Figure 1. Rotating ring illusion.

(A) A Styrofoam ring is seen at an angle to another ring as wobbling or rolling over the bottom ring despite physical implausibility. (B) At a slower speed, the rings are seen to rotate together revealing that they are glued together, and that the non-rigid rolling was an illusion. B differs from A only in turntable rpm. (C) Two rings rotate together with a fixed connection at the red segment. (D) Two rings wobble against each other shown by the connection shifting to other colors. (E) & (F) are the same as C & D except that the colored segments are black. Both pairs generate identical sequence of retinal images so that wobbling and rigid rotation are indistinguishable. To see the videos in the pdf file, we suggest downloading the file and opening it in Adobe Reader.