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Byung-Geun Khang, Barton L. Anderson; Color provides leverage to assess theories of lightness. Journal of Vision 2009;9(8):348. doi: 10.1167/9.8.348.
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A growing body of data has revealed a variety of phenomena that demonstrate the strong dependence of perceived lightness on context. Extensive debate continues over the underlying processes responsible for these effects. Some theories advocate that the visual system explicitly decomposes the image into layered representations, whereas other theories do not. Recent work from our lab has shown that the scission of images into transparent layers can induce strong transformations in both perceived lightness and color. This suggest the possibility that if scission qua transparency contributes to a transformation in perceived lightness, that similar effects should also arise for purely chromatic stimuli. To assess this possibility, we studied two stimuli, one that evokes a strong percept of transparency (Adelson's “tips and strips” illusion), and another that does not (Todorovic's “checkerboard-gradient” illusion). We compared the achromatic induction observed in each display to equiluminant chromatic variants of the same pattern. Each pattern can be treated as a superposition of two elements: a background (“strips”, or gradient); and targets (“tips” and diamond, or checkerboard); for the Adelson and Todorovic displays (respectively). The observer's task was to match perceived color or lightness of a matching display presented on a neutral random-dot background with one of two target elements in the test display. Our results revealed that a similar pattern of induction was observed for the chromatic and achromatic display that evoked a clear percept of transparency (Adelson's tips and strips display). However, a clear difference emerged for Todorovic's checkerboard-gradient illusion: whereas the effect for the checkboard + gradient was significantly larger than either component alone in the achromatic condition, the chromatic gradient alone produced essentially equivalent induction as the combined condition. We suggest that color may provide theoretical leverage to distinguish different models of how context affects perceived lightness.
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