Difference between revisions of "Illusion" - New World Encyclopedia

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:''This article is about the phenomenon known as an illusion. For the novel by Richard Bach, please see [[Illusions (novel)]]. Musical groups: For the English band see [[Illusion (UK band)]], for the group from Poland see [[Illusion (band)]]. For the Japanese software company, see [[Illusion Soft]].
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An '''illusion''' is a distortion of a sensory [[perception]], revealing how the brain normally organizes and interprets sensory stimulation. While illusions distort reality, they are generally shared by most people <ref> Solso, R. L. (2001). Cognitive psychology (6th ed.). Boston: Allyn and Bacon.ISBN 0-205-30937-2</ref>.
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Illusions can occur with each of the human [[sense]]s, but visual illusions are the most well known and understood. The emphasis on visual illusions occurs because [[Visual perception|vision]] often dominates the other senses. For example, individuals watching a ventriloquist will perceive the voice is coming from the dummy since they are able to see the dummy mouth the words<ref>McGurk,H. & MacDonald, J.(1976). "Hearing lips and seeing voices", Nature 264, 746-748.</ref>.
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Some illusions are based on general assumptions the brain makes during [[perception]]. These assumptions are made using organizational principles, like [[Gestalt]], an individual's ability of [[depth perception]] and motion perception, and perceptual constancy. Other illusions occur because of biological sensory structures within the human body or conditions outside of the body within one’s physical environment.
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==Cognitive approach==
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===Perceptual organization===
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[[Image:Illusion-9.gif|thumb|Left - Right Conflict]]
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[[Image:Duck-Rabbit_illusion.jpg|thumb|Duck-Rabbit illusion]]
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In order to make sense of the world it is necessary to organize incoming sensations into information which is meaningful. Gestalt psychologists believe one way this is done is by perceiving individual sensory stimuli as a meaningful whole<ref name="Myers">Myers, D. (2003). Psychology in Modules, (7th ed.) New York: Worth. ISBN 0-7167-5850-4 </ref>.[[Image:Facevase.JPG|left|thumb|Reversible figure and ground]]Gestalt organization can be used to explain many illusions including the Duck-Rabbit illusion where the image as a whole switches back and forth from being a duck then being a rabbit and why in the [[figure-ground]] illusion the figure and ground are reversible. [[Image:Kanizsatriangle.png|thumb|Kanizsa triangle]] In addition, Gestalt theory can be used to explain the illusory contours in the Kanizsa Triangle. Here a floating white triangle, which does not exist, is seen. The brain has a need to see familiar simple objects and has a tendency to created a "whole" image from individual elements <ref name="Myers">Myers, D. (2003). Psychology in Modules, (7th ed.) New York: Worth. ISBN 0-7167-5850-4 </ref>. Gestalt means "whole" in German. However, another explanation of the Kanizsa Triangle is based in [[evolutionary psychology]] and the fact that in order to survive it was important to see form and edges.  The use of perceptual organization to create meaning out of stimuli is the principle behind other well-known illusions including [[impossible objects]] ‎and sounds like the [[auditory illusion]], the [[Shepard tone]].
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===Depth and motion perception===
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Illusions can be based on an individual's ability to see in three dimensions even through the image hitting the retina is only two dimensional. The [[Ponzo Illusion]] is an example of an illusion which uses monocular cues of depth perception to fool the eye.[[Image:Ponzo_illusion.gif|left|thumb|Ponzo Illusion]] In the Ponzo illusion the converging parallel lines tells the brain the image higher in the visual field is further away therefore the brain perceives the image to be larger, although the two images hitting the retina are the same size. The [[Optical illusion]] seen in a [[diorama]]/[[false perspective]] also exploits assumptions based on monocular cues of [[depth perception]]. The [[M. C. Escher]] painting ''[[Waterfall]]'' exploits rules of depth and proximity and our understand of the physical world to create an impossible illusion.
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Like [[depth perception]], [[motion perception]] is responsible for a number of sensory illusions. Film [[animation]] is based on the illusion that the brain perceives a series of slightly varied images produced in rapid succession as a moving picture. Likewise, when we are moving, as we would be while riding in a vehicle, stable surrounding objects may appear to move. We may also perceive a large object, like an airplane, to move more slowly, than smaller objects, like a car, although the larger object is actually moving at a faster rate. The [[Phi phenomenon]] is yet another example of how the brain perceives motion. The Phi phenomenon is an illusion created when adjacent lights are blinked on and off to create a sense of motion as in Christmas lighting or a neon sign.
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????
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===Perceptual constancies===
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[[Image:Chubbillusion.gif|thumb|]]<!-- Image with unknown copyright status removed: [[Image:Trippy2.jpg|thumb|]] —>
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Perceptual constancies are sources of many illusions. Color constancy and brightness constancy are responsible for the fact that a familiar object will appear the same color regardless of the amount of light reflecting from it. An illusion of color difference can be created, however, when the luminosity of the area surrounding an unfamiliar object is changed. The color of the object will appear darker against a black field which reflects less light compared to a white field even though the object itself did not change in color. Like color, the brain has the ability to understand familiar objects as having a consistent shape or size. For example a door is perceived as rectangle regardless as to how the image may change on the retina as the door is opened and closed. Unfamiliar objects, however, do not always follow the rules of shape constancy and may change when the perspective is changed. The Shepard illusion of the changing table is an example of an illusion based on distortions in shape constancy.
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==Biological approach==
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===Vision===
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The Hermann [[grid illusion]] and [[Mach bands]] are two illusions that are best explained using a biological approach. [[Lateral inhibition]],  where in the receptive field of the retina light and dark receptors compete with one another to become active, has been used to explain why we see bands of increased brightness at the edge of a color difference when viewing Mach bands. Once a receptor is active it inhibits adjacent receptors. This inhibition creates contrast, highlighting edges. In the Hermann grid illusion the grey spots appear at the intersection because of the inhibitory response which occurs as a result of the increased dark surround <ref>Pinel, J. (2005) Biopsychology (6th ed.). Boston: Allyn & Bacon. ISBN 0-205-42651-4
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</ref>.
