A series of experiments is proposed that will use various non-linearities revealed by time-varying visual stimuli to analyze the human visual pathway. When an input signal passes through a non-linear site, new signal components are produced that were not present at its input. By carefully manipulating the visual stimuli that provide the input signal to the non-linearity, it is possible to distinguish the temporal properties of the visual pathways before and after each non-linear site. Three non-linearities will be studied. Each causes a burst of flicker to be perceived differently from a steady light of the same time-averaged intensity and chromaticity. The first, a compressive non-linearity, causes S-cone detected flicker to change in color; the second, also a compressive non-linearity, causes bursts of M- of L-cone detected flicker to change in color and saturation; and the third, an expansive non- linearity, causes bursts of M- or L-cone detected flicker to increase in apparent brightness. The primary aim of the proposed experiments is to use each non-linearity to dissect the early visual pathway. In some experiments, the non-linearity will be used as a recording electrode -- to measure the temporal frequency response of the visual system before the non-linearity; and in others it will be used as a stimulating electrode -- to measure the temporal frequency response of the visual system after the non-linearity. Preliminary evidence suggests that the temporal frequency response after each compressive non-linearity is characteristic of a chromatic pathway, while the response before each compressive non-linearity may more closely reflect the temporal frequency response of the receptors that the results of conventional temporal sensitivity measurements. It is proposed that the expansive non- linearity that affects M- and L-cone flicker is in a separate luminance pathway. The results of the proposed experiments will provide new insights into the postreceptoral organization of the visual system. Each non-linear site can provide a landmark at which psychophysical and physiological results can be compared. In the long-term, these experiments also may have important clinical implications, since it will be possible to use each non-linear site to localize and damage or deterioration that results from degenerative disease.
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