Hearing%20and%20Deafness%201.%20Anatomy%20

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Hearing and Deafness 1. Anatomy physiology

• Chris Darwin

Web site for lectures, lecture notes and
filtering lab http//www.lifesci.sussex.ac.uk/hom
e/Chris_Darwin/ look under "Teaching material
for students" "Perception Attention"
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Outer, middle inner ear
Protection Impedance match
Capture Amplify mid-freqs Vertical direction
coding
Frequency analysis Transduction
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Middle ear structure
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Stapedius reflex
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Conductive hearing loss

• Sounds dont get into cochlea
• Middle ear problems
• Helped by surgery and by amplification

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Outer, middle inner ear
Protection Impedance match
Capture Amplify mid-freqs Vertical direction
coding
Frequency analysis Transduction
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Cochlea
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Cochlea cross-section
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Travelling wave on basilar membrane sorts sounds
by frequency
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Reponse of basilar membraneto sine waves
Each point on the membrane responds best to a
different frequency high freq at base, low at
apex.
praat
amadeus
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Organ of Corti
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Inner hair cell
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Hair Cell Stereocilia
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Auditory nerve innervation
IHC (1) radial afferent (blue) lateral efferent
(pink)
OHC (2) spiral afferent (green) medial
efferent (red)
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Auditory nerve rate-intensity functions
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Phase Locking of Inner Hair Cells
Auditory nerve connected to inner hair cell tends
to fire at the same phase of the stimulating
waveform.
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Phase-locking
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Inner vs Outer Hair Cells
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Inner vs Outer Hair Cells
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OHC movement
Passive No OHC movement
Active With OHC movement
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OHC activity
OHCs are relatively more active for quiet sounds
than for loud sounds. They only amplify sounds
that have the characteristic frequency of their
place.

• Increases sensitivity (lowers thresholds)
• Increases selectivity (reduces bandwidth of
  auditory filter)
• Gives ear a logarithmic (non-linear) amplitude
  response
• Produce Oto-acoustic emissions

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Conductive vs Sensori-neural deafness
Mostly a combination of OHC and IHC damage
Becomes linear, so No combination tones Or
two-tone suppression
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Auditory nerve frequency-threshold curves
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Auditory tuning curves
Inner hair-cell damage
Healthy ear
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Outer-hair cell damage
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BM becomes linear without OHCs (furosemide
injection)
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Amplification greater and tuning more selective
at low levels
Robles, L. and Ruggero, M. A. (2001). "Mechanics
of the mammalian cochlea," Physiological Review
81, 1305-1352.
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Normal auditory non-linearities

• Normal loudness growth (follows Webers Law)
• Combination tones 880-gt1320
• Two-tone suppression
• Oto-acoustic emissions