听觉背后美丽而神秘的科学 Jim Hudspeth: The beautiful, mysterious science of how you hear

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演员: Jim Hudspeth


台词
Can you hear me OK?
各位可以听到我的声音吗?
Audience: Yes.
观众:可以。
Jim Hudspeth: OK. Well, if you can, it's really amazing,
吉姆 · 赫兹佩斯:好的。 如果你能听见,那真是不可思议。
because my voice is changing the air pressure where you sit
因为我的声音会改变你身边的气压,
by just a few billionths of the atmospheric level,
改变程度只有大气压的 几十亿分之一而已,
yet we take it for granted
但我们都理所当然地觉得
that your ears can capture that infinitesimal signal
耳朵能捕捉到这个 微乎其微的信号,
and use it to signal to the brain the full range of auditory experiences:
并将丰富的听觉体验传递给大脑:
the human voice, music, the natural world.
人声,音乐,大自然的声音。
How does your ear do that?
你的耳朵是怎样做到的呢?
And the answer to that is:
答案就是:
through the cells that are the real hero of this presentation --
通过细胞,也是本次演讲 真正的主角——
the ear's sensory receptors,
耳朵的感觉接收器,
which are called "hair cells."
被称为“毛细胞”。
Now, these hair cells are unfortunately named,
毛细胞虽然叫毛细胞,
because they have nothing at all to do with the kind of hair
但和我头顶越来越少的“毛”
of which I have less and less.
一点关系都没有。
These cells were originally named that by early microscopists,
早期的显微镜学家发现,
who noticed that emanating from one end of the cell
这些细胞的一端长有一小撮纤毛,
was a little cluster of bristles.
毛细胞的名字便由此而来。
With modern electron microscopy, we can see much better
有了现代的电子显微镜, 我们能更清楚地看见
the nature of the special feature that gives the hair cell its name.
让毛细胞得名的这个特征的细节,
That's the hair bundle.
那是毛束。
It's this cluster of 20 to several hundred fine cylindrical rods
它由二十到几百个 纤细的圆锥形小杆组成,
that stand upright at the top end of the cell.
直立在细胞的顶端。
And this apparatus is what is responsible for your hearing me right this instant.
正是这个器官, 让你此刻能听见我说话。
Now, I must say that I am somewhat in love with these cells.
不得不承认,我对这些细胞 多少有些着迷。
I've spent 45 years in their company --
它们陪伴了我 45 年——
(Laughter)
(笑声)
and part of the reason is that they're really beautiful.
原因之一是它们非常美丽,
There's an aesthetic component to it.
有一种美感。
Here, for example, are the cells
比如说,这是一只普通的鸡
with which an ordinary chicken conducts its hearing.
用来听声音的细胞。
These are the cells that a bat uses for its sonar.
这些是蝙蝠的声呐细胞。
We use these large hair cells from a frog for many of our experiments.
我们在许多实验中都采用 这些取自青蛙的大型毛细胞。
Hair cells are found all the way down to the most primitive of fishes,
一直到最原始的鱼类中, 都能发现毛细胞的身影,
and those of reptiles often have this really beautiful,
而爬行动物的毛细胞 通常呈现出这种非常美丽的、
almost crystalline, order.
近乎晶体状的有序结构。
But above and beyond its beauty,
但除去它的美丽不提,
the hair bundle is an antenna.
这个毛束是一根天线。
It's a machine for converting sound vibrations into electrical responses
它是一台将声音振动 转换成电学信号的机器,
that the brain can then interpret.
大脑随后可以破译这些电信号。
At the top of each hair bundle, as you can see in this image,
在这张图里能看到, 在每一簇毛束的顶上,
there's a fine filament connecting each of the little hairs,
都有一根纤细的丝,
the stereocilia.
把每根叫做静纤毛 的小纤毛连接起来——
It's here marked with a little red triangle.
就是红色小三角所指的地方。
And this filament has at its base a couple of ion channels,
这条细丝的根部 有若干个离子通道,
which are proteins that span the membrane.
