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Yang Sun, Steven Shevell; How does the third red-green photopigment of color-defect carriers contribute to color vision?. Journal of Vision 2007;7(9):671. doi: 10.1167/7.9.671.
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PURPOSE: The mother or female child of a male with X-chromosome-linked color-vision deficiency is a heterozygous carrier of the defective gene. A female carrier's defective gene is posited to be expressed, so carriers may have more than one type of M or L cone. An open question is how the carrier's extra cone pigment affects the neural signals encoding color. Here, alternative models considered how the signal from an extra red-green pigment combines with signals originating from the standard L and M cones. The models predicted individual differences in color matching among carriers, which were tested for carriers whose defective gene was assessed by examining the color vision of the color-defective father or son.
METHODS: The usual Rayleigh match using an anomaloscope as well as high-intensity Rayleigh matches using a 5-channel Maxwellian-view optical system were measured. The matches were compared to model predictions based on three different assumptions about the signal from the extra cone pigment: it is combined with the signal from (1) the standard L pigment, (2) the standard M pigment or (3) both pigments. Both spectral-sensitivity peak and optical density of the pigments were considered in the model.
RESULTS AND CONCLUSIONS: The male protans and their female obligate carriers exhibited various extents of shift from the normal Rayleigh match. The model successfully predicted the protan carriers' shifts under the assumption that the signal from their extra red-green pigment is combined with only the signal from the standard L pigment.
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