Abstract
In 1996 Mesland and Wertheim described a new motion illusion: when a monitor with a constantly moving sinusoidal grating was swayed near stationary observers, they perceived the grating as freezing or decelerating on the moving screen. The phenomena of “motion freezing” also arises with rotating patterns (Dürsteler, 2005). In order to measure the illusion effects I borrowed an experimental design from Gestalt psychology (K. Duncker, 1929). A central disk could be rotated independently from the surround. The “freezing rotation illusion” arises when the surround is rotating sinusoidally back and forth around a physically continuously and slowly rotating center.
First I measured the effect of surround rotation on center rotation perception. In half of the trials the surround was turning opposite to the center, in the other half, the surround was rotating in the same direction as the center. The observers had to estimate the rotational velocity of the center. Its perceived velocity was smaller in trials where centre and surround were rotating in the same than in the opposite direction.
In the second series of experiments I measured the effect of center rotation on surround rotation perception. There was no noticeable effect of the center rotation on the surround rotational velocity perception.
References:
K. Duncker. Über induzierte Bewegung. Psychol Forschung. 12:180-259. 1929.
B. S. Mesland and A. H. Wertheim. A puzzling percept of stimulus stabilization. Vision Res. 36:3325-3328. 1996.
M. R. Dürsteler. Eine neuartige Bewegungstäuschung: Duncker Illusion und “Motion Capture” im Widerstreit. Ophta. 3:19-26. 2005
http://web.unispital.ch/neurologie/vest/MotionIIlusion/