PROCESSING OF SHAPE,DISPARITY,AND SURFACES IN INFERIOR TEMPORAL CORTEX

The NIPS International COE Symposium " Neural Mechanisms of Visual Perception and Cognition"

Ichiro Fujita
Laboratory for Cognitive Neuroscience,Department of Biophysical engineering,Osaka University Graduate School,Osaka,Japan

   The reconstruction of 3−dimensional(3−D)surface structures from 2−D retinal images is a complex computational problem,and yet our visual system performs a remarkable feat in solving it. The underlying neuronal mechanisms responsible for accomplishing this task remain to be identified.
   We first behaviorally tested whether monkeys perceive surface structures in disparity−added stimuli in a similar way as we humans do(Uka et al・,1999)・Human subjects perceive two crossing bars,one in front of the other,When shown a cross with disparity added to its horizontal limb,and they also perceive neon−color spreading when shown a stereoscopic Redies−Spillmann figure・It has thus been hypothesized that the human visual system fo1lows the principle of generic image sampling in reconstructing 3−D surface structures(Nakayama and Shimojo,1992;Science,257:1357−1363)・Our experiments on macaque monkeys show that they,like humans,perceive two crossing bars and neon−color spreading and suggest that the principle of generic image sampling may also be applied to visual perception in monkeys.
   Having confirmed that monkeys perceive surface structures as humans do,we went on to explore the neurophysiological substrate for this process・The inferior temporal cortex(IT),a visual association cortex that is crucial for object vision,is known to contain neurons selectively responding to 2−D shape,color,and texture. We have discovered that many IT neurons are actual1y selective for both binocular disparity and shape.Furthermore the activity of some IT neurons encode information on the relative depth order of surfaces rather than the local disparity cues of the stimulus.We suggest that the visual pathway leading to the IT is critically involved in reconstructing 3−D structures from local disparity cues and 2-D shapes.

   This work is supported by grants from Japan Science and Technology Corporation(CREST),Science and Technology Agency of Japan(Special Coordination Funds for Promoting Science and Technology),and the Ministry of Education,Science,Sports and Culture.

References
Uka,T.,Tanaka,H.,Kato,M.,Fujita,I.(1997)Disparity sensitivity and representation of 3−dimensional surface structure in monkey inferior temporal cortex.Soc.Neurosci.Abstr.27:2063.
Uka,T.,Tanaka,H.,Kato,M., Fujita,I.(1999)Behavioral evidence for visual perception of 3−dimensional surface structures in monkeys.Vision Research, 2399−2410.


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