Editing Optical illusion (section)

== Cognitive illusions ==
[[File:NeptunesGrottoOrganPlayer.jpg|thumb|right|"The Organ Player" – [[Pareidolia]] phenomenon in [[Neptune's Grotto]] [[stalactite]] cave ([[Alghero]], [[Sardinia]])]]
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 the [[Germany|German]] physicist and physician [[Hermann von Helmholtz|Hermann Helmholtz]].<ref name="Eagleman2011">{{cite book|author=David Eagleman|title=Incogito: The Secret Lives of the Brain|url=https://books.google.com/books?id=nkPj3dNFYwoC&q=Helmholtz&pg=PT30|access-date=14 August 2013|date=April 2012|publisher=Vintage Books|isbn=978-0-307-38992-3|pages=33–|url-status=live|archive-url=https://web.archive.org/web/20131012233416/http://books.google.com/books?id=nkPj3dNFYwoC&lpg=PP1&pg=PT30&q=Helmholtz|archive-date=12 October 2013}}</ref> Cognitive illusions are commonly divided into [[ambiguous image|ambiguous illusions]], distorting illusions, paradox illusions, or fiction illusions.
* ''Ambiguous illusions'' are pictures or objects that elicit a perceptual "switch" between the alternative interpretations. The [[Necker cube]] is a well-known example; other instances are the [[Rubin vase]] and the "squircle", based on [[Kokichi Sugihara]]'s ambiguous cylinder illusion.<ref>{{cite web|title=An optical illusion that seems to be both a circle and a square is baffling the internet — here's how it works|author=Gili Malinsky|date=22 July 2019|language=en|website=Insider|url=https://www.msn.com/en-us/lifestyle/lifestyle-buzz/an-optical-illusion-that-seems-to-be-both-a-circle-and-a-square-is-baffling-the-internet-—-heres-how-it-works/ar-AAEHiPa?ocid=spartanntp}}</ref>
* ''Distorting'' or ''[[geometrical-optical illusions]]'' are characterized by distortions of size, length, position or curvature. A striking example is the [[Café wall illusion]]. Other examples are the famous [[Müller-Lyer illusion]] and [[Ponzo illusion]].
* ''Paradox illusions'' (or ''[[impossible object]] illusions'') are generated by objects that are paradoxical or impossible, such as the [[Penrose triangle]] or [[Penrose staircase|impossible staircase]] seen, for example, in [[M. C. Escher]]'s ''[[Ascending and Descending]]'' and ''[[Waterfall (M. C. Escher)|Waterfall]]''. The triangle is an illusion dependent on a cognitive misunderstanding that adjacent edges must join.
* ''Fictions'' are when a figure is perceived even though it is not in the stimulus, like with the [[Gaetano Kanizsa|Kanizsa]] triangle, using [[illusory contours]].<ref name="IllusoryContours">{{Cite book|title=The Perception of Illusory Contours|url=https://books.google.com/books?id=RPIxBwAAQBAJ|last1=Petry|first1=Susan|last2=Meyer|first2=Glenn E.|publisher=Springer; 1987th edition|date=2012-12-06|pages=696|isbn = 9781461247609|language=en}}</ref><ref name="CognitiveContours">{{Cite journal|title=Cognitive Contours|url=https://doi.org/10.1038/238051a0|access-date=2021-09-04|journal=[[Nature (journal)|Nature]]|year=1972|doi=10.1038/238051a0|language=en|last1=Gregory|first1=R. L.|volume=238|issue=5358|pages=51–52|pmid=12635278|bibcode=1972Natur.238...51G|s2cid=4285883|url-access=subscription}}</ref>