The rubber square illusion

ABSTRACT

We report a new illusion of elasticity in a rigid surface. A square frame is presented behind a concentric occluding cross. When the two surfaces are rotated rigidly, the square frame appears ôruberryö, that is, it appears to contract or expand during the rotation. The rubber square illusion is related to a number of other illusory phenomena involving motion and surface stratification. It is generally believed that these phenomena are due to suppression of potentially veridical motion signals at t-junctions signaling occlusions. However, in all previously reported phenomena the effect of t-junctions was confounded with effects due to surface relative motion, spatial integration, or relative contrast. Given that none of these potential confounds applies to our demonstration, the rubber square illusion provides critical evidence that t-junctions are sufficient to cause suppression of the corresponding motion signals.