DEVELOPMENT OF NAL-NL2

Transcription

1 DEVELOPMENT OF NAL-NL2 Harvey Dillon, Gitte Keidser, Teresa Ching, Matt Flax, Scott Brewer The HEARing CRC & The National Acoustic Laboratories creating sound value value TM TM

2 Prescribe hearing aids to: Make speech intelligible Make loudness comfortable Prescription affected by other things localization, tonal quality, detection of environmental sounds, naturalness.

3 Deriving optimal gains - step 1 Speech spectrum & level Loudness model Normal loudness Gain-frequency response Compare Intelligibility achieved Intelligibility model Amplified speech spectrum Loudness model Loudness (hearing impaired) Audiogram

4 The audiograms Inverted hearing loss profiles used Rejection criterion : -30<= G <=60, where G is the slope sum(h(f))/3 <=100, where f is in the set {0.5, 1, 2} khz

5 Deriving optimal gains - step 1 Audiogram 1 Speech level 1 Optimal gain frequency response Audiogram 1 Speech level 2 Optimal gain frequency response Audiogram 1 Speech level 3 Optimal gain frequency response Audiogram 2 Speech level 1 Optimal gain frequency response 200 audiograms x 6 speech levels 1200 gain frequency responses, each at 20 frequencies from 125 Hz to 10 khz

6 Overall prescription approach Psychoacoustics Assumptions, rationale Theoretical predictions Adjust Final formula Compare Speech science Empirical observations

7 Limiting compression ratio

8 Multi-dimensional equation A neural network H 250 H 500 H 1000 H 2000 H 8k SPL G 250 G 500 G 1000 G 2000 G 8k

9 The two key ingredients Speech spectrum & level Loudness model Normal loudness Gain-frequency response Compare Intelligibility achieved Intelligibility model Amplified speech spectrum Loudness model Loudness (hearing impaired) Audiogram

10 Psychoacoustics

11 Why are hearing thresholds so useful? Frequency selectivity Hearing thresholds Temporal resolution Central auditory processing Speech Perception proficiency Age Other Cognitive ability

12 BKB, VCV and CUNY

13 Factors affecting prescription

14 Gain; adults, medium input level (N = 187)

15 Preferred gain deviation from NAL-NL1 re gain preferred at 65 db SPL in db Gain for adults: low & high input levels Input level in db SPL Smeds et al Zakis et al Suggest that the compression ratio should be slightly higher, at least for clients with mild and moderate hearing loss

16 Gain variation (db) Binaural loudness correction Input level (db)

17 Empirical evidence: variations from NAL-NL1 Output level Children NAL-NL1 Adults Input level

18 Preferred gain deviation from NAL-RP (db) Adults congenital or acquired? Congenital (N=15) Acquired (N=28) LFA HFA

19 Effect of language Gain at each frequency depends on importance of each frequency Low frequencies more important in tonal languages Two versions of NAL-NL2 Tonal languages Non-tonal languages

20 Tonal versus non-tonal language Insertion gain in db NAL-NL1 30 Male, exp, non-tonal 25 Male, exp, tonal Frequency in Hz

21 Hearing threshold (db HL) Insertion Gain (db) Example audiogram: moderate sloping Frequency (Hz) k 2k 4k 8k db 65 db 80 db Frequency (Hz)

22 Hearing threshold (db HL) Insertion Gain (db) Example audiogram: flat 60 Frequency (Hz) k 2k 4k 8k db 65 db 80 db Frequency (Hz)

23 Hearing threshold (db HL) Insertion Gain (db) Example audiogram: steeply sloping Frequency (Hz) k 2k 4k 8k db 65 db 80 db Frequency (Hz)

24 Hearing threshold (db HL) Insertion Gain (db) Example audiogram: extreme ski-slope Frequency (Hz) k 2k 4k 8k db db db Frequency (Hz)

25 Hearing threshold (db HL) Insertion Gain (db) Example audiogram: reverse sloping Frequency (Hz) k 2k 4k 8k db 65 db 80 db Frequency (Hz)

26 Variables in NAL-NL2 Age Vent Tube RECD Comp speed Language Bi-uni Gender Experience REDD WBCT BWC UCT N I/O CR REUG RECD Depth Aid type Transducer AC' Blue = User i/p BC' AC ABG BC REIG RESR SSPL 2cc REAG CG ESCD MLE ESG Grey = internal variable Red = effect of saturation Dash-dot = alternatives Limiting type SSPL ES Green = stored data

27 A challenge for the profession is to devise fitting procedures that are scientifically defensible and the challenge for the individual audiologist is to choose the best procedures from whatever are available Denis Byrne, 1998

28 Acknowledgements This research was financially supported by the HEARing CRC established and supported under the Australian Government s Cooperative Research Centres Program