Déjà vu—that uncanny feeling of having experienced a situation before—has eluded explanation for centuries. Now the first study to use virtual reality to model the phenomenon in the laboratory is helping demystify the spooky illusion, revealing that the layout of a scene can trigger it.

Previous studies of déjà vu suggested the bizarre feeling most commonly concerns places. As such, cognitive psychologist Anne Cleary at Colorado State University in Fort Collins and her colleagues wanted to see if spaces modeled in virtual reality could experimentally replicate the striking experience.

The scientists had college students wear head-mounted video displays that immersed them in a 3-D virtual-reality depiction of a village of structures they called "Deja ville," which Cleary devised. The locale, created with the game The Sims 2 incorporated 128 scenes that were divided into pairs that secretly had objects such as chairs and artwork in the same places on a grid to create identical layouts in space.

The researchers found déjà vu most often occurred when new scenes were very similar to previously experienced scenes in terms of their spatial layout but not similar enough that people consciously recognized the resemblance. For instance, a virtual-reality museum scene might seem familiar because it had the same configuration as an earlier courtyard scene—the location of the central statue relative to the benches and rugs in the museum was the same as the location of the central potted plant relative to bushes and plants in the courtyard.

"One reason for the jarring sense that accompanies déjà vu may be the contrast between the sense of newness and the simultaneous sense of oldness—something unfamiliar should not also feel familiar," Cleary says. "A situation that resembles one in memory may be a particularly good candidate for producing that simultaneous recognition of newness alongside a sense of familiarity." Cleary and her colleagues detailed their findings in the June issue of Consciousness and Cognition.

There are many other theories about the origins of déjà vu, none of which are mutually exclusive, Cleary notes. For example, instead of a scene's layout sparking déjà vu, perhaps a single familiar element within an otherwise novel scene might produce the feeling. "We in fact have another virtual-reality study going on right now where we are investigating and finding support for this hypothesis," she says. Another possibility could lie in whether a person was distracted when they first experienced a scene, making it more difficult to recall with any detail. Such circumstances could increase the likelihood of later déjà vu because a greater variety of scenes could match that vague memory.

"Déjà vu has been an elusive phenomenon—something we have all experienced, but has been very difficult to isolate in the lab. Cleary's method provides for a way of consistently eliciting déjà vu in the lab so that we can uncover the mechanisms behind it," says cognitive psychologist Bennett Schwartz of Florida International University in Miami, who did not take part in this research.

As to whether or not the feeling that Cleary and her colleagues analyzed is the real feeling of déjà vu, "it's an amazing analogue," Schwartz observes. For example, he was on vacation for the first time in Scotland and experienced déjà vu while touring a castle. At the end of the tour he saw photographs from a movie he had seen five years earlier that had been shot in part at the castle. "Thus, I had seen the castle in the movie but I could not recall the specifics that would have allowed me to resolve the déjà vu until I saw the photos in the gift shop," Schwartz recollects. "I have heard many similar stories from others. So yes, I think Dr. Cleary's methodology captures something very real about déjà vu and is immediately applicable to any sensible explanation of déjà vu—that is, those explanations that do not involve a 'glitch in the Matrix.'"

This idea of misplaced familiarity not only helps provide an explanation for déjà vu other than superstition but also could help treat patients with memory problems.

"Our findings suggest that when people fail to retrieve something from memory, they can often still have a sense about their memories despite the failure to access the memory that is responsible for that sense," Cleary says. "People who are impaired at memory retrieval may benefit from training in how to rely on familiarity or intuition."

Even in people without memory afflictions, a better understanding of the feelings of familiarity and intuition may help solve problems. "In his book The Girl with The Dragon Tattoo, Stieg Larsson wrote about a gut feeling that the main character keeps having upon studying a picture album," Cleary observes, noting that the character Blomkvist cannot identify what in the set of pictures is causing the feeling that there is something of interest there, something that may help him to solve the case he's working on. "This illustrates how it might be beneficial for everyone, whether memory-impaired or not, to understand how such feelings of familiarity operate," Cleary asserts.

Virtual reality may also help scientists investigate other strange illusions that appear related to déjà vu. For déjà entendu, the feeling of having heard something before, one could incorporate sounds in virtual-reality scenarios. In the case of jamais vu—the feeling of novelty in response to something that should be familiar—some experts have speculated that this perception results from "oversaturation" of a memory, "such as when you stare at a word for too long and it starts to seem like it is not a word," Cleary says. "Perhaps there might be a way to investigate that idea in virtual reality by having people repeatedly experience the same scene."