1 pb anatomy
DESCRIPTION
bolehTRANSCRIPT
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Hearing and Deafness 1. Anatomy & physiology
Chris DarwinWeb site for lectures, lecture notes and filtering lab:http://www.lfesci.sussex.ac.uk/home/Chris_Darwin/
look under: "Teaching material for students" "Perception & Attention"
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ProtectionImpedance match
Capture; Amplify mid-freqsVertical direction coding
Frequency analysisTransduction
Outer, middle & inner ear
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Middle ear structure
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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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ProtectionImpedance match
Capture; Amplify mid-freqsVertical direction coding
Frequency analysisTransduction
Outer, middle & inner ear
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Cochlea
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Cochlea cross-section
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Travelling wave on basilarmembrane sorts sounds by frequency
distance along basilar membrane
amp
litu
de
of
vib
rati
on
base apex
high frequencies low frequencies
0
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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.
amadeus praat
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Organ of Corti
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Innerhair cell
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Hair CellStereocilia
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Auditory nerve innervation
OHC (2)spiral afferent (green)medial efferent (red)
IHC (1)
radial afferent (blue)lateral efferent (pink)
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Auditory nerverate-intensity functions
log amplitude (dB SPL)
100
80
60
40
20
sp
ikes
/ s
eco
nd
30 60 90
high spontaneous rate
low spontaneous rate
saturation
many
few
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Phase Locking of Inner Hair Cells
Auditory nerve connected to inner hair cell tends to fireat the same phase of the stimulating waveform.
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Phase-locking
pres
sure
-1
-0.5
0
0.5
1
0 0.2 0.4 0.6 0.8 1
Inter-spike IntervalsResponse to Low Frequency tones
time (t)
volta
ge
Response to High Frequency tones > 5kHzRandom intervals
time (t)
2 periods 1 period nerve spike
volta
ge
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Innervs
OuterHair Cells
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Inner vs Outer Hair CellsInner Hair Cells Outer Hair Cells
Sensory Motor
Afferent nerves Efferent nerves
Single row c.3 rows
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OHC movement
PassiveNo OHC movement
ActiveWith OHC movement
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OHC activity
Increases sensitivity (lowers thresholds) Increases selectivity (reduces bandwidth of auditory filter) Gives ear a logarithmic (non-linear) amplitude response Produce Oto-acoustic emissions
OHCs are relatively more active for quiet sounds than forloud sounds.They only amplify sounds that have the characteristicfrequency of their place.
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Conductive vs Sensori-neural deafness
Conductive Sensori-neural Sensori-neural
Origin Middle-ear Cochlea (IHCs) Cochlea (OHCs)
Thresholds Raised Raised Raised
Filter bandwidths Normal Normal Increased
Loudness growth Normal Normal Increased (Recruitment
Becomes linear, soNo combination tonesOr two-tone suppression
Mostly a combination ofOHC and IHC damage
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Auditory nerve frequency-threshold curves
log frequency
log
am
pli
tud
e (d
B S
PL
)
100
80
60
40
20
Characteristic Frequency
Normal Threshold
Normal bandwidth
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Auditory tuning curves
log frequency
log
am
pli
tud
e (d
B S
PL
) 100
80
60
40
20Characteristic Frequency
Normal Threshold
Abnormal Threshold
Normal bandwidth
Normal bandwidth
Healthy ear
Inner hair-celldamage
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Outer-hair cell damage
log frequency
log
am
pli
tud
e (d
B S
PL
) 100
80
60
40
20
Characteristic Frequency
Normal Threshold
Abnormal Threshold
Normal bandwidth
Abnormal bandwidth
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BM becomes linear without OHCs(furosemide injection)
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Amplification greater and tuningmore 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
Two-tone suppression
Oto-acoustic emissions