Editing Déjà vu (section)

==Explanations==

=== Split perception explanation ===
Déjà vu may happen if a person experienced the current sensory experience twice successively. The first input experience is brief, degraded, occluded, or distracted. Immediately following that, the second perception might be familiar because the person naturally related it to the first input. One possibility behind this mechanism is that the first input experience involves shallow processing, which means that only some superficial physical attributes are extracted from the stimulus.<ref>{{Cite book|title=The psychology of learning and motivation. Vol. 53|date=2010|publisher=Academic|author=Ross, Brian H.|isbn=9780123809063|location=London|oclc=668193814}}</ref>

=== Memory-based explanation ===
====Implicit memory====

Research has associated ''déjà vu'' experiences with good memory functions,<ref>{{cite journal | last1 = Adachi | first1 = N. | last2 = Adachi | first2 = T. | last3 = Kimura | first3 = M. | last4 = Akanuma | first4 = N. | last5 = Takekawa | first5 = Y. | last6 = Kato | first6 = M. | year = 2003 | title = Demographic and psychological features of déjà vu experiences in a nonclinical Japanese population | journal = Journal of Nervous and Mental Disease | volume = 191 | issue = 4| pages = 242–247 | doi=10.1097/01.nmd.0000061149.26296.dc| pmid = 12695735 | s2cid = 23249270 }}</ref> particularly long-term [[implicit memory]]. [[Recognition memory]] enables people to realize the event or activity that they are experiencing has happened before. When people experience déjà vu, they may have their recognition memory triggered by certain situations which they have never encountered.<ref name=":0" />

The similarity between a déjà-vu-eliciting stimulus and an existing, or non-existing but different, memory trace may lead to the sensation that an event or experience currently being experienced has already been experienced in the past.<ref name="Brown20042" /><ref name="Cleary2008">{{cite journal|vauthors=Cleary AM|year=2008|title=Recognition memory, familiarity and déjà vu experiences |journal=Current Directions in Psychological Science |volume=17 |issue=5|pages=353–357 |doi=10.1111/j.1467-8721.2008.00605.x |s2cid=55691148}}</ref> Thus, encountering something that evokes the implicit associations of an experience or sensation that cannot be remembered may lead to déjà vu. In an effort to reproduce the sensation experimentally, Banister and [[Oliver Zangwill|Zangwill]] (1941)<ref name="Banister1941a">{{cite journal |vauthors=Banister H, Zangwill, O |year=1941 |title=Experimentally induced olfactory paramnesia |journal=[[British Journal of Psychology]]|volume=32|issue=2 |pages=155–175 |doi=10.1111/j.2044-8295.1941.tb01018.x }}</ref><ref name="Banister1941b">{{cite journal|vauthors=Banister H, Zangwill, O |year=1941 |title=Experimentally induced visual paramnesias |journal=British Journal of Psychology|volume=32|pages=30–51 |doi=10.1111/j.2044-8295.1941.tb01008.x }}</ref> used [[hypnosis]] to give participants posthypnotic amnesia for material they had already seen. When this was later re-encountered, the restricted activation caused thereafter by the posthypnotic amnesia resulted in three of the 10 participants reporting what the authors termed "paramnesias".

Two approaches are used by researchers to study feelings of previous experience, with the process of recollection and familiarity. Recollection-based recognition refers to an ostensible realization that the current situation has occurred before. Familiarity-based recognition refers to the feeling of familiarity with the current situation without being able to identify any specific memory or previous event that could be associated with the sensation.<ref>{{Cite journal|last=Cleary|first=Anne M.|date=2008|title=Recognition Memory, Familiarity, and Déjà vu Experiences|journal=Current Directions in Psychological Science|language=en|volume=17|issue=5|pages=353–357|doi=10.1111/j.1467-8721.2008.00605.x|s2cid=55691148|issn=0963-7214}}</ref>

In 2010, O'Connor, Moulin, and Conway developed another laboratory analog of ''déjà vu'' based on two contrast groups of carefully selected participants, a group under posthypnotic amnesia condition (PHA) and a group under posthypnotic familiarity condition (PHF). The idea of PHA group was based on the work done by Banister and [[Oliver Zangwill|Zangwill]] (1941), and the PHF group was built on the research results of O'Connor, Moulin, and Conway (2007).<ref>{{Cite journal|last1=O'Connor|first1=Akira R.|last2=Moulin|first2=Chris J. A.|date=2013|title=Déjà vu experiences in healthy subjects are unrelated to laboratory tests of recollection and familiarity for word stimuli|journal=Frontiers in Psychology|volume=4|pages=881|doi=10.3389/fpsyg.2013.00881|pmid=24409159|issn=1664-1078|pmc=3842028|doi-access=free}}</ref> They applied the same puzzle game for both groups, "Railroad Rush Hour", a game in which one aims to slide a red car through the exit by rearranging and shifting other blocking trucks and cars on the road. After completing the puzzle, each participant in the PHA group received a posthypnotic amnesia suggestion to forget the game in the hypnosis. Then, each participant in the PHF group was not given the puzzle but received a posthypnotic familiarity suggestion that they would feel familiar with this game during the hypnosis. After the hypnosis, all participants were asked to play the puzzle (the second time for PHA group) and reported the feelings of playing.

