Functional specialization in human dorsal pathway for stereoscopic depth processing.

Binocular disparity, a primary cue for stereoscopic depth perception, is widely represented in visual cortex. However, the functional specialization in the disparity processing network remains unclear. Using magnetic resonance imaging-guided transcranial magnetic stimulation, we studied the causal contributions of V3A and MT+ to stereoscopic depth perception. Subjects viewed random-dot stereograms forming transparent planes with various interplane disparities. Their smallest detectable disparity and largest detectable disparity were measured in two experiments. We found that the smallest detectable disparity was affected by V3A, but not MT+ , stimulation. On the other hand, the largest detectable disparity was affected by both V3A and MT+ stimulation. Our results suggest different roles of V3A and MT+ in stereoscopic depth processing.