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Kara Emery, Vicki Volbrecht, David Peterzell, Michael Webster; Individual differences in hue scaling suggest mechanisms narrowly tuned for color and broadly tuned for lightness. Journal of Vision 2017;17(10):394. doi: https://doi.org/10.1167/17.10.394.
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Individual differences in color appearance judgments are large and reliable among color-normal observers, but for poorly understood reasons. In our recent factor analyses of hue-scaling functions (Emery et al. 2017ab, Vision Research), we found that the differences depended on multiple processes each tuned to a narrow range of stimulus hues, consistent with a multiple-channel or population code mediating color appearance, but not classic opponency. In the present work, we extended this analysis outside the equiluminant plane by sampling the colors of increments and decrements, to assess the tuning for both hue and lightness. Stimuli included 12 chromatic angles at 30-deg intervals along a circle of fixed contrast in the cone-opponent plane. Each was shown at five lightness levels (0.5, .7, 1, 1.4 and 2 times the 20 cd/m2 luminance of the gray background). The stimuli were displayed in random order in a uniform 2-deg field and were repeatedly pulsed until observers recorded the perceived proportion of red, green, blue, or yellow in the hue. Individual settings for 14 observers were factor-analyzed with PCA and Varimax rotation. The analysis revealed approximately seven systematically-tuned factors (i.e. with moderate to high loadings on 2 or more adjacent stimuli). Together these accounted for >80% of the total variance. The factors approximated our previous analyses in exhibiting narrow and unipolar tuning for chromatic angle. Across the lightness levels, however, the factors tended to show consistent loadings, suggesting for example, that there were strong correlations between how an individual scaled the hues of increments and decrements. No clear univariant factor emerged that was specific to increments or decrements, even though the average perceived hue varied with lightness. This pattern confirms that many independently varying dimensions determine inter-observer differences in hue judgments, and suggests that these dimensions co-vary (operate similarly) across a range of lightness levels.
Meeting abstract presented at VSS 2017
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