Figure 5.

Observers in Experiment 1 were not matching luminance. Plots of the one-dimensional MDS position against luminance reflected from the test cards. Each color represents a different context, with blue as Context 1, black as Context 2, and red as Context 3. Observers on the left received Instruction Set A (reflectance) and observers on the right received Instruction Set B (reflected light). The fact that the data do not fall along a single locus indicates that context has an effect on the relation between stimulus luminance and the perceptual representation. The clear effect is the change in illuminant intensity between Contexts 1/3 (blue/red) and Context 2 (black). The data for Contexts 1 and 3 appear to lie along a single curve, but because of the luminance gap between the stimuli for the two contexts, the data are not definitive in this regard.