Editing Optical illusion (section)

== Connections to psychological disorders ==

=== The rubber hand illusion (RHI) ===
[[File:Phantom-limb-illusion.jpg|thumb|A visual representation of what an amputee with [[Phantom limb|phantom limb syndrome]] senses]]
The [[rubber hand illusion]] (RHI), a [[Multisensory integration|multi-sensory]] illusion involving both [[visual perception]] and [[touch]], has been used to study how [[Phantom limb|phantom limb syndrome]] affects amputees over time.<ref name=":02"/> [[Amputation|Amputees]] with the syndrome actually responded to RHI more strongly than controls, an effect that was often consistent for both the sides of the intact and the amputated arm.<ref name=":02" /> However, in some studies, amputees actually had stronger responses to RHI on their intact arm, and more recent amputees responded to the illusion better than amputees who had been missing an arm for years or more.<ref name=":02" /> Researchers believe this is a sign that the [[body schema]], or an individual's sense of their own body and its parts, progressively adapts to the post-amputation state.<ref name=":02" /> Essentially, the amputees were learning to no longer respond to sensations near what had once been their arm.<ref name=":02" /> As a result, many have suggested the use of RHI as a tool for monitoring an amputee's progress in reducing their phantom limb sensations and adjusting to the new state of their body.<ref name=":02" />

Other research used RHI in the rehabilitation of amputees with [[Prosthesis|prosthetic]] limbs.<ref name=":1">Christ, Oliver; Reiner, Miriam (2014-07-01). "Perspectives and possible applications of the rubber hand and virtual hand illusion in non-invasive rehabilitation: Technological improvements and their consequences". Neuroscience & Biobehavioral Reviews. Applied Neuroscience: Models, methods, theories, reviews. A Society of Applied Neuroscience (SAN) special issue. 44: 33–44. [[Doi (identifier)|doi]]:10.1016/j.neubiorev.2014.02.013. [[ISSN (identifier)|ISSN]] 0149-7634</ref> After prolonged exposure to RHI, the amputees gradually stopped feeling a dissociation between the prosthetic (which resembled the rubber hand) and the rest of their body.<ref name=":1" /> This was thought to be because they adjusted to responding to and moving a limb that did not feel as connected to the rest of their body or senses.<ref name=":1" />

RHI may also be used to diagnose certain disorders related to impaired [[proprioception]] or impaired sense of [[touch]] in non-amputees.<ref name=":1" />

=== Illusions and schizophrenia ===
[[File:Perception-Action Cycle.png|thumb|Top-down processing involves using action plans to make perceptual interpretations and vice versa. (This is impaired in schizophrenia.)]]
[[Schizophrenia]], a mental disorder often marked by [[hallucination]]s, also decreases a person's ability to perceive high-order optical illusions.<ref name=":22"/> This is because schizophrenia impairs one's capacity to perform [[Top-down and bottom-up design|top-down]] processing and a higher-level integration of visual information beyond the primary visual cortex, [[Primary visual cortex|V1]].<ref name=":22"/> Understanding how this specifically occurs in the brain may help in understanding how visual [[distortion]]s, beyond imaginary [[hallucination]]s, affect schizophrenic patients.<ref name=":22"/> Additionally, evaluating the differences between how schizophrenic patients and unaffected individuals see illusions may enable researchers to better identify where specific illusions are processed in the [[Visual system|visual]] streams.<ref name=":22"/>
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File:Dualing Illusions.svg|thumb|An example of the [[peripheral drift illusion]]: alternating lines appear to be moving horizontally left or right.
	
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[[File:Bjorn Borg Hollow Face.jpg|thumb|An example of the [[Hollow-Face illusion|hollow face illusion]] which makes concave masks appear to be jutting out (or convex)]]
[[File:MotionBlindness.gif|thumb|An example of [[Motion-induced blindness|motion induced blindness]]: while fixating on the flashing dot, the stationary dots may disappear due to the brain prioritizing motion information.]]
One study on schizophrenic patients found that they were extremely unlikely to be fooled by a three dimensional optical illusion, the [[Hollow-Face illusion|hollow face illusion]], unlike non-affected volunteers.<ref name=":3">{{Cite journal|last1=Dima|first1=Danai|last2=Roiser|first2=Jonathan P.|last3=Dietrich|first3=Detlef E.|last4=Bonnemann|first4=Catharina|last5=Lanfermann|first5=Heinrich|last6=Emrich|first6=Hinderk M.|last7=Dillo|first7=Wolfgang|date=2009-07-15|title=Understanding why patients with schizophrenia do not perceive the hollow-mask illusion using dynamic causal modelling|url=http://www.sciencedirect.com/science/article/pii/S105381190900278X|journal=NeuroImage|language=en|volume=46|issue=4|pages=1180–1186|doi=10.1016/j.neuroimage.2009.03.033|pmid=19327402|s2cid=10008080|issn=1053-8119|url-access=subscription}}</ref> Based on [[Functional magnetic resonance imaging|fMRI]] data, researchers concluded that this resulted from a disconnection between their systems for [[Top-down and bottom-up design|bottom-up]] processing of visual cues and top-down interpretations of those cues in the [[Parietal lobe|parietal cortex]].<ref name=":3" /> In another study on the [[motion-induced blindness]] (MIB) illusion (pictured right), schizophrenic patients continued to perceive stationary visual targets even when observing distracting motion stimuli, unlike non schizophrenic [[Controlling for a variable|controls]], who experienced motion induced blindness.<ref name=":4">{{Cite journal|last1=Tschacher|author1-link=Wolfgang Tschacher|first1=Wolfgang|last2=Schuler|first2=Daniela|last3=Junghan|first3=Ulrich|date=2006-01-31|title=Reduced perception of the motion-induced blindness illusion in schizophrenia|url=http://www.sciencedirect.com/science/article/pii/S0920996405003701|journal=Schizophrenia Research|language=en|volume=81|issue=2|pages=261–267|doi=10.1016/j.schres.2005.08.012|pmid=16243490|s2cid=10752733|issn=0920-9964|url-access=subscription}}</ref> The schizophrenic test subjects demonstrated impaired cognitive organization, meaning they were less able to coordinate their processing of [[Motion perception|motion cues]] and stationary image cues.<ref name=":4" />