Processing of contrast polarity of visual images in inferotemporal cortex of the macaque monkey

Cells in the anterior part of the inferotemporal cortex (anterior IT) respond to moderately complex stimulus features of object images. To study dependency of their responses on contrast polarity of stimulus images, we selected cells with optimal stimuli that were defined only by shape and not related to texture or color, and examined effects of reversing the contrast of the image or removing it except for edges between dark and bright parts of the image ("outlining"). The contrast reversal produced a reduction of the response to the optimal stimulus by > 50% in 60% of tested cells; the outlining, in 70%. When the two transformations were considered together, 94% of the cells showed a reduction by > 50%. Effects of the transformations on shape selectivity were also studied by comparing responses to several different shapes each of whose contours were expressed in different ways. Statistically significant changes in relative effectiveness of the different shapes as a function of contour expression were observed in more than half of the cells. These results suggest that responses of individual cells in anterior IT carry information about contrast polarity as well as about shape.