modernising children’s hearing aid services sound field testing mchas team wave 4 sfr 17/05/04
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Modernising Children’s Hearing Aid Services
Sound Field TestingSound Field Testing
MCHAS TEAMMCHAS TEAM
Wave 4 SFR 17/05/04
Modernising Children’s Hearing Aid Services
What can aided sound field thresholds tell What can aided sound field thresholds tell us?us?
Modernising Children’s Hearing Aid Services
Aided ThresholdsAided Thresholds10
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Frequency (Hz)
A AA
AA
Modernising Children’s Hearing Aid Services
LimitationsLimitations
Relies on valid Relies on valid behavioural behavioural responseresponse
Modernising Children’s Hearing Aid Services
LimitationsLimitations
Limited frequency resolutionLimited frequency resolution
100
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.125 .25 .5 1 2 4 8Frequency (Hz)
A AA
A
Hea
ring
Thr
esho
ld
Modernising Children’s Hearing Aid Services
LimitationsLimitations
1401301201101009080706050403020
10 0 -10
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Frequency (Hz)
dB S
PL
(T
M)
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A A A A
No information on real ear output characteristics No information on real ear output characteristics HAHA
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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Frequency (Hz)
A A AA AA
A A A
A
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
Modernising Children’s Hearing Aid Services
Limitations Limitations
Inaccurate in regions of normal hearingInaccurate in regions of normal hearing
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125 250 500 1000 2000 4000 8000Frequency (Hz)
XX
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A A AA A A
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’.
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
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)
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)
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)
Modernising Children’s Hearing Aid Services
THANK-YOU!THANK-YOU!