Explaining Why It's Not Just Déjà Vu (All Over Again)
No matter how many times you experience déjà vu in your life, it never ceases to be a bizarre occurrence. 
While science has pretty much explained all the mystery out of awesome and strange things like the Northern Lights, eclipses, and those Magic Eye posters, it has failed to come up with a thorough explanation for déjà vu. 
Anne Cleary, a psychologist at Colorado State University, decided to put to the test that strange feeling where you could swear you had already experienced a present situation.
Cleary's theory is that déjà vu is connected to human recognition memory, which allows us to recognize that something happening right now has also happened before. There are two forms of human recognition memory: recollection and familiarity.
As you may have guessed (or could you almost swear somebody had told you this before?)
Recollection memory means you know why a particular moment seems familiar
—you can pinpoint the exact time or place when it happened before. For instance, a song comes on in a club and you recognize it because you remember dancing to that same song at a different club the Saturday before.
Familiarity-based memory is that nagging feeling that you know something is familiar but can't name why. That would be having a song come on in a club that you know you've heard before but have no idea when or where. The latter is where déjà vu falls.
To test familiarity-based recognition, Cleary gave her subjects a list of celebrity names. 
Later, they were shown a variety of celebrity photographs. Some of the faces had been on the list of names and some had not. Subjects were asked to identify the people in the photographs and indicate how likely it was that the celebrity's names had been on the earlier list. According to the report, "Even when the volunteers were unable to identify a celebrity by photo, they had a sense of which names they had studied earlier and which they had not. That is, they couldn't identify the source of their familiarity with the celebrity, but they knew the celebrity was familiar to them." Clearly ran the test again using names and photos of famous landmarks in place of celebrities and had similar results.
A bit of the memory was there, but, it was hazy and subjects were unable to connect it to the new experience.
Cleary worked off the idea that
memory is often stored in our brain as individual elements, like a jigsaw puzzle. When you fit all the pieces together correctly, your brain produces a complete, coherent memory. Oftentimes though, if certain elements of a new situation match certain elements of a previously stored memory, your brain will mix up the puzzle and convince you that you have actually experienced the present situation before. The more the elements overlap, the bigger the sense of déjà vu.
The second prong in the study was to find out what these trigger elements are. Cleary designed an experiment in which she gave volunteers a list of words to study. Afterward, they were given a word-recognition test. Some of the words had been on the list, some not, and some simply resembled words on the list (for example "lady" in place of "eighty"). 
When confronted with a new, similar-sounding word, subjects identified a sense of familiarity with it, even when they could not remember what the original, similar word on the list was. A parallel experiment using geometric shapes instead of words led to similar results.
Cleary's conclusion is that visual and audio fragments are able to create the sensation that an entire scene has been viewed before, even though it is actually brand new.
"Many parallels between explanations of déjà vu and theories of human recognition memory exist," Cleary concludes. "Theories of familiarity-based recognition and the laboratory methods used to study it may be especially useful for elucidating the processes underlying déjà vu experiences."
Maybe science is catching up, after all.
By Rachel Durfee
Popular Science
Did you hear 'em talkin' 'bout it on the radio
Did you try to read the writing on the wall
Did that voice inside you say I've heard it all before
It's like Deja Vu all over again
Day by day I hear the voices rising
Started with a whisper like it did before
Day by day we count the dead and dying
Ship the bodies home while the networks all keep score
Did you hear 'em talkin' 'bout it on the radio
Could your eyes believe the writing on the wall
Did that voice inside you say I've heard it all before
It's like Deja Vu all over again
One by one I see the old ghosts rising
Stumblin' 'cross Big Muddy
Where the light gets dim
Day after day another Momma's crying
She's lost her precious child
To a war that has no end
Did you hear 'em talkin' 'bout it on the radio
Did you stop to read the writing at The Wall
Did that voice inside you say I've seen this all before
It's like Deja Vu all over again
It's like Deja Vu all over again
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