1. The activity of single cortical cells in area 17 of anesthetized and unanesthetized cats was recorded in response to prolonged stimulation with moving stimuli. 2. Under the appropriate conditions, all cells observed showed a progressive response decrement during the stimulation period, regardless of cell classification, i.e., simple, complex, or hypercomplex. 3. The observed response decrement was shown to be largely cortical in origin and could be adequately described with an exponential function of the form R = Rf +(R1-Rf)e-t/T. Time constants derived from such calculations yielded values ranging from 1.92 to 12.45 s under conditions of optimal-stimulation. 4. Most cells showed poststimulation effects, usually a brief period of reduced responsiveness that recovered exponentially. Recovery was essentially complete in about 5-35 s. 5. The degree to which stimuli were effective at inducing response was shown to have significant effects on the magnitude of the response decrement. 6. Several cells showed neural patterns of response and recovery that suggested the operation of intracortical inhibitory mechanisms. 7. A simple two-process model that adequately describes the behavior of all the studied cells is presented. 8. Because the properties of the cells studied correlate well with human psychophysical measures of contour and movement adaptation and recovery, a causal relationship to similar neural mechanisms in humans is suggested.

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Using a two-choice visual discrimination paradigm, thresholds for size (gratings), parallelness (parallel vs. non-parallel lines), contour alignment (vernier offset), and angularity (polygon figures) were behaviorally determined in cats before and after ablations of portions of the geniculo-cortical system. Animals with a total loss of cortical area 17, and with a loss, in some cases, of up to 90% of areas 18 (with and without infringement into area 19), showed about a 30% reduction in grating acuity, a three-fold increase in parallelness and angularity thresholds, and a total loss of contour alignment ability. Control animals with ablations sparing area 17 showed no significant threshold changes. All animals were able to learn classic form discriminations postoperatively, but those with area 17-18 lesions at a somewhat slower than normal rate. Control procedures indicated that all tested discrimination capabilities did not depend on luminance differences between targets, local flux cues within the targets, or on the animals' use of residual portions of area 17 representing the peripheral visual field. Since the cat has multiple thalamo-cortical visual pathways, the results of the present study are consistent with the hypothesis that pathways parallel to the geniculo-striate system are capable of processing spatial information of considerable detail. The results also suggest, however, that the geniculo-striate system is uniquely necessary for the processing of the finest attributes of spatial contours.