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.
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