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Hey folx! I promised y'all a thread 
on how the Fourier transform helps us hear, and this is it 
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So buckle up, coz we are going to take a ride through one of the most interesting organs in the human body: the ear
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on how the Fourier transform helps us hear, and this is it !So buckle up, coz we are going to take a ride through one of the most interesting organs in the human body: the ear
!
The part of the ear you can see is the OUTER EAR. The funnel-like thing is the pinna, which collects & passes sounds to the eardrum.
Some animals, like cats
, have muscles there, so they can move it around to wherever the sound is coming from!
Some animals, like cats
, have muscles there, so they can move it around to wherever the sound is coming from!
The eardrum is a flap of cartilage. It vibrates with the sound waves. This vibration is then passed on to three little bones, called the hammer, the anvil and the stirrup. The stirrup is the SMALLEST named bone in the body!
The stirrup knocks on the door of the cochlea. The cochlea looks a lot like a snail 
! The bony structure that the cochlea lives in is called the BONY LABYRINTH, and you can see why!
! The bony structure that the cochlea lives in is called the BONY LABYRINTH, and you can see why!
Inside the cochlea's spiral, there is a sheet, all rolled up, known as the BASILAR MEMBRANE (BM).
This is where the magic happens: the membrane is connected to a lot of hair cells all over. These act like little sensors, which can detect the vibrations...
This is where the magic happens: the membrane is connected to a lot of hair cells all over. These act like little sensors, which can detect the vibrations...
...in the membrane and excite nerve fibers that will send signals to the brain.
But here's the fun part: because of how it is all rolled up, different parts of the membrane vibrate at different FREQUENCIES
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But here's the fun part: because of how it is all rolled up, different parts of the membrane vibrate at different FREQUENCIES
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The part of the BM closest to the stirrup reacts to high frequencies, like those of a flute, while the part right at the end vibrates when we hear really low frequency sounds, like a tuba!
That's like a Fourier transform! The BM is transforming the sound wave to the frequency domain and giving it's spectrum to the brain through the auditory nerve !
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This realisation by bioengineers led to a lot of awesome science. Now, scientists can model how the nerve fibers will be excited, based on what is the incoming sound!
How does this help though? Well, it can help us build better HEARING AIDS! Often, a person loses their hearing because the hair cells just aren't as sensitive to vibrations as they once were. This type of hearing loss can be corrected.
To do that, we implant electrodes into the cochlea 
! This is called a COCHLEAR IMPLANT. Instead of the ear, we can attach a microphone behind it and send the sounds to a small computer. This analyses the sound and figures out the electrical pulses that...
! This is called a COCHLEAR IMPLANT. Instead of the ear, we can attach a microphone behind it and send the sounds to a small computer. This analyses the sound and figures out the electrical pulses that...
...must be transmitted to the nerve fibers . How? By taking a Fourier transform! This signal is then given to a transmitting coil, also attached to a person's head along with the microphone. This whole thing is kept in place by magnets! The coil then...
. How? By taking a Fourier transform! This signal is then given to a transmitting coil, also attached to a person's head along with the microphone. This whole thing is kept in place by magnets! The coil then...
...passes the signal to the implant, which is surgically implanted into the fluid of the cochlea. The implant excites the nerve fibers with the signal, and they take it to the brain. And lo! The person can hear the sound !
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Now any sound is actually made up of two parts. The ENVELOPE is the slow variations in the sound, while the fast variations are the FINE STRUCTURE 
.
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Right now, most of those little computers that come with cochlear implants can only pick cues from the envelope of the signal, but can't figure out the fine structure. So CI users usually have problems with hearing in loud places and have difficulty appreciating music...
...but if we could incorporate cues from the fine structure of the sound too, we could help someone listen to music again 
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DISCLAIMER: this varies from user to user though. some users can appreciate a little bit of music. others can't.
!DISCLAIMER: this varies from user to user though. some users can appreciate a little bit of music. others can't.
If you liked the thread, retweet and ask me any questions you have. I will try and answer them all 
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