Illusory contours or subjective contours are a form of visual illusion where contours are perceived without a luminance

Luminance

Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through or is emitted from a particular area, and falls within a given solid angle. The SI unit for luminance is candela per square...

 or color change across the contour. Friedrich Schumann discovered illusory contours.

Examples

A classic example of illusory contours is the Kanizsa triangle, named after the psychologist Gaetano Kanizsa

Gaetano Kanizsa

Gaetano Kanizsa was an Italian psychologist and artist, founder of the Institute of Psychology of Trieste.Born to a Hungarian father and a Slovene mother, he attended the classic lyceum, and got the laurea at the University of Padova in 1938, writing a thesis about eidetic memory...

. This figure comprises three black circles with equal wedges cut out of them facing the center point and three black angles on a white background. But many observers see a white triangle on top of three black disks and an outline triangle. The white triangle appears brighter than the white background and shows a contour even in regions where there is no luminance change in the image.

The Ehrenstein illusion

Ehrenstein illusion

The Ehrenstein illusion is an optical illusion studied by the German psychologist Walter Ehrenstein in which the sides of a square placed inside a pattern of concentric circles take an apparent curved shape ....

 is another example form of illusory contour.

Explanation

It is thought that early visual cortical regions such as V2 are responsible for forming illusory contours.

See also

• Amodal perception
  Amodal perception
  Amodal perception is the term used to describe the perception of the whole of a physical structure when only parts of it affect the sensory receptors...
  
  
• Gestalt psychology
  Gestalt psychology
  Gestalt psychology or gestaltism is a theory of mind and brain of the Berlin School; the operational principle of gestalt psychology is that the brain is holistic, parallel, and analog, with self-organizing tendencies...
  
  
• Negative space
  Negative space
  Negative space, in art, is the space around and between the subject of an image. Negative space may be most evident when the space around a subject, and not the subject itself, forms an interesting or artistically relevant shape, and such space is occasionally used to artistic effect as the "real"...
  
  
• Reification
  Reification
  Reification generally refers to bringing into being or turning concrete.Specifically, reification may refer to:*Reification , making a data model for a previously abstract concept...
  
  

External links

• Illusory contours figures Many unpublished drawings (fr)