Nonlinear interactions in ganglion cell receptive fields

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Abstract
Intracellular responses of on-off type (class 3) frog retinal ganglion cells to a spatiotemporal random stimulus were recorded. The stimulus consisted of a 16 .times. 16 checkerboard, each square of which was independently modulated by a binary, random signal. Linear and nonlinear response properties around 256 points in the receptive field were determined by Wiener (white noise) identification. Cell responses in the excitatory receptive field were approximated with a purely linear response component and a 2nd-order, nonlinear component. Each component included contributions from all parts of the stimulus field. The nonlinear component describes interactions between any 2 points in the stimulus field. The nonlinear component consisted only of local interactions; nonlinear interactions between 1.2.degree. stimuli were inversely proportional to stimuli separation and were not observed for stimuli separated by > 3.5.degree.. Interactions occurred in a spatially overlapping fashion throughout the excitatory receptive field. The time course of the nonlinear interaction component was similar to the linear component but of opposite sign. The local nonlinear interaction varied only in amplitude across the receptive field while the spatial extent, overlap and time course were independent of position in the receptive field. Strong constraints are placed on possible functional models. The initial stage of retinal processing must consist of independent, parallel, local channels. The ganglion cell response must be produced by a weighted sum of the outputs of these local channels.