'An overwhelming sense of familiarity'
May 13, 2007 4:57 AM   Subscribe

In your opinion, what causes déjà vu? I mean the most common type - déjà vécu (already lived)?
posted by chuckdarwin to Science & Nature (33 answers total) 12 users marked this as a favorite
I read somewhere a while back (don't remember where) that the brain has two completely paths and processes for dealing with new information as opposed to old information-for example, turning onto a street you've never been down before is new information, turning down your own street on your way home from work is old information. Deja vu happens when signals get crossed and the new information goes through the old information processing system, so you feel as if you've seen/felt/heard/lived that moment or experience before.
This is probably a vast oversimplification, but to me the general idea makes sense.
posted by cilantro at 5:09 AM on May 13, 2007

I like the theory that's spelled out in the wikipedia article that suggests that deja vu is its a kind of screw up with your short term memory and you experience the same scene twice in rapid succession.
posted by Hildegarde at 5:15 AM on May 13, 2007

Response by poster: jozxyqk - Oops. I didn't look at the right spelling.

I did find this
posted by chuckdarwin at 5:28 AM on May 13, 2007

My understanding is similar to cilantro's. Deja Vu is a recent (immediate) memory processed through long-term memory paths.
posted by michswiss at 5:55 AM on May 13, 2007

Well, one cause is epilepsy. Before my sister's TLE was diagnosed, she was having deja vu several dozen times per day and didn't know that wasn't the way normal people's brains worked. When she started taking medication, it went away.
posted by jessamyn at 6:48 AM on May 13, 2007

Mod note: also, a whole bunch of "HURF DURF I've seen this question before" comments removed
posted by jessamyn (staff) at 6:49 AM on May 13, 2007

I get DejaVu that lasts for minutes sometimes, always with a feeling of impending doom. I like to think it's something extranatural, a glitch in the matrix if you will. The experience makes me empathic to those who see their dead parents or sprites and faeries.
posted by Mitheral at 7:16 AM on May 13, 2007

My pet theory that I've held for several years goes like this:

Your brain is a supercomputer with vast, vast resources being unused at most times. During some of that time, the brain randomly processes data both real and imagined, just because that's what it does.

In the vast expanses of spare processing, at some point your brain has imagined you talking to a woman in a red dress with a cast on her arm.

When you finally encounter a woman with a red dress and a cast on her arm, you remember that you've seen this before. It seems familiar, although you know it couldn't be.

For me, I get deja vu much more over dialog than visuals. I will find myself in the middle of a conversation knowing I've had this conversation before and being able to accurately predict what the other person is going to say.

I also like the "infinite branching universes" theory of our existence, so deja vu could also be when two branches intersect one another just briefly.

Or, it could be what the other posters said, above. :-)
posted by Ynoxas at 7:31 AM on May 13, 2007

Best answer: In my experience, deja vu occurs when elements of dreams I've had actually occur in real life. Considering that I have very vivid and prolific dreams almost every night, it's almost inevitable for them to overlap with my waking life in some ways, although sometimes the specificity with which it occurs is awe-inspiring.

If it's true that time does not really exist the way we sense it in our daily lives, then it makes a lot of sense that in other states of consciousness (dreams, drug experiences, the moments leading up to death or other traumatizing experiences), our grip on that concept of time, and our place in it, relaxes enough for us to attain a temporary glimpse of what consciousness is like without such limitations-- sort of analogous to the way that people are able to temporarily experience zero-gravity while still within our atmosphere. The natural laws that bind us to our world and our consciousness only apply to an extent; unfortunately the points at which they turn out to be flexible (with particular regards to consciousness, not gravity) are so incredibly subjective and difficult to document scientifically that whether they are meaningful is left up to the individual to decide.

For all the scientific discussions we've had about superstring theory etc. on MeFi, lots of people here seem to be pretty hardheaded when it comes to the concept of human consciousness directly apprehending itself from the perspective of other dimensions. I've always had a hard time figuring that one out.
posted by hermitosis at 7:47 AM on May 13, 2007 [2 favorites]

I subscribe to the theory that the 'here and now' is processed immediately and then makes its way to medium / long term memory. DejaVu occurs when the 'here and now' isn't processed immediately and so gets to medium / long term memory first. Hence, when it is processed, you have seemingly already experienced it.
posted by hmca at 7:52 AM on May 13, 2007

I always find this Python sketch seems to help the pondering of deja vu.
posted by MetaMonkey at 8:11 AM on May 13, 2007

I dont know if this is relevent... But: Once when I was really stoned (beginning of all great stories), I was watching this interview on tv, and I (believed I) could accurately predict everything the person was saying, and I was having this really uneasy feeling since I was sure I knew what the next scene would be in the interview, and sure enough it happened.

