Research note: a multidimensional scaling comparison of color metrics for response times and rated dissimilarities

Individual-differences multidimensional scaling was applied to a set of proximity data for equiluminant lights (Paramei & Cavonius, 1999) to explore any differences between two data collection procedures (rated dissimilarities, and same/different response times RTs]), as well as between color-normal and abnormal observers. Two conclusions emerged: (1) The pattern of similarities from observers with anomalous color vision can be understood in terms of a compressed color plane (the weighted Euclidean model of individual differences); and (2) there is evidence that the color "plane" is either curved or governed by a non-Euclidean distance function. When color-normal observers are examined in the weighted-Euclidean framework, minor differences emerge between RT and rating data. But the main distinguishing feature of RT data is a pattern of decreasing accuracy for larger color distances. This must be taken into account, since it can itself induce curvature.