does higher technology result in higher levels of benefit?
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Does Higher Technology Result in Higher Levels of
Benefit? BCASLPA
October 22, 2004
Ruth Bentlerwww.shc.uiowa.edu
What features? Dsp versus Analog Directional Mics Noise Reduction Feedback Cancellation
Dsp versus Analog Orange Juice or Tomato Juice Cardiovascular or Weight-Bearing Puppy or cable
Dsp versus Analog Orange Juice or Tomato Juice Cardiovascular or Weight-Bearing Puppy or cable
Digital versus analog Not a debate amongst (most) researchers Easy to contrive the design Often misleads the clinician E.G.
Wood & Lutman (March 2004, IJA)
Abstract Question: Are dsp hearing aids better
than analog (linear) hearing aids? Design: 100 first-time users, single-
blinded, wore the HAs for 5 weeks each APHAB, GHABP, QoL, Diary REAR, Speech-in-Noise
Results…
Results Better dsp performance at 75 dB inputs
(4%); no difference at 65 dB input No difference in QoL No difference in use time No difference in APHAB subscales (n=36) Difference in Satisfaction subscale of
GHABP in favor of dsp 60 preferred dsp; 31 preferred analog
Conclusions “ Dsp provides significantly better speech
recognition performance for raised speech in background noise than carefully fitted (“but not adjusted”) linear analog hearing aids.”
“Users report somewhat greater satisfaction…and less aversiveness to sound.
An indepth look at the facts… Gain/output not controlled (audibility??) Limiting versus peak clipping not
controlled (distortion??) Linear aids not adjusted to “comfort”, as
were dsp aids (blinded??) And, finally, features such as directional
mics, noise reduction and feedback cancellation were active in the dsp circuits…
So, one more time…The advantages of dsp hearing
aids (to the end user) lie in the features, if they lie at all…Manufacturer benefits?Dispenser benefits?
Directional Microphones?
What we know… One and two mic designs Low frequency compensation Mic noise goes up (and up) Many companies use mic noise algorithm
Quick Tutorial Ways to build directivity into a hearing aid
case: Single mic with two ports Two omni mics Combination of omni & directional mics Three mics Mic array
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Directional Microphone
Reading a Polar PlotReading a Polar Plot
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OmniDirectional MicrophoneOmniDirectional Microphone
Angle of signal source
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Polar plot for omnidirectional mic in free field
OmnidirectionalOmnidirectional CardioidCardioid
Hypercardioid Hypercardioid Supercardioid Supercardioid
Polar Response PatternFree field characteristics of different types of microphones (Knowles TB 21)
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Head, Pinnae, and Torso Effects on Omni-Directional Microphones
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Free FieldKEMAR
Dittberner, 2003
Dittberner, 2003
Head, Pinnae, and Torso Effects on Directional Microphones
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Head/pinna/torso effect
Head/pinna/torso effect
Wouters, 2003
Wouters, 2003
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Quick tutorial, cont. Ways to implement directionality in the
hearing aid case: Fixed polar pattern Program different polar patterns in different
memories Automatic directional mode Adaptive directional mode
Ways to quantify directivity Front-to-back ratio (FBR) Directivity Index (DI)
Theoretical Free field KEMAR -10
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2axp is the magnitude of the on-axis mean-square sound pressure microphone
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2,p is the magnitude of the off-axis mean-square sound pressure microphone response to a diffuse sound field.
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Figure 1c
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Figure 1a
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Laboratory Data We have 30-40 years of lab data and
trade-magazine evidence that Directional mics can improve SNR That enhancement is based on
# and placement of speakers Type/level/distance of noise Reverberation Baseline comparison (unaided, BTE/ITE, Omni) LF Compensation versus hearing levels
Laboratory Data AND, that lab data do not relate very well
to self-report data E.g., Walden, Surr & Cord (Hearing Journal,
2003)…
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Walden, Surr, & Cord, 2003
Laboratory Data And, we can’t predict directional
advantage: Ricketts & Mueller (JAAA, 2000) examined three
studies for effect on directional advantage: Slope of hearing loss Amount of high frequency hearing loss Aided omnidirectional advantage
In one study, found significant negative relationship between aided omnidirectional performance and directional advantage
Cord, Surr, Walden & Olsen (2002) Performance of directional microphone hearing aids in everyday life, JAAA, 295-307.
