digital noise reduction hearing aids: what is the evidence of … · bentler, r. a. (2005)....
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Digital Noise Reduction Hearing Aids: What is the Evidence of Benefit in Adults?
Lakshmi M.S.
Ayasakanta Rout
James Madison University
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Outline of the Presentation• How does digital noise reduction (DNR) work?
• What evidence do we have on benefits of DNR?
• Systematic review of the available evidence.
• DNR benefit in the pediatric population.
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• We have come a long way but we still have a long way to go
• In 2005 when CNN celebrated its 25 years, it counted the top 25 innovations during their existence.
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http://www.cnn.com/2005/TECH/01/03/cnn25.top25.innovations/
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A real digital hearing aid chip
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Evolution of the Integrated Circuit
Image courtesy: Steve Armstrong of Gennum5
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Evolution of the Integrated Circuit
Image courtesy: Steve Armstrong of Gennum6
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Evolution of the Integrated Circuit
Image courtesy: Steve Armstrong of Gennum7
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Evolution of the Integrated Circuit
Image courtesy: Steve Armstrong of Gennum8
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Evolution of the Integrated Circuit
Image courtesy: Steve Armstrong of Gennum9
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Evolution of the Integrated Circuit
Image courtesy: Steve Armstrong of Gennum10
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Evolution of the Integrated Circuit
Image courtesy: Steve Armstrong of Gennum11
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Making sense of the scale
Human hair100 µm
Small transistor65 nm
Size of an Atom0.1 nm
1 millimeter = 1,000 µm = 1,000,000 nm
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Benefits of faster chips• More processing power: implementation of
complex algorithms.
• More ancillary operations: e.g. saving audio samples of low battery indicator in 32 languages
• Hearing aids acting as personal devices: e.g. daily reminders about medication.
• Each generation of chip continues to get smaller while delivering more power.
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Algorithm Integration• Advanced hearing aids employ sophisticated
signal detection and analysis step.– What is the intensity of the signal?
– Is it loud or soft?
– Is it speech or noise?
– Which frequency bands contain noise?
– Is there a feedback loop?
• More and more signal processing algorithms are “talking to each other” before acting on the signal.
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Digital Noise Reduction
• How does it work?
• What is the clinical evidence?
• Clinical tips for fitting adults vs. children
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How do we separate speech from noise?
Speech
Noise
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How can we separate speech from noise?
Spee
ch v
s. N
ois
e
Temporal domain
Spectral domain
Spatial domain
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How can we separate speech from noise?
Spee
ch v
s. N
ois
e
Temporal domain
Spectral domain
Spatial domain
18
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Separating speech from noise in the temporal domain
• Modulation frequency
• Modulation depth
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Modulation frequency (Hz)
Mo
du
lati
on
Ind
ex
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0 2 4 8 16 32 64
Modulation frequency of speech
20Powers, Holube, and Wesselkamp (1999).
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Modulation frequency (Hz)
Mo
du
lati
on
Ind
ex
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0 2 4 8 16 32 64
Modulation frequency of noise
21Powers, Holube, and Wesselkamp (1999).
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-15
-10
-5
0
0 20 40 60 80 100Modulation frequency (Hz)
Gai
n r
edu
ctio
n (
dB
)
Noise reduction based on modulation frequency
22Powers, Holube, and Wesselkamp (1999).
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-15
-10
-5
0
0 20 40 60 80 100
Modulation depth (%)
Gai
n r
edu
ctio
n (
dB
)
Noise reduction based on modulation depth
23Powers, Holube, and Wesselkamp (1999).
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How can we separate speech from noise?
Spee
ch v
s. N
ois
e
Temporal domain
Spectral domain
Spatial domain
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Separating speech from noise in spectral domain
• Gain reduction at low frequencies
• Spectral subtraction
– Adaptive Wiener filtering
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Patient benefit with DNR• Digital noise reduction is effective at reducing
gain when there is no speech present.
• When speech and noise are present together, the noise reduction algorithm does not reduce gain.
– Improves comfort
– Does not improve intelligibility
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How can we separate speech from noise?
Spee
ch v
s. N
ois
e
Temporal domain
Spectral domain
Spatial domain
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Separating speech from noise in spatial domain
• Adaptive directionality
– Substantial evidence supporting benefits from directional microphones.
– Real world directional benefit is reduced compared to laboratory results.
– Hearing aids with adaptive directionality defaults to “omnidirectional” mode when there are multiple noise sources.
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Factors affecting directional benefit
• Frequency of the signal
• Venting / open fit
• Reverberation
• Distance between the two microphones
• Head angle
• Microphone matching
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Examples of DNR by manufacturers
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PERFORMANCE OF NOISE REDUCTION ALGORITHMS IN A LABORATORY SETTING
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Audio samples of DNR in commercially available hearing aids
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Oticon Phonak
Starkey Resound
Widex
Signia
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Real Ear Aided Response with and without DNR
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SYSTEMATIC REVIEW OF THE LITERATURE
Adult Patients
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Purpose of this review• In search of evidence
– Two systematic reviews in the literature (Bentler, 2005; Chong and Jenstad, 2018)
– No calculation of effect size
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Bentler, R. A. (2005). Effectiveness of directional microphones and noise reduction schemes in hearingaids: A systematic review of the evidence. Journal of the American Academy of Audiology, 16(7),473-484.
