Scientists Put Caterpillars in an Ultraquiet Chamber to Learn How They Hear Without Ears
Scientists Put Caterpillars in an Ultraquiet Chamber to Learn How They Hear Without Ears
科学家将毛毛虫放入超静音室，探究它们如何在没有耳朵的情况下“听见”声音
In a quiet summer garden, a caterpillar perches on a branch, munching serenely on leaves. A moment later it freezes. It senses danger—and just in time. From behind, a wasp approaches, sizing up its prey. 在宁静的夏日花园里，一只毛毛虫栖息在树枝上，悠闲地咀嚼着叶子。片刻之后，它突然僵住了。它察觉到了危险——而且恰逢其时。在它身后，一只黄蜂正悄然靠近，打量着它的猎物。
Tobacco hornworm caterpillars don’t look like they have ears, and yet they’re able to sense predators such as wasps. How does the caterpillar know a wasp is approaching? 烟草天蛾幼虫看起来并没有耳朵，但它们却能感知到黄蜂等捕食者。毛毛虫是如何知道黄蜂正在靠近的呢？
Scientists do not fully understand how this caterpillar’s senses work, but we are part of a team of biologists and engineers who want to figure it out. Our ongoing research suggests that tobacco hornworms can hear using tiny, supersensitive hairs on their body. 科学家们尚未完全了解这种毛毛虫的感官是如何运作的，但我们是一个由生物学家和工程师组成的团队，致力于解开这个谜题。我们正在进行的研究表明，烟草天蛾幼虫能够利用身体上细小且极其敏感的毛发来“听”声音。
Understanding the intricate biological mechanisms that allow this organism to perceive and interact with its environment would help solve a mystery of the natural world. It could also help scientists design new, cheaper microphone technology. 理解这种生物感知环境并与之互动的复杂生物机制，将有助于解开自然界的一个谜团。这也有助于科学家设计出新型、更廉价的麦克风技术。
Because the hornworms’ hairs are so sensitive, we have to study them in complete silence. And where better to study hearing than in the complete silence of an anechoic chamber? 由于天蛾幼虫的毛发非常敏感，我们必须在绝对安静的环境中进行研究。而还有什么地方比消声室（anechoic chamber）的绝对静谧更适合研究听觉呢？
What Happens in the Anechoic Chamber
消声室里发生了什么
What happens outside the anechoic chamber stays outside the anechoic chamber, because it is meticulously built that way. Anechoic chambers are some of the quietest places in the world. They are engineered specifically to block the entry of any undesired sounds. Heavy-duty steel springs support the “floating” chamber and keep it from touching the ground. This detachment isolates the space from outside vibrations or noise. 消声室外发生的一切都被隔绝在外，因为它的建造工艺极其严苛。消声室是世界上最安静的地方之一。它们经过专门设计，旨在阻挡任何不必要的噪音进入。重型钢弹簧支撑着这个“悬浮”的房间，使其与地面保持隔离。这种分离结构将空间与外部的振动或噪音隔绝开来。
In such a chamber, we studied the caterpillars’ responses to vibrations. Every day for a year, we set up a caterpillar on a platform and sent vibrations toward the platform at a variety of intensities. 在这样的房间里，我们研究了毛毛虫对振动的反应。在为期一年的时间里，我们每天将一只毛毛虫放在平台上，并向平台发送不同强度的振动。
To measure the movement and precise vibrations that traveled through the platform the caterpillar sat on, we used a device called an accelerometer. In response to vibrations, we sometimes saw the caterpillars jump; at other times they twitched or even shuddered from the sheer physical force. 为了测量毛毛虫所在平台上传递的运动和精确振动，我们使用了一种名为加速度计的设备。在感受到振动时，我们有时会看到毛毛虫跳跃；有时它们会抽搐，甚至因强烈的物理作用力而颤抖。
Through our observations, we pinned down the specific threshold where the caterpillars stopped reacting to vibrations. Any vibration weaker than that magnitude, and the caterpillar wouldn’t visibly react at all. 通过观察，我们确定了毛毛虫停止对振动做出反应的具体阈值。任何低于该强度的振动，毛毛虫都不会有明显的反应。
After noticing this consistent pattern, we decided to test more caterpillars inside the anechoic chamber, but this time using airborne sound as the stimulus. The idea here was that if the caterpillars are more sensitive to sound than they are to vibrations, they are probably hearing airborne sounds independent of any vibrations. 在注意到这一规律后，我们决定在消声室内测试更多的毛毛虫，但这次使用空气传播的声音作为刺激源。我们的想法是，如果毛毛虫对声音的敏感度高于对振动的敏感度，那么它们很可能是在独立于任何振动的情况下“听”到了空气中的声音。
Sound is broadly defined as a form of vibration or energy that becomes audible, meaning you can hear it with your ears. But here’s the catch: Sound also causes objects to vibrate. To make sure the caterpillar wasn’t just sensing the sound’s vibrations through the platform, we also used the accelerometer to measure the vibrations that the platform experienced from the sound. Our goal was to compare the platform vibrations produced in two distinct scenarios: when sound through the air was used as the stimulus versus when just direct vibrations were used as the stimulus. 声音被广义地定义为一种可听见的振动或能量形式，意味着你可以用耳朵听到它。但问题在于：声音也会导致物体振动。为了确保毛毛虫不是仅仅通过平台感知到声音引起的振动，我们还使用加速度计测量了平台因声音而产生的振动。我们的目标是比较两种不同场景下平台产生的振动：一种是以空气传播的声音作为刺激，另一种是仅以直接振动作为刺激。
