Spatial and temporal sensitivity of normal and amblyopic cats

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Abstract
The behavioral technique of conditioned suppression was used to measure spatial and temporal contrast sensitivity to counterphased, sine-wave gratings in 8 cats. These included 2 normally reared cats before and after bilateral ablations of cortical area 17 and part of area 18, 2 cats raised in total darkness, 2 cats raised with binocular lid suture and 2 cats raised with monocular lid suture. Visual deficits induced by cortical lesions or visual deprivation were evaluated with respect to the preoperative data of the normally reared cats. The cortical lesions had virtually no qualitative effect on the cat''s visual capacities. Contrast sensitivity was reduced at higher but not lower spatial frequencies. This can be described succinctly as a loss of spatial acuity. Dark-reared and binocularly sutured cats qualitatively exhibited poorer visual capacity than that of the cortically ablated animals. The contrast sensitivity resultant from these 2 forms of binocular deprivation was basically similar and consisted of significant sensitivity losses at all spatial and temporal frequencies. Much more than high spatial frequencies was affected, and this amblyopia cannot be characterized simply as a spatial acuity loss. Monocularly sutured cats had normal vision and contrast sensitivity with the non-deprived eye, but with the deprived eye they displayed the most severe amblyopia and poorest contrast sensitivity of any of the cats. Sensitivity losses were evident for all spatial and temporal frequencies and this amblyopia is more severe than a loss of spatial acuity. These psychophysical data are related to the status of W-, X- and Y-cell pathways in these cats. Sensitivity to low spatial frequencies and integrity of the Y-cell pathway is correlated with good visual capacity. Since Y-cells are uniquely sensitive to low spatial frequencies, then the Y-cell pathway seems sufficient and perhaps necessary for reasonable visual performance. Because the amblyopia of normally reared cats with lesions of striate cortex is far less severe than that of the lid-sutured and dark-reared cats, it follows that the constellation of deficits reported for striate cortex in these visually deprived cats cannot provide an adequate neural explanation for their amblyopia. Attempts to relate deprivation amblyopia to striate cortex abnormalities should thus be reconsidered.