Pattern and motion vision in cats with selective loss of cortical directional selectivity

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Abstract
Neurons in the visual cortex of cats reared in 8 Hz stroboscopic illumination show a profound loss of directional selectivity, but no detectable deficits in orientation selectivity, contrast sensitivity, and temporal frequency response, and only a slight reduction in spatial resolution. In the present study, spatial vision, temporal resolution, and a variety of motion detection and discrimination thresholds were examined behaviorally in such cats. These psychophysical measurements revealed nearly normal spatial and temporal vision, but severe abnormalities in visual discriminations based on differences in stimulus direction. Specifically, strobe-reared cats showed normal orientation discrimination and temporal frequency resolution, nearly normal contrast sensitivity at low spatial frequencies, and a slight reduction of sensitivity to high spatial frequencies. At high contrasts, the cats were able to discriminate opposite directions of motion over a wide range of visible speeds, and their performance was indistinguishable from that of normal cats. However, a comparison of contrast thresholds for detecting moving gratings and for discriminating their direction of motion revealed severe abnormalities in strobe-reared animals. At low spatial frequencies (0.28 cycles/deg), normal cats could discriminate the direction of grating motion at contrasts that were just barely visible, whereas the strobe-reared cats could detect the grating at contrasts similar to those required by normal cats, but required contrasts about 10 X the threshold to identify the direction of motion. Normal cats showed nearly identical contrast sensitivity for detecting and discriminating gratings of high spatial frequency at high temporal frequency (drift rates), but when the temporal frequency was low, their sensitivity for detection exceeded that for direction discrimination.(ABSTRACT TRUNCATED AT 250 WORDS)