Have you experienced deja-vu?
It's that shadowy feeling you get
when a situation seems familiar.
A scene in a restaurant plays out
exactly as you remember.
The world moves like a ballet
you choreographed,
but the sequence can't be based on a past experience
because you've never eaten here before.
This is the first time you've had clams,
so what's going on?
Unfortunately there isn't one single explanation
for deja-vu.
The experience is brief
and occurs without notice,
making it nearly impossible
for scientists to record and study it.
Scientists can't sit around
and wait for it to happen to them -
this could take years.
It has no physical manifestations
and in studies, it's described by the subject
as a sensation or feeling.
Because of this lack of hard evidence,
there's been a surplus of speculation over the years.
Since Emile Boirac introduced deja-vu
as a French term meaning already seen,
more than 40 theories attempt
to explain this phenomenon.
Still, recent advancements in neuroimaging
and cognitive psychology narrow down
the field of prospects.
Let's walk through three of today's more prevalent theories,
using the same restaurant setting for each.
First stop is dual processing.
We'll need an action.
Let's go with a waiter dropping a tray of dishes.
As the scene unfolds,
your brain's hemispheres process
a flurry of information:
the waiter's flailing arms,
his cry for help,
the smell of pasta.
Within milliseconds, this information zips
through pathways
and is processed into a single moment.
Most of the time, everything is recorded in-sync.
However, this theory asserts
that deja-vu occurs when there's a slight delay
in information from one of these pathways.
The difference in arrival times
causes the brain to interpret the late information
as a separate event.
When it plays over the already-recorded moment,
it feels as if it's happened before
because, in a sense, it has.
Our next theory deals with the confusion of the past
rather than a mistake in the present.
This is the hologram theory,
and we'll use that tablecloth to examine it.
As you scan its squares,
a distant memory swims up
from deep within your brain.
According to the theory,
this is because memories are stored
in the form of holograms,
and in holograms,
you only need one fragment
to see the whole picture.
Your brain has identified the tablecloth
with one from the past,
maybe from your grandmother's house.
However, instead of remembering
that you've seen this pattern at your grandmother's,
your brain has summoned up the old memory
without identifying it.
This leaves you stuck with familiarity
but no recollection.
Although you've never been in this restaurant,
you've seen that tablecloth
but are just failing to identify it.
Now, look at this fork.
Are you paying attention?
Our last theory is divided attention,
and it states that deja-vu occurs
when our brain subliminally takes in an environment
while we're distracted by one particular object.
When our attention returns,
we feel as if we've been here before.
For example, just now you focused on the fork
and didn't observe the tablecloth
or the falling waiter.