Figure 4.

Perceptual performance of the five subjects studied in detail. (A) In this vernier alignment test, subjects rotated the test line until it appeared colinear with the relevant arm of the inducing angle (see diagram). The subtense of the stimulus angle is plotted along the abscissa and the magnitude of the misperception, on the ordinate (mean and standard errors are shown). (B) Perceptual performance on the setting to a right-angle test, presented as in A. As indicated in the diagram, subjects rotated the test line until it appeared to make a right angle with the adjacent arm of the inducing angle. (C) Perceptual performance on the parallel setting test, presented as in A and B. In this case, subjects rotated the test line until it appeared parallel to the relevant arm of the adjacent angle. In all three of these tests, subjects overestimated the magnitude of acute angle stimuli and underestimated obtuse angles in systematically varying amounts.