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In this assignment I will present the theory of human hearing through the physiology and different parts of the ear explaining what they do, moreover I will look into the causes of hearing loss and the localization of sound.

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Outer ear - The outer ear is made up of the Pinna this is the helix shaped part of our hearing system on the side of our head, the helix disk constructions purpose is to funnel sound wave energy which at this stage of the hearing process is sound pressure wave energy or Gas as it travels through the air. The Pinna then directs this energy into our ear canal.

Ear canal - The ear canal or auditory canal once the Pinna has directed the sound wave energy it flows through this canal, its purpose is to funnel this energy down to the eardrum. Moreover the ear canal is also lined with earwax (Cerumen) the purpose is to trap and stop any potentially harmful particulate matter from reaching and damaging the eardrum as it is very sensitive and easily damaged.

Tympanic membrane - The tympanic membrane or eardrum is generally stated to be located as last of the outer ear processes as well as the start of the middle ear. The eardrum is a small cone shaped membrane about 8-10 mm across and is stretched like a drum head by small muscles, the purpose is to vibrate back and forth in reaction to sound energy. When sound energy hits the eardrum it then sends these vibrations on to three small bones that are directly connected to the eardrum. The eardrum is the first step of the ear to change the energy from gas or sound eave energy into kinetic or mechanical energy.

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Middle ear - The middle ear is located between the eardrum and ends at the oval window, passing the energy on from the outer ear trough to the inner ear to the brain for processing. First in the line of processes for the middle ear are the three small bones that are connected to the eardrum these three bones Hammer / Anvil and Stirrup. These bones pass the mechanical energy from the eardrum through to the oval window as the last bone the Stirrup is connect to the Oval-window and the first bone the Hammer, is connected to the eardrum.

Acoustic Reflex - This is a reaction via muscles that when stimulated by high levels of noise react. Two muscles surrounding the three small bones in our middle ear these muscles are called the Stapeidus and Tensor Tympani and they tense up and pull on these three bones that act as a linkage system pulling on the Hammer bone which is connected to the eardrum pulling it inwards to the middle ear and pulling the stirrup bone away from the the oval-window of the cochlea. What this does it hampers the transmission of vibrations from the outer and middle ear to the inner ear as a form of protection.

Oval-Window - The oval-window is a membrane that covers the entrance to the inner ear or the Cochlea. When sound wave energy hits the eardrum it vibrates sending these vibrations along the three small bones hammer, anvil an stirrup to the oval-window this is a natural amplification process as the mechanical sound energy being sent to the oval-window is 20x higher than it is when it hits the eardrum, this has to do with size as the eardrum is bigger than the oval-window membrane.

Round window - When mechanical energy enters going trough the oval-window into the cochlea the round window also vibrates in opposite phase as response to this mechanical energy entering the Cochlea via the oval-window.

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Inner ear - Mainly made up of the cochlea and the auditory nerve in relation to hearing and the hearing process. The Cochlea transforms the mechanical energy into electro chemical energy, the Cochlea is the small snail shell construction located at the inner most ear and it is filled with a fluid called (perilymph) and two membranes. The membranes acts like walls or blockages in the Cochlea and for the fluid to get from one side of the cochlea to the other the fluid has to travel through small hole in these walls. The vibrations from the oval-window are picked up and transmitted in this fluid and the hole in the walls of the cochlea.

The Cochlea has small hair fibers when the fluid moves in the cochlea these thousands of hairs on these walls are set into motion when the fluid moves there are around 24,000 of these hairs in four long rows.

Auditory nerve - This is a nerve made up of fibers that transmit electrical signals from the inner ear to the brain. The hair fibers in the Cochlea are linked to the Auditory nerve and so the electro chemical signals picked up in the fluid by these hairs are then sent on the the auditory nerve and then on to the brain for processing.

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Some causes of hearing loss are obvious like exposure to loud noises, sounds over 85dB are classed as potentially harmful when exposed for a period of time usually up to 5 minutes. Where as 120dB equivalent to a siren up to 1 minute of exposure would start to cause damage to our hearing. Exposure to damaging noise levels for our hearing will generally not mean a total loss of hearing depending on distance from the source of the noise and how long that noise is sustained, also the environment as a speaker in a room like a concert hall could potentially do more damage than a speaker out doors due to less interruptions and obstetrical in the sounds path to our ears. Within theses environments as for outdoors wind for example caries sound away and would subsequently give our ears a break whereas in doors there is no such obstetrical to the sound energy to our ears.

Age is another factor in hearing loss in the UK over 70% of people aged over 70 have some form of hearing loss although not total loss. As over the years especially depending on what you do day to day for example a musician being around music and loud sounds would possibly have a higher chance of having their hearing damaged to someone who does not work around or in loud environments a lot of the time.

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This has to do with your brain working our the timing between a sound reaching both of your ears. The Pinna which is the helix shaped structure that we can see on the sides of our head are the shape they are to best capture and fennel sound to our ear canal the Pinna also changes the frequency of the sound nit picks up based on the direction of the sound to our ear. Moreover our brain localize sound we hear by working out when the sound energy hits for example our right ear and the timing different to the sound reaching our left ear. Our brain compares the differences to precisely work out and localize where the sound in coming from. The volume can also play a factor because if the volume of the sound is louder in your left ears to your right that may mean that the source is close or more direct to your left ear meaning that the sound travels from the source straight to your left ear whereas the sound has to travel past and over your head of refract off surfaces in your environment to then be picked up by your right ear.

Interaural delay - This is time difference sound reaching our ears and what ear the sound reaches first either left to right, or right to left an our brains working our the difference to localize the source of the sound if its closer to the left or right.  As it provides a clue as to the angle and direction of the sound reaching our ears. As what side or our heads the sound is hitting the ear on that side of our head will pick up the sound quicker than the ear on the opposite side.

Inter aural intensity delay - This has to do with the energy of the sound vibrations and the angles that they reach our ear, as well as various refracted sounds within our environment and how this reaches our outer ear the Up, Horizontal and Down angles of frequencies as the horizontal location changes the frequencies profiles of the sounds. This change in frequency caused by the shape of our heads and the shaped of our Pinnas determines what the frequencies of the sound energy reaches our ears and is then used to determine the location of sound.

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This is what I have learn't from doing this assignment. Having researched the various aspects both explaining and outlining the physiology of our hearing the different parts to our hearing system and how we perceive sound both with timing and frequency differences that our brain uses to location the sources of sound.
I have learned about the different aspects of how our hearing works. I did not know sound changes as it flows through our auditory system however now understand this.

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http://www.workplaceintegra.com/hearing-articles/Ear-anatomy.html

Moodle resources

https://www.hear-it.org/The-middle-ear-1

https://www.hear-it.org/The-inner-ear-1

https://www.pinterest.co.uk/pin/563864815815655746/

https://www.actiononhearingloss.org.uk/about-us/our-research-and-evidence/facts-and-figures/

https://knowingneurons.com/2013/03/15/how-does-the-brain-locate-sound-sources/

https://www.nature.com/articles/17374

https://en.wikipedia.org/wiki/Acoustic_reflex