illusions

An illusion is a distortion of a sensory perception. Each of the human senses can be deceived by illusions, but visual illusions are the most well known. Some illusions are subjective; different people may experience an illusion differently, or not at all.

• Optical illusions, such the use of false perspective, exploit "assumptions" made by the human visual system. Such include motion illusion, grid illusions, etc.
• Mirages are optical distortions through the atmosphere that may be photographed. While the perceived reality (such as water in the desert) is illusory, the visual image (of a reflective surface) is real.
• Auditory illusions, such as the Shepard tone, exploit our hearing.
• Touch illusions exploit the human sense of touch.
• Stage magic is a popular form of entertainment based on illusion. Magicians use tricks to give their audiences the impression that seemingly impossible events have occurred. See magic (illusion).
• Mimes are known for a repertoire of illusions that are created by physical means. The mime artist creates an illusion of acting upon or being acted upon an unseen object. These illusions exploit the audience's assumptions about the physical world. Well known examples include "walls, "climbing stairs", "leaning", "descending ladders", "pulling and pushing", et cetera. Amongst mimes, these illusions are sometimes referred to as pantomime.

In psychiatry the term illusion refers to a specific form of sensory distortion. Unlike a hallucination, which is a sensory experience in the absence of a stimulus, an illusion describes a misinterpretation of a true sensation so it is perceived in a distorted manner. For example, hearing voices regardless of the environment would be a hallucination, whereas hearing voices in the sound of running water (or other auditory source) would be an illusion.

Perhaps less common than visual illusions (or maybe more subtle) touch illusions also exist (Robles-De-La-Torre & Hayward 2001). These "illusory" tactile objects can be used to create "virtual objects" (see the MIT Technology Review article The Cutting Edge of Haptics).

References

Flanagan, J.R., Lederman, S.J. Neurobiology: Feeling bumps and holes, News and Views, Nature, 412(6845):389-91 (2001).

Hayward V, Astley OR, Cruz-Hernandez M, Grant D, Robles-De-La-Torre G. Haptic interfaces and devices. Sensor Review 24(1), pp. 16-29 (2004).

Robles-De-La-Torre G. & Hayward V. Force Can Overcome Object Geometry In the perception of Shape Through Active Touch. Nature 412 (6845):445-8 (2001).

Robles-De-La-Torre G. The Importance of the Sense of Touch in Virtual and Real Environments. IEEE Multimedia 13(3), Special issue on Haptic User Interfaces for Multimedia Systems, pp. 24-30 (2006).

See also

• Trompe l'oeil
• Delusion
• Hallucination
• Helmholtz, Hermann von
• Augmented reality for a more radical approach to the possibility of illusion
• Maya (Hinduism)

External links

• Paradoxical objects. An example of touch illusions of shape.
• The Cutting Edge of Haptics Using touch illusions to create virtual objects with sharp borders. An article in MIT's Technology review by Duncan Graham-Rowe.
• Magicians of Illusion