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Deanne Leonard, Michael Webster; Cone-specific gain changes compensate color appearance for differences in spectral sensitivity. Journal of Vision 2007;7(9):790. doi: 10.1167/7.9.790.
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Color appearance shows complete compensation for age-related changes in lens pigment density (e.g. Werner and Schefrin JOSA 1993) and for eccentricity-dependent changes in macular pigment density (Beer et al. JOV 2005). However, the mechanisms underlying this compensation are not known. We examined whether the adjustment for macular pigment reflects differences in the intrinsic sensitivity of the cones (or cone-specific pathways), by measuring how achromatic settings are biased by chromatic adaptation in the fovea and periphery. The stimulus was a 20 cd/m2 circular field shown in an otherwise dark room. The field subtended 2 deg and was presented in the fovea or at an eccentricity of 8 deg. Subjects adjusted the chromaticity of the field until it appeared a neutral white, and settings were repeated either after dark adapting or during adaptation to different chromaticities in the field that varied S cone excitation over a large range spanning the nominal white point. Dark-adapted white settings at the two loci were similar, despite the large differences in spectral sensitivity predicted by differences in macular screening. Adapting to a high S-cone, purple field causes the test to appear yellowish green and thus shifts the white settings toward purple, while adapting to a low S-cone color induces the opposite aftereffects. The intermediate adapting S level that does not bias the white settings thus defines the neutral, baseline sensitivity of the chromatic mechanisms at the sites affected by the adaptation. These adaptation effects were again similar at the two eccentricities and had neutral points close to the dark adapted white point. Since the chromatic adaptation largely reflects cone-specific sensitivity changes, our results suggest that much of the neural compensation for color appearance may happen at an early cone-specific stage, perhaps by matching the intrinsic gains of the cones to the long-term history of stimulus exposure.
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