Fig. 9.

Crossover circuitry maintains linearity in the presence of high spatial contrast. Columns (a) and (b) show spiking histogram responses to partial gratings. Column c shows spiking histogram response of full grating where the bars of the grating invert so that there is no change in overall luminance at the receptive field center. The top of each column shows successive frames of the stimulus, in each case, back areas turn white, and white areas turn black, while grey areas maintain a constant, intermediate brightness. Control: Partial gratings elicit OFF responses in a and b, but minimal response to full grating in c. APB: Partial gratings still elicit OFF responses, but without ON crossover inhibition the full grating (c) also elicits a strong, nonlinear response. Wash: Linear behavior is restored to the full grating response in c. The gray images at the top of columns a-c each show three successive frames of the 0.5 sec/frame movie. Ordinate: spikes per second; abscissa time in seconds. (d) Histograms of linearity coefficient L with and without APB (histograms correspond to the same rows as (a-c)