Shepard tables

[1] It is one of the most powerful optical illusions, typically creating length miscalculations of 20–25%.

[2] To quote A Dictionary of Psychology, the Shepard table illusion makes "a pair of identical parallelograms representing the tops of two tables appear radically different" because our eyes decode them according to rules for three-dimensional objects.

[1] This illusion is based on a drawing of two parallelograms, identical aside from a rotation of 90 degrees.

One "table" seems long and narrow, with its longer dimension receding into the distance.

[3] The MIT Encyclopedia of the Cognitive Sciences explains the illusion as an effect of "size and shape constancy [which] subjectively expand[s] the near-far dimension along the line of sight.