Interactions between the rod and the cone pathways in the cat retina

The receptive field centers of 21 on-center X retinal ganglion cells in cat were tested with stimuli designed to detect nonlinear interactions between the rod and the cone systems. One red and one green stimulus light were always present, at a level such that modulation of the red light essentially affected only cones, and that of the green light only rods. The two lights could be superimposed spatially (overlapped configuration) or fall on separate subareas of the receptive field center (nonoverlapped configuration). In most cases, there was less complete summation of the responses to modulation of the lights in the overlapped than in the nonoverlapped configuration, with a corresponding difference in the summation of sensitivities. In 1/6 of the experiments, there was more complete summation of the responses to the lights in the overlapped configuration, with a corresponding difference in the summation of sensitivities. The mean magnitude of the interaction for all experiments was equivalent to an antagonistic interaction between the rod and cone pathways such that the signal in each was diminished by a quantity slightly greater than 30% of the signal in the other.