Sound Field Testing
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Modernising Children’s Hearing Aid Services
Sound Field TestingSound Field Testing
MCHAS TEAMMCHAS TEAM
Wave 4 SFR 17/05/04
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Modernising Children’s Hearing Aid Services
What can aided sound field thresholds tell What can aided sound field thresholds tell us?us?
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Modernising Children’s Hearing Aid Services
Aided ThresholdsAided Thresholds10
0
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140 125 250 500 1000 2000 4000 8000
Frequency (Hz)
A AA
AA
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Modernising Children’s Hearing Aid Services
LimitationsLimitations
Relies on valid Relies on valid behavioural behavioural responseresponse
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Modernising Children’s Hearing Aid Services
LimitationsLimitations
Limited frequency resolutionLimited frequency resolution
100
102030405060708090
100110120130140
.125 .25 .5 1 2 4 8Frequency (Hz)
A AA
A
Hea
ring
Thr
esho
ld
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Modernising Children’s Hearing Aid Services
LimitationsLimitations
1401301201101009080706050403020
10 0 -10
125 250 500 1000 2000 4000 8000
Frequency (Hz)
dB S
PL
(T
M)
XXXX
XX
XXXX XX
A A A A
No information on real ear output characteristics No information on real ear output characteristics HAHA
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Modernising Children’s Hearing Aid Services
LimitationsLimitations
Poor test-retest Poor test-retest reliabilityreliability
Need at least 15 dB Need at least 15 dB difference between difference between conditions before conditions before significant effect significant effect (Hawkins 1985)(Hawkins 1985)..
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140 125 250 500 1000 2000 4000 8000
Frequency (Hz)
A A AA AA
A A A
A
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Modernising Children’s Hearing Aid Services
LimitationsLimitations
Provide little indication of speech audibility, Provide little indication of speech audibility, especially when using WDRC.especially when using WDRC.
Seewald 2003
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Modernising Children’s Hearing Aid Services
Limitations Limitations
Inaccurate in regions of normal hearingInaccurate in regions of normal hearing
100
102030405060708090
100110120130140
125 250 500 1000 2000 4000 8000Frequency (Hz)
XX
X XX X
A A AA A A
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Modernising Children’s Hearing Aid Services
So………… what information is provided?So………… what information is provided?
An indication of the An indication of the child’s/infant’s auditory child’s/infant’s auditory performanceperformance
Good visual/auditory Good visual/auditory demonstration to parents demonstration to parents between ‘no hearing aids’ between ‘no hearing aids’ vs ‘hearing aids’.vs ‘hearing aids’.
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Modernising Children’s Hearing Aid Services
A word of cautionA word of caution
Be aware of possible interactions with Be aware of possible interactions with hearing aid features.hearing aid features.Number of channelsCompression speedNoise algorithmsActive feedback control
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Modernising Children’s Hearing Aid Services
What the Aided Threshold is and is notWhat the Aided Threshold is and is not
IS:IS: -index to reflect softest perceptible sound w/o vc-index to reflect softest perceptible sound w/o vc-Functional gain reflects gain for -Functional gain reflects gain for softest sound softest sound
(not (not conversational level)conversational level) IS NOT:IS NOT:
-Reflect gain for any input level other than soft-Reflect gain for any input level other than soft-Reflect gain for conversational sounds-Reflect gain for conversational sounds-Reflect loudness comfort-Reflect loudness comfort-Reflect processing of DSP aids eg. NR etc-Reflect processing of DSP aids eg. NR etc
Kuk, FKuk, F(AAA 2004)(AAA 2004)
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Modernising Children’s Hearing Aid Services
What Real-Ear Measure is and is notWhat Real-Ear Measure is and is not
IS:-Allows determination of physical output of IS:-Allows determination of physical output of hearing aid at different input levels:hearing aid at different input levels: **Gain for Gain for conversational, soft and loud soundsconversational, soft and loud sounds
**Effect of signal processing eg.compression, NR Effect of signal processing eg.compression, NR etcetc
IS NOT:-A perceptual response ie. Does not tell IS NOT:-A perceptual response ie. Does not tell how soft a child can hearhow soft a child can hear
-cannot predict aided threshold-cannot predict aided thresholdKuk, FKuk, F
(AAA 2004)(AAA 2004)
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Modernising Children’s Hearing Aid Services
So, should we be using both for a fuller So, should we be using both for a fuller picture?picture?
PerhapsPerhaps If so, what should be the optimal aided If so, what should be the optimal aided
threshold?threshold? Depends on criteria:Depends on criteria:
**Importance of hearing soft or low level inputImportance of hearing soft or low level input
sounds and meaningfulness of thesesounds and meaningfulness of these*Degree of hearing loss and possible dead*Degree of hearing loss and possible dead
regionsregions*Limitations of hearing aid (as discussed) *Limitations of hearing aid (as discussed)
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Modernising Children’s Hearing Aid Services
THANK-YOU!THANK-YOU!