In the PHA condition, if a participant reported no memory of completing the puzzle game during hypnosis, researchers scored the participant as passing the suggestion. In the PHF condition, if participants reported that the puzzle game felt familiar, researchers scored the participant as passing the suggestion. It turned out that, both in the PHA and PHF conditions, five participants passed the suggestion and one did not, which is 83.33% of the total sample.<ref>{{Cite journal|last1=O'Connor|first1=Akira R.|last2=Barnier|first2=Amanda J.|last3=Cox|first3=Rochelle E.|date=2008-09-02|title=Déjà Vu in the Laboratory: A Behavioral and Experiential Comparison of Posthypnotic Amnesia and Posthypnotic Familiarity|journal=International Journal of Clinical and Experimental Hypnosis|volume=56|issue=4|pages=425–450|doi=10.1080/00207140802255450|issn=0020-7144|pmid=18726806|hdl=10023/1647|s2cid=1177171|hdl-access=free}}</ref> More participants in PHF group felt a strong sense of familiarity, for instance, comments like "I think I have done this several years ago." Furthermore, more participants in PHF group experienced a strong ''déjà vu'', for example, "I think I have done the exact puzzle before." Three out of six participants in the PHA group felt a sense of déjà vu, and none of them experienced a strong sense of it. These figures are consistent with Banister and Zangwill's findings. Some participants in PHA group related the familiarity when completing the puzzle with an exact event that happened before, which is more likely to be a phenomenon of source amnesia. Other participants started to realize that they may have completed the puzzle game during hypnosis, which is more akin to the phenomenon of breaching. In contrast, participants in the PHF group reported that they felt confused about the strong familiarity of this puzzle, with the feeling of playing it just sliding across their minds. Overall, the experiences of participants in the PHF group is more likely to be the ''déjà vu'' in life, while the experiences of participants in the PHA group is unlikely to be real déjà vu.

A 2012 study in the journal ''[[Consciousness and Cognition]]'', that used virtual reality technology to study reported ''déjà vu'' experiences, supported this idea. This virtual reality investigation suggested that similarity between a new scene's spatial layout and the layout of a previously experienced scene in memory (but which fails to be recalled) may contribute to the ''déjà vu'' experience.<ref name="Cleary et al., 2012">{{cite journal | author = Cleary |title = Familiarity from the configuration of objects in 3-dimensional space and its relation to déjà vu: A virtual reality investigation | journal = [[Consciousness and Cognition]] | year = 2012 | volume = 21 | pages = 969–975 | issue = 2 | doi = 10.1016/j.concog.2011.12.010 | pmid = 22322010 | last2 = Brown | first2 = AS | last3 = Sawyer | first3 = BD | last4 = Nomi | first4 = JS | last5 = Ajoku | first5 = AC | last6 = Ryals | first6 = AJ|s2cid = 206954894 |display-authors=etal}}</ref> When the previously experienced scene fails to come to mind in response to viewing the new scene, that previously experienced scene in memory can still exert an effect—that effect may be a feeling of familiarity with the new scene that is subjectively experienced as a feeling that an event or experience currently being experienced has already been experienced in the past, or of having been there before despite knowing otherwise.
[[File:Functional magnetic resonance imaging.jpg|thumb|An example of an fMRI brain scan]]
In 2018 a study examined volunteers' brains under experimentally induced déjà vu through the use of fMRI brain scans. The induced "deja vu" state was created by getting them to look at a series of logically related and unrelated words. The researchers would then ask the participants how many words starting with a specific letter they saw. With related words such as "door, shutter, screen, breeze", the participants would be asked if they saw any words that started with "W" (i.e. Window, a term that was not presented to the participants). If they did note that they thought they saw a word that wasn't presented to them, then déjà vu was induced. The researchers would then examine the volunteers' brains at the moment of induced déjà vu. From these scans, they noticed that there was visible activity in regions of the brain associated with mnemonic conflict. This finding suggests that more research regarding memory conflict may be important in better understanding déjà vu.<ref>{{Cite journal |last1=Urquhart |first1=Josephine A. |last2=Sivakumaran |first2=Magali H. |last3=Macfarlane |first3=Jennifer A. |last4=O’Connor |first4=Akira R. |date=2021-08-09 |title=fMRI evidence supporting the role of memory conflict in the déjà vu experience |url=https://www.tandfonline.com/doi/full/10.1080/09658211.2018.1524496 |journal=Memory |language=en |volume=29 |issue=7 |pages=921–932 |doi=10.1080/09658211.2018.1524496 |pmid=30232927 |issn=0965-8211|hdl=10023/18521 |hdl-access=free }}</ref>