Called back users of directional mic hearing aids that fell into two groups Those who used them regularly (deemed
successful)(n=22) Those who did not, and used the default
omnidirectional mode (deemed unsuccessful)(n=26)
No predictive power in APHAB scores
Cord, Surr, Walden & Olsen (2002)
Microphone Performance Questionnaire (MPQ) indicated directional mics preferred when signal is in front (near) and noise is in back
All 48 participants reported being satisfied with their HAs in each mic configuration; although the directional mic used less often, equally satisfied with it when they did...
Walden and Walden (2004). Predicting success with hearing aids in everyday living, JAAA, 342-353.
Purpose of the study: Investigate relationship between two measures of hearing aid success (IOI-HA and HAUS) and demographic and audiometric measures.
No blinding; clinic appointment data (n=50) Not really a comparison of mic conditions,
although IOI-HA showed statistically significant difference across
the groups Omni only (n=29) Omni/Directional with a switch (n=21)
NO difference in HAUS across two groups
Walden, Surr, Cord, and Dyrland (2004). Predicting hearing aid microphone preference in everyday listening. JAAA, 365-396.
Purpose of the study: Define environments for which either the omnidirectional or directional mode was better (thus providing guidance): Talker location Noise location Distance Time Ease of listening (Indirectly assigned reverberation)
Cord, Surr, Walden & Dyrland (2004)
Beginning of a model! Mean estimated use time was 61.8% for
omni mode and 38.2% for directional mode.
Average use of the omni mode was 65% for 8 participants for whom the default setting was omni, and 58.9% for the 9 participants for whom the default was directional.
Thus, the question of importance (to me!)
Do experienced/trained users of hearing aids with directional microphones report better amplification outcomes in daily life than users of hearing aids without directional microphones?
(Infamous) Valente, Fabry & Potts (1995).Recognition of speech in noise with hearing aids using dual microphones, JAAA, 440-449.
Purpose: To determine the effectiveness of a directional mic (two omni design)
Two sites (25 at each) No blinding Although not a comparison to omni
design, PHAB (Site 1) and APHAB (Site 2) showed subjects performing above the mean benefit norms.
Preves, Sammeth, & Wynne (1999). Field trial evaluations of a switched directional/omnidirectional ITE hearing instrument (1999). JAAA, 273-284.
Purpose: To evaluate the usefulness of a switch-option directional microphone system
10 blinded subjects (single-blinded cross-over design) wore aids for 2 trials
Self-report inventories (after non-equalized trial and equalized trial) APHAB Subjective Comments
Preves, Sammeth, & Wynne, continued For Trial #1 (non-equalized)
APHAB: RV subscale showed directional mode significantly better (fewer reported problems)
Comments: If only one, 6/10 directional mode; Subjects “hesitant to give up” either mode
For Trial #2 (equalized) APHAB: RV and BN RV subscale showed
directional mode significantly better (fewer reported problems)
Comments: If only one, 6/10 directional mode; Subjects “hesitant to give up” either mode
Boymans and Dreschler (2000), Field trials using a digital hearing aid with active noise reduction and dual-microphone directionality, IJA, 260-268.
16 subjects (single-blinded cross-over design) wore aids for four consecutive field trials No noise reduction Directional mics only Noise reduction only Directional mics plus noise reduction
Boymans and Dreschler (2000) continued
“ Subjective” outcome measures Paired comparisons (only in the lab) APHAB
Boymans and Dreschler (2000) continued
Aversiveness Subscale: Significantly fewer problems with the directional mic only condition over the omnidirectional mic condition
Evidence: A little (related to aversiveness) (Have to wait for the noise reduction
answer!)