Chong, F. Y., & Jenstad, L. M. (2018). A critical review of hearing-aid single-microphone noise-reductionstudies in adults and children. Disability and Rehabilitation: Assistive Technology, 13(6), 600-608.
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Systematic review
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Systematic review• The review includes articles published from
the year 2000 to 2016.
• The effect size (r) is estimated for each study and overall effect size is calculated for each measure.
• Effect size here simply means the magnitude of DNR benefit or practical significance of DNR benefit.
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How to measure DNR benefit?
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DNR benefit
Speech understanding
Listening effortOther measures
- ANL
- Subjective rating
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Speech recognition outcome• A total of 12 studies compared DNR vs. No
DNR condition in 22 comparisons (different noise reduction algorithms, different strengths).
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Evidence• Out of 12, ten studies (20 comparisons out of
22) showed no significant improvement of speech recognition measure with DNR compared to no DNR condition.
• Effect size (r) was calculated for 7 comparisons out of 22 and it ranged from 0.09 (small) to 0.55 (large).
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Studies showing improvement with DNR
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Confidence interval of r
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Kuk, F., Peeters, H., Lau, C., & Korhonen, P. (2011). Effect of maximum power output and noisereduction on speech recognition in noise. Journal of the American Academy ofAudiology, 22(5), 265-273.
Peeters, H., Kuk, F., Lau, C., & Keenan, D. (2009). Subjective and objective evaluation of noisemanagement algorithms. Journal of the American Academy of Audiology,20(2), 89-98.doi:10.3766/jaaa.20.2.2
Study Effect size 95% Confidence interval
Peeters et al. (2009) 0.50 0.04 to 0.78
Kuk et al. (2011) 0.51 -0.13 to 0.85
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Evidence cont…• The overall (or average) effect size was small
(0.28) with zero credibility interval.
• Zero credibility interval translates to zero effect of DNR on speech recognition measure in population 95% of the time.
• This was due to huge sampling error variance in the studies.
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LISTENING EFFORT
Evidence
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Listening effort
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• Results in lesser rating of effort compared to no DNR conditionSubjective rating
• Reduces cognitive effort and makes it available for secondary task
• Reaction time and performance are compared across conditions
Dual-task paradigm
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Evidence
• Four studies (24 comparisons) investigated the effect of DNR on listening effort.
• Two studies (three comparisons) showed significant improvement (or reduction) in listening effort with DNR algorithm.
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ANL and other subjective measures
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Acceptable Noise Level
(ANL)
Speech naturalness
Noise annoyance
Ease of communication
Overall preference
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Evidence• Eight studies (41 comparisons) examined the
effect of DNR on subjective rating and two studies on Acceptable Noise Levels (ANL).
• Four studies (22 comparisons) showed significant improvement in subjective ratings
• Two studies (two comparisons) showed significant improvement in ANLs.
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Summary• Effect size was calculated for 7 studies (12
comparisons).
• The effect size (r) ranged from 0.066 (small) to 0.74 (large).
• The overall effect size was calculated for listening effort and subjective ratings together and there was a medium effect (0.46 ±10).
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SYSTEMATIC REVIEW OF THE LITERATURE
Pediatric Patients
515151
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DNR benefit in children
• Children are more affected by noise compared to adults.
• DNR may help children to participate in multi-speaker conversations and discussions compared to FM systems.
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HOW TO MEASURE DNR BENEFIT??
DNR benefit
Speech recognition
outcome
Speech language outcome
HA self-report and parent report
outcome
McCreery, R. W., Venediktov, R. A., Coleman, J. J., & Leech, H. M. (2012). An evidence-based systematic review of directional microphones and digital noise reduction hearing aids in school-age children with hearing loss. American Journal of Audiology, 21(2), 295-312.
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Speech Recognition outcome
• Four studies explored the effect of DNR on speech recognition and found no significant improvement with DNR.
• The effect size (r) ranged from -0.04 to 0.24 (McCreery et al., 2012). This is similar to small effect size (r= 0.28) seen with adults.
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Speech and language outcomes• The studies investigated the effect of DNR on
novel word learning and word categorization.
• All three studies showed no significant improvement in word learning or categorization with DNR algorithm.
• The effect size (r) estimated ranged from 0.10 (small) to 0.54 (large) (McCreery et al., 2012).
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Hearing aid self report and parental report
• Three studies used self report and/or parental report to examine the effect of DNR.
• DNR had no significant effect.
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SUMMARY AND CONCLUSION
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• Noise reduction algorithms do not improve speech recognition significantly in adults and children.
• It helps to improve subjective perception such as quality, ease of listening.
• There is dearth of evidence to show DNR benefit on listening effort.
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