Soc. Neurosci. Abstr. 1997.10

DISPARITY SELECTIVE NEURONS AND REPRESENTATION OF 3-DIMENSIONAL SURFACE STRUCTURE IN THE INFERIOR TEMPORAL CORTEX OF THE MACAQUE MONKEY. T.

Uka*, H. Tanaka, M. Kato, and I. Fujita Dept. of Cognitive Neurosci., Osaka Univ. Med. Sch., Osaka 565, Japan

Neurons in the monkey inferior temporal cortex (IT) are known to respond to 2-dimensional visual features of objects. However, little is known about the representation of 3-dimensional features in IT. Here we investigated whether IT neurons also encode information on the 3-dimensional (3-D) surface structure of objects.
We recorded extracellular neuronal activity in IT of a Japanese macaque monkey performing a fixation task. During each fixation period, various visual stimuli was presented on a color display, adding crossed or uncrossed disparity to the stimuli, using a liquid crystal stereoscopic modulator. The response to the stimuli of 22% of the neurons analyzed changed upon addition of crossed or uncrossed disparity. In another population of neurons we sampled, we further investigated the properties of disparity selectivity by perceptually segmenting a cross into two bars, one in front of the other, by addition of disparity to either the horizontal or the vertical arms. Twenty-six percent of the neurons that responded to a cross shape responded differentially to such crosses. In some of these neurons, the preferred disparity reversed when the addition of disparity changed from the horizontal arm to the vertical arm, indicating that this differential responsiveness depended on perceived 3-D structure (i.e., a horizontal bar in front of a vertical bar or vice versa), regardless of the type of disparity (crossed or uncrossed) added. We suggest that these neurons do not merely detect the disparity added to the stimulus, but encode the 3-D surface structure of objects. Supported by grants from CREST.

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