Color spaces of color-normal and color-abnormal observers reconstructed from response times and dissimilarity ratings

With multidimensional scaling analysis, color spaces were reconstructed fro m reaction times (RTs) required to make same-different judgments of pairs o f 15 equiluminant colors and rom dissimilarity ratings between them. In add ition to normal trichromats, observers with red-green color deficiency were tested. Two main purposes were served by this study: (1) to compare spatia l representations of colors derived from discriminative RTs with those deri ved from dissimilarity measures and (2) to examine whether the task may sel ectively affect the dimension reflecting, in color-abnormal spaces, the def icient red-green mechanism. Contradicting our hypothesis of lower dimension ality of RT spaces, as compared with rating spaces, no consistent differenc es in solution dimensionality were found. However, configurations derived f rom the two measures diverged. The rating procedure yielded the most logica l results for recovering color space. The RT configuration revealed contrac tion in the tritanopic direction, indicating longer color processing when t he short-wavelength mechanism is involved, and in addition, for color-abnor mal observers, clustering in the protanopic and deuteranopic directions, in dicating even longer processing by the deficient red-green mechanism. This finding implies that RTs are suitable for detecting temporal differences in color processing but, for that very same reason, rather ill-suited for rec onstructing color spaces.