Representation of stereoscopic edges in monkey visual cortex.

Form perception in random-dot stereograms is based on information that resides in the correlation between the two images, but is not present in either image alone. We have studied the coding of stereoscopic figures in the neural activity of areas V1 and V2 of alert behaving monkeys. While cells in V1 generally responded according to the disparity of the surface at the receptive field, we found cells in area V2 that responded selectively to the figure edges. These cells signaled the location and orientation of contrast borders as well as stereoscopic edges, and were often selective for the direction of the step in depth. We concluded that stereoscopic edges are explicitly represented in area V2.