COLLABORATIVE RESEARCH: RUI: Perceptual Grouping Effects on Perceived Lightness

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BCS-0002050PI: Cataliotti The human visual system perceives shades of gray with remarkable accuracy despite large changes in the intensity of the illumination and the brightness of surrounding surfaces. For example, a middle gray piece of paper will generally appear middle gray regardless if it illuminated by a bright light or a dim light. The change in illumination results in retinal images that are also very different, yet in most cases the paper is perceived as middle gray. Lightness contrast and other errors have been studied in an attempt to understand more fully the visual system's design and logic in determining shades of gray. Simultaneous lightness contrast (SLC) has been one of the most widely studied of these errors. SLC is illustrated by placing a gray target on a white background and a physically identical gray target on a black background. The target on the white will appear darker than the target on black. Models attempting to explain SLC can be grouped into two main categories: 1) models that treat SLC as a residual byproduct of low-level retinal processes, namely, lateral inhibition, and 2) models based on perceptual grouping processes that must take place above the retinal level in the visual pathway. Perceptual grouping models are not well defined in terms of physiological structuresand functions. The main goal of the proposed project is to more fully explore the roles perceptual grouping processes play in determining perceived surface color. The research will focus on three novel paradigms recently discovered in the PIs' lab. One set of experiments will involve a variation of SLC in which two gray targets appear to move across their respective backgrounds. Another set of experiments will require the observer to fuse gray targets presented to one eye with backgrounds presented to the other eye. In a third set, the observer will judge the lightness of sequentially presented targets in an effort to understand the effect of the perceived gray shade of one surface on the perceived gray of a subsequently viewed surface. Experiments will test whether these recently discovered phenomena are primarily the results of retinal processes or perceptual processes that occur at a higher level in the visual system. The results of these experiments will contribute to a better understanding of the mechanisms underlying these effects, their location, and the interaction between subsystems involved in determining perceived surface color. In short, the search field for neurological mechanisms important for perceived surface color will be narrowed. Models based on perceptual grouping may be better operationally defined in terms of neurobiology. This research will contribute to the fields of perceptual psychology, neuropsychology and artificial intelligence.