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Amy Mac, Katherine Tregillus, Frederick A. A. Kingdom, Michael A. Webster; Painted faces: misperceiving shading as pigmentation. Journal of Vision 2014;14(10):825. doi: 10.1167/14.10.825.
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© ARVO (1962-2015); The Authors (2016-present)
Many lightness illusions reflect the discounting of shadows and shading by the visual system so that equivalent luminances appear as different lightnesses; or conversely, cases where shadows are not discounted because they are instead misperceived as surfaces. We explored a novel form of these illusions created simply by mirroring side-lit objects. When the two halves of a side-lit face are each mirrored to form a pair of symmetric faces, the face formed by the shaded side is perceived to be darkly pigmented. These effects can be measured by a matching task in which observers adjust the lightness or texture of a uniform comparison patch to match the perceived skin tone on either side of the face. The matches are similar for the two sides of the original side-lit face, yet can strongly differ between the two mirrored faces. The magnitude of the illusion is dependent on cues to the actual angle and directionality of the illuminant, as well as the surface structure of the object, and we explore the inferences and stimulus cues underlying this dependence. For example, the effect is largely absent in simple shapes such as uniform spheres, and for faces depends critically on the point at which the image is mirrored and on which directly lit surfaces this includes. Notably, when only one side of the face is shown, the shaded side again defaults to a pigmented percept, though this again diminishes rapidly as cues to the actual lighting are included.
Meeting abstract presented at VSS 2014
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