就是一种跨越细胞膜的蛋白。
And here's how it works.
它的工作原理是这样的。
This rat trap represents an ion channel.
这个“捕鼠夹”代表了一个离子通道。
It has a pore that passes potassium ions and calcium ions.
它有个开孔, 能让钾离子和钙离子通过。
It has a little molecular gate that can be open, or it can be closed.
它有个小小的分子门, 可以打开,也可以关上。
And its status is set by this elastic band which represents that protein filament.
它的状态是由这根代表了 蛋白连接丝的橡皮带设定的。
Now, imagine that this arm represents one stereocilium
想象一下,这条手臂 代表了一根静纤毛,
and this arm represents the adjacent, shorter one
而这条手臂则代表了旁边 更短的一根静纤毛,
with the elastic band between them.
它们之间由橡皮带连接。
When sound energy impinges upon the hair bundle,
当声音能量冲击到毛束时,
it pushes it in the direction towards its taller edge.
它会将毛束朝更高的一端推动。
The sliding of the stereocilia puts tension in the link
纤毛滑动,使得连接丝中产生张力,
until the channels open and ions rush into the cell.
直到通道打开,离子冲进细胞里。
When the hair bundle is pushed in the opposite direction,
当毛束被朝反方向推动时,
the channels close.
离子通道就关上了。
And, most importantly,
最重要的是,
a back-and-forth motion of the hair bundle,
声波会让毛束前后来回运动,
as ensues during the application of acoustic waves,
离子通道就会交替着
alternately opens and closes the channel,
打开、关闭,
and each opening admits millions and millions of ions into the cell.
每次打开都会让 数以百万的离子进入细胞。
Those ions constitute an electrical current
这些离子形成电流,
that excites the cell.
让细胞兴奋。
The excitation is passed to a nerve fiber,
这种兴奋状态被传递给神经纤维,
and then propagates into the brain.
随后传导进大脑。
Notice that the intensity of the sound
这个反应的程度
is represented by the magnitude of this response.
代表了声音的强度。
A louder sound pushes the hair bundle farther,
更响的声音会把毛束推得更远,
opens the channel longer,
离子通道打开的时间更久,
lets more ions in
进入细胞的离子更多,
and gives rise to a bigger response.
反应也就更强。
Now, this mode of operation has the advantage of great speed.
这种运行模式的好处是速度极快。
Some of our senses, such as vision,
我们的某些感官,比如视觉,
use chemical reactions that take time.
利用的是耗时的化学反应。
And as a consequence of that,
因此,如果我以
if I show you a series of pictures at intervals of 20 or 30 per second,
每秒 20 到 30 张的间隔 给你看一系列图片,
you get the sense of a continuous image.
你就会产生看到了 连续图像的感觉。
Because it doesn't use reactions,
因为毛细胞不使用化学反应,
the hair cell is fully 1,000 times faster than our other senses.
它比我们的其他感官 要快整整 1000 倍。
We can hear sounds at frequencies as great as 20,000 cycles per second,
我们能听到每秒高达 2 万个周期(2 万赫兹)的频率,
and some animals have ever faster ears.
而有些动物的耳朵更灵敏。
The ears of bats and whales, for example, can respond to their sonar pulses
比如说,蝙蝠和鲸鱼的耳朵
at 150,000 cycles a second.
能探测到它们每秒 15 万个周期 (15 万赫兹)的声呐信号。
But this speed doesn't entirely explain why the ear performs so well.
但这个速度并不能完全解释 为什么耳朵的性能如此出色。
And it turns out that our hearing benefits from an amplifier,
事实上,我们的听觉 得益于一种扩音器,
something called the "active process."
它被称为“有源放大 (active process)”。
The active process enhances our hearing
有源放大能增强我们的听力,
and makes possible all the remarkable features that I've already mentioned.
并让我刚刚提到过的 所有卓越性能得以实现。
Let me tell you how it works.
