The average 20 year old knows between 27,000 and 52,000 different words.

一般一個 20 歲的人認識 27,000 至 52,000 個不同的字。

By age 60, that number averages between 35,000 and 56,000.

到 60 歲時，該數目一般落在 35,000 至 56,000 之間。

Spoken out loud, most of these words last less than a second.

將這些字唸出來的話，大部份的字花不到一秒鐘。

So with every word, the brain has a quick decision to make: which of those thousands of options matches the signal?

聽到每個字時，大腦都必須快速做決定：上千個選項中有哪一個符合你聽到的聲音？

About 98% of the time, the brain chooses the correct word.

大約 98% 的時間，大腦會選出正確的字。

But how?

但是大腦是如何做到的呢？

Speech comprehension is different from reading comprehension, but it's similar to sign language comprehension — though spoken word recognition has been studied more than sign language.

言語理解不同於閱讀理解，但類似於手語理解 ── 雖然人們對口語辨識的研究比手語多。

The key to our ability to understand speech is the brain's role as a parallel processor, meaning that it can do multiple different things at the same time.

我們能夠理解言語的關鍵在於大腦能夠並行處理，意思是它可以同時處理很多不同的事。

Most theories assume that each word we know is represented by a separate processing unit that has just one job: to assess the likelihood of incoming speech matching that particular word.

大多數的理論假設我們所知道的每個字分別由只負責一項工作的處理單元來代表：該工作是評估傳入的言語和特定單字匹配的可能性。

In the context of the brain, the processing unit that represents a word is likely a pattern of firing activity across a group of neurons in the brain's cortex.

對大腦來說，代表單字的處理單元很可能是大腦皮層中 一組神經元的激發活動。

When we hear the beginning of a word, several thousand such units may become active, because with just the beginning of a word, there are many possible matches.

當我們聽到一個字的開頭音節時，可能會有幾千個處理單位活躍起來，因為一個字的開頭音節會有很多可能的匹配。

Then, as the word goes on, more and more units register that some vital piece of information is missing and lose activity.

繼續講字的其他音節時，更多的單元會發現缺乏某個重要的訊息，隨之失去活性。

Possibly well before the end of the word, just one firing pattern remains active, corresponding to one word.

可能在字唸完之前，只有一個處理單位保持活躍，並對應於一個字。

This is called the "recognition point."

這就是所謂的「識別點」。

In the process of honing in on one word, the active units suppress the activity of others, saving vital milliseconds.

在琢磨一個字的過程中，活躍的單位會抑制其他單位的活動，省下重要的毫秒。

Most people can comprehend up to about 8 syllables per second.

大多數的人每秒最多可以理解 8 個音節。

Yet, the goal is not only to recognize the word, but also to access its stored meaning.

但是，目標不只是辨識那個字，還要找出它的內在含義。

The brain accesses many possible meanings at the same time, before the word has been fully identified.

在某個字還沒完全被辨識出之前，大腦會同時找出許多可能的字義。

We know this from studies which show that even upon hearing a word fragment — like "cap"— listeners will start to register multiple possible meanings, like captain or capital, before the full word emerges.

我們從研究中了解到， 即使只是聽到字的片段 — 譬如 「首」— 聽者也會開始找多種可能的字義，比如「首領」或「首都」， 在整個字唸完前就會這麼做。

This suggests that every time we hear a word, there's a brief explosion of meanings in our minds, and by the recognition point the brain has settled on one interpretation.

這間接說明著我們每次聽到一個字時，腦中會很快地迸出許多字義，到達識別點時， 大腦已選中一個字義。

The recognition process moves more rapidly with a sentence that gives us context than in a random string of words.

如果提供有上下文的句子，而不是隨機一串單字時， 識別過程的速度會加快。

Context also helps guide us towards the intended meaning of words with multiple interpretations, like "bat," or "crane," or in cases of homophones like "no" or "know."

上下文也會引導我們了解具有多種解釋的字的正確意思，例如「蝙蝠 (球棒)」 或「吊車 (鶴)」，或在同音詞的情況下， 例如 "no (不)" 或是 "know (知道)"。

For multilingual people, the language they are listening to is another cue, used to eliminate potential words that don't match the language context.

對於會多種語言的人而言， 他們正在聽的語言是另一種提示，能夠幫他們排除不符合這個語言可能會出現的單字。

So, what about adding completely new words to this system?

那麼，如果要在這個系統中加入全新的單字呢？

Even as adults, we may come across a new word every few days.

即便是成年人，也有可能每隔幾天就會遇到一個新的單字。

But if every word is represented as a fine-tuned pattern of activity distributed over many neurons, how do we prevent new words from overwriting old ones?

但是，如果每個字都被視為一種精細的活動模式，且分佈在許多神經元上，我們如何避免新的單字覆蓋舊的單字呢？

We think that to avoid this problem, new words are initially stored in a part of the brain called the hippocampus, well away from the main store of words in the cortex, so they don't share neurons with others words.

我們認為，為了避免這個問題，新的字會先存在大腦海馬迴中，離大腦皮層中的主要單字儲存區很遠，所以它們不會和其他單字共用神經元。

Then, over multiple nights of sleep, the new words gradually transfer over and interweave with old ones.

經由多個夜晚的睡眠，新的單字會逐漸轉移過來， 和舊的單字交織在一起。

Researchers think this gradual acquisition process helps avoid disrupting existing words.

研究者認為， 這種緩慢獲得新字的過程有助於避免干擾現有的單字。

So in the daytime, unconscious activity generates explosions of meaning as we chat away.

所以在白天聊天時，無意識的神經元活動會迸出許多字義來。

At night, we rest, but our brains are busy integrating new knowledge into the word network.

到了晚上，我們在休息，但是大腦忙著將新知識整合到單字網絡中。

When we wake up, this process ensures that we're ready for the ever-changing world of language.

這個過程確保我們醒來時，已經為不斷改變的語言世界做好準備了。

At TED, we're passionate about the human capacity to share ideas.

在 TED，我們對人們分享知識的能力充滿熱情。

That's why the TED-Ed team created a program to help you mine your life experience for ideas and stories worth sharing, and then craft those experiences into compelling talks.

因此，TED-Ed 團隊創造了一個計畫來協助你挖掘你的生活經驗，以獲取值得分享的想法和故事，然後將這些經驗轉化為引人入勝的演講。

It's called TED Master Class, and you can learn more and download the app at ted.com/masterclass.

這個計畫叫作 TED Master Class，你可以在 ted.com/masterclass 下載程式並了解更多。