In reflection all I believe that happened is, the effect the weed was having on my memory was that stuff was going into my memory before I was perceiving it as 'here and now'. Which is why whilst I was sure I knew what they were about to say, I didnt know exactly what it was until after they'd said it, then I confirmed it in my mind.
posted by chrisbucks at 8:11 AM on May 13, 2007

Response by poster: Here's the funny part, hermitosis: that whole superstring/13 dimensions thing has also been my pet theory for years. If there are all these other dimensions, and one of them is, say, two weeks off... you could have a dream wherein you're somehow exposed to information that is two weeks in the future. Said info is buried in your unconscious until it's triggered by the event in 'real time'.

Then again, I'm no expert on string theory.

Don't get me started on how ADHD is caused by television; I've been droning on that one for about 15 years.
posted by chuckdarwin at 8:27 AM on May 13, 2007

It really seems this is an experience that can be personally understood but rarely meaningfully shared with others; when we encounter a scientific theory or discovery, or an idea presented through literature or the arts, ther eis little we can do but note the extent to which we have been shattered or deepened or reinforced, and the proceed through life accordingly, doing what we can to remember and occasionally relive that experience. The rare times when people are able to articulate their understandings to each other seem to make it all worthwhile, but ultimately it only must be worthwhile, defensible, or understood by yourself, which can relieve you of an incredible burden.

People can re-explain superstring, evolution, and other theories to me until they are blue int he face, trying to convince me that they dont mean or imply what I seem to think they do, but I accept this (with good humor) as a display of their own lack of imagination and spirit of exploration. Am I missing the point, or are they? As long as what we are talking about is theoretical and intangible and seems to have no bearing on what we order for lunch, and as long as I take the same pains to educate myself as they do, its only significance is in the degree to which it inspires us.
posted by hermitosis at 9:05 AM on May 13, 2007

In my experience, deja vu occurs when elements of dreams I've had actually occur in real life.

When I experience deja vu, my immediate reaction is to say "I had a dream about this!" since that is the feeling it creates. There was no dream, just the deja vu.

The explanation that made the most sense to me was a left brain / right brain theory. One part of your brain gets the info just slightly ahead of the other, creating the mental illusion of a memory.

Hey... I feel like I have typed that comment before.

WAIT! And that one too! And that one! Aghh!!!
posted by The Deej at 9:36 AM on May 13, 2007

A very good article on research into deja vu comes from Scientific American Mind.

The more I read about it, the more I'm inclined to believe it's brain misfire, either filing a short-term memory in long term, or sensory inputs getting out of sync. I seem to have quite a bit more deja vu than the average person, I also have been diagnosed with uncommon memory problems. It also gets worse when my body chemistry is out of whack.
posted by Ookseer at 9:38 AM on May 13, 2007

Nearly every one of my deja vu experiences shares a common trait: during the experience, I think "I've had this deja vu before."
posted by Deathalicious at 10:07 AM on May 13, 2007 [3 favorites]

"Nearly every one of my deja vu experiences shares a common trait: during the experience, I think "I've had this deja vu before.""

Me too! Its really weird, for me its not just usually a momentary sensation its usually at least 1 minute or a set of circumstances that I cant possibly have experienced before but I feel like I have, and then I feel like the last time I'd had it I felt like it was deja vu and remember thinking the same things to myself about it... in a strange feedback loop kind of way
posted by missmagenta at 10:58 AM on May 13, 2007

I think it would be hasty to consider that all "deja vu" experiences derive from the same phenomenon. Which is why Ookseeker can have vaguely similar experiences that may or may not even be examples of the same phenomena.

To throw a spin on it, it works in reverse for me too. The nightmare in which one's teeth are all falling out is pretty common, and I hoped that knowledge would help me stop having it. Instead, I'm so accustomed to deja vu in my waking life that now in dreams when my teeth suddenly start coming loose, I start telling anyone around me, "Oh fuck, this is just like that dream I always have!"
posted by hermitosis at 11:03 AM on May 13, 2007

I meant to say that Ookseeker and I can have vaguely similar experiences that may not be examples of the same...
posted by hermitosis at 11:06 AM on May 13, 2007

I had one particular occurance of deja vu that I am certain must have happened before. Absolutly posative, it happened six years ago and I still remember it perfectly because it was so intense. It wasn't even a very important event, I was about to give a presentation and I handed over a poster. It scared me.
posted by thebrokenmuse at 12:43 PM on May 13, 2007

For all the scientific discussions we've had about superstring theory etc. on MeFi, lots of people here seem to be pretty hardheaded when it comes to the concept of human consciousness directly apprehending itself from the perspective of other dimensions. I've always had a hard time figuring that one out.

