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Igor Juricevic, Kyle McDermott, Michael A. Webster; Observer vs. environmental variations in color appearance. Journal of Vision 2009;9(14):85. doi: https://doi.org/10.1167/9.14.85.
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© ARVO (1962-2015); The Authors (2016-present)
Adaptation strongly affects visual appearance, and thus how the world looks to an individual depends on which world they are adapted to. Previously we developed a model to simulate how color appearance should vary within a single standard observer when they are adapted to different color environments. Here we compare these variations to the converse case of different observers — with different spectral sensitivities — that are adapted to the same environments. The adaptation was modeled as gain changes in the cones and in multiple post-receptoral channels tuned to different color-luminance directions. For each channel sensitivity is adjusted so that the average response within the target environment equals the mean response to a reference environment, and images are then rendered based on the adapted channel responses. Spectral sensitivities for different observers are simulated based on estimates of normal variations in color vision. Changes in color appearance were modeled by variations in the foci for basic color terms within the Munsell palette of the World Color Survey, based on determining the stimulus coordinates that would generate equivalent color-luminance angles in the responses of different observers. Comparisons across different environments allows us to assess the relative influence of observer vs. environmental variations in shaping color appearance, and also the extent to which adaptation can compensate for sensitivity differences in observers. For example, we show that chromatic and contrast adaptation cannot undo the effects of sensitivity changes and thus predict incomplete color constancy across observers (in the same way that adaptation cannot completely discount a change in illumination and thus leads to imperfect color constancy within an observer). We also extend the model to predict color appearance in color-deficient observers. Simulations of what individuals with visual deficiencies can see typically filter the images to adjust for the changes in color or contrast sensitivity of the observer, but may not capture how images actually appear if these sensitivity losses are compensated by processes such as adaptation. In our simulations colors are again scaled so that the average signals are again equated across channels, but should appear less determinant in color-deficient observers because this scaling affects both signal and noise. Our model thus predicts why observers with reduced sensitivity may nevertheless perceive the world as perceptually balanced.
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