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[[Lateral inhibition]] has also been used to explain the Hermann [[grid illusion]], but this has recently been [[grid illusion#The cause of both Scintillating and Hermann grid illusions|disproved]]
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===Other senses===
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Illusions can occur with the other senses including that of taste, smell and touch. It was discovered that even if some portion of the taste receptor on the tongue became damaged that illusory taste could be produced by tactile stimulation. <small> Todrank, J & Bartoshuk, L.M., 1991</small>.  Evidence of [[Olfactory]] illusions occurred when positive or negative verbal labels were given prior to olfactory stimulation
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<small> Herz R. S. & Von Clef J., 2001</small>. Examples of [[Tactile illusion|Touch illusion]]s include [[Phantom limb]], the [[Thermal grill illusion]], and the tactile illusion which occurs when the middle finger is crossed over the pointer finger and the fingers are ran along the bridge of the nose to the tip with one finger on each side of the nose . In this illusion two “noses” are felt at the tip. Interestingly, with [[Tactile illusion|Touch illusion]]s similar brain sights are activated during illusory stimulation as actual stimulation <small> Gross, L 2006 </small>.
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===Disorders===
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Some illusions occur as result of an illness or a disorder. While these types of illusions are not shared with everyone they are typical of each condition. For example migraine suffers often report [[Fortification illusions]]….
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==Physical  approach==
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*[[Mirage]]s are optical distortions through the atmosphere that may be [[photography|photographed]]. While the perceived reality (such as water in the desert) is illusory, the visual image (of a reflective surface) is real.
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*[[Rainbow]]s
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* Antisolar rays
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* Reflection
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* Refraction
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==Paranormal activity and illusion==
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* Illusions as an explanation for [[paranormal]] activity, though this is debated.
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**[[UFO]]s
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**"hot hand" pattern recognition
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**[[Loch Ness monster]]
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==Illusion in art and magic==
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*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)]].
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*In [[fantasy]] works, actual [[magic (fantasy)|magic]] may work by affecting the senses or producing an image, rather than producing a real change; this magic is frequently called illusion to distinguish it from more substantive forms of magic.
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*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
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In [[psychiatry]] and [[philosophy]] 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.
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Perhaps less common than visual illusions (or maybe more subtle) [http://www.roblesdelatorre.com/gabriel/haptics.htm touch illusions] also exist ([http://www.roblesdelatorre.com/gabriel/GR-VH-Nature2001.pdf Robles-De-La-Torre & Hayward 2001]). These "illusory" tactile objects can be used to create "virtual objects" (see the MIT Technology Review article [http://www.technologyreview.com/read_article.aspx?id=17363&ch=biotech&sc=&pg=1 The Cutting Edge of Haptics]).
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==References ==
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<references/>
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*{{cite journal|author=Flanagan, J.R., Lederman, S.J.|url=http://brain.phgy.queensu.ca/flanagan/papers/FlaLed_NAT_01.pdf|title=Neurobiology: Feeling bumps and holes, News and Views|journal=Nature|volume=412|issue=6845|pages=389–91|year=2001}}
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* {{cite journal|author=Hayward V, Astley OR, Cruz-Hernandez M, Grant D, Robles-De-La-Torre G|url=http://www.roblesdelatorre.com/gabriel/VH-OA-MC-DG-GR-04.pdf|title=Haptic interfaces and devices|journal=Sensor Review |volume=24|issue=1|pages=16–29|year=2004}}
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*{{cite journal|author=Robles-De-La-Torre G. & Hayward V.|url=http://www.roblesdelatorre.com/gabriel/GR-VH-Nature2001.pdf|title=Force Can Overcome Object Geometry In the perception of Shape Through Active Touch|journal= Nature|volume=412|issue=6845|pages=445–8|year=2001}}
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*{{cite journal|author=
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Robles-De-La-Torre G.|url=http://www.roblesdelatorre.com/gabriel/GR-IEEE-MM-2006.pdf|title=The Importance of the Sense of Touch in Virtual and Real Environments|journal=IEEE Multimedia|volume=13|issue=3, Special issue on Haptic User Interfaces for Multimedia Systems|pages=24–30|year=2006}}
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== See also ==
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* [[Trompe l'oeil]]
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* [[Auditory illusions]]
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* [[Delusion]]
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* [[Hallucination]]
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* [[Simulated Reality]]
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* [[Hermann von Helmholtz|Helmholtz, Hermann von]]
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* [[Augmented reality]] for a more radical approach to the possibility of illusion
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* [[Maya (Hinduism)]]
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== External links ==
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<!-- Please do not add links to sites that just show optical illusions. Such links will be considered spam. There are a lot of sites showing optical illusions on the web, but we have plenty of more complete examples and illustrations within Wikipedia, so external links are largely unnecessary. —>
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* [http://www.ophtasurf.com/en/illusion.htm Ophtasurf]. A complete website dealing with illusions with a lot of explanations.
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* [http://www.roblesdelatorre.com/gabriel/haptics.htm Paradoxical objects]. An example of touch illusions of shape.
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*[http://www.technologyreview.com/read_article.aspx?id=17363&ch=biotech&sc=&pg=1 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.
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* [http://www.magiciansofillusion.com Magicians of Illusion]
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<!-- Text that will we be worked in later: Some illusions are [[subjective]]; different people may experience an illusion differently, or not at all. Classic Illusion Sheds New Light on the Neural Site of Tactile Perception. PLoS Biol 4(3): e96 DOI: 10.1371/journal.pbio.0040096
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Published: February 28, 2006>—>
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{{Credit1|Illusion|106980869|}}

