What is an optical illusion? An optical illusion occurs when the image as it is perceived by the brain is different from reality. Illusions are formed as a result of mistaken judgment or erroneous vision. The brain tricks us into seeing something that does not correspond to what it actually is. Depending on how we are looking at an image, we might see things differently. For example, in one well-known type of optical illusion, we are asked if we see a vase or two faces. In this type of illusion, the brain relates the images to its assumptions or knowledge. Typically the brain sees the background as the ground and the object in the center as the "object,' but the cases like the 'vase' versus the 'two faces' can be ambiguous. The illusions that depend on brain processing are called cognitive illusions. Looking for a long amount of time at changing patterns, a certain color, or a certain degree of brightness also can affect what we "see." Staring tires our eyes, and as a certain amount of brightness tires our eyes,and as a result, we may perceive things differently. In short, the tiring of our eyes following an excessive exposuer to a certain kind of visual can cause optical illusions. These are called physiological optical illusions. An example of a physiological illusion is an "afterimage." Have you ever looked at a light and then the image of the light stayed in your eyes after you looked away? This optical illusion is mostly the result of the operation of the "cones" in one's eyes. Some artists like to create optical illusions in their painting. These include M.C. Escher, Piet Mondrinan,and victor vasarely. They use color,shape, and curvature to affect visual perception. Othe artists create optical illusions just for fun, such as Professor Akiyoshi Kitaoka's works of anomalous motion illusion. Check out his website.