MODELING THE SPATIOTEMPORAL MODULATION RESPONSE OF GANGLION-CELLS WITH DIFFERENCE-OF-GAUSSIANS RECEPTIVE-FIELDS - RELATION TO PHOTORECEPTORRESPONSE KINETICS

Difference-of-Gaussians (DOG) models for the receptive fields of retin al ganglion cells accurately predict linear responses to both periodic stimuli (typically moving sinusoidal gratings) and aperiodic stimuli (typically circular fields presented as square-wave pulses). While the relation of spatial organization to retinal anatomy has received cons iderable attention, temporal characteristics have been only loosely co nnected to retinal physiology. Here we integrate realistic photorecept or response waveforms into the DOG model to clarify how far a single s et of physiological parameters predict temporal aspects of linear resp onses to both periodic and aperiodic stimuli. Traditional filter-casca de models provide a useful first-order approximation of the single-pho ton response in photoreceptors. The absolute time scale of these, plus a time for retinal transmission, here construed as a fixed delay, are obtained from flash/step data. Using these values, we find that the D OG model predicts the main features of both the amplitude and phase re sponse of linear cat ganglion cells to sinusoidal flicker. Where the s implest model formulation fails, it serves to reveal additional mechan isms. Unforeseen facts are the attenuation of low temporal frequencies even in pure center-type responses, and the phase advance of the resp onse relative to the stimulus at low frequencies. Neither can be expla ined by any experimentally documented cone response waveform, but both would be explained by signal differentiation, e.g. in the retinal tra nsmission pathway, as demonstrated at least in turtle retina.