Hearing
Anatomy of the Ear
How the Ear Works
How the Ear Works
The outer ear
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The pinna, which is the external part of the
ear, collects sounds and funnels them through
the auditory canal to the tympanic membrane
(the eardrum), which marks the boundary
between the outer ear and the middle ear
How the Ear Works
The middle ear
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The malleus, incus, and stapes (also called the
hammer, anvil and stirrup) vibrate in reaction to
sound waves from the auditory canal
The stapes’ movement creates
vibrations on the oval
window, which covers
the inner ear
How the Ear Works
The inner ear
 The cochlea contains in the basilar membrane about
16,000 hair cells that are the receptor cells for hearing
 Fluid in the cochlea is displaced, causing the hair cells
to move, in turn causing the sensation of hearing
 When these hair cells or auditory nerve fibers are
damaged, a person suffers nerve deafness
 Conduction deafness is hearing loss due to damage to
the mechanical system carrying sound waves to the
cochlea
What We Hear
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Loudness
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Pitch
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The dimension of auditory experience related to
the intensity of a pressure wave.
The dimension of auditory experience related to
the frequency of a pressure wave.
Timbre (pronounced “TAM-bur”)
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The distinguishing quality of sound; the
dimension of auditory experience related to the
complexity of the pressure wave.
How We Distinguish Pitch

Pitch is the quality of a sound perceived as
high or low and is determined by the
frequency of the sound wave
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Humans can perceive sound wave frequencies
from about 20 to 20,000 Hertz
Place theory contends that there is a specific
place along the basilar membrane in the inner
ear that will correspond to a particular
frequency.
Frequency theory contends that the
frequency of a sound wave is mimicked by the
firing rate of the hair cells across the entire
basilar membrane
How We Distinguish Pitch
Both theories have validity
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According to the volley principle, Frequency theory
explains our perception of sound up to about 5000 Hz.
Because 5000 times per second is the upper limit for the
firing rate using the volley principle, Frequency theory
would not be able to explain how we perceive higher
frequencies
Hence, Frequency theory explains the perceptions of lower
pitched sounds (< 500 Hz) and Place theory explains how
we perceive higher frequencies (> 5000 Hz)
For frequencies between 500 and 5000 Hz, both theories are
correct, and hence we have better pitch perception in this
range
From Sound Wave to Perception
1.
2.
3.
4.
Pinna Tympanic Membrane (eardrum)
bones of inner ear (hammer, anvil, stirrup)
COCHLEA (primary hearing organ)
Cochlea is filled w/ fluid, which further
transmits vibrations to thin membrane- Basilar
Membrane
BM = Transduction; tiny hairs on BM tickle the
sensory nerves
Neural message is sent to Temporal Lobe
How Sound Waves Become
Auditory Sensations
Tympanic membrane –
The eardrum
Copyright © Allyn and Bacon 2006
How Sound Waves Become
Auditory Sensations
Cochlea –
Where sound
waves are
transduced
Copyright © Allyn and Bacon 2006
How Sound Waves Become
Auditory Sensations
Auditory nerve –
Neural pathway
connecting the ear
and the brain
Copyright © Allyn and Bacon 2006
Auditory Localization
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Sounds from different
directions are not identical
as they arrive at left and
right ears
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Loudness
Timing
Phase
The brain calculates a
sound’s location by using
these differences.
Copyright © Allyn and Bacon 2006
Conduction Deafness
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An inability to hear resulting from damage to
structures of the middle or inner ear
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Conductive hearing loss is often only mild and is never
worse than a moderate impairment.
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Generally, with pure conductive hearing loss, the quality
of hearing (speech discrimination) is good, as long as
the sound is amplified loud enough to be easily heard.
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Possible Causes
Ear wax build up
Fluid inside the inner ear, like from an inner ear
infection.
If the bones of the ear get a buildup of calcium
Sensorineural Deafness… or
Nerve Deafness
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An inability to hear, linked to a deficit in the body’s
ability to transmit impulses from the cochlea to the
brain, usually involving the auditory nerve or higher
auditory processing centers
It can be mild, moderate, severe, or profound, to the point
of total deafness.
 Possible Causes
 Long-term exposure to environmental noise
 Genetic
 Disease or illness
 Medications
 Physical trauma
Pre-Lingual Deafness

These are people that are born deaf