The essence of science is verifiability; it is therefore unlikely to have any kind of real scientific discussion of your theory, unless you can propose a means to test it somehow.

Your analogy to string theory is good, sicne it has largely the same problem.
posted by blenderfish at 2:07 PM on May 13, 2007

One of the little phenomena of the brain that always made me think was this: When I'm standing at a crosswalk and I see the little green man appear, it always feels to me like I take an extended pause before I start moving. Then I read a Richard Dawkins book that shed light on the situation, using the example of a clock's second hand seeming to lag when one first looks at it.

Basically, your brain makes assumptions: that the red hand across the street is NOT going to suddenly turn into a green dude; that the little metal tine pointing to the 9 on a clock is NOT going to suddenly be pointing right above the 9. And based on these assumptions, it your brain creates a perception of the world for you that is usually pretty reliable. But when your brain realizes that the red hand changed into a green dude, it not only updates your current perception, but (and this is the trick) it also effectively back-dates your perception so that you feel like you perceived the change when it occured instead of slightly later due to your laggy brain. Therefore, the paralyzed pause I feel at the crosswalk comes from me thinking I could have started moving before I could have. And the second hand on my watch seems to lag because my brain takes a breif moment to notice the movement and reverse-engineer a memory of it occuring for me.
posted by chudmonkey at 2:39 PM on May 13, 2007 [1 favorite]

I once worked for a physiological psych prof who thought deja vu resulted when the chemical environment that accompanies the feeling of certainty* was created accidentally in the brain without the standard referents of certainty - i.e., no strong memory or logical inference present, but the chemistry occurred anyway. That might also explain the "I've had this deja vu before" feeling; it's just a continuation of trying to make sense of the unfocused but strong feeling of certainty.
posted by mediareport at 2:49 PM on May 13, 2007

*assuming such a chemical environment exists was baseline for his branch of psychology, of course
posted by mediareport at 2:50 PM on May 13, 2007

Ditto the notion that it's a "familiarity chemical" or physiological mode that invests the moment with a sense of repetition; it could be ANY moment and deja vu would happen if the recipe is correct.
posted by rleamon at 7:22 PM on May 13, 2007

For all the scientific discussions we've had about superstring theory etc. on MeFi, lots of people here seem to be pretty hardheaded...

Why is it hardheaded to consider that the most sensible explanation of something is probably right?
I have TLE and have experienced quite a lot of deja vu, as well as various similar categories of feelings - intensic general nostalgic feelings and jamais vu (intense unfamiliarity / feeling like you've never been somewhere when in actuality you know it well) for example. That these experiences are likely to be due to different methods of data reception in my brain seems very likely - it is a simple and beautiful theory that deja vu is the same information traveling two different paths so that in a certain sense you have been there before, micro-seconds before you knew you were.

I don't think this is reductionist or insufficiently interesting. It is a much better explanation than the vague idea that somehow deja vu is connected to dreams and therefore to some larger consciousness. That doesn't really answer anything or give us anything to work with. It doesn't supply new comprehension of anything. The best kind of understanding is the kind that helps us ask new questions, helps us reconsider other issues, and makes us dig further. If deja vu is information traveling two pathways, does that mean we think in two places at once? what unifies the different pathways together into one sense of consciousness? etc...

Really you do not need something like deja vu to discover the weirdness of consciousness - it's right there in the experience of consciousness. Deja vu is not particulary strange as a manifestation of consciousness, in that it can be understood as patterns of matter as well, but it is just as strange as all types of consciousness, in that translating those patterns of matter into the experience of mind is as mysterious as it's ever been.
posted by mdn at 7:24 PM on May 13, 2007 [2 favorites]

My personal opinion: the feeling of complete recognition of present circumstances is just that - a feeling - related to, but not the same as, the "aha!" feeling of having just understood something properly for the first time. And, in much the same way as you can "aha!" your way to total misunderstanding, it's not necessarily reliable.

On preview: what mediareport's psych prof said.

It's also self-sustaining. It's such a powerful and unusual feeling that it commands almost complete attention to itself, rather than to the details of what is putatively being re-experienced; this in turn makes the feeling easier to sustain. That is: once a déjà vu episode is triggered, every perception starts being filtered through that déjà vu experience rather than through any genuine comparison against things remembered. The usual process of cross-checking against memory is short-circuited, and everything perceived ends up propping up the déjà vu until it's run its course.

