Gestalt is originally a German word that is now used as an English term. It is mostly utilized in a psychological context. Gestalt psychology is a theory of mind and brain, describing the Gestalt effect.

Key Properties

- Emergence
- Reification
- Multistability
- Invariance.


Emergence is demonstrated by the perception of the Dog Picture, which depicts a Dalmatian dog sniffing the ground in the shade of overhanging trees. The dog is not recognized when trying to identify its parts (feet, ears, nose, tail, etc.) and inferring the dog from those component parts. Instead, the dog is perceived as a whole, all at once.
external image 260px-Emergence.jpg


Reification is the constructive or generative aspect of perception, by which the experienced percept contains more explicit spatial information than the sensory stimulus on which it is based.
For instance, a triangle will be perceived in picture A, although no triangle has actually been drawn. In pictures B and D the eye will recognise disparate shapes as "belonging" to a single shape, in C a complete three-dimensional shape is seen, where in actuality no such thing is drawn.

external image 260px-Reification.jpg


Multistability is the tendency of ambiguous perceptual experiences to pop back and forth unstably between two or more alternative interpretations. This is seen for example in the Necker cube, and in Rubin's Figure / Vase illusion shown to the right. Other examples include the 'three-pronged widget' and artist M.C. Escher's artwork and the appearance of flashing marquee lights moving first one direction and then suddenly the other.
external image 260px-Multistability.jpgexternal image magnify-clip.png


Invariance is the property of perception whereby simple geometrical objects are recognized independent of rotation, translation, and scale; as well as several other variations such as elastic deformations, different lighting, and different component features. For example, the objects in A in the figure are all immediately recognized as the same basic shape, which are immediately distinguishable from the forms in B. They are even recognized despite perspective and elastic deformations as in C, and when depicted using different graphic elements as in D.
Web-based forums and email providers rely on invariance of human perception to prevent automated bots from exploiting the services. A CAPTCHA test presents a distorted image of letters and numbers, not readable by computers, and prompts user to correctly type the string.
Emergence, reification, multistability, and invariance are not separable modules to be modeled individually, but they are different aspects of a single unified dynamic mechanism.
For a mathematical example of such a mechanism using the cubes of psychologists' block design tests, see Block Designs in Art and Mathematics and The Kaleidoscope Puzzle.

external image 260px-Invariance.jpg


The most basic rule of gestalt is the law of prägnanz. This law says that we try to experience things in as good a gestalt way as possible. In this sense, "good" can mean several things, such as regular, orderly, simplistic, symmetrical, etc. The other gestalt laws are:
  • Law of Closure - Our mind adds missing elements to complete a figure.
  • Law of Similarity - Our mind groups similar elements to an entity. The similarity depends on relationships constructed about form, color, size and brightness of the elements.
  • Law of Proximity - Regional or chronological closeness of elements are grouped by our mind and seen as belonging together.
  • Law of Symmetry - Symmetrical images are seen as belonging together regardless of their distance.
  • Law of Continuity - The mind continues a pattern, even after it stops.
  • Law of Common Fate - Elements with the same moving direction are seen as a unit.

Figure-ground minds have an innate tendency to perceive one aspect of an event as the figure or foreground and the other as the ground or the background.
Under the gestalt theory, these laws not only apply to images, but to thought processes, memories, and our understanding of time.
Examples of the Gestalt experience include the perception of an incomplete circle as a whole or a pattern of dots as a shape - the mind completes the missing pieces through extrapolation. Studies also indicate that simple elements/compositions where the meaning is directly perceived do not offer as much a challenge to the mind as complex ones and hence the latter are preferred over the former.
The major problem with the Gestalt laws of Pragnanz is that they are descriptive not explanatory. For example, one cannot explain how humans see continuous contours by simply stating that the brain "prefers good continuity". Computational models of vision have had more success in explaining visual phenomena.

Wikipedia. Gestalt Psychology. Retrieved from Last accessed on February 18th 2007.
[Chandler, 1997] Daniel Chandler, Visual Perception 6, University of Texas at Austin, Retrieved at April 8, 2007.
[Pedroza, 2005] Carlos Pedroza, Visual Perception: Gestalt Laws, College of Education, San Diego State University. Retrieved at April 8, 2007.