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Rhea Eskew, Quanhong Wang, David P. Richters; A five-mechanism model of hue sensations. Journal of Vision 2004;4(8):315. doi: 10.1167/4.8.315.
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We have been able to isolate, for the first time, a nonclassical (‘higher-order’) color detection mechanism and to estimate its cone weights. Here we describe a model of the hue signals generated within this and the classical four mechanisms. Detection contours in the (L,S) and (M,S) planes of cone contrast space were measured in the presence of dynamic red-green masking noise (to desensitize the red and green mechanisms). Five linear mechanisms were necessary and sufficient to model detection performance. The discriminability of pairs of threshold-level stimuli was also measured in order to confirm the identification of the mechanisms. Those pairs that could be discriminated were assumed to be detected by different mechanisms (Eskew et al 2001). As expected, there were five. We also studied the color percepts generated by these mechanisms using scaling methods. The results indicate that, in addition to red, green, yellow, and blue, there is an independent purple mechanism (rather than purple hues being the result of joint activity in the blue and red mechanisms), that all five mechanisms appear to be “labeled lines”, and that it is possible to predict color appearance at threshold from a detection model, without added assumptions.
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