Aided Soundfield Testing - University of Manchester

Aided Soundfield Testing - University of Manchester

Sound Field Testing MCHAS TEAM Wave 4 SFR 17/05/04 Modernising Childrens Hearing Aid Services What can aided sound field thresholds tell us? Modernising Childrens Hearing Aid Services Aided Thresholds 10 0 10 20 A 30 40

A A A 50 A 60 70 80 90 100 110 120 130 140 125

250 500 1000 2000 Frequency (Hz) 4000 8000 Modernising Childrens Hearing Aid Services Limitations Relies on valid behavioural response Modernising Childrens Hearing Aid Services Limitations Hearing Threshold

Limited frequency resolution 10 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 A A .125

.25 .5 A A 1 24 Frequency (Hz) 8 Modernising Childrens Hearing Aid Services Limitations dB SPL (TM) No information on real ear output characteristics HA 140 130 120 110

100 90 80 70 60 50 40 30 20 10 0 -10 X X A 125 250 500 X

A X A 1000 X A 2000 4000 X 8000 Frequency (Hz) Modernising Childrens Hearing Aid Services Limitations Poor test-retest reliability

10 0 10 20 30 40 50 AA A A 60 70 A A A A A A

80 90 100 110 120 130 140 125 250 500 1000 2000 4000 Frequency (Hz) 8000 Need at least 15 dB difference between conditions before significant effect

(Hawkins 1985). Modernising Childrens Hearing Aid Services Limitations Provide little indication of speech audibility, especially when using WDRC. Seewald 2003 Modernising Childrens Hearing Aid Services Limitations Inaccurate in regions of normal hearing 10 0 10 20 30 40 50 60 70 80

90 100 110 120 130 140 X A X A A X 125 250 A X

A A X 500 1000 2000 4000 Frequency (Hz) X 8000 Modernising Childrens Hearing Aid Services So what information is provided? An indication of the childs/infants auditory performance

Good visual/auditory demonstration to parents between no hearing aids vs hearing aids. Modernising Childrens Hearing Aid Services A word of caution Be aware of possible interactions with hearing aid features. Number of channels Compression speed Noise algorithms Active feedback control Modernising Childrens Hearing Aid Services What the Aided Threshold is and is not IS: -index to reflect softest perceptible sound w/o vc -Functional gain reflects gain for softest sound (not conversational level) IS NOT: -Reflect gain for any input level other than soft -Reflect gain for conversational sounds

-Reflect loudness comfort -Reflect processing of DSP aids eg. NR etc Kuk, F (AAA 2004) Modernising Childrens Hearing Aid Services What Real-Ear Measure is and is not IS:-Allows determination of physical output of hearing aid at different input levels: *Gain for conversational, soft and loud sounds *Effect of signal processing eg.compression, NR etc IS NOT:-A perceptual response ie. Does not tell how soft a child can hear -cannot predict aided threshold Kuk, F (AAA 2004) Modernising Childrens Hearing Aid Services So, should we be using both for a fuller picture? Perhaps

If so, what should be the optimal aided threshold? Depends on criteria: *Importance of hearing soft or low level input sounds and meaningfulness of these *Degree of hearing loss and possible dead regions *Limitations of hearing aid (as discussed) Modernising Childrens Hearing Aid Services THANK-YOU! Modernising Childrens Hearing Aid Services

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