让我讲讲它的工作原理。
First of all, the active process amplifies sound,
首先,有源放大过程能放大声音,
so you can hear, at threshold, sounds that move the hair bundle
因此你能听见的最小声音
by a distance of only about three-tenths of a nanometer.
可以低到让毛束移动仅 0.3 纳米。
That's the diameter of one water molecule.
这相当于一个水分子的直径。
It's really astonishing.
非常惊人。
The system can also operate
这个系统也可以
over an enormously wide dynamic range.
在极其宽广的动态范围下运行。
Why do we need this amplification?
我们为什么需要这种扩音?
The amplification, in ancient times, was useful
在古时候,这种放大很有用,
because it was valuable for us to hear the tiger before the tiger could hear us.
因为赶在老虎听见我们之前, 听见老虎的声音是性命攸关的。
And these days, it's essential as a distant early warning system.
而在现代,它则是重要的 远距离早期预警系统。
It's valuable to be able to hear fire alarms
它有利于我们听见火警声,
or contemporary dangerous such as speeding fire engines or police cars or the like.
或者当代的危险信号, 如疾驰的救火车或警车之类。
When the amplification fails, our hearing's sensitivity plummets,
当扩音系统损坏时, 我们的听觉灵敏度会骤降,
and an individual may then need an electronic hearing aid
个体可能需要借助电子助听器
to supplant the damaged biological one.
以弥补损坏的生物听觉系统。
This active process also enhances our frequency selectivity.
有源放大过程也能增强 我们对频率的辨识。
Even an untrained individual can distinguish two tones
即使是未经训练的常人也可以区分
that differ by only two-tenths of a percent,
相差仅 0.2% 的两个音调,
which is one-thirtieth of the difference between two piano notes,
也就是相邻钢琴音调 差距的 30 分之一,
and a trained musician can do even better.
一位训练有素的音乐家 还能辨认得更准。
This fine discrimination is useful
这样精细的辨识能力
in our ability to distinguish different voices
有利于我们分辨不同人的声音,
and to understand the nuances of speech.
以及理解话语中细微的差别。
And, again, if the active process deteriorates,
同样的,如果有源放大的效果下降,
it becomes harder to carry out verbal communication.
言语交流将变得更加困难。
Finally, the active process is valuable in setting the very broad range
最后,有源放大过程有利于扩大
of sound intensities that our ears can tolerate,
耳朵能忍受的声音强度范围,
from the very faintest sound that you can hear, such as a dropped pen,
从能听见的最弱声响, 比如,笔掉在地上的声音,
to the loudest sound that you can stand --
到能忍受的最大声响,
say, a jackhammer or a jet plane.
比如,地钻或者喷气式飞机。
The amplitude of sounds spans a range of one millionfold,
声音强度的范围 可达 100 万倍之广,
which is more than is encompassed by any other sense
这个幅度超过了任何其他感官,
or by any man-made device of which I'm aware.
或是我所知的任何人造设备。
And again, if this system deteriorates,
同样,如果这个系统受损,
an affected individual may have a hard time
一个受其影响的人可能会很难
hearing the very faintest sounds
听见微弱的声响,
or tolerating the very loudest ones.
或忍受巨大的声响。
Now, to understand how the hair cell does its thing,
为了理解毛细胞如何履行职责,
one has to situate it within its environment within the ear.
我们得先把它置于 耳内的环境里。
We learn in school that the organ of hearing
上学时我们曾学过,听觉器官
is the coiled, snail-shaped cochlea.
是卷曲的、蜗牛状的耳蜗。
It's an organ about the size of a chickpea.
这个器官如同一颗鹰嘴豆那么大,
It's embedded in the bone on either side of the skull.
镶嵌在头骨两侧的骨头里。
We also learn that an optical prism
我们还学过,一个光学棱镜
can separate white light into its constituent frequencies,
能把白光分解成不同的组成频率,
which we see as distinct colors.
