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Sarah Elliott, Eric Roth, Jennifer Highsmith, John Werner, Michael Webster; Individual differences in chromatic contrast adaptation. Journal of Vision 2010;10(7):390. doi: 10.1167/10.7.390.
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Pre-cortical color channels are tuned primarily to the SvsLM or LvsM cone-opponent (cardinal) axes, but appear elaborated in the cortex to form higher-order mechanisms tuned to both cardinal and intermediate directions. Psychophysical evidence for these mechanisms includes adaptation to temporal chromatic contrast. Adapting to any axis of color space selectively reduces perceived contrast along the adapting axis, implying channels that can be selectively tuned to this axis. Previous studies have found that the degree of selectivity for non-cardinal axes varies even for the small number of observers tested (Krauskopf et al., 1982; Webster & Mollon, 1994). Here we tested a larger sample of color-normal observers to explore individual differences in color contrast adaptation, to examine whether differences are larger for cardinal vs. noncardinal axes (e.g., because they reflect channels that arise at different visual levels). Observers adapted to a 2 Hz temporal modulation along the LvsM or SvsLM axis, or along 2 intermediate axes chosen to be midway between the cardinal axes. Test stimuli included 8 fixed-contrast chromaticities falling on either side of the 4 adapting axes. After an initial adaptation (2 min), 1-sec test pulses were interleaved with 4-sec top-ups in a 2° field above a central fixation cross, with the test colors matched by adjusting the color of a concurrent reference stimulus presented in a field below fixation. Changes in the perceived test chromaticities were fit with ellipses to estimate the selectivity of the adaptation for each of the 4 axes. The strength of adaptation varied widely across observers; all observers showed significant though reduced selectivity along non-cardinal axes. Inter-observer differences in these adaptation effects could reflect normal variation in the distribution of cortical color mechanisms and/or the adaptability of these mechanisms.
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