Recorded activity of single neurons in the portion of the striate cortex representing the central visual field in young adult anesthetized cats before, during, and after prolonged stimulation by grating patterns (bars, edges, and spots). Findings support the assumption that perceptual changes result from changes in the distribution of activity within the responding population of neurons but not the assumption that the effect of adaptation on each neuron of the population is to reduce its sensitivity to all stimuli: The present study found that after adaptation to a particular grating, the sensitivity of a single neuron to that grating may be reduced more than its sensitivity to other gratings.