在我们眼里就是不同的颜色。
In an analogous way,
与之类似,
the cochlea acts as sort of an acoustic prism
耳蜗就像是一个声学棱镜,
that splits apart complex sounds into their component frequencies.
能把复杂的声音分解成 不同的组成频率。
So when a piano is sounded,
所以,在弹奏钢琴时,
different notes blend together into a chord.
不同的音符会混合成一个和弦。
The cochlea undoes that process.
耳蜗将这个过程逆转,
It separates them and represents each at a different position.
把声音分解,并将每一个 组成部分在不同位置表达出来。
In this picture, you can see where three notes --
在这张图里,你可以看见三个音符——
middle C and the two extreme notes on a piano --
中央 C 和钢琴两端的音符——
are represented in the cochlea.
在耳蜗内部被呈现的位置。
The lowest frequencies go all the way up to the top of the cochlea.
最低的频率会到达耳蜗的顶部。
The highest frequencies, down to 20,000 Hz,
高达 2 万赫兹的最高频率
go all the way to the bottom of the cochlea,
则会到达耳蜗的底部,
and every other frequency is represented somewhere in between.
所有其他频率都在中间 的某个地方表示出来。
And, as this diagram shows,
另外,如图所示,
successive musical tones are represented a few tens of hair cells apart
连续的音调在耳蜗表面的表达位置
along the cochlear surface.
相隔几十个毛细胞。
Now, this separation of frequencies
而今,这种频率的分离
is really key in our ability to identify different sounds,
对我们区分不同声音至关重要,
because very musical instrument,
因为每件乐器,
every voice,
每个人声,
emits a distinct constellation of tones.
都能发出一组与众不同的特定音调。
The cochlea separates those frequencies,
耳蜗将这些频率进行分离,
and the 16,000 hair cells then report to the brain
1 万 6 千个毛细胞 随之将每个频率的数量
how much of each frequency is present.
汇报给大脑。
The brain can then compare all the nerve signals
大脑接下来便将 所有的神经信号进行比对,
and decide what particular tone is being heard.
判断出听到了哪个特定音调。
But this doesn't explain everything that I want to explain.
但这还没有涵盖我想解释的一切。
Where's the magic?
其魔力在何处?
I told you already about the great things that the hair cell can do.
我已经为各位介绍了 毛细胞有多厉害。
How does it carry out the active process
那么它是如何进行有源放大,
and do all the remarkable features that I mentioned at the outset?
并完成我开始时 提到的所有非凡特性的?
The answer is instability.
答案是:不稳定性。
We used to think that the hair bundle was a passive object,
我们曾经认为, 毛束是一个被动物体,
it just sat there, except when it was stimulated.
没有外界刺激的时候, 它是静止不动的。
But in fact, it's an active machine.
但事实上,它是一个主动的机器。
It's constantly using internal energy to do mechanical work
它一直在使用内部能量 进行机械工作,
and enhance our hearing.
并增强我们的听力。
So even at rest, in the absence of any input,
即使在静息状态, 没有任何输入信号的情况下,
an active hair bundle is constantly trembling.
一根活跃的毛束 也一直不停地在颤动,
It's constantly twitching back and forth.
不停地前后抖动。
But when even a weak sound is applied to it,
但当哪怕是很微弱的声响接触到它时,
it latches on to that sound and begins to move very neatly
它便立刻揪住那个声响, 并开始步调一致地
in a one-to-one way with it,
和那个声音进行一对一的运动,
and by so doing, it amplifies the signal about a thousand times.
与此同时,也将信号 放大了约一千倍。
This same instability also enhances our frequency selectivity,
同样的不稳定性也能增强 我们对频率的辨识度,
for a given hair cell tends to oscillate best
因为某个毛细胞摆动的最佳频率,
at the frequency at which it normally trembles
一般是它在不受刺激时
when it's not being stimulated.
自然抖动的频率。
So, this apparatus not only gives us our remarkably acute hearing,
所以,这个“机器”不仅 让我们有了非常敏锐的听觉,
but also gives us the very sharp tuning.
