Harvey Dillon, Gitte Keidser, Teresa Ching, Matt Flax, Scott Brewer - - PowerPoint PPT Presentation

creating sound valueTM

DEVELOPMENT OF NAL-NL2

Harvey Dillon, Gitte Keidser, Teresa Ching,

Matt Flax, Scott Brewer

The HEARing CRC & The National Acoustic Laboratories

www.hearingcrc.org

creating sound valueTM

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Prescribe hearing aids to:

• Make speech intelligible
• Make loudness comfortable
• Prescription affected by other things

– localization, – tonal quality, – detection of environmental sounds, – naturalness.

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Compare

Deriving optimal gains - step 1

Speech spectrum & level Gain-frequency response Amplified speech spectrum Loudness model Normal loudness Loudness model Loudness (hearing impaired) Audiogram Intelligibility model Intelligibility achieved

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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

The audiograms

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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

Deriving optimal gains - step 1

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Overall prescription approach

Theoretical predictions Empirical

• bservations

Psychoacoustics Speech science Assumptions, rationale Final formula Compare Adjust

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Limiting compression ratio

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Multi-dimensional equation A neural network

H250 H500 H1000 H2000 H8k SPL G250 G500 G1000 G2000 G8k

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The two key ingredients

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

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Psychoacoustics

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Why are hearing thresholds so useful?

Hearing thresholds Speech Perception proficiency Frequency selectivity Temporal resolution Central auditory processing Other Age Cognitive ability

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BKB, VCV and CUNY

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Factors affecting prescription

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Gain; adults, medium input level

(N = 187)

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• 2
• 1.5
• 1
• 0.5

0.5 1 1.5 Preferred gain deviation from NAL-NL1 re gain preferred at 65 dB SPL in dB 50 80 Input level in dB SPL Smeds et al. 2006 Zakis et al. 2007

Gain for adults: low & high input levels

Suggest that the compression ratio should be slightly higher, at least for clients with mild and moderate hearing loss

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Binaural loudness correction

1 2 3 4 5 6 7 20 40 60 80 100 120 Input level (dB) Gain variation (dB)

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Empirical evidence: variations from NAL-NL1

Input level Output level

Adults Children NAL-NL1

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Adults – congenital or acquired?

• 14
• 12
• 10
• 8
• 6
• 4
• 2

Preferred gain deviation from NAL-RP (dB) LFA HFA

Congenital (N=15) Acquired (N=28)

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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

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5 10 15 20 25 30 35 40 100 1000 10000 Frequency in Hz Insertion gain in dB NAL-NL1 Male, exp, non-tonal Male, exp, tonal

Tonal versus non-tonal language

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Example audiogram: moderate sloping

5 10 15 20 25 30 35 40 100 1000 10000 Frequency (Hz) Insertion Gain (dB)

250 125 500 1k 2k 4k 8k 20 40 60 80 100 120

Frequency (Hz) Hearing threshold (dB HL)

50 dB 65 dB 80 dB

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5 10 15 20 25 30 35 40 100 1000 10000 Frequency (Hz) Insertion Gain (dB)

250 125 500 1k 2k 4k 8k 20 40 60 80 100 120

Frequency (Hz) Hearing threshold (dB HL)

50 dB 65 dB 80 dB

Example audiogram: flat 60

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5 10 15 20 25 30 35 40 100 1000 10000 Frequency (Hz) Insertion Gain (dB)

250 125 500 1k 2k 4k 8k 20 40 60 80 100 120

Frequency (Hz) Hearing threshold (dB HL)

50 dB 65 dB 80 dB

Example audiogram: steeply sloping

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5 10 15 20 25 30 35 100 1000 10000 Frequency (Hz) Insertion Gain (dB)

250 125 500 1k 2k 4k 8k 20 40 60 80 100 120

Frequency (Hz) Hearing threshold (dB HL)

50 dB 65 dB 80 dB

Example audiogram: extreme ski-slope

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5 10 15 20 25 30 100 1000 10000 Frequency (Hz) Insertion Gain (dB)

250 125 500 1k 2k 4k 8k 20 40 60 80 100 120

Frequency (Hz) Hearing threshold (dB HL)

50 dB 65 dB 80 dB

Example audiogram: reverse sloping

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Variables in NAL-NL2

AC BC' REDD ABG BC REIG N BWC WBCT REAG REUG Bi-uni Gender Age Experience RESR CG RECD MLE SSPL2cc Limiting type SSPLES ESCD Aid type I/O Vent Tube UCT

Blue = User i/p Grey = internal variable Red = effect of saturation Dash-dot = alternatives Green = stored data

CR Comp speed Language AC' ESG Depth RECD Transducer

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“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

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Acknowledgements

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This research was financially supported by the HEARing CRC established and supported under the Australian Government’s Cooperative Research Centres Program www.hearingcrc.org www.nal.gov.au