Figure 3.1 | Turning the Tables, an Example of a Misperception | The two tabletops appear to have different dimensions and shapes. Surprisingly, however, they are identical. To convince yourself, measure one and then compare it to the other. Even knowing this, you cannot make your brain see them as identical.
(From Mind Sights: Original Visual Illusions, Ambiguities, and Other Anomalies, by R. N. Shepard, 1990, New York: W.H. Freeman/Henry Holt.)