These clues, in turn, could help unlock the secrets of the human brain.
“Déjà vu is inappropriate behavior by the brain,” says Brown, professor in SMU’s Department of Psychology and a leading researcher on memory. “By shedding light on this odd phenomenon, we can better understand normal memory processes.”
Published in the May issue of “Psychological Science,” the study significantly extends research on the déjà vu theory of “double perception,” which suggests that a quick glance at a scene can make it appear strangely familiar when it is fully perceived moments later.
“This is easy to imagine in today’s distracted society,” Brown says. “Let’s say you enter a new museum, glancing at artwork while talking on your cell phone. Upon hanging up, you look around and sense you’ve been there long ago.”
According to double perception theory, the initial glance created a mushy memory without time-space context, Brown says. “When you then consciously register the scene, the brain connects the two memories — and you get that spooky feeling.”
Brown and Marsh re-created this experience in the laboratory using unique symbols. In their trials, a symbol was flashed at a subliminal level on a computer screen, followed by a longer view of the same or a different symbol, or no symbol.
When a flash was followed by its identical symbol, participants were five times more likely to say they had seen that symbol sometime before the experiment.
“We pushed memory around,” Brown says. “We changed people’s views of their personal past by instilling a false sense of a previous encounter.”
In pushing its participants’ memories to a time and place outside the laboratory, the new study goes beyond the few previous studies of double perception that have been conducted in the past 100 years. Those studies used words or names, rather than symbols.
“Words and names are contaminated because study participants actually could have encountered them before the experiment,” Brown says, “but it’s extremely unlikely that they ever had encountered our symbols. Our study more closely parallels a quick glance at an unfamiliar object in the real world.”
In addition to double perception, researchers have other theories about the cause of déjà vu, which is French for “already seen.” These theories include a brief dysfunction in the brain, such as a seizure, and “episodic familiarity,” when a forgotten memory connects with part of the present experience.
Brown and Marsh tested episodic familiarity in a 2008 study published in “Psychonomic Bulletin & Review,” in which participants were quickly shown photos of college campuses they had never visited. Upon returning to the laboratory several weeks later, they viewed a series of new and old campus photos and judged whether they had been to the locations. The study showed that the initial brief exposure increased participants’ beliefs that they had visited these colleges — when, in fact, they hadn’t.
“Déjà vu is such a rare event, with potentially numerous causes,” Brown says. “If we can nudge people a little bit in that direction, we can learn the mechanisms behind it.” — Sarah Hanan
“Psychological Science” research article: Creating Illusions of Past Encounter Through Brief Exposure
Alan S. Brown
SMU Research News: Who and Why? Déjà Vu gets another look
SMU Department of Psychology
Dedman College of Humanities and Sciences