Contribution of the ventral visual pathway to stereopsis.
The visual system has a remarkable capability of deriving 3-D surface structure from two retinal images. The computation for stereopsi starts in the striate cortex(V1), where signals from the two eyes converge onto single neurons and binocular disparity information is encorded. Properties of V1 cells, however, do not account for a number of aspects of stereo perception, suggesting that subsequent processing in cortical areas beyond V1 is responsible for consious perception of stereoscopic depth. It has long been believed that binocular disparity information is routed exclusively to the dorsal visual pathway. In fact, binocular signals for stereopsis are processed both along the ventral and dorsal pathways. Cells in the ventral pathway areas solve the binocular correspondence problem, compute relative disparity between visual features, and exhibit activities correlated with behavioral judgment of fine disparity discrimination, whereas those in the dorsal pathway areas encode binocular correlation, signal local absolutedisparity, and are involved in judgment of coarse disparity. Psychophysics in human subjects suggests that perception of plane-in-depth depends on the ventral pathway mechanisms. Thus, the two cortical pathways contribute to stereopsis in a complimentary manner.