This project defines features of primate retinal function in the magnocellular (MC) and parvocellular (PC) pathways at the retinal ganglion cell (RGC) level. These features are adaptation and its spatial spread, the structure of RGC spike trains and the chromatic response of cells of the MC-pathway. It tests hypotheses about retinal physiology and about how retinal signals underlie performance. Precise knowledge obtained about retinal output provides a reference for interpreting cortical and behavioral data and for interpreting visual deficits in retinal disease. When a background continuously changes in luminance or chromaticity, as it does in most environments, the psychophysical detectability of superimposed test stimuli changes in complex ways. Under such conditions, the responses of RGCs are likely determined both by early retinal adaptation processes and by interactions of the response to the test with the response to the background. The relative influences of these effects on detection, and their spatial characteristics, will be measured. New techniques make it possible to measure information content and stimulus detectability in neuronal spike trains. Luminance and chromatic information contents (i.e., bits/sec, bits/spike) transmitted by cells of the MC- and PC-pathways will be measured using natural time series. In separate experiments, the detectability and spatiotemporal precision in responses to more conventional stimuli will be assessed. The MC-pathway provides a physiological substrate for a psychophysical luminance channel tapped in photometric tests. However, the MC-pathway shows chromatic response components whose signature is apparent psychophysically. The underlying physiological mechanism of these responses, and their spatial properties will be assessed.
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