Yueh, Souza, McDowell, Collins, Loovis, Hedrick, Ramsey, & Deyo (2001). Randomized trial of amplification strategies, Archives Oto, H&NS, 127:1197-1204
Purpose: To compare the effectiveness of an ALD, a non-programmable, non-directional hearing aid, and programmable directional hearing aid against the absence of amplification
60 subjects randomly assigned to four Tx groups (slight caveat here)
Yueh, Souza, McDowell, Collins, Loovis, Hedrick, Ramsey, & Deyo, continued
Self-report inventories used at baseline (before randomization) and at 1 and 3 mo: HHIE “Clinimetric” analysis of diaries APHAB Denver Scale of Communication Function Use time (recorded daily in diaries) Willingness to pay
Yueh, Souza, McDowell, Collins, Loovis, Hedrick, Ramsey, & Deyo, continued
HHIE: Significant difference in two hearing aid “tails” (P = .05) Standard (omnidirectional) Programmable (directional)
APHAB: Programmable significantly higher HHIE: Programmable significantly higher Willingness-to-pay
29% monthly income for standard 78% monthly income for programmable
Yueh, Souza, McDowell, Collins, Loovis, Hedrick, Ramsey, & Deyo, continued
HHIE: Significant difference in two hearing aid “tails” (P = .05) Standard (omnidirectional) Programmable (directional)
APHAB: Programmable significantly higher HHIE: Programmable significantly higher Willingness-to-pay
29% monthly income for standard 78% monthly income for programmabl
CAUTION!
Ricketts, Henry, Gnewikow (2003). Full time directional versus user selectable microphone modes in hearing aids, Ear & Hearing, 424-439.
Purpose: To examine benefit across omni and directional modes of hearing aid use Experienced, n = 15, cross-over design Blinding not possible
Self-report measures PHAB (6 subscales) New subscales
Source front (SF) Source back/localization (SB/L)
Log of usage
Within-subjects factor: Mic condition PHAB subscales: less benefit for omni in BN Two new subscales
SF: Less benefit for omni than full time or user-switchable directional
SBL: Less benefit for full time directional than omni or user-switchable directional
Use time
Evidence: A little
Palmer, Bentler, Mueller, and Powers (2005) Evaluation of a Second-Order Directional Microphone Hearing Aid:Self Report Outcomes (In Review)
49 subjects (within subject, before-after design) Self-report inventories only used to assess
benefit from amplification Diary was used to assist in differentiating
between omni, adaptive directional and fixed directional modes 34 of 49 had a preference (1/3, 1/3, 1/3) Evidence: Little
Noise Reduction
Noise Reduction From Dreschler, Verschuure, Ludvigsen,
Westerman, (IJA, 2001): Number of channels Time constants Degree of gain reduction as a function of
frequency Amount of noise reduction as a function of the
ratio between modulated and unmodulated components of the signal (“sensitivity”)
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Four approaches to reducing noise
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Widex (Diva)
Sonic Innovations
Siemens (Triano)
Starkey (Axent)
And so the important question… Do users of digital noise reduction
schemes currently implemented in wearable hearing aids report better amplification outcomes in daily life than users of hearing aids without noise reduction?
This effort… Noise reduction studies prior to 1995 Noise reduction studies since 1995 Total number of studies meeting criteria: 2.5
Peer-reviewed Self-report Blinded Appropriate design (n, statistics, etc)
…if I could understand the titles…
Olhede SC. Walden AT. Noise reduction in directional signals using multiple morse wavelets illustrated on quadrature Doppler ultrasound. IEEE Transactions on Biomedical Engineering. 50(1):51-7, 2003 Jan.
Thomas CG. Harshman RA. Menon RS. Noise reduction in BOLD-based fMRI using component analysis. Neuroimage. 17(3):1521-37, 2002 Nov
El-Mohri Y. Antonuk LE. Zhao Q. Maolinbay M. Rong X. Jee KW. Nassif S. Cionca C. A quantitative investigation of additive noise reduction for active matrix flat-panel imagers using compensation lines. Medical Physics. 27(8):1855-64, 2000 Aug
Data?
