Using NeuronC, a simulation language developed by R Smith, University of Pennsylvania, we built a computer model of a central part of the outer retina. Distribution of cones and chemical synapses of different signs are similar to those that can be found in the primate retina. Horizontal cells of the same type are electrically coupled. There are no electrical synapses between horizontal cells of different types.
Cones are presynaptic to horizontal cells and get inhibitory feedback from the same cells.
The receptive field area of the different cells is modulated by the amount of electric coupling of the horizontal cells. Stimulating the retina with lights of different wavelengths over the visible spectrum produces monophasic hyperpolarisations in the horizontal cells similar to those that have been found by recordings in the monkey retina. By variation of retinal illumination in two stimulus fields, horizontal cell coupling, and efficiency of feedback onto cones we examined the conditions under which colour constancy can be found in the cone and bipolar signals.