NEURAL PROCESSING OF BINOCULAR DISPARITY AND SURFACE DEPTHS IN MONKEY INFERIOR
Ichiro Fujita Graduate School of Engineering Science, Osaka University, and CREST, Japan Science and Technology Corpomtion,
Machikancyama 1-3, Toyonaka, Osaka 650-8531, Japan
When binocular disparity is given to a part of 2-dimensional (2-D) shape, we perceive a 3-D structure consisting of multiple surfaces at different depths and orientations. While such 2-D retinal images may be interpreted in many ways, the visual system reliably calculates the most probable 3-D structure from sparse local disparity cues. A neural representation of the perceived 3-D structure is, therefore, created somewhere in the brain, after the detection of binocular disparity. Neurons in the ventral visual pathway leading to the inferior temporal cortex (IT) have been known to respond to surface characteristics of objects such as color, 2-D shape, and texture. On the other hand, neurons responding to binocular disparity has been found along the magnocellular-dominated stream in earlier cortices and then along the dorsal pathway leading to the parietal cortex, In order to perceive 3-D surfaces, however, the brain must know the depth as well as other attributes of a surface such as its shape. We have recently found that the IT in the macaque monkey contains many neurons (more than 50% of the neurons tested) sensitive to both disparity and shape. We have further demonstrated that the activity of some IT neurons encode information on the perceived relative depths of surfaces rather than the local disparity cues of the stimulus. We suggest that the IT integrates shape and disparity information, and the ventral visual pathway leading to the IT is involved in reconstructing 3-D structures from local disparity cues.