还让我们能敏锐地分辨音调。
I want to offer you a short demonstration
关于这一点,
of something related to this.
我想为各位进行一段简短的演示。
I'll ask the people who are running the sound system
我会请负责音响系统的工作人员
to turn up its sensitivity at one specific frequency.
调高系统针对某个 特定频率的敏感度。
So just as a hair cell is tuned to one frequency,
就像毛细胞被调至某个特定频率,
the amplifier will now enhance a particular frequency in my voice.
现在扩音器会增强 我声音中的某个特定频率。
Notice how specific tones emerge more clearly from the background.
留意一下,特定的声调是如何 更清晰地从背景音里浮现出来。
This is exactly what hair cells do.
毛细胞的作用正是这样。
Each hair cell amplifies and reports one specific frequency
每个毛细胞会放大 并汇报某个特定频率,
and ignores all the others.
而忽略所有其他频率。
And the whole set of hair cells, as a group, can then report to the brain
整套毛细胞,作为一个组合, 随后便能向大脑汇报
exactly what frequencies are present in a given sound,
一个声音中具体包含了哪些频率,
and the brain can determine what melody is being heard
大脑就能依此判断 我们听到了什么旋律,
or what speech is being intended.
或是声音是在说什么。
Now, an amplifier such as the public address system
像广播系统这样的扩音器
can also cause problems.
也可能造成问题。
If the amplification is turned up too far,
如果增幅过度,
it goes unstable and begins to howl
它会变得不稳定,开始嚎叫,
or emit sounds.
或是发出杂音。
And one wonders why the active process doesn't do the same thing.
你或许会纳闷,为什么 有源放大不会发生同样的问题。
Why don't our ears beam out sounds?
我们的耳朵为什么不会发射声音?
And the answer is that they do.
而回答是:它们是会出声的。
In a suitably quiet environment, 70 percent of normal people
在一个足够安静的环境里, 70% 的正常人
will have one or more sounds coming out of their ears.
耳朵里会发出一种或多种声音。
(Laughter)
(笑声)
I'll give you an example of this.
让我给各位举个例子。
You will hear two emissions at high frequencies
你会听到来自正常人耳的
coming from a normal human ear.
两个高频率声响。
You may also be able to discern background noise,
你或许还能辨别出背景噪音,
like the microphone's hiss,
像是麦克风的嘶嘶声、
the gurgling of a stomach, the heartbeat, the rustling of clothes.
肚子的咕咕声、心跳声、 衣服的摩擦声。
(Hums, microphone hiss, dampened taps, clothes rustling)
(嗡嗡声、麦克风杂音、 水龙头的水声、衣物沙沙声)
This is typical.
这是比较典型的。
Most ears emit just a handful of tones,
大多数耳朵只会发出少数几种声调,
but some can emit as many as 30.
但有的能发出 30 种之多。
Every ear is unique, so my right ear is different from my left,
每只耳朵都是独特的, 所以我的右耳和我的左耳不同,
my ear is different from your ear,
我的耳朵和你的耳朵不同,
but unless an ear is damaged,
但除非耳朵受到损害,
it continues to emit the same spectrum of frequencies
它会在若干年,甚至数十年内,
over a period of years or even decades.
持续发出特定谱系的频率。
So what's going on?
这是怎么回事?
It turns out that the ear can control its own sensitivity,
事实上,耳朵能够控制 它自身的灵敏度,
its own amplification.
和自身的扩音幅度。
So if you're in a very loud environment, like a sporting event
如果你在一个很吵的环境里, 比如,体育赛事
or a musical concert,
或者音乐会现场,
you don't need any amplification,
你不需要对声音进行任何放大,
and the system is turned down all the way.
于是系统的扩音幅度就被调到最小。
If you are in a room like this auditorium,
如果你在像这个演讲厅 一样的房间里,
you might have a little bit of amplification,
你或许需要对声音进行少许放大,
but of course the public address system does most of the work for you.
