Nearly two-thirds of all people experience deja vu at least once in a lifetime. Déjà vu is an apparent similarity of the current situation to something in the indefinite past. But despite its prevalence, surprisingly little data is gathered about the physiological nature of the déjà vu phenomenon. It’s complicated to gather information on deja vu because it’s hard to recall the details of a short experience that took place perhaps months and years ago. In addition, often a sense of deja vu dominates the other senses, reality seemingly doubles.

Déjà vu comes from French and literally means “already seen”. Earlier psychologists interpreted the phenomenon of deja vu as a disease, an illusion or hallucination of memory.

Patients with schizophrenia and epilepsy experience higher frequency of deja vu. In addition, it is very difficult to determine whether experience of patients with schizophrenia sensations correlate with those of healthy person. Patients with schizophrenia often experience depersonalization and prolonged deja vu. In the case of patients with epilepsy, a sense of deja vu often precedes seizures and also differs in duration from a sense of deja vu of healthy people (minutes rather than seconds). The same “picture” may be repeated from attack to attack, and also accompanied by changes in emotions and thoughts of the patient (there’s no time for this to happen in case of healthy person).

Healthy people often have deja vu experience in the evening in the company of others, while listening to someone, being tired after uneasy non-pleasant mental activity, physical stress or excessive alcohol consumption.

Frequency of deja vu decreases with age. The exception is rather low incidence of déjà vu in teenagers.

Frequency of déjà vu increases with increasing number of education years (9 years of education – 20% of respondents have experienced deja vu, 9-12 years- 44%, 13 years – 50%)

Those who travel frequently often experience deja vu.

Strong correlation is stated between the ability to remember dreams and experiencing deja vu. Often people say their deja vu repeats their dreams. If we are faced with similar situations as seen in our dreams the feeling of déjà vu may appear.

Hypotheses of explaining the nature of deja vu can be divided into four categories: dual-processing (delayed vision), neurological hypothesis, hologram theory (referring to memory) and double perception (divided attention).

Dual processing (delayed vision) hypothesis

Dual processing hypothesis is based on the idea that the two mnemonics (storing) processes which typically operate in concert, suddenly begin to work asynchronously, or one of the processes is activated in the absence of the other. For example, Gloor (1990) proposed the idea that the recollection of something and feeling familiarity of this something is two independent cognitive functions that normally operate in concert. Then memories are accompanied by a sense of familiarity. But if these two processes suddenly occur independently – a person feels something familiar in unfamiliar situation – there comes a sense of deja vu.

So-called Bergson’s hypothesis can also be attributed to this category of hypotheses. Once again, consider two processes – this time the perception of sensory information and its storage. The process of remembering always follows the perception of sensory information like a shadow. But if, suddenly, in the process of sensory information perception immediately goes its storage, this may result in feeling deja vu.





Neurological hypotheses

Neurological hypotheses consider deja vu as an instant delay in the transfer of information from the sensory receptors to the response information handling areas of the brain. One of the hypotheses explains deja vu as delayed perception of sensory information in one of the hemispheres of the brain compared to the other, while sensory information is normally supplied simultaneously to the two hemispheres.

Hologram theory and other memory hypotheses

Memory hypotheses suggest that some aspects of the current situation are really familiar, but the source of this similarity is forgotten.

One hypothesis in this category claims that deja vu may be caused by some familiar object, which in this case we did not know or recognize, because it is in a completely different context. Then the feeling of familiarity is transferred to the situation in general.

Sno and Linszen (1990) proposed a holographic explanation of deja vu. Memories, under this hypothesis, represent a unique pattern of neuronal activity. If any element of the current situation coincides with the element previously experienced, memory is activated. If this component activates only subconscious memories we experience a feeling of deja vu. If “all” memory is activated one merely recalls the previous situation.

Hypothesis of emotional connection also belongs to this category. Thus, some factor (a person seen, name heard, or even the smell of perfume) can cause an emotional reaction. If the subconscious emotion is not properly connected with the source of memories, one can perceive the emergence of emotions as feeling familiarity with unfamiliar situations.

Double perception and other attention hypotheses

The essence of the attention hypotheses is that our perception of sensory information is divided into two streams: subliminal perception where a person does not pay attention to the object while looking at it; and conscious – the object is observed attentively. This second view of the object gives the feeling that we have seen this before (deja vu), not realizing that we have seen that just now.

Also, there’s the hypothesis of Inattentional blindness, also known as perceptual blindness. Recent studies indicate that people often don’t pay attention to the object that is in the visible region, provided they’re focused on some other object within visible region.

Or, for example, imagine a person coming into the room, talking on a cell phone and looking straight ahead at some object. After that, looking at the subject consciously may result in a feeling of deja vu.

Perhaps the effect of inattentional blindness is caused by inhibitory mechanism – perception of the visual scene can suppress the perception of the other part. When a person looks again immediately after at the same visual scene, originally “depressed” areas are deblocked and when matchedwith their current perception create a sense of deja vu.

Some scientists are quite pessimistic about the possibility to explain the nature of deja vu, because of its brevity and lack of mechanisms to initiate it. Single proven and accepted by all the explanation has not been found yet. The hypothesis of attention and memory acquires the greatest support among scientists. Hopefully, application of modern advanced research methods will allow to explore all the features of our memory and explain this mysterious feeling of “deja vu”.