Modernising Children’s Hearing Aid Services 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 A A A A A

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

Modernising Children’s Hearing Aid Services Limitations  Limited frequency resolution

Modernising Children’s Hearing Aid Services Limitations Frequency (Hz) dB SPL (TM) X X X X X X AA A A  No information on real ear output characteristics HA

Modernising Children’s Hearing Aid Services Limitations  Poor test-retest reliability  Need at least 15 dB difference between conditions before significant effect (Hawkins 1985). A A A A A A A A A A

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

Modernising Children’s Hearing Aid Services Limitations  Inaccurate in regions of normal hearing X X X X X X A A A A A A

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

Modernising Children’s 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 Children’s Hearing Aid Services A word of caution  Take care in testing setup:  Loudspeaker & listener in calibrated positions  Quiet room  No movement  Ascending warble tones  Stimulus duration approx 1 sec  5 dB steps  Inter-stimulus interval of at least 5 sec  Individual ear information Nelson 2003 AAA

Modernising Children’s Hearing Aid Services A word of caution  A 5 year old child with a dB flat loss is fitted with a power WDRC DSP hearing (no volume control) & analogue linear power hearing aid with volume control. Would you expect any differences? Frequency (Hz) A A A A Hearing Threshold A WDRC DSP Aid A A AA A Frequency (Hz) Hearing Threshold Linear Aid Nelson 2003 AAA Linear aid volume control had been increased prior to testing.

Modernising Children’s 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 Children’s 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 -cannot predict aided threshold Kuk, F (AAA 2004)

Modernising Children’s 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 sounds and meaningfulness of these *Degree of hearing loss and possible dead regions regions *Limitations of hearing aid (as discussed)

Modernising Children’s Hearing Aid Services THANK-YOU!