Sound Field Testing MCHAS TEAM Wave 4 SFR

Sound Field Testing MCHAS TEAM Wave 4 SFR 17/05/04 Modernising Children’s Hearing Aid Services

What can aided sound field thresholds tell us? Modernising Children’s Hearing Aid Services

Aided Thresholds 10 0 10 20 A 30 40 A A 50 A A 60 70 80 90 100 110 120 130 140 125 250 500 1000 Frequency (Hz) 2000 4000 8000 Modernising Children’s Hearing Aid Services

Limitations Ø Relies on valid behavioural response Modernising Children’s Hearing Aid Services

Limitations Hearing Threshold Ø 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 42 Frequency (Hz) 8 Modernising Children’s Hearing Aid Services

Limitations d. B SPL (TM) Ø 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 1000 X A X 4000 2000 8000 Frequency (Hz) Modernising Children’s Hearing Aid Services

Limitations Ø Poor test-retest reliability 10 0 10 20 30 40 50 AA A A 60 70 A A A 80 90 100 110 120 130 140 125 250 500 1000 Frequency (Hz) 2000 4000 8000 Ø Need at least 15 d. B difference between conditions before significant effect (Hawkins 1985). Modernising Children’s Hearing Aid Services

Limitations Ø Provide little indication of speech audibility, especially when using WDRC. Seewald 2003 Modernising Children’s Hearing Aid Services

Limitations Ø Inaccurate in regions of normal hearing 10 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 X A A X 125 250 500 1000 Frequency (Hz) A X A A X X 2000 4000 8000 Modernising Children’s Hearing Aid Services

So………… what information is provided? Ø An indication of the child’s/infant’s auditory performance Ø Good visual/auditory demonstration to parents between ‘no hearing aids’ vs ‘hearing aids’. Modernising Children’s Hearing Aid Services

A word of caution Ø Be aware of possible interactions with hearing aid features. ØNumber of channels ØCompression speed ØNoise algorithms ØActive feedback control Modernising Children’s Hearing Aid Services

What the Aided Threshold is and is not Ø IS: -index to reflect softest perceptible sound w/o vc -Functional gain reflects gain for softest sound (not conversational level) Ø 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 Children’s Hearing Aid Services

What Real-Ear Measure is and is not Ø 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 Ø IS NOT: -A perceptual response ie. Does not tell how soft a child can hear -cannot predict aided threshold Kuk, F (AAA 2004) Modernising Children’s Hearing Aid Services

So, should we be using both for a fuller picture? Ø Perhaps Ø If so, what should be the optimal aided threshold? Ø 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 Children’s Hearing Aid Services

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