Deficits in speed discrimination following lesions of the lateral suprasylvian cortex in the cat.

We examined the role of the lateral suprasylvian (LS) cortex in motion perception by testing the ability of three cats to detect moving targets and to discriminate differences in stimulus direction and speed before and after making bilateral ibotenic acid lesions in LS. The lesions had little or no effect on contrast sensitivity for detecting moving sinusoidal gratings. Moreover, we found no deficits in discriminating opposite directions of motion: the cats discriminated grating directions at threshold contrasts. All three cats, however, showed permanent deficits in discriminating differences in speed and in flicker rate. The deficits were most pronounced at higher temporal and spatial frequencies and at lower contrasts. This result suggests that LS plays an important role in the analysis of stimulus speed. It appears that information needed for discriminating opposite directions of motion may be signalled by visual areas outside LS.