How do animals see in the dark? - Anna Stöckl

翻译人员: Cynthia Zhang 校对人员: Amy Lu

To human eyes, the world at night is a formless canvas of grey.

在人类眼中，夜晚的世界是无序杂乱的灰色

Many nocturnal animals, on the other hand,

而对于夜间动物而言

experience a rich and varied world bursting with details, shapes, and colors.

它们眼中的世界更为精彩： 充满各类细节、形状、颜色

What is it, then, that separates moths from men?

蛾子与人类的眼睛到底有何不同？

Moths and many other nocturnal animals see at night

蛾子与其他的夜间动物能夜间视物

because their eyes are adapted to compensate for the lack of light.

因为它们的眼睛可以自动调节适应 缺少光线的情况

All eyes, whether nocturnal or not,

所有动物的眼睛，无论是不是夜间动物

depend on photoreceptors in the retina to detect light particles,

都是依靠视网膜上的光感器来捕捉 光线粒子

known as photons.

也就是光子

Photoreceptors then report information about these photons to other cells

然后，光感器向大脑和视网膜内

in the retina and brain.

其他细胞报告光子的信息

The brain sifts through that information and uses it to build up an image

大脑通过筛选信息来建立

of the environment the eye perceives.

眼睛所看到的周围环境的图像

The brighter the light is, the more photons hit the eye.

光线越强，越多光子进入眼睛

On a sunny day,

阳光明媚的天气

upwards of 100 million times more photons are available to the eye

你的眼睛接收的光子比多云阴暗的夜晚

than on a cloudy, moonless night.

多一亿倍

Photons aren't just less numerous in darkness,

在黑暗中光子并不会减少数量

but they also hit the eye in a less reliable way.

但它们进入眼球的方式更不稳定

This means the information that photoreceptors collect

这意味着光感器收集的信息会

will vary over time,

随着时间的流逝而改变

as will the quality of the image.

图片的质量也会下降

In darkness, trying to detect the sparse scattering of randomly arriving photons

黑暗中想要捕捉到随机分散 又稀少的光子

is too difficult for the eyes of most daytime animals.

对于日间动物的双眼 是个困难的任务

But for night creatures, it's just a matter of adaptation.

但对于夜间动物它们只需要适应一下

One of these adaptations is size.

它们需要调整尺寸

Take the tarsier, whose eyeballs are each as big as its brain,

以眼镜猴为例，它们的眼球和大脑 一般大小

giving it the biggest eyes compared to head size of all mammals.

是哺乳动物中眼球大脑相对值最大的

If humans had the same brain to eye ratio, our eyes would be the size of grapefruits.

如果人类拥有同等的相对值， 我们的眼睛会像葡萄柚一样大

The tarsier's enlarged orbs haven't evolved to make it cuter, however,

眼镜猴的大眼球不是为了显得可爱

but to gather as much light as possible.

而是为了捕捉到尽可能多的光

Bigger eyes can have larger openings, called pupils,

眼睛越大，瞳孔越大

and larger lenses,

晶状体越大

allowing for more light to be focused on the receptors.

越多的光能够聚集在光感器上

While tarsiers scan the nocturnal scene with their enormous peepers,

眼镜猴用巨大的双眼扫描夜间景象

cats use gleaming eyes to do the same.

而猫用细小闪光的双眼也能做到

Cats' eyes get their shine from a structure called the tapetum lucidum

它们使用脉络膜层来获得图像

that sits behind the photoreceptors.

这个结构在光感器后方

This structure is made from layers of mirror-like cells containing crystals

这种结构是由多层镜状细胞组成

that send incoming light bouncing back towards the photoreceptors

细胞中含结晶体，其作用是反射接收的光线 传递给光感器

and out of the eye.

并将光送出眼睛

This results in an eerie glow,

这造成了一种诡异的光流

and it also gives the photoreceptors a second chance to detect photons.

光感器因此有机会再次侦测光子

In fact, this system has inspired the artificial cats' eyes we use on our roads.

实际上，这种结构是车辆远光灯的灵感 来源

Toads, on the other hand, have adapted to take it slow.

而另一种动物，蟾蜍习惯了慢慢来

They can form an image

它们的眼睛能构成一幅图像

even when just a single photon hits each photoreceptor per second.

即使每个光感器每秒只能捕捉一个光子

They accomplish this with photoreceptors

秘诀在于它们的光感器比人类的

that are more than 25 times slower than human ones.

慢了不止25倍

This means toads can collect photons for up to four seconds,

这意味着蟾蜍能接收光子长达4秒

allowing them to gather many more than our eyes do

因此它们在视觉间隔中收集的信息

at each visual time interval.

比我们更多

The downside is that this causes toads to react very slowly

这个系统的缺点就是减缓了 蟾蜍的反应速度

because they're only receiving an updated image every four seconds.

因为它们每四秒才能收到 一次信息更新

Fortunately, they're accustomed to targeting sluggish prey.

幸运的是，它们习惯捕食行动缓慢的猎物

Meanwhile, the night is also buzzing with insects,

夜晚充斥着昆虫的鸣叫声

such as hawk moths,

比如说鹰蛾

which can see their favorite flowers in color, even on a starlit night.

即使夜晚没有任何光源，它们也能看见 花朵的颜色

They achieve this by a surprising move -

它们达成这点的方式令人惊奇

getting rid of details in their visual perception.

去除视觉接收系统中所有的细节

Information from neighboring photoreceptors is grouped in their brains,

相邻光感器的信息在大脑处理时 放在了一起

so the photon catch of each group is higher

因此每个群组的光子捕捉

compared to individual receptors.

比单一光感器的数量多

However, grouping photoreceptors loses details in the image,

然而，以群组为单位的光感器 失去了图像的种种细节

as fine details require a fine grid of photoreceptors,

因为完整的细节呈现需要精密网格 状的光感器

each detecting photons from one small point in space.

每个光感器在每个点都要捕捉到光子

The trick is to balance the need for photons with the loss of detail

这种方法牺牲了细节，平衡光子数量

to still find their flowers.

蛾子仍然能找到花朵

Whether eyes are slow, enormous, shiny, or coarse,

无论双眼速度是快是慢，是大是小 是亮是暗，是粗是细

it's the combination of these biological adaptations

它们都是生物适应性的组合

that gives nocturnal animals their unique visual powers.

给予了夜间动物独一无二的视力

Imagine what it might be like to witness through their eyes

想象我们通过它们双眼看世界的景象

the world that wakes up when the Sun goes down.

太阳落下之后夜世界的绮丽