Kanizsa triangle

• The Kanizsa triangle is an optical illusion first described by the Italian psychologist Gaetano Kanizsa in 1955.
• In the accompanying figure a white equilateral triangle is perceived, but in fact none is drawn. 
• This effect is known as a subjective or illusory contour. 
• Also, the nonexistent white triangle appears to be brighter than the surrounding area, but in fact it has the same brightness as the background.