SAP - The Ear Lesson

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The Ear

listening manClose your eyes for a moment, and listen to the sounds around you. Maybe you hear birds, clicks of a keyboard, breathing, water rushing, or other sounds. Do you know how these external stimuli reach your brain for processing? It's through the process of audition.

Learn about the parts of the ear in the activity below:

Problems in various parts of the ear can lead to hearing loss. Sustained exposure to loud noises can cause long-term or permanent hearing loss. If you've ever heard ringing in your ears after a concert or sporting event, you've probably damaged the hair cells in your cochlea to some degree. Damage to these hair cells that results in hearing loss is known as sensorineural hearing loss (or nerve deafness). Doctors can now use cochlear implants, which do the job of converting sounds into neural signals, to restore hearing for patients with sensorineural hearing loss.  

Deafness or difficulties hearing can also result from conduction hearing loss. This happens when the eardrum or the bones of the middle ear are affected. Sometimes infants are born without one of these parts. Other times a head injury or infection causes damage to these bones. Conduction deafness can be treated with surgery, antibiotics, or a conduction hearing aid.

Three theories seek to explain how the ear converts pitch into a neural message that the brain can understand.

Place Theory says that hairs in different places in the cochlea vibrate only for certain sounds. According to this theory, there is a place in the cochlea for each pitch to be heard and converted into a neural signal. Autopsies of human cadavers and experiments on animals show that this theory is partially correct, at least for high-pitched sounds, but there seem to be no special places for lower-pitched sounds. Frequency Theory says that the hair cells vibrate at the speed of the sound vibration they experienced. Higher pitched sounds vibrate more quickly, sending quick pulses up the auditory nerve. Autopsies of human cadavers and experiments on animals show that this theory is partially correct, at least for low pitched sounds, but since nerve cells can't fire more than 1000 times per second, this theory doesn't explain very high pitched sounds that have wave frequencies above 1000 waves per second. Volley Theory explains how high pitched sounds get to the brain through a modified understanding of frequency theory. It says that nerve cells take turns firing as quickly as they can, and their combined frequency reaches over 1000 fires per second, so the brain can interpret a high sound from that combination.

Modern psychologists believe that humans perceive pitch through a combination of these three theories.

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