Effects of adaptation and intensity on candidate sensory codes for photoreceptor response duration: Implications for visual persistence
Abstract
This thesis studied the effects of light adaptation and flash intensity on the duration of bio-electric signals evoked in photoreceptors. It also explored possible sensory codes for assessing receptor response duration. And it compared these results with behavioral measures of visual persistence. One variable, namely, adaptation, has long been known to affect the timing of visual responses, but earlier more restricted work (Nisly & Wasserman, 1987) found no adaptation effect on several particular measures related to visual persistence. The present expanded work indicates, however, that an adaptation effect is present when the state of adaptation is varied by about 3.5 log units. Code-dependent direct, inverse, invariant, and U-shaped trends related flash intensity to photoreceptor response duration. Many behavioral studies have also shown that intensity has either direct or inverse effects on visual persistence. Different models of these results have been proposed and the present thesis tested the ability of the task-dependent model and the intensity-dependent model to explain both the direct and inverse intensity effects. The test first looked at the receptor responses evoked by single light flashes and then looked at the interactions produced by double flashes. This research suggests that a melding of the two models may be most useful if other variables are also taken into account. An additional aim of the present research was to explore further the properties of several candidate sensory codes which behavioral paradigms have implicated in visual persistence. Some of these had been given preliminary tests (Nisly & Wasserman, 1989). These candidates had been proposed as correlates of various behavioral paradigms. These proposed correlates did yield most expected trends, but the present thesis only qualitatively corroborated the expectations which generated this research and numerous quantitative discrepancies were found between data and theory. The persistence problem is therefore still incompletely understood.
Degree
Ph.D.
Advisors
Wasserman, Purdue University.
Subject Area
Psychobiology|Neurology
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