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Hearing or Audition

Module 14

Hearing

Our auditory sense

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The Stimulus Input: Sound Waves

Sound waves are composed of compression and rarefaction of air molecules.

Acoustical transduction: Conversion of sound pressure waves into neural

impulses in the hairs cells of the inner ear.

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Sound Characteristics

1. Frequency (pitch)2. Intensity (loudness)3. Quality (timbre)

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Frequency (Pitch)

Frequency (pitch):

Dimension of frequency

determined by wavelength of

sound.

Wavelength: The distance from

the peak of one wave to the peak

of the next.

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Intensity (Loudness)

Intensity (Loudness):

Amount of energy in a wave

determined by amplitude relates

to perceived loudness.

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Loudness of Sound

70dB

120dB

Richard K

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ages

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Quality (Timbre)

Quality (Timbre): Characteristics of sound from a zither and a guitar allows the ear to

distinguish between the two.

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Zither

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Overtones

Overtones: Make the distinction among musical instruments possible.

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The Ear

Dr. Fred H

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Pinna

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The EarOuter Ear: Pinna. Collects sounds. The sound travels down the Auditory canal until it reaches the eardrum. Or tympanic membrane.

Middle Ear: Chamber between eardrum and cochlea containing three tiny bones (hammer or malleus, is connected to the anvil or incus,which is connected to the stirrup or stapes all three are known as the ossicles) that concentrate the vibrations of the eardrum on the cochlea’s oval window. (membrane similar to the eardrum.)

Inner Ear: Innermost part of the ear, containing the cochlea, semicircular canals, and vestibular sacs.The cochlea is a structure shaped like a snail’s shell filled with fluidSemi circular canals determine balance.

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CochleaCochlea: Coiled, bony, fluid-filled

tube in the inner ear that transduces sound vibrations to

auditory signals.As the oval window vibrates, the fluid moves. The floor of the cochlea is the basilar membrane lined with hair cells. These hair cells are connected to the organ of corti which are neurons activated by movement of the hair cells.

Transduction in the ear• Sound waves hit the eardrum

then anvil then hammer then stirrup then oval window.

• Everything is just vibrating.• Then the cochlea vibrates.• The cochlea is lined with

mucus called basilar membrane.

• In basilar membrane there are hair cells.

• When hair cells vibrate they turn vibrations into neural impulses which are called organ of Corti.

• Sent then to thalamus up auditory nerve.

It is all about the vibrations!!!

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Theories of AuditionPlace Theory suggests that sound

frequencies stimulate basilar membrane at specific places resulting in perceived

pitch. Usually sound waves between 5,000 to 20,000 hz but not below 5000.

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Place Theory

• Different hairs vibrate in the cochlea when they different pitches.

• So some hairs vibrate when they hear high and other vibrate when they hear low pitches.

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Theories of Audition

Frequency Theory states that the rate of nerve impulses traveling up the auditory nerve

matches the frequency of a tone, thus enabling us to sense its pitch. Usually up to 4000 hertz.

Explains the perception of lower sounds.

SoundFrequency

Auditory NerveAction Potentials

100 Hz200 Hz

Frequency Theory

• All the hairs vibrate but at different speeds.

• Volley Theory: individual neurons can only fire about 1000 times per second/ neurons alternate firing to achieve a combined frequency of 4,000 per second

• Place theory accounts for high pitched sounds (above 5,000 to 20,000 hz)

• Frequency for low pitched sounds. (4000 hz)

• In between a combination of the two

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Localization of Sounds

Because we have two ears sounds that reach one ear faster than the other makes

us localize the sound.

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Localization of Sound

1. Intensity differences2. Time differences

Time differences as small as 1/100,000 of a second can lead to localize sound. Head

acts as “shadow” or partial sound barrier.

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Hearing Loss

Conduction Hearing Loss: Hearing loss caused by damage to the mechanical system (eardrums or ossicles) that conducts sound waves to the cochlea.

Sensorineural Hearing Loss: Hearing loss caused by damage to the cochlea’s receptor cells or to the auditory nerve, also called nerve deafness. Hearing aids are of no use to an individual with nerve damage.Tinnitus: ringing sensation following exposure to loud sounds.

DeafnessConduction Deafness

• Something goes wrong with the sound and the vibration on the way to the cochlea.

• You can replace the bones or get a hearing aid to help.

Nerve (sensorineural) Deafness

• The hair cells in the cochlea get damaged.

• Loud noises can cause this type of deafness.

• NO WAY to replace the hairs.

• Cochlea implant is possible.

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Hearing Deficits

Older people tend to hear low frequencies well but suffer hearing loss for high frequencies.

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Deaf Culture

Cochlear implants are electronic devices that enable the brain to hear sounds.

Cochlear ImplantDeaf Musician

EG

Images/ J.S. W

ilson ©

Wolfgang G

stottner. (2004) Am

erican Scientist, V

ol. 92, Num

ber 5. (p. 437)