsis Barlow et al. A number of physiologists have suggested that disparity might be encoded by a shift of receptive-eld position According to this position-shift model, disparity selective cells combine the outputs of similarly shaped, monocular receptive elds from diierent retinal positions in the left and right eyes. More recently, Ohzawa et al. (1990) and DeAngelis et al. (1991, 1995) have suggested that disparity sensitivity might instead be a result of interocular phase shifts. In this phase-shift model, the centers of the left-and right-eye receptive elds coincide, but the arrangement of receptive eld subregions is diierent. This chapter presents a formal description and analysis of a binocular energy model of disparity selectivity. According to this model, disparity selectivity results from a combination of position-shifts and/or phase-shifts. Our theoretical analysis suggests how one might perform an experiment to estimate the relative contributions of phase and position shifts to the disparity selectivity of binocular neurons, based on their responses to drifting sinusoidal grating stimuli of diierent spatial frequencies and disparities. We also show that for drifting grating stimuli, the binocular energy response (with phase and/or position shifts) is a sinusoidal function of disparity , consistent with the physiology of neurons in primary visual cortex (area 1