Name: 【TED-Ed】為什麼聽得見？聽力科學大解密 (The science of hearing - Douglas L. Oliver)
Uploaded: 2018-07-11T21:01:04.000Z
Duration: 5 min 17 s

But then an annoying whine interrupts the peace,

但是突然一陣哀鳴聲擾亂了平靜

You dispatch the offending mosquito,  and calm is restored.

你處理了那隻惱人的蚊子，重拾了寧靜

How did you detect that noise from afar and target its maker with such precision?

你是如何在遠處就偵測到噪音，並且精準瞄準到噪音來源的呢？

The ability to recognize sounds  and identify their location

is possible thanks to the auditory system.

That's comprised of two main parts:  the ear and the brain.

The ear's task is to convert sound energy into neural signals;

耳朵負責把聲能轉換為神經訊號

the brain's is to receive and process  the information those signals contain.

大腦則負責接收並處理這些訊號涵蓋的訊息

we can follow a sound  on its journey into the ear.

我們可以跟隨聲音進到耳朵的旅程

that travel as waves of pressure  through particles in air,

is actually filled  with saltwater-like fluids.

So, the first problem to solve  is how to convert those sound waves,

所以第一個要解決的問題，是如何把這些聲波

The solution is the eardrum,  or tympanic membrane,

解決方式是藉由中耳，或稱為鼓膜

Those convert the large movements of the eardrum

這些構造將鼓膜的大動作轉換成

into pressure waves  in the fluid of the cochlea.

it hits the eardrum and makes it vibrate  like the head of a drum.

它會拍擊鼓膜，使之如同鼓面般震動

The vibrating eardrum jerks a bone  called the hammer,

震動的鼓膜拉扯一支稱為錘子的骨頭

which hits the anvil and moves the third bone called the stapes.

它再敲擊砧骨，移動第三個稱作鐙骨的骨頭

Its motion pushes the fluid  within the long chambers of the cochlea.

它的動作會推動耳蝸長道中的液體

the sound vibrations have finally been converted into vibrations of a fluid,

聲音的震動終於被轉換成了液體中的震動

and they travel like a wave  from one end of the cochlea to the other.

A surface called the basilar membrane  runs the length of the cochlea.

一個稱作基底膜的表層位在耳蝸的底部

It's lined with hair cells that have  specialized components

內部排列有許多毛髮細胞，其中有稱為硬纖毛的

which move with the vibrations of the cochlear fluid and the basilar membrane.

會隨著耳蝸液體和基底膜的震動而移動

This movement triggers a signal  that travels through the hair cell,

這項動作會觸發訊號，透過毛髮細胞

then onward to the brain,  which interprets it as a specific sound.

然後上達大腦，才會將之翻譯成一種特定聲音

When a sound makes  the basilar membrane vibrate,

only selected ones,  depending on the frequency of the sound.

取決於聲音的頻率，只有幾個特定的會移動

This comes down to some fine engineering.

At one end,  the basilar membrane is stiff,

vibrating only in response to short wavelength, high-frequency sounds.

只會對短波長、高頻率的聲音做出震動反應

vibrating only in the presence of longer wavelength, low-frequency sounds.

只對長波長、低頻率的聲音有反應

So, the noises made by the seagull  and mosquito

因此，海鷗和蚊子製造出來的聲音

vibrate different locations  on the basilar membrane,

The brain still has another  important task to fulfill:

大腦還有另一項重要的任務要達成：

identifying where a sound is coming from.

For that, it compares the sounds  coming into the two ears

為了做到這點，它會比較進到兩耳的聲音

A sound from directly in front of you will reach both your ears at the same time.

來自你正前方的聲音會同時到達你的雙耳

You'll also hear it at the same intensity  in each ear.

你的兩耳聽見聲音的強度也會相同

However, a low-frequency sound  coming from one side

然而，一個來自側邊的低頻聲音

will reach the near ear microseconds  before the far one.

會早一百萬分之一秒抵達較近的耳朵，才到較遠的

And high-frequency sounds will sound more intense to the near ear

高頻的聲音在近耳中聽起來會強度較高

because they're blocked  from the far ear by your head.

因為他們和遠耳之間有你的頭隔絕

These strands of information  reach special parts of the brainstem

這些一條條訊息抵達腦幹中特別的部位

that analyze time and intensity differences between your ears.

那區負責分析兩耳間的時間和強度差異

They send the results of their  analysis up to the auditory cortex.

他們將分析出的結果傳送到聽覺外皮

Now, the brain has  all the information it needs:

現在，大腦有所有需要的訊息了：

the patterns of activity  that tell us what the sound is,

and information about  where it is in space.

Hearing loss is the third most common  chronic disease in the world.

聽力喪失是世界上第三常見的慢性疾病

Exposure to loud noises  and some drugs can kill hair cells,

曝露於大噪音和一些藥物皆會殺死毛髮細胞

preventing signals from traveling  from the ear to the brain.

使得訊號無法從耳朵傳達到大腦

Diseases like osteosclerosis freeze  the tiny bones in the ear

如骨硬化病這種疾病會硬化耳中的小骨頭

to make us think there's a sound  when there isn't one.

讓我們在沒有聲音的時候以為有聲音

our hearing is an incredible,  elegant system.

我們的聽力是個驚奇、優雅的系統

Our ears enclose a fine-tuned piece  of biological machinery

我們的耳朵具有精確的生理結構

that converts the cacophony of vibrations  in the air around us

能夠將我們周遭空氣中的一切雜音震動

that distinguish claps, taps,  sighs, and flies.

區別出拍手聲、水龍頭、嘆息聲和蒼蠅