THE NEURAL CODING OF STEREOSCOPIC DEPTH

STEREOPSIS is a process by which the visual system gauges the relative depth of objects in three-dimensional space by measuring minute posit ional differences between left and right images. According to the stan dard notion, this information is thought to be encoded in the primary visual cortex by differences in receptive field (RF) positions for the two eyes. We have developed an alternative model by which stereoscopi c information is coded and transformed through a hierarchical chain of processing in the primary visual cortex. Initially, first-order neuro ns of the visual. cortex, simple cells, encode depth information by a scheme based on differences in internal receptive field structure betw een left and right eyes. Further abstraction of information is achieve d by a subset of second-order neurons, complex cells, that are well su ited for the detection of depth information in a manner unaffected by positional variations of objects. We review physiological evidence fro m studies of the cat and monkey that are relevant to the proposed sche me.