EFFECTS OF CHANGES IN STIMULUS CONTRAST POLARITY SIZE, AND POSITION ON CELL RESPONSES IN THE MACAQUE INFEROTEMPORAL CORTEX.
M. ITO, I. FUJITA, H. TAMURA AND K. TANAKAI
Lab. for Neural Information Processing and lnformation Science Lab., RIKEN,
PRESTO, JRDC, Wako, Saitama 351-01, JAPAN.
Soc. Neurosci. Abstr. 19: 771.
A feature of object vision is invariance in our perception of size, position, and to some extent of contrast polarity of the visual image. To gain an insight into the mechanisms of this invariance, we determined the stimulus features critical for activation of individual cells in area TE of the inferotemporal cortex, and examined how changes in contrast polarity, size and position of the critical stimuli influenced their responses.
Recordings were made in anesthetized, immobilized monkeys (M. fuscata). After isolation of a single cell activity, we presented several tens of 3D objects to search for effective stimuli. Video-images of effective stimuli were simplified step by step to determine the simplest features which evoked the maximal responses. Effects of changes in contrast polarity, size and position were then examined. (1) The majority of cells (11/13, 85%) selectively responded to solid, stimuli and not to their shape shown in line contour. Contrast reversal eliminated the responses in 82% of these cells (9/11). The remaining 2 cells selectively responded to the line contour of the stimuli. (2) Stimulus size was doubled at least 5 times. Responses were specific to a particular size in 67% of cells (8/12): responses greater than half of the maximal response were restricted within 2 doublings of size. The other 4 cells responded well to a wide range of sizes (more than 3 doubles). (3) Stimulus selectivity was tested at. different positions within the large receptive fields. Effectiveness of a critical stimulus and its modification was compared at each stimulus location. In 75% of cells (9/12), selectivity was essentially the same at different positions, but the
magnitude of responses varied. In 3 cells, optimal stimuli were slightly different at different locations. We conclude that responses of individual TE cells are still limited in terms of invariance for contrast polarity, size and position.