Complicated substructure from simple circularly symmetric Gaussian processes within the centers of goldfish ganglion cell receptive fields.

The center of the receptive field of some retinal ganglion cells exhibits an interesting fine structure: the relative amplitudes of responses to onset and responses to offset of a small spot of light varies systematically as the spot is positioned at various places within the center. Although this pattern may appear complicated, a simple model can account for it in detail. The model postulates that the ganglion cell receives input from separate ON and OFF processes within the center of its receptive field. These processes have the form of Gaussian functions and are laterally displaced from each other. These central ON and OFF input processes are not associated with the additional antagonistic surround of the receptive field. The model is examined for various parameters of the input processes. The observed systematic variation in the ratio of offset to onset responses is predicted when the two processes are of nearly equal width (standard deviation of the Gaussians). Receptive fields made of more than two Gaussians produce various patterns, depending on the relative standard deviations of the Gaussians. Oblong fields, reminiscent of those found in visual cortex, may be generated from a relatively small number of circularly symmetric Gaussian processes.