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R. T. Eskew, D. P. Richters; Potential mechanisms of long-term adaptation in color vision, and a failure to find evidence for them. Journal of Vision 2008;8(17):26. doi: 10.1167/8.17.26.
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In an interesting and provocative paper, Neitz and colleagues (2002) provided evidence that wearing colored contact lenses over an extended period could produce long-term changes in unique yellow settings. They interpreted the shifts as being due to the long-term chromatic exposure altering the relative gains (cone weights) within the red-green color mechanism, but there are other plausible interpretations. One possibility that we considered is that the lenses cause a relative change in the internal noise associated with the L and M-cone inputs to the hue mechanism, which could produce larger shifts in hue at low retinal illuminances than at high, an idea that might be consistent with the recent findings of Belmore & Shevell (2008). This talk will summarize this and other possible reasons for the shifts in unique yellow, and describe a study that was designed to test between some of these alternatives. We measured monochromatic unique yellows, and also measured detection contours and binary hue classifications (“red” vs. “green”) in the (L,M) plane. Unfortunately, however, we were unable to consistently produce clear shifts in unique yellow by long-term wearing of red lenses. Although initial results looked promising (encouraging data from two observers were presented at FVM in 2006), additional observers and additional data on the first two observers ultimately failed to replicate the basic finding of a hue shift. Our unique yellow settings, with our unpracticed observers, were much more variable than those of Neitz et al (2002). In most cases, our observers (like those of Belmore & Shevell) failed to show a convincing return to baseline after lens wearing stopped, suggesting perhaps that whatever small changes we observed in unique yellow were either permanent, which seems unlikely, or spurious. Most importantly, neither the detection contours nor the hue classification judgments showed any evidence of a change due to wearing the lenses.
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