Visual illusions

Illusions of space and motion have fascinated students of vision for over 2,000 years, but it is only in the last century and a half that they have assumed a central position in psychology (Wade, 2005). Psychologists would now say that an illusion occurs when there is a mismatch between the proximal stimulus (the projection of the stimulus onto the retina) and perception. The term visual spatial illusion is now applied mainly to such mismatches in size and orientation of specific two-dimensional figures. They were not referred to as geometrical-optical illusions until the mid-nineteenth century, and many novel spatial illusions were named after those who first described them (Robinson, 1998).