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An '''optical illusion''' is characterized by [[visual perception|visually perceived]] images that, at least in common sense terms, are deceptive or misleading. Therefore, the information gathered by the eye is processed by the brain to give, on the face of it, a [[percept]] that does not tally with a physical measurement of the stimulus source. A conventional assumption is that there are physiological illusions that occur naturally and cognitive illusions that can be demonstrated by specific visual tricks that say something more basic about how human perceptual systems work.
 
An '''optical illusion''' is characterized by [[visual perception|visually perceived]] images that, at least in common sense terms, are deceptive or misleading. Therefore, the information gathered by the eye is processed by the brain to give, on the face of it, a [[percept]] that does not tally with a physical measurement of the stimulus source. A conventional assumption is that there are physiological illusions that occur naturally and cognitive illusions that can be demonstrated by specific visual tricks that say something more basic about how human perceptual systems work.
   
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|[[image:Optical.greysquares.arp.jpg|250px|thumb|right|An optical illusion. Square A is exactly the same shade of grey as square B. See [[Same color illusion]]]]
 
|[[image:Optical.greysquares.arp.jpg|250px|thumb|right|An optical illusion. Square A is exactly the same shade of grey as square B. See [[Same color illusion]]]]
 
|-
 
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==Physiological illusions==
 
==Physiological illusions==
'''Physiological illusions''', such as the [[afterimage]]s following bright lights or adapting stimuli of excessively longer alternating patterns (contingent perceptual aftereffect), are presumed to be the effects on the eyes or brain of excessive stimulation of a specific type - brightness, tilt, color, movement, and so on. The theory is that stimuli have individual dedicated neural paths in the early stages of visual processing, and that repetitive stimulation of only one or a few [[channels]] causes a [[physiological]] [[imbalance]] that alters perception.
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'''Physiological illusions''', such as the [[afterimage]]s following bright lights or adapting stimuli of excessively longer alternating patterns (contingent perceptual aftereffect), are presumed to be the effects on the eyes or brain of excessive stimulation of a specific type - brightness, tilt, color, movement, and so on. The theory is that stimuli have individual dedicated neural paths in the early stages of visual processing, and that repetitive stimulation of only one or a few channels causes a [[physiological]] imbalance that alters perception.
   
[[Image:Illusion_movie.ogg]] Example movie which produces distortion illusion after you watch it and look away.
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[[Image:Illusion_movie.ogg]]
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Example movie which produces distortion illusion after you watch it and look away.
   
 
==Cognitive illusions==
 
==Cognitive illusions==
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*[[Chubb illusion]]
 
*[[Chubb illusion]]
 
*[[Cornsweet illusion]]
 
*[[Cornsweet illusion]]
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*[[Delboeuf illusion]]
 
*[[Ebbinghaus illusion]]
 
*[[Ebbinghaus illusion]]
 
*[[Ehrenstein illusion]]
 
*[[Ehrenstein illusion]]
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*[[Sander illusion]]
 
*[[Sander illusion]]
 
*[[Size-weight illusion]]
 
*[[Size-weight illusion]]
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*[[Vertical–horizontal illusion]]
 
*[[Watercolor illusion]]
 
*[[Watercolor illusion]]
 
*[[White's illusion]]
 
*[[White's illusion]]
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*[[Zollner illusion]]
 
*[[Zollner illusion]]
   
Many famous artists have worked extensively with optical illusions, including [[M.C. Escher]], [[Salvador Dalí]], [[Giuseppe Arcimboldo]], [[Marcel Duchamp]], [[Oscar Reutersvärd]], and [[Charles Allan Gilbert]].Optical illusion is also used in film by the technique of [[forced perspective]].
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Many famous artists have worked extensively with optical illusions, including M.C. Escher, Salvador Dalí, Giuseppe Arcimboldo, Marcel Duchamp, Oscar Reutersvärd, and Charles Allan Gilbert.Optical illusion is also used in film by the technique of [[forced perspective]].
   
 
==Gallery==
 
==Gallery==
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Image:Lilac-Chaser.gif|<p align=center>[[Lilac chaser]]</p>
 
Image:Lilac-Chaser.gif|<p align=center>[[Lilac chaser]]</p>
 
</gallery>
 
</gallery>
 
   
   
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* [[Fata morgana (mirage)|Fata Morgana]]
 
* [[Fata morgana (mirage)|Fata Morgana]]
 
* [[Forced perspective]] - application used in film and architecture to create the illusion of larger, more distant objects.
 
