Reaction Time as a Measure of the Discriminability of Large Colour Differences

The discriminability of colours along two axes in chromaticity space has been studied by measuring the time that a normal observer requires to decide whether two colours are identical or different. By means of a multidimensional scaling program, these data were used to generate a space in which the distance between pairs of colours increases as the response time decreases. The results of this analysis suggest that colours that lie along straight lines in the C.1.E.-(ul,v') diagram lie on curves in discriminability space; and that conventional representations of colour space overestimate the discriminability of red from green. When targets are of small area and brief duration, reaction times are particularly long for colours that lie along a tritanopic confusion line (roughly, a line from yellow to violet). Combinations of these colours should therefore be avoided when choosing colours for colour-coding applications.