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Peter J. Kohler, Sergey V. Fogelson, Eric A. Reavis, Peter U. Tse; The neural basis of lightness and color constancy in the visual system. Journal of Vision 2011;11(11):351. doi: 10.1167/11.11.351.
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© ARVO (1962-2015); The Authors (2016-present)
In order to extract reliable information about objects in the world from activations on the retina, the visual system must discount variations in the retinal image that occur with changing viewing conditions. Such perceptual constancy operations occur across a range of different stimulus properties. For lightness and color constancy, the challenge is to discount the illuminant and recover the reflectance of a given surface, based only on the light hitting the retina (Palmer, 2000). This means that a difference in lightness or color can be perceived between surfaces that in fact reflect light of the same wavelength, if they are placed in contexts that suggest different illuminations (Adelson, 2000). We presented identical target surfaces within contexts that made them appear different in lightness, as well as reference stimuli that subjects had previously adjusted to match the perceived lightness in each context. An additional experiment was performed using identical target surfaces within contexts that led to a difference in perceived color. We limited our analysis to voxels in visual areas that responded specifically to target surfaces and used multi-voxel pattern analysis (Haxby, 2001) to identify areas where it was possible to distinguish between surfaces with different perceived reflectance, despite identical stimulus wavelengths. This analysis identified areas that carry information about perceived reflectance. We also tested whether correlations between patterns of activation evoked by a target surface and its corresponding reference surface were higher than correlations between patterns evoked by the target and a surface having the same actual luminance/hue. This analysis identified areas that code perceived reflectance rather than properties of light hitting the retina. Because our experience is of inferred reflectance rather than of the wavelengths sampled at the retina, determining the stage in visual processing where these constancy operations occur provides information about the neural correlates of visual experience.
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