I don't believe that existence of the feeling of déjà vu calls for any re-interpretation of physical reality except perhaps that of internal brain processes.

I've got it filed under "assorted brain farts".
posted by flabdablet at 7:38 PM on May 13, 2007

The nightmare in which one's teeth are all falling out is pretty common, and I hoped that knowledge would help me stop having it.

Not to threadjack, but I have this dream all the time and as a result have a pretty weird phobia about anything to do with teeth and the falling out/extraction thereof. I didn't know it was so common.
posted by ScarletSpectrum at 8:22 PM on May 13, 2007

And a resounding "yea, sister!" to what mdn said about normal, everyday conscious awareness being the weirdest thing there is.

At the risk of descending into chatfilter: for me, the whole thing comes down to my complete and abject failure to understand the nature of time.

Here is the root of the difficulty:

Einstein, in Special Relativity, proposed a framework for understanding objective (i.e. shared) reality that does not assume any notion of shared simultaneity for observers moving relative to one another. That is: if I am in motion relative to you, and two events perceivable by both of us occur (conventionally, flashes of lightning), and careful measurement by you reveals them to be simultaneous from your point of view, careful measurement by me will, in general, not reveal them to be simultaneous from mine.

Special Relativity has been well tested and can be taken to be "true" for all purposes within its field of applicability. Its big cousin, General Relativity, has a wider field of applicability, but reduces to SR as appropriate.

SR provides a way for you to predict the discrepancy (departure from simultaneity) that I will measure, given your own measurements and knowledge of our relative velocities. Such discrepancies will in general be small, and will never be wild enough to make causality run backwards: if you perceive that event A happens before event B, but I perceive that event B happens before event A, then events A and B must be separated far enough in space that no light-speed signal could travel between them. The lack of simultaneity does not imply causal chaos.


if event A happens to be internal to me personally, and some external event is B, and I measure the two as simultaneous: then, depending on your state of motion relative to me, you might well find that B precedes A, is simultaneous with A, or follows A - that is: my "now" (the set of all events simultaneous with me-here-now) is not necessarily your "now". Every observer, in motion relative to me, has a "now" that's different from mine; and SR tells us how to cross-correlate their features reliably.


the whole notion of "now" being all that exists, and the entire Universe being a process of that "now" unfolding, is a crock. Given enough observers moving in enough directions at high enough speeds, we could map substantial portions of reality in full 4D, not just 3D + time "slices".


determinism is true, "free will" is an illusory process of reconciling what has just happened with what is about to happen, the only possible future I have is the one I will actually end up experiencing, and I really am more like a long 4D pink worm tapering down to a single fertilized egg at one end and (hopefully) dispersing into the tree roots at the other, than like the 3D ape-shaped entity I generally appear to be.


what is it, exactly, that's apparently engaged in moving along this worm from the sharp end to the dispersed end, and waving the frilly bits on the side about along the way, what is that motion relative to, and is there a way I can slow it down so I can get a decent look around?

Am I, in fact, akin to a 3D pinball whizzing through a 4D playfield at lightspeed?

Also: is there a point-like "me" physically bouncing around inside various bits of brain at any given instant (like Jim Carrey and Kate Winslet in "Eternal Sunshine of the Spotless Mind"), or am I a little localized cloud of "pretty-much-here, pretty-much-now"? If the latter, what's my approximate time-wise "thickness" in milliseconds?

I'm not currently smoking anything, and have been musing on this stuff since well before I ever was :-)
posted by flabdablet at 8:34 PM on May 13, 2007

Do your deja vu seem to have a theme? I know this is weird, but many of mine seem to involve donuts for some reason. I have no idea why.
posted by rcavett at 8:36 PM on May 13, 2007

Not to threadjack, but I have this dream all the time and as a result have a pretty weird phobia about anything to do with teeth and the falling out/extraction thereof. I didn't know it was so common.
posted by ScarletSpectrum

Very common. I have that dream once in a while. I think sometimes it's caused by griding my teeth. The pressure creates a dream that my teeth are breaking.

Some people say that it means you are afraid of losing something, or are experiencing a feeling of loss. I think I am experiencing a feeling of teeth grinding. :)
posted by The Deej at 11:20 PM on May 13, 2007

Response by poster: This thread rocks. Thanks for all the interesting theories!

We're basically looking at:

1. Brains just do this; it's a glitch.

2. Some mysterious aspect of time/space/reality is somehow involved.

3. Consciousness is weird.
posted by chuckdarwin at 3:55 AM on May 14, 2007

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