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8/24/2015
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Welcome toCochlear Dead Regions and Implications for Fittings
Presenter:
Ted Venema PhDAudiologist, Speaker, Author
Fran VincentMembership and
Marketing Manager
Ted Annis Senior Marketing Specialist
IHS Organizers:
Housekeeping
This presentation is being recorded
CE credit is available! Visit ihsinfo.org for details
Note taking handouts are available at ihsinfo.org on the webinar page. Feel free to download now!
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Agenda
Describe cochlear dead regions in terms of cochlear hair cells and the cochlear traveling wave
Outline audiograms associated with cochlear dead regions
Explain the rationale for the Threshold Equalizing (TEN) test
State some examples and implications of cochlear dead regions for hearing aid fittings
Q&A (enter questions in Question Box any time)
COCHLEAR HAIR CELLS, THE TRAVELING WAVE
& COCHLEAR DEAD REGIONS
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Cross Section of the Cochlea
TemporalBone
Helicotrema
SpiralLigament
ScalaVestibuli
ScalaMedia
ScalaTympani
SpiralGanglia
BasilarMembrane
Figure 1.2 Venema, T. Compression for Clinicians 2nd edition, Cengage 2006
Normal Inner & Outer Hair Cells
Figure 1.7 Venema, T. Compression for Clinicians, 2nd edition, Cengage 2006
Inner Hair cells
Afferent
Send soundinformation to the brain
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Damaged Outer Hair Cells
Figure 1.8 Venema, T. Compression for Clinicians, 2nd edition, Cengage 2006
Outer Hair cells
Efferent
Receive soundinformation from the brain
Outer Hair Cells: The Active Cochlear Mechanism
Note how embedded
OHCs actually pull tectorial membrane
down
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Cochlear Dead RegionsAre Not Due to Outer Hair Cell Damage
OHCs amplify & sharpen traveling wave peak Damage: reduces basilar membrane vibration
Without OHCs one would have about 50‐60 dB SNHLThis is the most common degree of HL (Presbycusis!)
More severe SNHL means IHC damage as wellOHCs give about 50 dB gain for lows; 65 dB gain for highs
Loss of sharpening traveling wave: Results in increased difficulty hearing in noiseSlight drop in speech discrimination, but not much
Outer Hair Cell Contributions to the Traveling Wave
BasilarMembrane
Displacement
BasilarMembrane
TravelingWave
Envelope ofTraveling Wave
OHCsSharpen
Peak
1. Amplify2. Sharpen
Figure 1.5 Venema, T. Compression for Clinicians, 2nd edition, Cengage 2006
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The Traveling Wave: Naturally Sharpened vs Aided
Natural traveling wave:2 peaks from 2 tones close in Hz
SNHL with OHC damage:smaller rounded peaks
Aided traveling wave:enlarges peaks but cannot sharpen
Figure 1.2 Venema, T. Compression for Clinicians 2nd edition, Cengage 2006
Cochlear Dead Regions However,Are Due to Inner Hair Cell Damage
OHCs tend to die before IHCs They are the moving part; more susceptible to aging and noise
If OHC damage causes about 50‐60 dB SNHL…More severe SNHL means IHC damage as well
IHC damage really deteriorates Speech Discrimination!B/c garbled message is sent on to the brain
Question: What audiograms suggests cochlear dead spots?To understand that, look at next few slides!
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The Asymmetrical Traveling Wave
BasilarMembrane
BasilarMembrane
Displacement
Intense Low‐Hztraveling wave moves
entire Basilar Membrane
Envelopes
Intense High‐Hztraveling wave moves
Basilar Membrane only at base
Upward Spread of Masking
BasilarMembrane
BasilarMembrane
Displacement
Intense Low‐Hztraveling wave (TW) movesentire Basilar Membrane
Envelopes
Note that the Low‐Hzenvelope covers
a soft High‐Hz TW envelope
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It Doesn’t Work the Other Way Around
BasilarMembrane
BasilarMembrane
Displacement
Soft Low‐Hz TW movesmainly the apicalBasilar Membrane
Envelopes
Intense High‐Hztraveling wave still moves
Basilar Membrane only at base
AUDIOGRAMS ASSOCIATED WITH COCHLEAR DEAD REGIONS
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O
O
O
O
OOO O O
Apex Base
Low‐Hz Dead Regions Can Therefore…Masquerade as Moderate Reverse HL
Low‐Hz Traveling waveIn totally dead IHC region
Will stimulate healthy hair cellsIn mid & high‐Hz regions
Asymmetrical traveling waveSteep front; shallow, longer “tail”
Total deafness in lows Looks like moderate low‐Hz SNHL
High‐Hz Dead Regions However…Have to Be Severe, Precipitous SNHL
OO OO
O
O
O
O O
Apex Base
OO
High‐Hz Traveling waveIn totally dead IHC region
Will stimulate healthy hair cellsIn mid & low‐Hz regions
Steep wave front must be intenseFor this to happen
Due to asymmetrical TW shapeSevere precipitous SNHL actuallylooks like mirror image of TW front
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For example…
OO OO
O
O
O
OO
Apex Base
OO
For Example…
OO OO
O
O
O
OO
Apex Base
OO
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For Example…
OO OO
O
O
O
OO
Apex Base
OO
“Cookie‐Bite” AudiogramsA Combination of the Above
O
O
O
O
OO
O
O
O
Apex Base
O
O
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TESTING FOR COCHLEAR DEAD REGIONS: THE THRESHOLD EQUALIZING NOISE
(TEN) TEST
TEN Test Noise
It is a broad band noise, delivered ipsilateral to tone
Has unique spectral shape
For normal HL, gives equal masked thresholds
Eg. 50 dB TEN gives 50 dB HL across all Hz’s
So no, you cannot use your speech masking noise
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TEN Noise Spectrum“
Hz
RelativedB
100 10,000
+10
‐20
Eg: 30 dB TEN…
Gives 30 dB HLThresholds
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Main Assumption Behind TEN Test
Soft ipsilateral TEN noise (eg. 30 dB HL) will elevate thresholds for low‐Hz tones.
