William H. Seiple, PhD

We direct our research efforts toward exploring the human visual system using electrophysiologic and psychophysical techniques, which provides a link between animal neurophysiology and subjective reports of visual phenomena, i.e., human psychophysics. We attempt to understand visual processes in humans, apply this knowledge to elucidating the sites and mechanisms of visual loss in patients with ophthalmologic disease, and apply these findings to developing new clinical diagnostic tests.

Most recently, we explored the changes in temporal processing that occur as a function of light adaptation. It is a common observation that the highest resolvable temporal frequency increases as a function of the level of light to which the visual system is exposed. We examined the sites of these gain changes by comparing the temporal responsiveness of the human retinal photoreceptors to psychophysi-cal temporal sensitivity. Our results suggest that most of the adaptation-dependent changes in temporal sensitivity occur at the level of the cone photoreceptors.

These findings have been applied to understanding the losses in temporal sensitivity that occur in patients with retinitis pigmentosa, an inherited retinal degeneration. In this work, the cone system sensitivity loss induced by disease sites were examined by comparing electrophysiologic and psychophysical data. We reasoned that if the disease process primarily affects the outer retina, then both measures of temporal sensitivity should show deficits. If, on the other hand, the disease process primarily affects postreceptoral sites, only the psychophysical results should be abnormal. The combined results provided evidence for an outer retinal locus for cone temporal sensitivity losses in patients with retinitis pigmentosa.