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Do You Hear What I Hear? The outer ear funnels sound waves to the eardrum. The bones or ossicles (Hammer {malleus}, Anvil {incus} & Stirrups {stapes}) of the middle ear amplify & relay the eardrum’s vibrations through to the inner ear, the oval window of the fluid-filled cochlea. The resulting pressure changes in the cochlear fluid cause the basilar membrane to ripple, bending the hair cells on the surface (16,000). Hair cell movements trigger impulses at the base of the nerve cells, whose fibers converge to form the auditory nerve, which sends neural messages to the thalamus & on the auditory cortex.

How do we detect loudness? NOT from intensity of hair cell’s response A soft, pure tone activates only the few cells attuned to its frequency Given louder sounds its neighbor hair cells also respond…the brain interprets loudness from the NUMBER of activated hair cells!

Two theories to help us understand pitch perception… Place Theory: theory linking the pitch we hear with the place where the cochlea’s membrane is stimulated. -Different frequencies of sound waves are said to vibrate different places on the cochlea. These places are wired to different parts of the auditory cortex in the brain so the sound can be processed correctly. Frequency Theory: theory that the rate of nerve impulses traveling up the auditory nerve matches the frequency of a tone, enabling us to sense its pitch. -The entire cochlea is believed to vibrate at a particular frequency, sending the signal of the quality of sound to the brain. (100 waves/sec then 100 pulses/sec travel up the auditory nerve)

Why does our own voice sound unfamiliar when we hear it on a recording? When we speak, we hear both the sound conducted by air waves to the outer ear & that carried directly to auditory nerve by bone conduction. –click your teeth, or munch a crunch *The strictly air-conducted sound that others normally hear (when we hear our voices on tape) is thinner. You can hear the sound waves conducted by bone if you plug your ears & talk in a normal voice.

Hearing Loss Damage to hair cells account for most hearing loss. (i.e.:carpet fibers…) “Earplugs or walk away.” –After exposure to loud noise, when your ears ring, ears are alerting us to possible hearing damage

What are the common causes of hearing loss? Why does controversy surround cochlear implants? Conduction Hearing Loss: damage to the mechanical system that conducts sound waves to the cochlea. (punctured eardrum; ossicles lose ability to vibrate) Sensorineural Hearing Loss:damage to the cochlea’s receptor cells or the auditory nerves; (“nerve deafness” disease, heredity, aging, prolonged exposure to damaging noise) Cochlear Implant:device converting sounds into electrical signals & stimulating the auditory nerve through electrodes threaded into the cochlea.

If you are a hearing person, imagine that you had been born deaf. Do you think you would want to receive a cochlear implant? Does it surprise you that most lifelong deaf adults do not desire implants for themselves or their children?