The Science and Psychology Behind Déjà vu (#85)

Todays episode is courtesy of one of our lovely patrons (and also a familiar face to this podcast) – thank you Llinos for suggesting the topic of….. Déjà vu!

Déjà vu is the feeling that one has lived through the present situation before. The term déjà vu is French and means, literally, "already seen." And was coined in 1876 by French philosopher and psychical researcher Émile Boirac. But people had the experience long before it had a name. 

Over the centuries, humans often took déjà vu as evidence of what they already believed. Sigmund Freud looked at déjà vu and saw repressed desires. Carl Jung thought the experience was related to the collective unconscious. Plato described something similar to déjà vu as evidence of past lives. And of course, there’s the modern Hollywood-hatched idea that déjà vu results from a glitch in the Matrix. It’s not hard to understand why déjà vu got a reputation for being a little woo-woo and supernatural.

Those who have experienced the feeling describe it as an overwhelming sense of familiarity with something that shouldn't be familiar at all. Say, for example, you are traveling to England for the first time. You are touring a cathedral, and suddenly it seems as if you have been in that very spot before. Or maybe you are having dinner with a group of friends, discussing some current political topic, and you have the feeling that you've already experienced this very thing -- same friends, same dinner, same topic.

The phenomenon is rather complex, and there are many different theories as to why déjà vu happens. Although some interpret déjà vu in a paranormal context, mainstream scientific approaches reject the explanation of déjà vu as "precognition" or "prophecy” It is an anomaly of memory whereby, despite the strong sense of recollection, the time, place, and practical context of the "previous" experience are uncertain or believed to be impossible.

As much as 70 percent of the population reports having experienced some form of déjà vu. A higher number of incidents occurs in people 15 to 25 years old than in any other age group. People who travel often or frequently watch films are more likely to experience déjà vu than others. Furthermore, people also tend to experience déjà vu more in fragile conditions or under high pressure, and research shows that the experience of déjà vu also decreases with age.

Two types of déjà vu are recognized: the pathological déjà vu usually associated with temporal-lobe epilepsy (where déjà vu can occur just prior to a seizure, or even during the seizure in the moments between convulsions) or that which, when unusually prolonged or frequent, or associated with other symptoms such as hallucinations, may be an indicator of neurological or psychiatric illness. OR the non-pathological type characteristic of healthy people, about two-thirds of whom have had déjà vu experiences.

Since déjà vu occurs in individuals with and without a medical condition, there is much speculation as to how and why this phenomenon happens. These include: 

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. 

Memory-based explanation

Implicit memory

Research has associated déjà vu experiences with good memory functions. 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. 

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. 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 Zangwill (1941) 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 3 of the 10 participants reporting what the authors termed "paramnesias".

Other scientists have attempted to bring on déjà vu using virtual reality. One study found that participants reported experiencing déjà vu when moving through the virtual reality Sims video game when one scene was purposefully created to spatially map to another. (For example, all of the bushes in a virtual garden were replaced with piles of trash to create a junkyard with the same layout.)

Beyond this general explanation, there are dozens of theories that attempt to explain why our memories might malfunction in this way. Some say it’s like a short in the circuits in our brain leading to long- versus short-term memory so that new incoming information goes straight to long term memory instead of making a stop in the short-term memory bank. Others blame the rhinal cortex—the area of the brain that signals that something feels familiar—for somehow being triggered without the memories to back it up.

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 elaborations, 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. 

Dual neurological processing

In 1964, 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. 

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.

Whichever way you slice it, déjà vu presents a major hurdle for researchers attempting to study it - the experience typically lasts no more than a few seconds and there’s no warning of when it’s about to happen, making it extremely difficult to study. Much that is known about déjà vu is based on surveys. Still, researchers have come up with novel ways to study it in the wild.

Different Types of Deja

But did you know that déjà vu isn’t the only kind of deja that you can experience? Swiss scholar Arthur Funkhouser suggests that there are several "déjà experiences" and asserts that in order to better study the phenomenon, the nuances between the experiences need to be noted. 

Jamais vu

Jamais vu (from French, meaning "never seen") is any familiar situation which is not recognized by the observer.

Often described as the opposite of déjà vu, jamais vu involves a sense of eeriness and the observer's impression of seeing the situation for the first time, despite rationally knowing that they have been in the situation before. Jamais vu is more commonly explained as when a person momentarily does not recognize a word, person, or place that they already know. Jamais vu is sometimes associated with certain types of aphasia, amnesia, and epilepsy.

Theoretically, a jamais vu feeling in a sufferer of a delirious disorder or intoxication could result in a delirious explanation of it, such as in the Capgras delusion, in which the patient takes a known person for a false double or impostor. If the impostor is himself, the clinical setting would be the same as the one described as depersonalization, hence jamais vus of oneself or of the very "reality of reality", are termed depersonalization (or surreality) feelings.

The feeling has been evoked through semantic satiation. Chris Moulin of the University of Leeds asked 95 volunteers to write the word door 30 times in 60 seconds. Sixty-eight per cent of the subjects reported symptoms of jamais vu, with some beginning to doubt that door was a real word. 

The experience has also been named "vuja de" and "véjà du". 

Déjà vécu

Déjà vécu (from French, meaning "already lived") is an intense, but false, feeling of having already lived through the present situation. Recently, it has been considered a pathological form of déjà vu. However, unlike déjà vu, déjà vécu has behavioral consequences. Because of the intense feeling of familiarity, patients experiencing déjà vécu may withdraw from their current events or activities. Patients may justify their feelings of familiarity with beliefs bordering on delusion. 

Presque vu

Presque vu (from French, meaning "almost seen") is the intense feeling of being on the very brink of a powerful epiphany, insight, or revelation, without actually achieving the revelation. The feeling is often therefore associated with a frustrating, tantalizing sense of incompleteness or near-completeness. 

Déjà rêvé

Déjà rêvé (from French, meaning "already dreamed") is the feeling of having already dreamed something that is currently being experienced. 

Déjà entendu

Déjà entendu (literally "already heard") is the experience of feeling sure about having already heard something, even though the exact details are uncertain or were perhaps imagined.