How the contrast gain control modifies the frequency responses of cat retinal ganglion cells.

1. A model is proposed for the effect of contrast on the first-order frequency responses of cat retinal ganglion cells. The model consists of several cascaded low pass filters ('leaky integrators') followed by a single stage of negative feed-back. 2. Values of time constants and gain of the components in this model were chosen to approximate (with least-squared deviation) experimentally measured first-order frequency responses. In the experiments used for the analysis, the visual stimulus was a sine grating modulated by a sum of sinusoids. 3. For both X cells and Y cells, the over-all gain and the time constants of the cascade of low pass filters were insensitive to contrast. 4. In all cells, the gain-bandwidth product of the negative feed-back loop was markedly increased with increasing contrast. 5. The effect of stimulation in the periphery of the receptive fields on the first-order frequency response to a centrally placed spot was identical to the effect of increasing contrast in the grating experiments. In all cases, the gain-bandwidth product of the negative feed-back loop was the only model parameter affected by peripheral stimulation. 6. A similar effect of non-linear summation was investigated for two bars located in the receptive field periphery. 7. This analysis of the contrast gain control mechanism is compared with other models of retinal function.