The Human Body - Localisation of Sound

[falcosenna1 8,320]

The Human Body - Localisation of Sound

Has this ever happened to you? You’re playing several hours and every battle you join is worse than the one before. When you’ve finally found a nice game that’s not about to turn into a loss, you all of a sudden hear the lovely voice of your mom. “Clean up your room, please!” or “Could you please lay the table?”. You turn your head from your screen in her direction and shout back: “Wait, 5 more minutes and my battle is finished!” Does this sound familiar? Now, how is it possible you turn your head in the right direction? When she shouts to lay the table, she probably is preparing dinner in the kitchen. However, when she calls to clean up your room, she could be standing anywhere. Though, you perfectly know what direction her voice comes from, but how?  

 

 

General perception of sound

The ability to determine the localisation of a sound source is just one of the wonders of the human central nerve system which I’ll try to explain in this article. As most of you probably know, sound propagates in the form of waves. These sound waves go through your outer ear and bump into the eardrum which is called the membrana tympani. This membrane is connected to the malleus, the first of our three ossicles in our middle ear. These ossicles amplify the power of the sound waves that hit our eardrum.  Next, we have the inner ear where the actual auditory organ or organ of Corti is located. The stapes, the last of the three ossicles, is connected to the fenestra ovalis (oval window) which is the opening between the middle and inner ear. Via the stapes and the fenestra ovalis, sound waves propagate towards the inner ear which actually consist of 2 parts, an outer labyrinth filled with perilymph and an inner labyrinth filled with endolymph. The sound waves (which are no waves anymore actually) let the perilymph vibrate. Vibrations in the perilymph result in vibrations of the endolymph and that’s where the auditory organ is found. These vibrations cause movements of our hair cells’ cilia. Mechanosensitive ion channels open due to these movements resulting in the depolarisation of the hair cells. That’s how sound waves are turned into electrical signals in neurons. These inner hair cells connect to afferent nerve fibers of the auditory nerve and these fibers connect to several nuclei (cores) in our central nerve system so that the electrical signals finally reach the auditory cortex, the part of the cerebellum (brain) responsible for the perception and processing of auditory stimuli.

 

PS: When I’m talking about one core connecting to another, I mean the conduction of the electrical signal from one neuron to another which takes place in a core or nucleus in our nerve system.

 

Inside the spoiler, you can find pictures to give some visual clarification.

 

 

 

 

 

 

 

 

 

 

 

 

The localisation of sound 

With this knowledge in your head, we can go on with the explanation regarding the localisation of sound. We start in the cochlear (=auditory) nerve which brings electrical signals generated in our inner hair cells to two cochlear/auditory nuclei, to the ventral and dorsal cochlear nucleus of our brainstem. Let’s leave the dorsal cochlear nucleus aside as our interest goes to the localisation of sound. The conduction route via this dorsal nucleus has other functionalities.  

 

So we now are in the ventral cochlear nucleus. From this nucleus neurons rise up to another nucleus in our brainstem, namely the nucleus olivaris superior. This nucleus can be divided into 2 parts, a lateral and medial segment. The medial segment is important for the localisation of a sound source that produces sound waves with frequencies below 3000 Hz. In this medial segment, we find EE-cells (excitatory-excitatory cells) which are excited by signals (stimuli) from both ears. The lateral segment is important to locate sound sources producing sound waves with higher frequencies, above 3000 Hz. In the lateral segment, EI-cells (excitatory-inhibitory cells) are found, meaning these cells will be excited by signals from one ear and inhibited by signals from the contralateral ear. The mechanism for the localisation of sound is quite the same in both segments. It’s based on phase differences of sound waves between your left and right ear for frequencies below 3000 Hz and differences in sound intensity for frequencies above 3000 Hz. These differences simply exist because there’s a certain distance between both your ears causing these small, but seemingly incredibly important differences. Depending on the phase difference (below 3000 Hz) or the difference in intensity (above 3000 Hz) only 1 neuron (1 cell) of all EE-cells (below 3000 Hz) or EI-cells (above 3000 Hz) will be activated. This means that a different neuron (cell) will be activated for different phase differences or intensity differences (between left and right ear). The location of this activated neuron in the medial or lateral segment of the nucleus olivaris superior represents the location of the sound source and that’s how the localisation of sound is possible.

 

 

 

 

So next time your mom yells to lay the table or clean your room, try not to clamor back, but think about the wonderful mechanism in your central nerve system that makes it possible to know where your mom is shouting from making you able to turn your head in the appropriate direction in case you want to call back.

 

Hopefully you liked and learned something from my very first article. 

Edited February 3, 2017 by falcosenna1

[Quarks 2,255]

Edits:

like, 2 commas were added

 

Also, my brain hurts and that is a good thing. Falco has returned to us. Great article. Though in the future, change the title from "The Science Behind", cause I already did that in my articles.

Edited February 2, 2017 by Quarks

[falcosenna1 8,320]

Edits:

like, 2 commas were added

 

Also, my brain hurts and that is a good thing. Falco has returned to us. Great article. Though in the future, change the title from "The Science Behind", cause I already did that in my articles.

Thanks. And oops, my bad, won't use "The science behind" in the future. If you want, you can change it to "The human body - Localisation of sound" instead.  :)

 

Edit: I've edited one of the pictures in the article as I had forgotten to mark one important structure.

Edited February 2, 2017 by falcosenna1

[CuT_TheRe_HeaRTs_OuT 640]

Are you studying medicine or what ?!! 

[Hex 11,520]

Title changed as per request.

[Spit_Fyre 334]

I just got inspired to jot down an epic, totally random turret idea after reading this!

 

The Echo Location Turret

 

How does it work? It homes in on the nearest tank that's making noise - either in chat or when shooting but not just driving (TO silencers are the best) - and wrecks them! Shots can be fired in all directions. So if it's surrounded by a chattering group of tanks, it goes berserk and explodes, killing them all. MUAHAHAHA.

[falcosenna1 8,320]

Are you studying medicine or what ?!! 

Yeah. :p  I was doubting about writing and publishing a medical tinted article, because I can imagine most players are not really interested in it. Though I decided to write this because I find it so weird that the activation of 1 single neuron makes us able to know where sound comes from. It's a mechanism we constantly use, unconsciously. 

 

Title changed as per request.

Thanks. :)

 

I just got inspired to jot down an epic, totally random turret idea after reading this!

 

The Echo Location Turret

 

How does it work? It homes in on the nearest tank that's making noise - either in chat or when shooting but not just driving (TO silencers are the best) - and wrecks them! Shots can be fired in all directions. So if it's surrounded by a chattering group of tanks, it goes berserk and explodes, killing them all. MUAHAHAHA.

Oooh, great you got inspired by the article. :D

[williew 1,999]

Awesome work Falco, a very interesting read! :)

[falcosenna1 8,320]

Awesome work Falco, a very interesting read! :)

Thanks williew! :D

[NERF836 202]

Nice article my brain died during the first paragraph so that means it's written perfectly!!

[Electra 733]

Beyond my expectation! :d 

[falcosenna1 8,320]

Nice article my brain died during the first paragraph so that means it's written perfectly!!

Beyond my expectation! :D

Thank you! :)