Revision as of 17:05, 10 February 2007


This article is about the phenomenon known as an illusion. For the novel by Richard Bach, please see Illusions (novel). Musical groups: For the English band see Illusion (UK band), for the group from Poland see Illusion (band). For the Japanese software company, see Illusion Soft.

An illusion is a distortion of a sensory perception, revealing how the brain normally organizes and interprets sensory stimulation. While illusions distort reality, they are generally shared by most people [1]. Illusions can occur with each of the human senses, but visual illusions are the most well known and understood. The emphasis on visual illusions occurs because vision often dominates the other senses. For example, individuals watching a ventriloquist will perceive the voice is coming from the dummy since they are able to see the dummy mouth the words[2]. Some illusions are based on general assumptions the brain makes during perception. These assumptions are made using organizational principles, like Gestalt, an individual's ability of depth perception and motion perception, and perceptual constancy. Other illusions occur because of biological sensory structures within the human body or conditions outside of the body within one’s physical environment.

Cognitive approach

Perceptual organization

File:Illusion-9.gif
Left - Right Conflict
Duck-Rabbit illusion

In order to make sense of the world it is necessary to organize incoming sensations into information which is meaningful. Gestalt psychologists believe one way this is done is by perceiving individual sensory stimuli as a meaningful whole[3].

File:Facevase.JPG
Reversible figure and ground

Gestalt organization can be used to explain many illusions including the Duck-Rabbit illusion where the image as a whole switches back and forth from being a duck then being a rabbit and why in the figure-ground illusion the figure and ground are reversible.

File:Kanizsatriangle.png
Kanizsa triangle

In addition, Gestalt theory can be used to explain the illusory contours in the Kanizsa Triangle. Here a floating white triangle, which does not exist, is seen. The brain has a need to see familiar simple objects and has a tendency to created a "whole" image from individual elements [3]. Gestalt means "whole" in German. However, another explanation of the Kanizsa Triangle is based in evolutionary psychology and the fact that in order to survive it was important to see form and edges. The use of perceptual organization to create meaning out of stimuli is the principle behind other well-known illusions including impossible objects ‎and sounds like the auditory illusion, the Shepard tone.

