Binocular correspondence in stereoscopic vision

For binocular stereoscopic vision to be possible, the visual nervous system needs to perform two tasks with the information available from the left and right eyes. First, features visible from the left eye must be paired up with the corresponding feature as seen from the right eye's vantage point. Second, the geometric information from the matched binocular features must be transformed into an estimate of binocular disparity. In this sense, the paper by Barlow, Blakemore and Pettigrew1 represents the first complete proposal for the neural mechanisms underlying binocular correspondence and the per­ception of stereoscopic depth. They proposed that the feature selectivity of visually-responsive neurons should have a central role in sorting out which visual features in the left eye should match with those in the right eye and that the same group of neurons should provide signals from which binocular disparity could be extracted to signal depth. In short, for the cat's visual system, the neurons in cortical area VI were proposed to be involved in both binocular matching and the recovery of stereoscopic depth. Neurons in VI have a number of obvious monocular feature selectivities that can be exploited for binocular matching, namely the local orientation, spatial frequency and spatial phase of regions of the image's luminance (black/white) contrast. The beha­vioural significance of these features is also con­firmed by numerous psychophysical studies of the stereoscopic capabilities of human vision. Other feature selectivities in VI, such as colour, may have