HAMBURG — “We have all some experience of a feeling,” English author Charles Dickens wrote in his 1849 novel David Copperfield, “of what we are saying and doing having been said and done before, in a remote time of our having been surrounded, dim ages ago… of our knowing perfectly what will be said next, as if we suddenly remembered it!”
Get On This Day In History delivered straight to your inbox ✉️ each day! Sign up here.
That is an accurate description of the phenomenon of déjà vu — and perhaps the first recorded in literature. Most people have experienced the sensation at some point, and there has long been speculation about what might be behind it.
Are they memories of a past life? Is it extrasensory perception that allows us to see into the future? Or are our thoughts just playing tricks on us?
Systematic research into déjà vu (French for “already seen”) only began in this century. In 2003, psychologist Alan Brown reviewed the scientific literature that had been published up to that point and came up with some statistics: Around two-thirds of all people experience déjà vu at some point in their lives.
The frequency decreases with age, and the experiences are mainly triggered by the physical environment, less often by conversational situations. In conclusion, Brown highlighted the lack of psychological research on the subject and wished for further clarification using more sophisticated methods.
Now an EU research project is trying to further examine this elusive phenomenon. The Polish psychologist Krystian Barzykowski is involved. His original research topic is involuntary autobiographical memories, spontaneous flashes of memory that come to us seemingly with no cause.
During a research stay in Grenoble, France, he discussed it with the neuropsychologist Chris Moulin, who teaches there and was interested in déjà vu. The question soon arose: Could the two phenomena be related? With the difference, of course, that in one case we remember a specific event, while in the other we only have this strange feeling of familiarity.
“Nobody had thought it like that until then,” Barzykowski says looking back.
The déjà vu generator
The two formulated an idea. Perhaps there is a continuous spectrum of these autobiographical memories. At one end are the concrete experiences that we dig out of our memory. At the other end is déjà vu, where we are convinced that an experience is not just a memory but the reliving of a past scene. In the middle of the memory spectrum could lie well-known phenomena like this: you see a person on the tram and know for sure that you have seen him or her before, but you are not able to place the person.
Barzykowski and Moulin wrote up their theory and published it in 2022 in the Behavioral and Brain Sciences. This journal often prints articles with interesting new ideas and then invites researchers to supplement these texts with comments and their own essays: The pair’s article drew 27 responses from around the world. And nobody seemed to reject their new research approach.
She succeeded in evoking this feeling of perplexity in the test subjects.
“I like this idea from Barzykowski and Moulin,” says Anne Cleary, a cognitive scientist at Colorado State University. “It makes sense to see déjà vu as a form of spontaneous cognition. We don’t have it intentionally.” Cleary is probably the most prominent déjà vu researcher and one of the few who has succeeded in creating déjà vu in the laboratory. She calls her method the “déjà vu generator.”
This generator is based on an experiment with virtual reality (VR). Cleary constructed 3D scenes that she presented to her test subjects using data glasses. Some environments had structural similarities to virtual spaces that the test subjects had already been shown earlier during the experiment: for example, one scene showed a hospital hallway that resembled the dimly lit nightclub shown in another scene.
For each new environment, the question was asked: Does this sound familiar to you? Do you perhaps have a sense of déjà vu? She succeeded in evoking this feeling of perplexity in the test subjects, especially when the environment had been experienced in a similar form before, but the test subject was unable to remember it specifically.
Something missing
Cleary explained the mechanism as follows: As soon as a new situation feels familiar, but we don’t know exactly why, we turn our gaze introspectively and search our memory for the cause. If this search in memory fails, a déjà vu can occur.
One reason for such a memory failure can be that the new situation is structurally similar to an old one but not in terms of content. For example, the furniture and other objects in a room might be arranged in a similar way to a situation in the past.
The result was spectacular. But something still seemed to be missing: What about that eerie feeling of knowing what would happen next?
Cleary’s team decided to test that, too, using VR scenes in which the people move through a 3D artificial world. For example, in the first scene, the hospital, participants turned left at a hallway intersection. In the second scene, the nightclub, the movement stopped just before the intersection, and the participants were asked: Where do we go next?
Cleary expected that people would now rely on their unconscious memory when making predictions and would mostly orient themselves to the left — just as they had in the hospital. But that was not the case. Why?
An epiphany
“It took me a few years to have an epiphany,” the researcher says. “I had asked the wrong question, namely whether they could predict the future.” Instead, she should have asked whether they felt they could predict the future. And really, as soon as she asked that question, many test subjects said: Yes, that’s how I feel!
Feeling is also an important keyword for Barzykowski. Too often, says the researcher, we see memory as a retrieval of stored information. But our memory is not a computer hard drive.
“We don’t just remember things that we can verbalize and explain. Where were we? Who were we with?” We often only recall feelings from the past that cannot necessarily be pinned down in time and space. Déjà vu could be an emotional memory.
The same applies to involuntary autobiographical memories. Barzykowski and Moulin believe that they are not actually that involuntary. Most of them do not spring into our consciousness out of nowhere, but are triggered by external stimuli.
We feel déjà vu although we rationally know it is impossible.
“The human memory system is constantly active,” says Chris Moulin, “It tries to make sense of the environment. This sometimes triggers memories.”
Over the next two years, the two researchers are planning their own experiments, and at the same time they want to discuss things with philosophers who study human memory — and metacognition, i.e. thinking about thinking.
Because the striking thing about déjà vu is not just the feeling of having already experienced something, but the fact that we feel it although we rationally know it is impossible. Researchers like Barzykowski, Moulin and Cleary are trying to explain déjà vu together with other memory phenomena.
“There can be no theory of autobiographical memory that does not include déjà vu,” Moulin says. “Déjà vu is not just a funny byproduct of memory. We have to take it seriously.”
