Stereoscopic illusory contours--cortical neuron responses and human perception.

In human perception, figure-ground segregation suggests that stereoscopic cues are grouped over wide areas of the visual field. For example, two abutting rectangles of equal luminance and size are seen as a uniform surface when presented at the same depth, but appear as two surfaces separated by an illusory contour and a step in depth when presented with different retinal disparities. Here, we describe neurons in the monkey visual cortex that signal such illusory contours and can be selective for certain figure-ground directions that human observers perceive at these contours. The results suggest that these neurons group stereoscopic cues over distances up to 8 degrees. In addition, we compare these results with human perception and show that the mean stimulus parameters required by these neurons also induce optimal percepts of illusory contours in human observers.