Talk by Professor Ichiro Fujita
Osaka University Graduate School of Frontier Biosciences, Japan
- 15 Nov 2012 14:30
- 15 Nov 2012 16:00
- INM-6, Bldg. 15.22, Seminar Room 3009, 1. OG
Stereopsis: 3D world viewed with two eyes and two cortical pathways
The human brain can derive 3-dimensional depth structure of objects and surfaces from two flat images on the two retinae. This magnificent, mysterious, yet daily experienced ability is dubbed stereopsis. Due to the horizontal displacement from each other, our two eyes view the world from slightly different vantage points. This causes a tiny positional difference in the visual images in the two eyes. The brain exploits this small difference, or binocular disparity, to compute depth.
The neural processing for binocular depth perception starts in the primary visual cortex (V1). However, this does not necessarily mean that V1 neurons directly underlie stereoscopic depth perception. In fact, properties of V1 cells do NOT account for a number of aspects of stereopsis, suggesting that subsequent processing in cortical areas beyond V1 is responsible for conscious perception of stereoscopic depth. It has long been believed that binocular disparity information is processed along the visual pathway projecting from V1 to the parietal cortex (dorsal pathway). Studies from our and other laboratories in the past 15 years, however, have revealed that binocular disparity signals are processed both along the dorsal pathway and the pathway projecting from V1 to the temporal cortex (ventral pathway). We thus use the two major cortical pathways for stereopsis. Why?
Recent studies are now answering this question; the two cortical pathways contribute to stereopsis in a different manner. Neurons in the ventral pathway areas solve the binocular correspondence problem, compute relative disparity between adjacent visual features, and underlie fine disparity discrimination. Those in the dorsal pathway areas encode binocular correlation, signal local absolute-disparity, and are involved in judgment of coarse disparity and in control of vergence angle.