Walden, Surr, Cord, Edwards, Olson (2000). Comparison of benefits provided by different hearing aid technologies, JAAA,540-560.
40 HI subjects using Resound BZ5 Omni Dir NR + Dir
Field Ratings (for NR versus NR+Dir)No reported differences in speech understanding
Dir + NR rated significantly more comfortable than Omni
No difference in Sound Quality and Naturalness
Boymans and Dreschler (2000), Field trials using a digital hearing aid with active noise reduction and dual-microphone directionality, Audiology, 260-268.
Widex SENSO 16 HI subjects, single-blinded crossover design Lab data plus 3 consecutive field trials of 4
weeks each Self report via Dutch APHAB individual
items Significantly less aversiveness for sudden loud
sounds Significantly better understanding of speech in car
noise
Alcantara, Moore, Kuhnel, Launer (2003) Evaluation of the noise reduction system in a commercial digital hearing aid. IJA, 34-42.
Alcantara et al (2003) Eight experienced HI HA users wore new aid for
3 months No improvement for SRTs; no decrement for
sound quality while listening to four different kinds of background noise, all performed in the laboratory setting (“satisfaction with the noise reduction algorithm”)
Level of evidence: Weak/Low
Feedback Cancellation
What did we do? Roll off the highs Plug the vent Remake the earmold Turn down the VCW Dampen the peaks Adjust the gain in the narrow band Hold the mold in tighter…
Feedback Cancellation Do users of feedback cancellation
schemes currently implemented in wearable hearing aids report better amplification outcomes in daily life than users of hearing?
Feedback Cancellation Do users of feedback cancellation
schemes currently implemented in wearable hearing aids notice adifference?
This effort… Total number of related articles on feedback
cancellation: 20
Total number in IEEE Transactions: 8
Total number in peer-reviewed: 7
Total number published in JASA (no field data): 7
Total number meeting self-report critera: 0
Feedback Canceller: Gain MarginN=57 ears (19 @ U of MN;38 @ Starkey)
[U of MN data: Price and Nelson (2001)]
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Summary
• All feedback management systems evaluated allowed gain to be increased beyond the point of feedback
• The phase cancellation systems do not appear to affect the spectral components of speech when analyzed at the phoneme level.
• Band reduction and/or notch filtering affect the spectral components of speech when analyzed at the phoneme level.
Freed & Soli (2004 IHCON) How effective id the algorithm at preventing
oscilliation? How effective is the algorithm at reducing
oscillatory peaks? Does the algorithm sacrifice gain in any
frequency band? How robust is the algorithm when presented with
tonal input signals? Power Concentration Ratio (PCR) Aided Stable Gain (ASG) Extraneous Frequency Ratio (EFR)
AnswersQ1 No, not without consideration of the
featuresQ2 Maybe, although the issue of training
needs further investigationQ3 Maybe, but only in the sound
quality/easy listening domainQ4 No field data available, but this
question may be answered by laboratory findings as well
From Randall Robey (ASHA Leader, 2004):
“ Evidence may take many forms, from expert opinions to meta-analysis. Each form should not be equally persuasive that a certain (procedure) should become an aspect of recommended.”
“…the greater the scientific rigor, the more potent the evidence.”
From Christine Dollaghan (ASHA Leader, 2004): “The most common feeling seems to be …
anxiety that EBP will turn out to be one more unrealistic demand placed upon already over-burdened professionals.”
From Bentler at al. ( Ear and Hearing, 2003)
“Clinician is ethically obligated to accurately represent the potential benefits and advantages of (the) hearing aid.”
“This obligation can only be met by ongoing and critical review of the evidence supporting effectiveness.”
“(And) it is incumbent upon researchers to provide clinicians fair and accurate evaluations of new technologies.”
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