Figure 1.

The three psychophysical tasks. (A, B) Tilt illusion. (A) Stimulus arrangement, showing an example case where the target is oriented at 45° (dashed line) but appears as tilted clockwise owing to the surround (tilted counter-clockwise from 45°). (B) Example of psychometric curves for trials with surround tilted ±15° from the target; the separation of the curves (measured by the difference in their points of subjective equality [PSEs] to 45°) estimates the magnitude of the tilt illusion. (C, D) Structure from motion. (C) Two clouds of white and black dots moving rightwards or leftwards, respectively, could be perceived as a cylinder rotating about its vertical axis, with bistable direction: clockwise or counter-clockwise. (D) Probability density function of the normalized phase durations for each percept. The dashed line shows the mean of the distributions, which by definition is equal to 1. (E, F) Binocular rivalry. (E) Stimulus display, made of two orthogonal Gabors presented dichoptically. (F) Probability density function of the normalized phase durations for each eye (deprived and nondeprived). Same format as in (D).