Shepard Tables

Shepard tables, also called the Shepard tabletop illusion, is an optical illusion published by Stanford psychologist Roger Shepard in 1990 in which two tabletops, drawn as identical parallelograms rotated ninety degrees from each other, appear to be dramatically different sizes and shapes when depicted as three-dimensional tables. The visual system automatically applies rules for interpreting two-dimensional line drawings as three-dimensional objects, so one parallelogram is read as a long, narrow table receding into the distance while the other is read as a short, nearly square one, even though their outlines are congruent. Shepard noted that understanding intellectually how the illusion works does almost nothing to weaken its perceptual effect, illustrating how automatic this kind of depth processing is.