Sound Field Testing

1. Sound Field Testing MCHAS TEAM

3. Aided Thresholds Reflects the softest sound that the child can hear with the hearing aid on.Reflects the softest sound that the child can hear with the hearing aid on.

4. Limitations Relies on valid behavioural response Need to be aware of limitations before interpret results……..Need to be aware of limitations before interpret results……..

5. Limitations Limited frequency resolution

6. Limitations No information on real ear output characteristics HA

7. Limitations Poor test-retest reliability Need at least 15 dB difference between conditions before significant effect (Hawkins 1985).

8. Limitations Provide little indication of speech audibility, especially when using WDRC. Aided thresholds reflects the softest sounds that are audible in real-life situations. This is NOT gain applied for conversational and loud situations.Aided thresholds reflects the softest sounds that are audible in real-life situations. This is NOT gain applied for conversational and loud situations.

9. Limitations Inaccurate in regions of normal hearing

10. 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’.

11. A word of caution Be aware of possible interactions with hearing aid features. Number of channels Compression speed Noise algorithms Active feedback control Multiple channels need less gain per channel to get the same overall loudness (rely on channel summation). This is only really possible when amplifying BB signals, when presenting pure tone won’t get channel summation and therefore may get poorer (higher) aided thresholds when using Xchannel aid compared with single channel aid. Fast attack, slow release aids may go into compression if loud sound in room, ie praise for VRA task etc Noise algorithms……. May only activate strategy for loud sounds so will depend on specific algorithmMultiple channels need less gain per channel to get the same overall loudness (rely on channel summation). This is only really possible when amplifying BB signals, when presenting pure tone won’t get channel summation and therefore may get poorer (higher) aided thresholds when using Xchannel aid compared with single channel aid. Fast attack, slow release aids may go into compression if loud sound in room, ie praise for VRA task etc Noise algorithms……. May only activate strategy for loud sounds so will depend on specific algorithm

12. 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 Multiple channels need less gain per channel to get the same overall loudness (rely on channel summation). This is only really possible when amplifying BB signals, when presenting pure tone won’t get channel summation and therefore may get poorer (higher) aided thresholds when using Xchannel aid compared with single channel aid. Fast attack, slow release aids may go into compression if loud sound in room, ie praise for VRA task etc Noise algorithms……. May only activate strategy for loud sounds so will depend on specific algorithmMultiple channels need less gain per channel to get the same overall loudness (rely on channel summation). This is only really possible when amplifying BB signals, when presenting pure tone won’t get channel summation and therefore may get poorer (higher) aided thresholds when using Xchannel aid compared with single channel aid. Fast attack, slow release aids may go into compression if loud sound in room, ie praise for VRA task etc Noise algorithms……. May only activate strategy for loud sounds so will depend on specific algorithm

13. A word of caution A 5 year old child with a 90-100 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?

14. 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)

15. 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)

16. 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)

17. THANK-YOU!