====Cryptomnesia====

Another possible explanation for the phenomenon of ''déjà vu'' is the occurrence of [[cryptomnesia]], which is where information learned is forgotten but nevertheless stored in the brain, and similar occurrences invoke the contained knowledge, leading to a feeling of familiarity because the event or experience being experienced has already been experienced in the past, known as "déjà vu". Some experts suggest that memory is a process of reconstruction, rather than a recollection of fixed, established events. This reconstruction comes from stored components, involving emotions, distortions, and omissions. Each successive recall of an event is merely a recall of the last reconstruction. The proposed sense of recognition (déjà vu) involves achieving a good match between the present experience and the stored data. This reconstruction, however, may now differ so much from the original event it is as though it had never been experienced before, even though it seems similar.<ref>{{cite encyclopedia|last=Youngson|first=R.|title=Deja Vu|url=http://www.credoreference.com/entry/rsmhealth/deja_vu|encyclopedia=The Royal Society of Medicine Health Encyclopedia|publisher=Dr R.M. Youngson|access-date=1 October 2012}}</ref>

====Dual neurological processing====
In 1965, Robert Efron of Boston's Veterans Hospital proposed that ''déjà vu'' is caused by dual neurological processing caused by delayed signals. Efron found that the brain's sorting of incoming signals is done in the temporal lobe of the brain's left hemisphere. However, signals enter the temporal lobe twice before processing, once from each hemisphere of the brain, normally with a slight delay of milliseconds between them. Efron proposed that if the two signals were occasionally not synchronized properly, then they would be processed as two separate experiences, with the second seeming to be a re-living of the first.<ref>{{Cite journal|vauthors=Efron R|date=September 1963|title=Temporal perception, aphasia and déjà vu|journal=Brain: A Journal of Neurology|volume=86|issue=3|pages=403–424|issn=0006-8950|pmid=14063892|doi=10.1093/brain/86.3.403}}</ref><ref>{{cite web|url=http://science.howstuffworks.com/science-vs-myth/deja-vu4.htm|title=How Déjà Vu Works|date=11 April 2006}}</ref>

===Dream-based explanation===
Dreams can also be used to explain the experience of déjà vu, and they are related in three different aspects. Firstly, some ''déjà vu'' experiences duplicate the situation in dreams instead of waking conditions, according to the survey done by Brown (2004). Twenty percent of the respondents reported their ''déjà vu'' experiences were from dreams and 40% of the respondents reported from both reality and dreams. Secondly, people may experience ''déjà vu'' because some elements in their remembered dreams were shown. Research done by Zuger (1966) supported this idea by investigating the relationship between remembered dreams and ''déjà vu'' experiences, and suggested that there is a strong correlation. Thirdly, people may experience ''déjà vu'' during a dream state, which links ''déjà vu'' with dream frequency.<ref>{{cite journal
 | title =déjà vu
 | date=2018 | pmc=6028740 | last1=Curot | first1=J. | last2=Valton | first2=L. | last3=Denuelle | first3=M. | last4=Vignal | first4=J. P. | last5=Maillard | first5=L. | last6=Pariente | first6=J. | last7=Trébuchon | first7=A. | last8=Bartolomei | first8=F. | last9=Barbeau | first9=E. J. | journal=Brain Stimulation | volume=11 | issue=4 | pages=875–885 | doi=10.1016/j.brs.2018.02.016 | pmid=29530448 }}</ref> Some researchers, including Swiss scientist Arthur Funkhouser, firmly believe that precognitive dreams are the source of many déjà vu experiences. Researchers also connected evidence of precognitive dreams experiences to déjà vu experiences that occurred anywhere from one day to eight years later.<ref name="q684">{{cite web | last=Obringer | first=Lee Ann | title=How Déjà Vu Works | website=HowStuffWorks | date=1970-01-01 | url=https://science.howstuffworks.com/science-vs-myth/deja-vu.htm | access-date=2024-10-07}}</ref>

===Collective unconscious===
Collective Unconscious is a controversial theory created by [[Carl Jung]] that has been used to explain the phenomenon of ''déjà vu''. His theory was that all people have a shared pool of knowledge that has been passed down through generations and we can unconsciously access this knowledge. Some of said knowledge would be about certain archetypes like mother, father and hero or possibly about basic situations, emotions or other patterns. If we can access shared knowledge déjà vu could potentially be an effect of recognizing one of the collectively stored patterns.