Depth and motion perception

Illusions can be based on an individual's ability to see in three dimensions even through the image hitting the retina is only two dimensional. The Ponzo Illusion is an example of an illusion which uses monocular cues of depth perception to fool the eye.

Ponzo Illusion

In the Ponzo illusion the converging parallel lines tells the brain the image higher in the visual field is further away therefore the brain perceives the image to be larger, although the two images hitting the retina are the same size. The Optical illusion seen in a diorama/false perspective also exploits assumptions based on monocular cues of depth perception. The M. C. Escher painting Waterfall exploits rules of depth and proximity and our understand of the physical world to create an impossible illusion.

Like depth perception, motion perception is responsible for a number of sensory illusions. Film animation is based on the illusion that the brain perceives a series of slightly varied images produced in rapid succession as a moving picture. Likewise, when we are moving, as we would be while riding in a vehicle, stable surrounding objects may appear to move. We may also perceive a large object, like an airplane, to move more slowly, than smaller objects, like a car, although the larger object is actually moving at a faster rate. The Phi phenomenon is yet another example of how the brain perceives motion. The Phi phenomenon is an illusion created when adjacent lights are blinked on and off to create a sense of motion as in Christmas lighting or a neon sign. ????

Perceptual constancies

File:Chubbillusion.gif

Perceptual constancies are sources of many illusions. Color constancy and brightness constancy are responsible for the fact that a familiar object will appear the same color regardless of the amount of light reflecting from it. An illusion of color difference can be created, however, when the luminosity of the area surrounding an unfamiliar object is changed. The color of the object will appear darker against a black field which reflects less light compared to a white field even though the object itself did not change in color. Like color, the brain has the ability to understand familiar objects as having a consistent shape or size. For example a door is perceived as rectangle regardless as to how the image may change on the retina as the door is opened and closed. Unfamiliar objects, however, do not always follow the rules of shape constancy and may change when the perspective is changed. The Shepard illusion of the changing table is an example of an illusion based on distortions in shape constancy.

Biological approach

Vision

The Hermann grid illusion and Mach bands are two illusions that are best explained using a biological approach. Lateral inhibition, where in the receptive field of the retina light and dark receptors compete with one another to become active, has been used to explain why we see bands of increased brightness at the edge of a color difference when viewing Mach bands. Once a receptor is active it inhibits adjacent receptors. This inhibition creates contrast, highlighting edges. In the Hermann grid illusion the grey spots appear at the intersection because of the inhibitory response which occurs as a result of the increased dark surround [4].

Lateral inhibition has also been used to explain the Hermann grid illusion, but this has recently been disproved

Other senses

Illusions can occur with the other senses including that of taste, smell and touch. It was discovered that even if some portion of the taste receptor on the tongue became damaged that illusory taste could be produced by tactile stimulation. Todrank, J & Bartoshuk, L.M., 1991. Evidence of Olfactory illusions occurred when positive or negative verbal labels were given prior to olfactory stimulation Herz R. S. & Von Clef J., 2001. Examples of Touch illusions include Phantom limb, the Thermal grill illusion, and the tactile illusion which occurs when the middle finger is crossed over the pointer finger and the fingers are ran along the bridge of the nose to the tip with one finger on each side of the nose . In this illusion two “noses” are felt at the tip. Interestingly, with Touch illusions similar brain sights are activated during illusory stimulation as actual stimulation Gross, L 2006 .

Disorders

Some illusions occur as result of an illness or a disorder. While these types of illusions are not shared with everyone they are typical of each condition. For example migraine suffers often report Fortification illusions….

Physical approach

  • 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.
  • Rainbows
  • Antisolar rays
  • Reflection
  • Refraction

Paranormal activity and illusion

Illusion in art and magic

  • 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).
  • In fantasy works, actual magic may work by affecting the senses or producing an image, rather than producing a real change; this magic is frequently called illusion to distinguish it from more substantive forms of magic.
  • 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 and philosophy 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
ISBN links support NWE through referral fees

  1. ↑ Solso, R. L. (2001). Cognitive psychology (6th ed.). Boston: Allyn and Bacon.ISBN 0-205-30937-2
  2. ↑ McGurk,H. & MacDonald, J.(1976). "Hearing lips and seeing voices", Nature 264, 746-748.
  3. ↑ 3.0 3.1 Myers, D. (2003). Psychology in Modules, (7th ed.) New York: Worth. ISBN 0-7167-5850-4
  4. ↑ Pinel, J. (2005) Biopsychology (6th ed.). Boston: Allyn & Bacon. ISBN 0-205-42651-4

See also

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

External links


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