* [[Forced perspective]] - application used in film and architecture to create the illusion of larger, more distant objects.
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* [[Geometrical-optical illusions]]
 
* [[Gravity hill]]
 
* [[Gravity hill]]
 
* [[Hermann von Helmholtz]]
 
* [[Hermann von Helmholtz]]
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==External links==
 
==External links==
 
{{Commons|Optical illusion}}
 
{{Commons|Optical illusion}}
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* [http://oohmybrain.com ooh my brain optical illusions]
 
* [http://moillusions.com mighty optical illusions]
 
* [http://moillusions.com mighty optical illusions]
 
* [http://mightyillusions.blogspot.com/ Mighty Illusions Blog: Still Growing]
 
* [http://mightyillusions.blogspot.com/ Mighty Illusions Blog: Still Growing]

Latest revision as of 07:32, July 6, 2014

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Main article: Illusions (perceptual)

An optical illusion is characterized by visually perceived images that, at least in common sense terms, are deceptive or misleading. Therefore, the information gathered by the eye is processed by the brain to give, on the face of it, a percept that does not tally with a physical measurement of the stimulus source. A conventional assumption is that there are physiological illusions that occur naturally and cognitive illusions that can be demonstrated by specific visual tricks that say something more basic about how human perceptual systems work.

Optical.greysquares.arp

An optical illusion. Square A is exactly the same shade of grey as square B. See Same color illusion

Grid illusion

The Scintillating grid illusion or Hermann grid illusion. Dark spots seem to appear and disappear very quickly at the intersections

Gradient.illusion.arp

Simultaneous Contrast Illusion. The grey bar is the same shade throughout

Illusion4

An optical illusion. The two circles seem to move when the viewer's head is moving forwards and backwards while looking at the black dot.

OpticalIllusionStJohnLateran

Floor tiles at the Basilica of St. John Lateran in Rome. The pattern creates an illusion of three-dimensional boxes.

Grifo mágico

Magic tap, which appears to float in the sky with an endless supply of water. In actuality, there is a pipe hidden in the stream of water.


Physiological illusionsEdit

Physiological illusions, such as the afterimages following bright lights or adapting stimuli of excessively longer alternating patterns (contingent perceptual aftereffect), are presumed to be the effects on the eyes or brain of excessive stimulation of a specific type - brightness, tilt, color, movement, and so on. The theory is that stimuli have individual dedicated neural paths in the early stages of visual processing, and that repetitive stimulation of only one or a few channels causes a physiological imbalance that alters perception.

File:Illusion movie.ogg Example movie which produces distortion illusion after you watch it and look away.

Cognitive illusionsEdit

Cognitive illusions are assumed to arise by interaction with assumptions about the world, leading to "unconscious inferences", an idea first suggested in the 19th century by Hermann Helmholtz. Cognitive illusions are commonly divided into ambiguous illusions, distorting illusions, paradox illusions, or fiction illusions.

(a). Ambiguous illusions are pictures or objects that elicit a perceptual 'switch' between the alternative interpretations. The Necker cube is a well known example; another instance is the Rubin vase.

(b). Distorting illusions are characterized by distortions of size, length, or curvature. A striking example is the Café wall illusion. Another example is the famous Mueller-Lyer illusion.

(c). Paradox illusions are generated by objects that are paradoxical or impossible, such as the Penrose triangle or impossible staircases seen, for example, in M. C. Escher's Ascending and Descending and Waterfall. The triangle is an illusion dependent on a cognitive misunderstanding that adjacent edges must join.

(d). Fictional illusions are defined as the perception of objects that are genuinely not there to all but a single observer, such as those induced by schizophrenia or a hallucinogenic substance. These are more properly called hallucinations.

Well-known illusionsEdit

Many famous artists have worked extensively with optical illusions, including M.C. Escher, Salvador Dalí, Giuseppe Arcimboldo, Marcel Duchamp, Oscar Reutersvärd, and Charles Allan Gilbert.Optical illusion is also used in film by the technique of forced perspective.

GalleryEdit


See alsoEdit

References & BibliographyEdit

Key textsEdit

BooksEdit

  • Purves D, Lotto B (2002) Why We See What We Do: An Empirical Theory of Vision. Sunderland, MA: Sinauer Associates.

PapersEdit

  • Eagleman, D.M. (2001) Visual Illusions and Neurobiology. Nature Reviews Neuroscience. 2(12): 920-6. (pdf)
  • Gregory Richard (1997) Knowledge in perception and illusion. Phil. Trans. R. Soc. Lond. B 352:1121-1128 (pdf)
  • Purves D, Lotto RB, Nundy S (2002) Why We See What We Do. American Scientist 90 (3): 236-242.
  • Purves D, Williams MS, Nundy S, Lotto RB (2004) Perceiving the intensity of light. Psychological Rev. Vol. 111: 142-158.
  • Yang Z, Purves D (2003) A statistical explanation of visual space.Nature Neurosci 6: 632-640.

Additional materialEdit

BooksEdit

  • A. Seckel, The Art of Optical Illusions, Carlton Books, 2000

PapersEdit

  • Google Scholar
  • Cooper, A. C. G. & Humphreys, G. W. A New Object-Based Visual Illusion. Psychonomic Bulletin & Review.

External linksEdit

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