Figure 1.

(a) The distinction between thresholds for saturation and for hue shown in a portion of the MacLeod–Boynton chromaticity diagram. R, T and D indicate the chromaticities of reference, target and distractor stiumuli respectively. (b) A section of the MacLeod–Boynton diagram showing the reference stimuli used in our main experiment. R, G and B indicate the chromaticities of the individual guns of our CRT monitor; and the solid triangle connecting these points shows the gamut of available chromaticities. Q1, Q2, Q3 and Q4 indicate our numbering of the four quadrants of the diagram. D65 indicates the white point, metameric to Illuminant D65. The dotted line at the bottom of the diagram indicates part of the spectrum locus. Inset: spatial configuration of the stimulus array. (Online version in colour.)