Freezing Rotation Illusion app for iPhone and iPad

In 2006 the "Freezing Rotation Illusion won the first prize in the "Best Visual Illusion of the Year Contest". Here an interactive application is presented where the user has a choice of different stimuli. He can change the size and the opacity and all relevant motion parameters of the center and the surround stimuli. A continuously rotating central texture (center) is presented together with a patterned surround oscillating back-and-forth. Generally, rotation of the surround induces Misperceptions of the center’s angular velocity, which are known as “induced rotational motion”: a physically rotating center is perceived as turning faster, when counter-rotating with its surround, and turning slower when co-rotating. However during co-rotation additional velocity misperceptions are observed:

(1) A percept of motionless center (“freezing rotation illusion”) arises when the average angular velocity of the surround is fixed to a much higher value than that of the center, and the appropriate oscillation frequency is set.

(2) A percept of the center sticking to its surround (“rotational motion capture”) arises when the average angular velocity of the surround is lower than the center velocity, but higher than a given fraction of it.

Reference:
Lorincz and MR. Duersteler "The Freezing Rotation Illusion" in Oxford Companion of Visual Illusions, eds. A. Shapiro and D. Todorovic (New York, NY: Oxford University Press)
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