This project concerns how sensitivity of vision varies in different parts of the eye. Visual images are focussed on the retina, which contains a small region called the fovea for high- resolution and color analysis of the visual world. There is some evidence that mechanisms for visual processing may be different in the fovea from mechanisms in the parafoveal areas in the rest of the retina. Adaptation is one process in which visual sensitivity, measured by visibility of an object against a background, is influenced by background illumination. Mechanisms for such sensitivity involve lateral interactions among targets and backgrounds of different colors, but psychophysical and electrophysiological studies show disagreement on how independent the mechanisms are for color adaptation. While most psychophsyical studies of adaptation have concentrated on the fovea, most electrophysiological studies are done on cells lying outside the fovea. This project will use adaptation to test the organization of sensitivity control at the fovea compared to the parafoveal areas. If a small test target is displayed against a small background, the sensitivity to the target is less than when the background is large. This effect of background size is called spatial sensitization, and is a useful tool for exploring sensitivity control. Here the sensitization will be coupled with the effects of chromatic adaptation by using different colors of target and background. The spatial extent of sensitization functions will be measured under appropriate chromatic adaptation conditions, at several different retinal locations. The results will give information about how the neural organization of cells in the retina differs between fovea and parafoveal locations. This work will have an impact on color vision studies, where the interpretation of several phenomena are tied to foveal versus parafoveal differences. Results also will be important to studies of retinal organization, and sensitivity of sensory systems in general, directly addressing links between psychophysics and physiology.
