Ames Window

The Ames window, also called the Ames trapezoid, is an optical illusion device consisting of a flat, trapezoid-shaped image on a piece of cardboard that is shaped and shaded so that it looks like a rectangular window. Both faces of the cardboard carry the same image, and the whole shape is mounted so it can rotate continuously around a vertical axis. When it turns, a viewer does not see it spin all the way around: instead it appears to stop and reverse, oscillating back and forth through less than a full turn, because the visual system assumes the shape is a true rectangle receding in depth rather than a trapezoid. The illusion was discovered by the American perceptual psychologist Adelbert Ames Jr. in 1947 and belongs to a family of Ames illusions demonstrating how built-in assumptions about shape and depth can override the actual optical information reaching the eye. This description is adapted from Wikipedia contributors under CC BY-SA 4.0; changes were made. https://creativecommons.org/licenses/by-sa/4.0/