Figure 8.

Observers' judgments across slants in Experiment 2B are accounted for by stimulus luminance. Plots of one-dimensional MDS representation against luminance of the test cards for Experiment 2B. Each color shows a different slant context. The colors are red (42), green (28), cyan (14), blue (0), yellow (−21), and magenta (−42). The fact that the data across slants fall along a single locus indicates that observers' judgments are being made on the basis of stimulus luminance, with no effect of slant on the relation between luminance and the perceptual representation. The red and blue lines show the representations from Experiment 2A (Figure 6); distance preserving transformations were applied to bring them into register with the representation derived for 2B. The fact that these lines are difficult to see beneath the data is an indication of the good agreement. Figure S7 provides a fuller view of the transformed solutions. Note that these transformed solutions provide exactly the same account of the dissimilarity data as the untransformed solutions shown in Figure 6, because MDS determines representations only up to a distance preserving transformation. Observers EJH and WPU received Instruction Set A (reflectance). Observers EBV, PNC, and RMB received Instruction Set B (reflected light).