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  • You hear the gentle lap of waves,

    你聽見輕柔的海浪聲

  • the distant cawing of a seagull.

    和遠處海鷗的叫聲

  • But then an annoying whine interrupts the peace,

    但是突然一陣哀鳴聲擾亂了平靜

  • getting closer, and closer, and closer.

    聲音越來越近,越來越近

  • Until...whack!

    直到 ...... 啪!

  • 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

    成功識別並且定位聲音來源

  • is possible thanks to the auditory system.

    都多虧於聽覺系統

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

    系統有兩大組成:耳朵和大腦

  • 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

  • To understand how that works,

    為了理解運作過程

  • 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

  • The source of a sound creates vibrations

    聲音的來源製造出震動

  • that travel as waves of pressure through particles in air,

    形成聲波穿透空氣中的粒子

  • liquids,

    或是液體

  • or solids.

    和固體

  • But our inner ear, called the cochlea,

    但是我們的內耳,稱為耳蝸

  • is actually filled with saltwater-like fluids.

    其實填滿了像是鹹水的液體

  • 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

  • wherever they're coming from,

    轉換為液體中的波動

  • into waves in the fluid.

    無論他們來自哪裡

  • The solution is the eardrum, or tympanic membrane,

    解決方式是藉由中耳,或稱為鼓膜

  • and the tiny bones of the middle ear.

    以及中耳的細小骨頭

  • 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.

    耳蝸中液體的壓力波

  • When sound enters the ear canal,

    當聲音進到耳道

  • 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

  • Once there,

    一旦抵達

  • 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.

    他們像是波浪般在耳蝸中來回

  • 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

  • called stereocilia,

    特有構造

  • 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

  • into the auditory nerve,

    遊走到聽覺神經

  • 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,

    當一種聲音使基底膜震動時

  • not every hair cell moves -

    並非所有毛髮細胞都會移動

  • 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.

    這其中牽涉了一些精細的操作

  • At one end, the basilar membrane is stiff,

    在一端,基底層是堅硬的

  • 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

  • The other is more flexible,

    另一端則較為彈性

  • 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,

    會震動基底層不同的位置

  • like playing different keys on a piano.

    就好比按下鋼琴不同的按鍵

  • But that's not all that's going on.

    但旅程還沒結束

  • 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.

    識別聲音的來源

  • 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

  • to locate the source in space.

    來定位空間中的聲音來源

  • 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,

    告知我們聲音為何的運動軌跡

  • and information about where it is in space.

    以及它在空間中的位置資訊

  • Not everyone has normal hearing.

    並非所有人都有正常的聽力

  • 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

  • so they no longer vibrate.

    讓他們不再能夠震動

  • And with tinnitus,

    至於耳鳴

  • the brain does strange things

    大腦做出奇怪的事

  • 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

  • But when it does work,

    但是當一切正常運作時

  • 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

  • into precisely tuned electrical impulses

    轉換為精確的電子脈衝

  • that distinguish claps, taps, sighs, and flies.

    區別出拍手聲、水龍頭、嘆息聲和蒼蠅

You hear the gentle lap of waves,

你聽見輕柔的海浪聲

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B2 中高級 中文 美國腔 TED-Ed 聲音 液體 耳朵 大腦 毛髮

【TED-Ed】為什麼聽得見?聽力科學大解密 (The science of hearing - Douglas L. Oliver)

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    April Lu 發佈於 2018 年 07 月 11 日
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