How do animals see in the dark? - Anna Stöckl
-
0:07 - 0:12To human eyes, the world at night
is a formless canvas of grey. -
0:12 - 0:14Many nocturnal animals, on the other hand,
-
0:14 - 0:20experience a rich and varied world
bursting with details, shapes, and colors. -
0:20 - 0:23What is it, then, that separates moths
from men? -
0:23 - 0:26Moths and many other nocturnal animals
see at night -
0:26 - 0:30because their eyes are adapted
to compensate for the lack of light. -
0:30 - 0:33All eyes, whether nocturnal or not,
-
0:33 - 0:37depend on photoreceptors in the retina
to detect light particles, -
0:37 - 0:39known as photons.
-
0:39 - 0:43Photoreceptors then report information
about these photons to other cells -
0:43 - 0:45in the retina and brain.
-
0:45 - 0:48The brain sifts through that information
and uses it to build up an image -
0:48 - 0:51of the environment the eye perceives.
-
0:51 - 0:54The brighter the light is,
the more photons hit the eye. -
0:54 - 0:56On a sunny day,
-
0:56 - 1:00upwards of 100 million times
more photons are available to the eye -
1:00 - 1:03than on a cloudy, moonless night.
-
1:03 - 1:05Photons aren't just less numerous
in darkness, -
1:05 - 1:09but they also hit the eye
in a less reliable way. -
1:09 - 1:12This means the information
that photoreceptors collect -
1:12 - 1:13will vary over time,
-
1:13 - 1:16as will the quality of the image.
-
1:16 - 1:21In darkness, trying to detect the sparse
scattering of randomly arriving photons -
1:21 - 1:24is too difficult for the eyes
of most daytime animals. -
1:24 - 1:28But for night creatures,
it's just a matter of adaptation. -
1:28 - 1:31One of these adaptations is size.
-
1:31 - 1:36Take the tarsier, whose eyeballs
are each as big as its brain, -
1:36 - 1:40giving it the biggest eyes compared
to head size of all mammals. -
1:40 - 1:45If humans had the same brain to eye ratio,
our eyes would be the size of grapefruits. -
1:45 - 1:49The tarsier's enlarged orbs haven't
evolved to make it cuter, however, -
1:49 - 1:52but to gather as much light as possible.
-
1:52 - 1:55Bigger eyes can have larger openings,
called pupils, -
1:55 - 1:57and larger lenses,
-
1:57 - 2:00allowing for more light to be focused
on the receptors. -
2:00 - 2:04While tarsiers scan the nocturnal scene
with their enormous peepers, -
2:04 - 2:08cats use gleaming eyes to do the same.
-
2:08 - 2:12Cats' eyes get their shine from
a structure called the tapetum lucidum -
2:12 - 2:15that sits behind the photoreceptors.
-
2:15 - 2:19This structure is made from layers
of mirror-like cells containing crystals -
2:19 - 2:22that send incoming light
bouncing back towards the photoreceptors -
2:22 - 2:24and out of the eye.
-
2:24 - 2:26This results in an eerie glow,
-
2:26 - 2:30and it also gives the photoreceptors
a second chance to detect photons. -
2:30 - 2:36In fact, this system has inspired the
artificial cats' eyes we use on our roads. -
2:36 - 2:40Toads, on the other hand, have adapted
to take it slow. -
2:40 - 2:41They can form an image
-
2:41 - 2:46even when just a single photon
hits each photoreceptor per second. -
2:46 - 2:48They accomplish this with photoreceptors
-
2:48 - 2:51that are more than 25 times slower
than human ones. -
2:51 - 2:54This means toads can collect photons
for up to four seconds, -
2:54 - 2:57allowing them to gather many more
than our eyes do -
2:57 - 3:00at each visual time interval.
-
3:00 - 3:04The downside is that this causes toads
to react very slowly -
3:04 - 3:08because they're only receiving
an updated image every four seconds. -
3:08 - 3:11Fortunately, they're accustomed
to targeting sluggish prey. -
3:11 - 3:15Meanwhile, the night is also buzzing
with insects, -
3:15 - 3:17such as hawk moths,
-
3:17 - 3:21which can see their favorite flowers
in color, even on a starlit night. -
3:21 - 3:23They achieve this by a surprising move -
-
3:23 - 3:26getting rid of details
in their visual perception. -
3:26 - 3:30Information from neighboring
photoreceptors is grouped in their brains, -
3:30 - 3:32so the photon catch of each group
is higher -
3:32 - 3:35compared to individual receptors.
-
3:35 - 3:38However, grouping photoreceptors
loses details in the image, -
3:38 - 3:42as fine details require a fine grid
of photoreceptors, -
3:42 - 3:46each detecting photons from one
small point in space. -
3:46 - 3:50The trick is to balance the need
for photons with the loss of detail -
3:50 - 3:51to still find their flowers.
-
3:51 - 3:54Whether eyes are slow, enormous,
shiny, or coarse, -
3:54 - 3:57it's the combination
of these biological adaptations -
3:57 - 4:01that gives nocturnal animals their unique
visual powers. -
4:01 - 4:04Imagine what it might be like to witness
through their eyes -
4:04 - 4:07the world that wakes up
when the Sun goes down.
- Title:
- How do animals see in the dark? - Anna Stöckl
- Description:
-
View full lesson: http://ed.ted.com/lessons/how-do-animals-see-in-the-dark-anna-stockl
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? Anna Stöckl uncovers the science behind night vision.
Lesson by Anna Stöckl, animation by TED-Ed.
- Video Language:
- English
- Team:
- closed TED
- Project:
- TED-Ed
- Duration:
- 04:23
Jessica Ruby approved English subtitles for How do animals see in the dark? - Anna Stöckl | ||
Jessica Ruby accepted English subtitles for How do animals see in the dark? - Anna Stöckl | ||
Jessica Ruby edited English subtitles for How do animals see in the dark? - Anna Stöckl | ||
Jennifer Cody edited English subtitles for How do animals see in the dark? - Anna Stöckl |