Figure 3. The results of 2AFC psychophysical experiments on human subjects and macaque monkeys. A, B, Examples of psychometric functions obtained from human subject LF when tested for illusory rotary and radial motion with the real expansion and CW rotation tasks. Green, black, and magenta represent −45°, 0°, and +45° tilted Gabors. Positive and negative values on the x-axis represent the speed of different types of flow motion patterns as indicated underneath, while the circles show the response frequency as a function of physical speed, and the circle sizes represent the repeat times of that speed condition through using the staircase method (see Materials and Methods). C, Box plots show the distributions of individual Δ PSE values from all nine subjects. Real expansion condition on the left and real CW rotation condition on the right. D, E, Examples of psychometric functions from human subject LF, testing perception of illusory rotation using real contraction, and illusory radial motion using real CCW rotation. Same conventions as in A and B. F, Box plots show the distribution of individual Δ PSE values across all nine subjects. Real contraction condition on the left and real CCW rotation condition on the right. G, H, Examples of psychometric functions from a single day of testing in monkey WJ using the same physical manipulations of the same Pinna–Brelstaff figures as those in A and B. I, Box plots show the distributions of Δ PSE values over 7 d from two monkeys, WJ and DX. J, K, Examples of psychometric functions for monkey WJ obtained from a single day with the same physical manipulation of the same Pinna–Brelstaff figures as those in A and B. L, Box plots show the distribution of Δ PSE values over 7 d from two monkeys. Asterisks denote statistical significance at **p < 0.01; ***p < 0.001.