Low‐Hz cochlear dead region resulting in 50 dB HL thresholds
Apex(lows)
Base(highs)
Why? Because “thresholds” in dead region come from high Hz’sThey do not truly arise from the low‐Hz hair cells
If the HL Is a True Moderate Low‐Hz SNHL (Not a Dead Region)
The soft ipsilateral TEN will have little effect
It will mask the healthy high‐Hz thresholds
And elevate them as a result…
But the low‐Hz thresholds won’t hear the TEN
And the thresholds will be unchanged
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Apex(lows)
Base(highs)
Main Assumption Behind TEN Test
Soft ipsilateral TEN noise (eg. 30 dB HL) will elevate thresholds for high‐Hz tones.
High‐Hz cochlear dead region resulting in 80 dB HL thresholds
Why? Because “thresholds” in dead region come from low Hz’sThey do not truly arise from the high‐Hz hair cells
If the HL Is a True Severe High‐Hz SNHL (Not a Dead Region)
The soft ipsilateral TEN will have little effect
It will mask the healthy low‐Hz thresholds
And elevate them as a result…
But the high‐Hz thresholds won’t hear the TEN
And the thresholds will be unchanged
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SOME EXAMPLES AND IMPLICATIONS FOR FITTINGS
Client with Mild‐Moderate SNHL Cochlear Dead Spots Not Suspected
Masked symbols: thresholds with 30 dB TEN
Figure 2.5 Venema, T. Compression for Clinicians,2nd edition, Cengage 2006
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Client with Profound High‐Hz SNHL Cochlear Dead Spots Suspected
Masked symbols: thresholds with 30 dB TEN
Figure 2.6 Venema, T. Compression for Clinicians,2nd edition, Cengage 2006
Client with Profound High‐Hz SNHL Cochlear Dead Spots Suspected
Masked symbols: thresholds with 50 dB TEN
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Moderate Reverse SNHLFit the transitions
Not the worst thresholds!
OO
O
O
OOO O O
Apex Base
OO OO
O
O
O
O
Apex Base
OO
Severe precipitous high‐Hz SNHLFit the transitions
Not the worst thresholds!
Implications For Fitting
Fitting the “Left Corner” Audiogram??
A “bridge” between
Hearing Aids
&
Cochlear Implants
Frequency Transposition…
125 250 500 1000 2000 4000 8000-10
0
10
20
30
40
50
60
70
80
90
100
110
120
OO
OOOO O O OOO
X XXXXX X X X X X
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Ever Wonder What Sounds Are Like for People with Dead Regions?
Recall testing those with reverse SNHLI suspect dead low‐Hz regions when reliability is poorer for lows,but I’ve never asked them what the pure tones sounded like.
Recall testing those with pronounced, precipitous SNHLThese clients tell me the highs sound like a “scratch,”or that the highs feel like a “tickle.”
Others have reports from their subjects as wellThey report tones in dead regions sound like noise however, this observation is inconsistent.
Ratings of clarity Cannot be used as reliable indicators of dead cochlear regions.
Keep It Simple
“You don’t need a weatherman to tell you where the wind blows” ~Bob Dylan
Wet your finger and stick it in the air!
If you see the suspicious audiograms, then suspect cochlear dead regions
Present tone so client can hear it, then ask as to its quality
If poor, then don’t amplify in those Hz’s!
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• Moore, BCJ (2001). Dead regions in the cochlea: Diagnosis, perceptual consequences, and implications for the fitting of hearing aids. Trends in Amplification 5(1)
• Moore, BCJ (2001). Dead regions in the cochlea: Implications for the choice of high‐frequency amplification. In Seewald, RC & Gravel, JS, eds, A Sound Foundation through Early Amplification, Phonak AG
• Moore, BCJ (2004) New Version of the TEN test with calibrations in dB HL. Ear & Hearing 25(5): 478‐487.
• Moore BCJ. Testing for Cochlear Dead Regions: Audiometer implementation of the TEN(HL) Test.
Hearing Review. 2010;17(1):10‐16,48.
• Venema, TH. Compression for Clinicians (2006); Ch 2Cengage Publishing ISBN 1‐4180‐0959‐8
References
Questions
Enter your question in the Question Box on your webinar dashboard
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THANK YOU FOR ATTENDING!
Contact Ted Venema, PhD:
For more info on obtaining a CE credit
for this webinar:
www.ihsinfo.org
