It’s fair to say that Dr Anne Cleary, a professor at Colorado State University, never intended to study déjà vu. Cleary is a cognitive psychologist and was studying memory when she read Dr Alan Brown’s book The Déjà Vu Experience in 2004. In his book, Brown called on scientists to evaluate existing theories of déjà vu using current methodologies and models. The challenge he set, according to Cleary, was in “taking decades-old hypotheses from the literature that had never been tested before, and presenting those in terms that scientists could process and understand, as testable hypotheses that had actually never been tested, but could be tested. And he pointed out ways that scientists, using methods available at the time, could approach this”.
In her own words, Cleary was inspired.
Many of us are familiar with déjà vu – the odd feeling of having experienced something before, when you know differently. Taken from the French language, déjà vu literally translates to “already seen”. While in English we lump all déjà events under one umbrella, the French have a number of categories of “already” experiences. Déjà rêvé, for example, generally describes the feeling of having already dreamed something before experiencing it in waking life, while déjà goûté is the feeling of having already tasted something.
Being a memory researcher, Cleary was interested in memory-based déjà vu hypotheses. “The source memory framework is the idea that we might find a situation familiar to us, that we also recognise as new, because we’ve experienced it at some point, perhaps in a different context, or just something very similar to it,” she explains. “So what we are experiencing really is a sense of familiarity that is coming from a real memory, but we are failing to call to mind the source of that familiarity.”
Using virtual reality to investigate déjà vu
In one of Cleary’s earliest déjà vu experiments in 2012, published in Consciousness and Cognition, 24 participants were individually fitted with a virtual-reality visor and navigated through 32 study-scenes, followed by 32 test-scenes. In this experiment, half of the test-scenes were designed to mirror earlier study-scenes in terms of spatial layout – so, for example, a garden scene would be created with hedge and wall placement mirroring that of rubbish placement in a junkyard scene. The navigation path was also identical. While, on average, 41% of mirrored test-scenes were able to be identified by participants, Cleary and colleagues also found that participants were significantly more likely to experience déjà vu when they were “immersed in a scene that shared the same spatial layout as something viewed earlier, but they couldn’t retrieve the memory”.
On her decision to use spatial layout to elicit déjà vu, Cleary explains: “There is something special about scenes and places when it comes to human memory, but also when it comes to déjà vu. Research on autobiographical memory and human memory, in general, is starting to point towards the idea that scenes and places, in particular, might play a special role in our ability to remember our past. And that the parts of our brain that are responsible for navigating through spaces might be playing a critical role in our ability to recall our past experiences.”
Cleary is referring to the 2014 Nobel Prize-winning discovery of “grid” and “place” cells, believed to be involved in spatial mapping, navigation and memory. The discovery of these cells has also played a part in better understanding the connection between déjà vu and seizures.
Illuminating the link between déjà vu and seizures
“There is a known link between seizure activity and frequent or chronic déjà vu as part of the seizure aura,” explains Cleary. “In cases where people have this kind of seizure-related déjà vu, it seems to be right near those areas [of the brain] where we think the grid cells are, and those areas of the brain that are responsible for processing our place in space.”
But is seizure-related déjà vu the same as the déjà vu most people experience? Interestingly, it seems not.
To test this hypothesis, Cleary and colleagues recruited a patient who frequently experiences déjà vu as part of an epileptic condition.
“Like a lot of people who have seizure-related déjà vu, he reports that he can tell the difference between when déjà vu is happening because of a seizure, versus when it’s what he would call ‘normal’,” says Cleary. “And so we ran him through our paradigm with the virtual reality scenes to see if he would have déjà vu… and what was really interesting was that he reported having déjà vu, but he said that they were the ‘normal’ kind… and we were recording his brain activity at the time, so we knew he wasn’t having seizures at the time either.”
The case study, published in December in Epilepsy & Behaviour, highlights the fact that déjà vu can also be cause for concern. Cleary herself has been contacted by several individuals reaching out for help with sudden chronic déjà vu.
“There are medical reasons why people can experience frequent déjà vu,” she says. “People often reach out to me from the general public because they are suddenly having déjà vu very frequently. And that can be an indicator of what’s called focal seizure activity, when it’s happening multiple times a day, or even multiple times a week.”
Why does déjà vu sometimes feel like seeing the future?
Another curious aspect of déjà vu is its connection with feelings of premonition. Many people report having déjà vu events where they knew what was about to happen, right down to what people would say. Cleary is often approached by individuals wanting to share their experiences. “There were just stories coming out of the woodwork from people who were not at all superstitious, but who definitely felt like they really had this experience and that it was intense,” she says.
Cleary was intrigued. Using the virtual reality program, Cleary and colleagues ran 74 participants through the study and test-scenes, pausing the navigation before the final turn on test-scenes to ask participants if they had a sense of the direction the last turn would take. That study, published in Psychological Science, revealed that while participants’ predictions were no more accurate than chance, they had significantly stronger feelings that they could predict the last turn when experiencing déjà vu. “When people feel like they are having déjà vu,” says Cleary, “they feel quite strongly, very often, that they can predict the next turn, even though they can’t. We’ve since replicated that a number of times now, across a number of different studies. It’s a very robust, rather large effect.”
In unpublished research, Cleary and colleagues examined if this predictive bias was also associated with déjà entendu – the feeling of having already heard something, when hearing it for the first time. Using musical puzzlers, in which well-known songs were embedded within classical music, Cleary found the same feelings of premonition when asking participants if they could predict the pitch of the final musical note. “And even more interestingly,” says Cleary, “we made it even more impossible to predict by just randomly assigning [the note] to either the left or right speaker. When people were experiencing déjà entendu for a musical piece, they felt very strongly that they knew the direction that the next sound was going to come from.”
How studying déjà vu has helped us understand human memory
Going back to where it all started, Cleary is now a co-author on the second edition of Brown’s book: The Déjà Vu Experience. “I took him up on his call,” says Cleary, “and so did others. As a result, the book catalysed a lot of the research that has been done since that first edition, leading to a lot of what we now know about déjà vu, that was not known at the time of the first edition of the book. A lot of that work came out of my own lab and my own collaborations with others over the years and a lot of that work continues today”.
Cleary plans to continue her study in déjà, overlapping sound and virtual scenes to determine the effect on déjà vu experiences. “Most of the time we go through life we’re not paying attention to our memory – we take it for granted. When déjà vu occurs, suddenly your attention is drawn to your memory, its operation, and how it works… As a memory researcher, I think the experience itself is a window into how our memories work.”