Geons are a small set of basic shapes used to identify objects in the world around us according to the theories of Irving Biederman (1987). All objects which we are able to recognize can be constructed from the set of these basic shapes, of which there are a limited and small number (Biederman suggests 36 of them).

Due to the small number of these basic shapes, our mind is able to quickly identify these objects. This identification takes place through a series of dilations, rotations and reflections. In fact, in the identification of basic shapes, it has been shown that the time to identify any basic shape is directly related to its degree from a recognized orientation. For example, if I present the letter A to you, it will take you a proportionally longer amount of time to recognize the letter rotated 120 degrees than if it were only rotated 90 degrees. Multiple orientations of figures can be pre-recognized by your brain, allowing one to improve at games such as tetris.

Some exaples of these basic shapes are cylinders, extruded triangles, cones, etc.

Geons turn out to be very useful in image recognition and processing, face recognition, and a host of other visual computations.

Medin, Ross and Markman. Cognitive Psychology, 3rd Edition. Orlando: Harcourt, Inc., 2001.