SELECTIVITY VARIATIONS IN MONKEY INFERIOR TEMPORAL NEURONS FOR INTACT AND CONTOUR-DELETED LINE DRAWINGS
Gy. Sáry1, Gy. Kovács1, K. Köteles1, Gy. Benedek1, J. Fiser2*, and I. Biederman3. 1 Dept. of Phys., Albert Szent-Györgyi Medical University, Szeged, H-6720, Hungary, 2Dept. of Brain and Cogn. Sci.., University of Rochester,  Rochester NY 14627, USA 3 Dept. of Psychology, University of Southern California, Los Angeles, CA 90089, USA
   In human object identification experiments, members of a complementary pair of contour-deleted line drawings (CD1 and CD2), with every other vertex and line deleted from each part, prime each other as well as they prime themselves (Biederman & Cooper, 1991). Can this similarity in priming between CDs and the original intact line drawings (LD) be correlated with responses of shape selective cells in the inferior temporal cortex (IT) of macaques? CD1, CD2 and LD of the same shapes were presented to a fixating rhesus monkey, while extracellular single unit activity was recorded from IT. Forty-eight of the 51 neurons responded to the LDs (net mean firing rate 11.3 Hz).Thirty and 29 cells responded also to CD1 and CD2, respectively. Firing rates were, however, substantially lower for the CDs (mean = 7.4 Hz; no significant difference between CD1and CD2), reflecting, perhaps, the lowered identifiability of CD stimuli and their equivalence. Twenty-five neurons responded selectively to the LDs but most these neurons did not maintain selectivity for the CDs of the same objects. For those cells that were responsive to the CDs, reduced selectivity that mirrored of the LDs was evidenced. Thus in fixating monkeys, contour deletion has far more potent effects on IT cell activation than is evident from the modest increase in difficulty, and equivalent priming that humans manifest when identifying such images.
Supported by: McDonnell JSMF 96-44