Figure 2. Effect of shape on the rotating-ring illusion.

Pairs of rings with different shapes rotated around a vertical axis. When the speed is slow (1 deg/sec), all three shapes are seen as rotating. At medium speed (10 deg/sec), the circular rings seem to be wobbling against each other, but the other two shapes seem rigid. At fast speeds (30 deg/sec), nonrigid percepts dominate irrespective of shape features.