DESCRIPTION (Investigator's Abstract): This research investigates visual processes that mediate perception of color and brightness in complex scenes. It is well known that the appearance of an objective in a natural scene does not depend on only the light reflected from the object. A light in one part of the visual field can affect the appearance of another light. Most previous research has employed very simple visual stimuli (for example, a small test patch on a chromatic adapting background or within a chromatic surround) to explore the visual mechanisms by which one light affects another. While this work has revealed fundamental properties of the visual pathway, there is widespread agreement that perception of color and brightness in complex scenes cannot be fully explained by these mechanisms. Quantitative studies of color and brightness in complex visual displays rarely have been designed to seek properties of the human visual system. Many of these studies measured changes in appearance caused by altering the spectral distribution of the illuminating light. Recent theoretical models suggest how information implicit in receptoral quantal absorptions may be exploited to maintain (approximate) color constancy. This work, however, seldom considers the neural processes that must be involved. The research proposed here will isolate and quantitatively assess neural processes, beyond mechanisms of simple chromatic adaptation and contrast, that mediate the color and brightness of complex visual stimuli. Recent results from my laboratory reveal that such processes are observed with even "slightly complex" stimuli (e.g., a chromatic adapting background with a small region of superimposed achromatic light some distance away from the test patch). By presenting a test light on an adapting field and varying another light in a region not adjacent to the test, changes in color and brightness of the test are measured while contrast (at the edge of the test) is held constant. Properties of neural mechanisms beyond adaptation and contrast will be determined by varying the features (e.g., size, location, chromaticity, retinal illuminance, homogeneity) of nonadjacent light. Visual mechanisms in monocular and in central binocular pathways will be distinguished using haploscopically presented stimuli. A long-term goal of this research is to provide sensitive and reliable psychophysical techniques to aid in the diagnosis of eye disorders.