It's that shadowy feeling you get when a situation seems familiar.

這是一種當你處在一個似曾相似的情況下會有的模糊感覺。

A scene in a restaurant plays out exactly as you remember.

腦袋浮出一幕，跟你記憶裡的餐廳相同。

The world moves like a ballet you've choreographed, but the sequence can't be based on a past experience because you've never eaten here before.

整個世界像跳起了芭蕾舞，而你就是編舞者，但因為你從沒在這吃過飯，所以不能根據過去的經驗來跳。

This is the first time you've had clams.

這是你第一次吃蛤蜊。

So, what's going on?

究竟是怎麼回事？

Unfortunately, there isn't one single explanation for déjà vu.

可惜目前既視感沒有單一的解釋。

The experience is brief and occurs without notice, making it nearly impossible for scientists to record and study it.

這個感覺很短暫，且會在沒有預料下發生，讓科學家幾乎沒辦法紀錄和研究。

Scientists can't simply sit around and wait for it to happen to them ⏤ this could take years!

總不能讓科學家整天坐在那等待既視感發生，有可能要花好幾年！

It has no physical manifestations, and in studies, it's described by the subject as a sensation or feeling.

既視感沒有具體的證據，且在研究中，人們也總是把它歸類為一種感覺或知覺。

Because of this lack of hard evidence, there's been a surplus of speculation over the years.

因為缺乏確鑿的證據，多年來都充斥著各種臆測。

Since Emile Boirac introduced déjà vu as a French term meaning "already seen", more than 40 theories attempt to explain this phenomenon.

從埃米勒·博伊萊克將既視感用法文定義為「似曾相識」後，有超過 40 種理論試圖解釋這個現象。

Still, recent advancements in neuroimaging and cognitive psychology narrow down the field of prospects.

然而，近代的神經成像和認知心理學的發展壓縮了這個領域的可能性。

Let's walk through three of today's more prevalent theories using the same restaurant setting for each.

讓我們套用前面餐廳的假設，用三種目前最普遍的說法來解釋。

First up is dual processing.

首先是雙重歷程理論。

We'll need an action.

用一個動作解釋。

Let's go with a waiter dropping a tray of dishes.

服務生打翻了一盤的菜餚。

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.

隨著畫面出現，你的腦半球開始處理一連串的資訊： 服務生揮舞雙臂、大喊求援、義大利麵的香味。

Within milliseconds, this information zips through pathways and is processed into a single moment.

在千分之一秒內，這個訊息透過路徑迅速穿梭， 最後合為一個獨立的動作。

Most of the time, everything is recorded in-sync.

大多數的時間，所有事都會被同步記錄在大腦。

However, this theory asserts that déjà vu occurs when there's a slight delay in information from one of these pathways.

這個理論主張若有資訊在大腦途徑之中出現些微延誤，就會出現既視感。

The difference in arrival times causes the brain to interpret the late information as a separate event.

訊息抵達的時間差會使大腦將晚期的資訊解讀成獨立的事件。

When it plays over the already-recorded moment, it feels as if it's happened before because, in a sense, it has.

當大腦播放已記錄過的記憶，感覺就像以前有發生過一樣，因為就某種情況而言，的確是如此。

Our next theory deals with a confusion of the past rather than a mistake in the present.

下個理論是處理過去的混淆，而不是現在的錯誤。

This is the hologram theory, and we'll use that tablecloth to examine it.

這就是全像原理，我們用這張桌布來檢視它。

As you scan its squares, a distant memory swims up from deep within your brain.

你細看上頭的格紋，一段模糊的回憶從你的大腦深處浮現。

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.

根據這個理論，是因為記憶是以全像圖的形式儲存在腦中，你只需要一個片段就能看見全部。

Your brain has identified the tablecloth with one from the past, maybe from your grandmother's house.

你的大腦認為以前看過這張桌布，也許和奶奶家裡的是同一張。

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.

然而你並沒有想起你在奶奶家中見過這圖案，大腦是喚起了一段久遠的記憶，卻沒有辨認出它。

This leaves you stuck with familiarity, but no recollection.

這讓你產生熟悉感，卻毫無記憶。

Although you've never been in this restaurant, you've seen that tablecloth, but are just failing to identify it.

雖然你從沒去過這間餐廳，但有看過那張桌布，可是卻無法辨認它。

Now, look at this fork.

接下來看看這把叉子。

Are you paying attention?

你有專心看嗎？

Our last theory is divided attention, and it states that déjà vu occurs when our brain subliminally takes in an environment while we're distracted by one particular object.

最後是分散性專注力理論，主張既視感發生於我們分心在某個物件上時，大腦下意識接受了外在環境。

When our attention returns, we feel as if we've been here before.

當我們注意力回歸時，我們會覺得自己以前有來過這裡。

For example, just now, you focused on the fork and didn't observe the tablecloth or the falling waiter.

例如剛才你正專注盯著叉子，完全沒有注意到桌布和要跌倒的服務生。

Although your brain has been recording everything in your peripheral vision, it's been doing so below conscious awareness.

你的大腦以邊緣視野記錄了一切，但都是在自我知覺的狀況下進行。

When you finally pull yourself away from the fork, you think you've been here before, because you have, you just weren't paying attention.

當你終於把注意力從叉子上移開，你會以為你有來過這裡， 因為你有過，只是沒注意到而已。

While all three of these theories share the common features of déjà vu, none of them propose to be the conclusive source of the phenomenon.

儘管以上三種理論皆有掌握既視感常見的特點，卻沒有任何一個能提出這個現象的確定來源。

Still, while we wait for researchers and inventers to come up with new ways to capture this fleeting moment, we can study the moment ourselves.

我們期待研究員與發明家能提出更好的方法，來捕捉這稍縱即逝的瞬間，我們也能自行研究此現象。

After all, most studies of déjà vu are based on first-hand accounts, so why can't one be yours?

畢竟多數既視感的研究都來自第一手的描述，那何不把你的經驗分享出來？

The next time you get déjà vu, take a moment to think about it.

當既視感再度出現時，花點時間想看看。

Have you been distracted?

你是否分心了？

Is there a familiar object somewhere?

四周有沒有熟悉的景物？

Is your brain just acting slow?

是你的大腦突然慢半拍嗎？

Or is it something else?

還是另有其因？