Central and Peripheral Processes in Visual Adaptation

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DESCRIPTION (provided by applicant): The aim of this research is to understand neural pathways that mediate color and brightness perception in natural viewing. Matching, discrimination and appearance of color and brightness have been studied extensively with simple visual fields but little is known about the color perception of objects within complex, dynamic scenes typical of natural viewing. Simple fields can severely underestimate the influence of context on color and brightness. Even studies of color constancy are concerned mainly with color perception under changes of illumination. By comparison, each line of research here focuses on color perception within a complex context that varies over space and/or time. There are five lines of research, each chosen to reveal fundamental principles of vision that mediate perception of complex scenes. The first tests neural representations for color perception with inhomogeneous chromatic background patterns. The aim is to understand color perception with any spatiochromatic pattern. The second investigates integration of retinally separated regions, all of which are stimulated by a single object. The separated regions result from partial occlusion by other objects in the foreground. Perceptual grouping integrates the separated regions so one sees a single object but grouping also affects color perception. The third line of research examines perceptual binding of color to form. An object has many attributes such as shape, depth, direction of motion and color. The attributes must be integrated for the percept of a unified object. This research uses a novel, recently discovered paradigm that gives clear and sustained errors in color binding. The paradigm is leveraged to test alternative theories of binding color to form. The fourth line of work examines temporally varying background light. Simple temporally varying context, as in classical studies, fails to explain the influence of more complex temporal patterns that can occur outside the laboratory. The cause is a neural nonlinearity, which will be characterized by this study. The fifth set of experiments tests alternative theories of very-long-term chromatic adaptation (over days or weeks), which reflects neural plasticity implicit in natural viewing. Gradual changes in color appearance over many days reveal adaptation to the chromatic environment. Each line of research investigates basic neural processes of color and brightness perception that are neither well understood nor assessed by current clinical tests. Many of the underlying neural processes are cortical. Perception of integrated objects within complex scenes is a fundamental aspect of normal vision. This research provides essential underpinnings for diagnostic procedures that can reveal previously unidentified deficits in visual processing. Psychophysical measurements of color and brightness will test alternative theories. Quantitative modeling will incorporate characteristics of visual pathways from physiological studies.