As a culture, we have difficulty letting go of the outdated notion that memory is a reliable tape recorder. Even memories for important events, such as eyewitness accounts of crimes, are usually riddled with imperfections, distortions, and lacunae. Perhaps our irrational faith in memory's accuracy stems from our personal investment in remembering precisely where we parked the car, or our terror that memory's imperfections signal the early warning signs of senility. Memory researchers are increasingly breaking free from this mind set to examine memory difficulties as a vehicle to develop a better understanding of normal memory function.1 Solid scientific research on phenomena such as déjà vu is now beginning to emerge for the first time.
When memory fails, we are frustrated, but when memory appears to make up things, we may become even more concerned. A number of recent demonstrations have shown how easy it is to implant "memories"...
A RANDOM FIRE
Courtesy of Alan S. Brown
Suppose a déjà vu is nothing more than a spontaneous misfiring in the brain that is unconnected to any external experience? We think little about a muscle twitch, but when this same sort of neurological spasm causes a disruption in our higher cognitive centers, we are much more disturbed. Speculation about this electrical problem in the brain began with the observation that some patients with epilepsy experience déjà vu during the preseizure aura. Such patients nearly always have a seizure focus in the hippocampus or amygdala of the temporal lobe, a structure that handles familiarity assessments and information encoding. Thus, it seems reasonable to speculate that a random electrical discharge in this area of the brain could create an unbidden sense of familiarity that is not elicited by the present experience, leading to a déjà vu.
Occasionally, individuals report constant déjà vu due to illness, injury, or traumatic stress. An extended EEG recording with such individuals would help to track down the physiology of déjà vu. Also, some prescription medications have been shown to increase déjà vu frequency in anecdotal reports, and controlled investigation of such medications may help identify neurotransmitter alterations related to déjà vu.
OUT OF SYNC
Information traveling from sensory organs to higher cortical processing centers appears to route through several tracks. That is, multiple copies race through the brain to a final destination where the sensory impressions are merged into a unitary experience. If one of these two tracks gets briefly impeded, or slowed down, by a minor synaptic mishap, the brain could experience two separate copies of the same sensory experience rather than one integrated message. Given the rarity of such an event, the brain may not have the capacity to identify that the duplicate message arrived only milliseconds rather than months earlier, and déjà vu results. We are investigating this possibility through a split-screen presentation of visual information. An identical image is presented in varying degrees (milliseconds) of asynchrony to the right and left visual fields. We predict that when presented with a novel stimulus, a slight separation between the presentations of the two images may elicit a false sense of familiarity.
IN FRONT OF YOUR NOSE
Courtesy of Alan S. Brown
To evoke a déjà vu-like phenomena, subjects are shown a series of pictures – including images of campuses they say they have never visited – and ask them locate the "+." One week later, the same images are shown mixed with new scenes and subjects are asked if they have ever been to the locations shown.
Have you ever looked for your glasses and they are right on your desk? We routinely fail to fully process the objects and people around us, causing us often to miss things that are obvious. Nevertheless, this information still registers in our memories.4 For instance, research on inattentional blindness demonstrates that we often overlook an unanticipated stimulus object when it accompanies another object that we are looking for.5 Even when we deny that this item was shown to us, our altered response to a subsequent encounter with this same stimulus demonstrates that it made an imprint on memory. In short, the brain is primed to respond to this stimulus even though we don't consciously remember experiencing it.
Taking this lab result into the real world, when we are lost in a phone conversation or our own thoughts, the sights and sounds around us make an impression on the brain, even if not on our conscious awareness. Moments later when we hang up the phone or snap out of our inner world, we are struck by the familiarity of what we are now looking at with full awareness. The subconscious brain worked to perfection; it sends a recognition alert that the imperfect conscious brain misinterprets as false familiarity. Several laboratory studies over the past decade have verified the possibility that a fleeting glance moments before can trigger a reaction that resembles déjà vu.67
PULLED FROM MEMORY'S ATTIC
What we attend to gets stored in the brain, but much of what we don't attend to also resides somewhere in memory. Some of the many sights and sounds that we encounter each day may connect to these hidden memory fragments of experiences from months or years ago, and this conjunction can trigger a rush of familiarity, positive affect, or even anxiety, that we label as déjà vu.8 For example, the phrase that a friend just uttered duplicates the prose from a novel read last year; the lamp in the corner of a restaurant lounge is identical to one in your sister's living room; the mannerisms of a person you just met duplicate those of your elementary school principal. Your implicit memory correctly signals "oldness," but you are unable to connect this with a specific memory. In the absence of an obvious connection, you are thrown into a state of familiarity without reference, and generalize the sensation to the entire setting.
We are currently working on several research projects guided by this notion. Students get a superficial glance at a series of pictures as they identify the location of a small "+" embedded somewhere on each one. A week later, they return to the lab to view these old scenes mixed in with new ones, and indicate whether they have actually visited the location shown. Students are occasionally fooled into thinking that they have been to the previously glanced location, evoking a false sense of familiarity that resembles déjà vu.
As the above interpretations clearly illustrate, advances in our understanding of how the brain works allow us to put déjà vu on a solidly scientific basis in a way that was not possible several decades ago. Even the strange subjective impressions that many feel during déjà vu, such as precognition and dream connections, can be explained within an empirical framework.67 I believe that through the memory illusion of déjà vu, the brain is sending us clues about how it routinely processes and interprets our experiences. Déjà vu may serve as a rich mental mother lode of ideas that can have broad cognitive implication. This evanescent cognitive imperfection can tell us much about normal memory function; we just need to learn how to listen more carefully.
Alan S. Brown, a professor of psychology at Southern Methodist University, studies human memory. He is the author of
He can be contacted at