不过当然了,广播系统 已经帮你完成了大部分工作。
And finally, if you go into a really quiet room
最后,如果你进入 一个非常安静的房间,
where you can hear a pin drop,
安静得落针可闻,
the system is turned up almost all the way.
那么系统的扩音幅度就会 被调到几乎是最大值。
But if you go into an ultraquiet room such as a sound chamber,
但如果你走进一个 超级安静的房间,比如说消音室,
the system turns itself up to 11,
系统会自动调到最大值,
it goes unstable
因而它会变得不稳定,
and it begins to emit sound.
于是开始发出声音。
And these emissions constitute a really strong demonstration
这些被释放的声音非常有力地展示了
of just how active the hair cell can be.
毛细胞有多活跃。
So in the last minute, I want to turn to another question that might come up,
那么在最后一分钟里,我想 谈谈一个各位可能会问的问题:
which is: Where do we go from here?
我们的研究之后将如何发展?
And I would say that there are three issues
我认为在未来,
that I would really like to address in the future.
我很想研究的课题有三个。
The first is: What is the molecular motor
其一:负责毛细胞
that's responsible for the hair cell's amplification?
扩音作用的分子马达是什么?
Somehow, nature has stumbled across a system
大自然似乎设法误打误撞地发现了
that can oscillate or amplify at 20,000 cycles per second,
一个能以 2 万赫兹,甚至更高的频率
or even more.
振动或扩音的系统。
That's much faster than any other biological oscillation,
这比任何别的生物振动都快,
and we would like to understand where it comes from.
我们也想弄明白它是怎么来的。
The second issue is how the hair cell's amplification is adjusted
第二个课题是,毛细胞的扩音作用
to deal with the acoustic circumstances.
是如何调节并匹配 周围的声学环境的。
Who turns the knob to increase or decrease the amplification
是谁转动旋钮, 在安静环境中增强扩音,
in a quiet or in a loud environment?
在吵闹环境中降低扩音的?
And the third issue is one that concerns all of us,
第三个课题和我们每个人息息相关,
which is what we can do about the deterioration of our hearing.
也就是针对听力衰退 我们能做些什么。
Thirty million Americans,
三千万美国人,
and more than 400 million people worldwide,
还有全世界范围内超过 4 亿人,
have significant problems on a daily basis
每天在嘈杂环境中、
with understanding speech in a noisy environment
或在电话里试图理解对话时,
or over the telephone.
都会明显感到困难。
Many have even worse deficits.
有些人的听力缺陷更加严重,
Moreover, these deficits tend to get worse with time,
甚至还会随着时间而进一步恶化,
because when human hair cells die,
因为当人体的毛细胞凋亡后,
they're not replaced by cell division.
它们不会通过细胞分裂得到补充。
But we know that nonmammalian animals can replace their cells,
但我们知道,非哺乳动物 能够更换它们的(毛)细胞,
and those creatures' cells are dying and being replaced throughout life,
这些生物的(毛)细胞在一生中 不停地死亡、更换,
so the animals maintain normal hearing.
使得这些动物能维持正常听力。
Here's an example from a little zebra fish.
这是来自一条小斑马鱼的例子。
The cell at the top will undergo a division
顶端的细胞会进行分裂,
to produce two new hair cells.
产生两个新的毛细胞。
They dance for a little bit,
它们会手舞足蹈一会儿,
and then settle down and go to work.
然后便安顿下来,专心工作。
So we believe that if we can decode the molecular signals that are used
因此,我们相信, 如果我们能够解码
by these other animals to regenerate their hair cells,
其他这些动物用来 再生毛细胞的分子信号,
we'll be able to do the same thing for humans.
我们就能为人类做同样的事情。
And our group and many other groups are now engaged in research
目前,我们的团队和 许多其他团队都致力于研究
trying to resurrect these amazing hair cells.
如何让这些美妙的毛细胞复活。
Thank you for your attention.
谢谢各位的聆听。
(Applause)
(掌声)