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E. Economou, A. Gilchrist; Target luminance affects the size and locus of error in Simultaneous Contrast Illusion. Journal of Vision 2001;1(3):428. doi: https://doi.org/10.1167/1.3.428.
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According to anchoring theory (Gilchrist et al, 1999) Simultaneous Lightness Contrast is a product of perceptual organization. For each target, a lightness computation is performed in both of two frameworks: local (each target and its background), and global (whole display). A weighted average of these computations represents each target's final lightness. The Simultaneous Contrast illusion is held to result from the local computations. There are two responsible factors: First, on the black background, a strong anchoring effect pulls the target (highest luminance in its local frame) towards white. Second, on the white background, a weak scaling effect darkens the target as the perceived range in that frame expands slightly towards the full black/white range. Changing target luminance affects these differently. Lightening both targets decreases the contribution of the anchoring component by reducing the discrepancy between local and global computations for the target on black, while on the white background, the contribution of the scaling component is increased because the physical range in the local framework is even more truncated. Two specific predictions follow when targets become lighter: (1) illusion size should decrease, and (2) the main error should gradually shift from the target on black to the target on white. Both of these predictions were confirmed in two experiments in which Munsell matches were obtained for target pairs of three different luminance values (dark, middle and light gray). These results are not consistent with traditional accounts based on lateral inhibition mechanisms.
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