We noticed that this time the caterpillars continued reacting to the sound even beneath their threshold of response to the direct vibrations. This finding suggested that they were hearing the airborne sounds. 我们注意到，这一次，即使在低于它们对直接振动的反应阈值时，毛毛虫仍然对声音做出了反应。这一发现表明，它们确实听到了空气中的声音。
Finding the Caterpillars’ “Ears”
寻找毛毛虫的“耳朵”
So, where are their “ears?” Or rather, what are their “ears?” 那么，它们的“耳朵”在哪里？或者更确切地说，它们的“耳朵”是什么？
There are two ways of hearing sound: from the sound waves’ pressure and from the velocity of the particles making up the sound waves. 听觉有两种方式：一种来自声波的压力，另一种来自构成声波的粒子的速度。
For the longest time, scientists have associated hearing with tympanal organs. A tympanal organ in most mammals is a membrane that vibrates in response to pressure from sound waves. Its vibration moves the bone structures adjacent to it as well. 长期以来，科学家们一直将听觉与鼓膜器官联系在一起。在大多数哺乳动物中，鼓膜器官是一层因声波压力而振动的薄膜。它的振动也会带动邻近的骨骼结构。
In most insects that respond to sound pressure, the structure analogous to the tympanal organ is a sac filled with air. They perceive any vibrations to this sac as sound. 在大多数对声压有反应的昆虫中，类似于鼓膜器官的结构是一个充满空气的囊。它们将作用于该囊的任何振动感知为声音。
But caterpillars pose a challenge to this typical hearing system, because they can hear but do not have obvious tympanal membranes. After digging into some past research and examining the caterpillars under the microscope, we spotted the distinctive hairs on their bodies. 但毛毛虫对这种典型的听觉系统提出了挑战，因为它们能听见声音，却没有明显的鼓膜。在深入研究了一些过往文献并用显微镜观察毛毛虫后，我们发现了它们身上独特的毛发。
Thus, our next project began. We removed their hairs and compared their responses to sound before and after the hair removal. Sometimes we surgically removed all the hairs by plucking them with tweezers under the microscope, and sometimes we strategically targeted a few. 于是，我们的下一个项目开始了。我们去除了它们的毛发，并比较了去除前后它们对声音的反应。有时我们会在显微镜下用镊子拔掉所有的毛发，有时则有针对性地去除几根。
The result was striking: The caterpillars’ defensive reactions decreased dramatically across various sound frequencies depending on which specific hairs were removed. While our research continues, and we haven’t yet published our results in a journal, this work is allowing us to piece together the caterpillar hearing puzzle and investigate which of these hairs are tuned to register different sound frequencies. 结果令人震惊：根据被去除毛发的不同，毛毛虫在不同声频下的防御反应显著降低。虽然我们的研究仍在继续，且尚未在期刊上发表结果，但这项工作使我们能够拼凑出毛毛虫听觉的拼图，并研究这些毛发中哪些是专门用于感知不同声频的。
This line of research into how insects hear sounds using specialized, microscopic hairs could inspire a new generation of acoustic tools. Standard microphones are devices that contain membranes within them that can detect sound pressure levels. By mimicking these biological systems, such as using structures like these hairs in place of membranes, future microphones could be designed to instead measure the air particle velocity caused by sound, alongside the sound pressure levels. 这种关于昆虫如何利用特化的微小毛发感知声音的研究，可能会激发新一代声学工具的诞生。标准麦克风是内部包含薄膜的设备，可以检测声压级。通过模仿这些生物系统，例如使用类似毛发的结构代替薄膜，未来的麦克风可以被设计成在测量声压级的同时，测量由声音引起的空气粒子速度。
Microphones that can detect air particle velocity would also be able to determine the direction of origin of the sound wave. In the case of microphone designs for hearing aids, a microphone that is able to track both sound pressure and air particle velocity could provide the user with information on both volume and direction of the sound wave. And studying caterpillars’ hearing systems and imitating how their “hearing hairs” work could inspire such directional microphones. 能够检测空气粒子速度的麦克风还能确定声波的来源方向。在助听器的麦克风设计中，能够同时追踪声压和空气粒子速度的麦克风，可以为用户提供关于声波音量和方向的信息。研究毛毛虫的听觉系统并模仿其“听觉毛发”的工作原理，可能会为这种定向麦克风提供灵感。
This article is republished from The Conversation under a Creative Commons license. 本文根据知识共享许可协议（Creative Commons license）从《对话》（The Conversation）转载。