Date of Award
Doctor of Philosophy (PhD)
The axons of retinal ganglion cells convey the signals from which the brain constructs its visual percept of the world. The considerable processing done in the retina is implicit in these signals; it is therefore desirable to understand this processing in some detail. Only one aspect of retinal processing is considered--the spatial interactions within either the center or the surround of the receptive field of the ganglion cell. A generalized model for this restricted processing is proposed: the independent signals in each of two separately stimulated areas may undergo non-linear transformation; the two areas may interact at one or several levels, ultimately converging on a final common pathway (the ganglion cell); a further non-linear transformation may be performed on the combined signal in the final common pathway. To examine the features of such a model, two separate areas within the center of a receptive field are stimulated, both individually and simultaneously. A wide range of intensities is used. Two methods of analysis are applied to these data; each is intended to elucidate particular features of the model. The first method of analysis, the method of response-summation, compares responses when each spot is illuminated separately with responses when both spots are presented together. A graph is presented of the responses to simultaneous stimulation (physiological sum) as a function of the arithmetically summed responses to each spot alone at the same intensity; the independent parameter is intensity. The plot (response-summation) is not affected by non-linearities which occur before the first interaction of the two areas; if there are no nonlinearities at or after the first interaction this plot must be a straight line of unity slope. If there are non-linearities at or after the first interaction of the areas, some other function will be obtained; an analysis is given of the expected forms of this curve for a number of possible non-linearities which might reasonably be postulated.
Levine, Michael William, "An Analysis of Spatial Summation in the Receptive Fields of Goldfish Retinal Ganglion Cells" (1972). Student Theses and Dissertations. 541.