00:00Since immemorial times, humans have been sharing the planet with other species.
00:05Each one having a unique perception of reality in terms of color, speed and sound.
00:11Today, thanks to technological advances,
00:14we are able to understand how animals perceive our sound universe.
00:18So, why not try to see the world through their ears?
00:22Let's start with man's best friend.
00:24The dog.
00:25It is well known that dogs perceive time differently from us.
00:30The most common idea is that a human year would be equivalent to 7 years of dogs.
00:35But what do they perceive exactly when we call them by their name?
00:39Dogs experience the world more slowly than we do,
00:43affecting their perception of time, but also of sound.
00:47Let's say you called Medor to go for a walk.
00:50You speak at a normal pace, as usual.
00:53But for Medor, your voice seems slowed down,
00:56as if you had set the reading speed to 75% on a music app.
01:02You probably heard that dogs have a wider range of hearing than humans,
01:07and that they can capture sounds at great distances.
01:10It's quite true.
01:12The average human ear perceives sounds between 20 Hz and 20 kHz,
01:18with a better hearing among young people, which tends to decrease with age.
01:23It is scientifically proven.
01:25On the other hand, dogs can hear up to 45 kHz, well beyond our perception.
01:32Some breeds of dogs known for hunting require a particularly fine hearing.
01:37However, dogs are not as skilled as we are to recognize sounds.
01:42Where a human can easily distinguish A-B from B-C,
01:45a dog does not show such a discernment.
01:48This is called frequency selectivity.
01:51The scientific explanation for this is that different parts of the cochlea respond to different frequencies.
01:58This is what the human ear looks like from the inside.
02:02And this is what a dog's ear looks like.
02:05The cochlea, this spiral-shaped structure, is filled with a liquid similar to salty water.
02:12At the heart of the cochlea are tiny hairs that vibrate according to the frequency of the sounds received.
02:19Some of these hairs are activated by high-pitched sounds,
02:22while others react more to lower notes.
02:27Dogs really seem to be the best friends of man,
02:31and even share our tendency to lose hearing as we age.
02:35Human hearing is at its peak in our youth.
02:39A study from the University of New South Wales
02:42reveals that a child can hear sounds up to 24 kHz.
02:46This ability to perceive very high-pitched sounds decreases with age,
02:51and an elderly person can no longer hear anything beyond 8 kHz.
02:56This means that she can probably no longer hear the birds singing or even the sound of the microwave.
03:02In dogs, as in humans, this loss of hearing is linked to the degeneration of the small hairs in the cochlea.
03:09And what about cats?
03:12They can hear frequencies even higher than dogs,
03:16going slightly beyond 60 kHz.
03:19This ability is particularly useful for hunting small rodents
03:23that emit sounds almost imperceptible to humans.
03:26Thanks to its fine nose, a cat can detect a mouse hidden in a bush more than 30 meters away.
03:34Curiously, while dogs perceive the world more slowly than we do,
03:39cats experience life about 9% faster than we do.
03:44You have probably heard of infrasound and ultrasound.
03:49Let's play a little game.
03:51We will give you an example of sound, and you will have to guess whether it is an infrasound or an ultrasound.
03:57Would you say that the sound of moving tectonic plates is an infrasound or an ultrasound?
04:02The correct answer is infrasound.
04:05Here is another example.
04:07The movement of ants in an underground tunnel is also an infrasound.
04:12Infrasounds are sounds of very low frequency, below 20 Hz,
04:16that we cannot hear, but that elephants can perceive.
04:21When you look at elephants, the first thing you notice is their big ears.
04:27Everything in their house is quite imposing, but their ears are quite remarkable compared to ours.
04:34These large leaves of cabbage allow them to capture much longer sound waves than the ones we are used to.
04:41This means that they can detect the movement of clouds and physically hear the approach of rain.
04:47This ability is precious to them, because it tells them when to go to the sources of water, for example.
04:54Elephants also use infrasounds to communicate with each other by hitting the ground with their feet,
05:01thus generating powerful, but almost inaudible vibrations.
05:05Thanks to the nerve endings in their feet and their bones,
05:09they can capture these vibrations, a bit like a phone call.
05:14Speaking of vibrations, how can a snake be charmed by a flute if it has no ears?
05:20In reality, the snake does not follow the music, but the light tapping of the charmer's feet on the ground.
05:27For humans, sound waves are mainly carried by the air.
05:32On the other hand, snakes, in direct contact with the ground, perceive the environment through vibrations.
05:39Devoid of earplugs, their inner ear is connected to their jaw.
05:44In addition, vibrations are transmitted from bone to bone inside the snake,
05:49a phenomenon known as osteophony, literally meaning that snakes listen with their bones.
05:55If it worked that way for humans, sound waves could literally cause shivers along our spine.
06:02Well, humans listen to us through the air, elephants and snakes through the ground.
06:07But what about aquatic animals?
06:11Contrary to what one might think, water does not impede the hearing of dolphins.
06:15They emit sound waves of very high frequency, classified as ultrasound.
06:21They produce clicks in order to scan their environment in search of food and other animals.
06:27The sounds that come back to them allow them to precisely identify what is around them.
06:32To put it simply, dolphins see with their ears.
06:36This ability, called echolocation, is a form of navigation by sound.
06:44You've certainly heard of sonar, haven't you?
06:48This instrument is used by ships to detect objects underwater.
06:52A sonar emits rapid sound impulses that bounce off the seabed and return to the sender,
06:58allowing them to measure the depth of the water, locate wrecks and discover geological formations.
07:05This is exactly what dolphins do to locate themselves in their environment.
07:09According to National Geographic, humans can detect frequencies reaching 100 kHz
07:15when they dive underwater, almost equal to dolphins.
07:19Imagine using echolocation to locate yourself underwater.
07:23Scientists do not understand exactly why this happens, but they have two hypotheses.
07:29This could be related to the way sound spreads differently through water,
07:34or to the way our ears process sound in this environment and how our brain interprets it.
07:40It is not only dolphins that use sound to locate themselves.
07:44bats do the same.
07:46Living often in dark environments, or even totally dark,
07:50they cannot really count on their vision.
07:53However, their hearing is so developed that they practically do not need their eyes to move.
07:58Although the brain of a bat is small, it can map its environment in detail,
08:04allowing it to easily locate its prey.
08:07What about rodents?
08:09If you have ever observed a mouse or a bat,
08:12you have probably deduced that they were born on springs.
08:15Funny fact!
08:17Compared to humans, a bat perceives the world around it at twice the speed.
08:22Thus, what seems fast and nervous to us seems rather calm from the point of view of this rodent.
08:28In terms of hearing, a mouse can hear up to 91 kHz, which is incredibly high.
08:36Fascinating, isn't it?
08:39For more UN videos visit www.un.org
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