理研 フロンティア 思考電流、新技術事業団さきがけ２１、理研 情報科学
EFFECTS OF CHANGES IN
STIMULUS CONTRAST POLARITY ON CELL RESPONSES IN THE MACAQUE INFEROTEMPORAL
Ito, M., Fujita, I., Tamura, H. and Tanaka, K.
Neurosci. Res.Suppl. 18: s186
Area TE of the macaque inferotemporal cortex is thought to be crucial
for object vision and most cells in TE respond selectively to particular
complex features of objects. To understand how these selective responses
represent the images of objects, we examined their sensitivity for changes
in contrast polarity of the optimal stimuli.
Recordings were made in anesthetized, immobilized monkeys(Macaca fuscata). After isolation of single cell activity, we first determined the optimal stimulus. Several tens of 3D objects were presented to search for effective stimuli. Video-images of effective stimuli were simplified step by step to determine the necessary and sufficient features for the maximal responses. Then, the contrast polarity of the image was reversed or the feature was expressed only with outlines, and changes of responses were examined. The contrast reversal decreased the responses by more than 65% in a majority of cells (31/45,69%), and the outlilne-expression of the critical feature did not activate a majority (13/19, 68%). The contrast sensitive cells are distributed throughout a most anterior-posterior range of TE (from A20 to A3.9). Several modifications of the critical feature were made to examine if the selectivity remains after the contrast reversal. In 75% of cells (9/12), the selectivity seen under appropriate contrast polarity was partly changed under the reversed contrast or outline-expression. We conclude that the contrast polarity is an important factor for image representation by most cells in area TE.