Name: TED-ED】動物はどうやって暗闇を見るのか？- アンナ・シュテックル (【TED-Ed】How do animals see in the dark? - Anna Stöckl)
Uploaded: 2021-01-14T06:27:37.000Z
Duration: 4 min 23 s
Description: VoiceTubeの動画で発音を聞きながら英語表現を覚えよう！学べる英語：

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

Many nocturnal animals, on the other hand,

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

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

Moths and many other nocturnal animals see at night

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

depend on photoreceptors in the retina to detect light particles,

Photoreceptors then report information about these photons to other cells

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

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

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

Photons aren't just less numerous  in darkness,

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

This means the information  that photoreceptors collect

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

is too difficult for the eyes of most daytime animals.

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

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

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

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

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

Bigger eyes can have larger openings, called pupils,

allowing for more light to be focused on the receptors.

While tarsiers scan the nocturnal scene with their enormous peepers,

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

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

that send incoming light bouncing back towards the photoreceptors

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

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

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

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

that are more than 25 times slower  than human ones.

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

allowing them to gather many more than our eyes do

The downside is that this causes toads to react very slowly

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

Fortunately, they're accustomed to targeting sluggish prey.

Meanwhile, the night is also buzzing with insects,

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

getting rid of details  in their visual perception.

Information from neighboring photoreceptors is grouped in their brains,

so the photon catch of each group is higher

However, grouping photoreceptors loses details in the image,

as fine details require a fine grid of photoreceptors,

each detecting photons from one small point in space.

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

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

it's the combination  of these biological adaptations

that gives nocturnal animals their unique visual powers.

Imagine what it might be like to witness through their eyes

the world that wakes up when the sun goes down.

字幕リスト動画再生

TED-ED】動物はどうやって暗闇を見るのか？- アンナ・シュテックル (【TED-Ed】How do animals see in the dark? - Anna Stöckl)

brain

perceive

structure

world