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Ana Radonjić, Oscar Escobar, Stephen Ivory, Alan Gilchrist; The role of articulation and proximity in the effect of depth on lightness. Journal of Vision 2008;8(6):286. doi: 10.1167/8.6.286.
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We tested several competing predictions made by the coplanar ratio principle (Gilchrist, 1977) and the anchoring theory: one concerning the role of articulation and one concerning the proximity of the highest luminance to the target. (1) According to the anchoring theory, the depth effect reported originally by Gilchrist, although strong, would have been even stronger had the two differently illuminated planes been articulated (that is, had they contained more patches). One group of 20 observers viewed the dihedral planes display of Gilchrist (1977) with two equi-luminant target tabs, one attached to an illuminated white background and one attached to a shadowed black background. A second group of 20 observers viewed the same display except that both white and black backgrounds were replaced by Mondrian patterns consisting of 20 patches ranging from white to black. We did obtain a stronger depth effect using articulated planes. (2) According to the coplanar ratio principle proposed by Gilchrist, the lightness of a target surface depends on the luminance ratio between that target and its adjacent, coplanar neighbor. But according to the anchoring theory, target lightness depends on the ratio between the target and the highest coplanar luminance, even if the highest luminance is not adjacent. Twenty observers viewed the articulated display described above, in which the target, that was perceived to lie in the illuminated plane, was adjacent to a coplanar white surface. A separate group of 20 observers viewed a modified display in which the white surface in the illuminated plane was at least 3 patches away from the target, which was surrounded solely by gray shades between middle gray and black. The results support the prediction of the anchoring theory, showing that a target adjacent to a white surface does not appear darker than a target remote from the white surface.
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