scholarly journals Effects of Wireless Remote Microphone on Speech Recognition in Noise for Hearing Aid Users in China

2021 ◽  
Vol 15 ◽  
Author(s):  
Jing Chen ◽  
Zhe Wang ◽  
Ruijuan Dong ◽  
Xinxing Fu ◽  
Yuan Wang ◽  
...  
Keyword(s):  
Speech Recognition ◽  
Hearing Aids ◽  
Signal To Noise Ratio ◽  
Hearing Aid ◽  
Recognition Performance ◽  
Speech In Noise ◽  
Hearing In Noise ◽  
Recognition Ability ◽  
Noise Test ◽  
Test Distance

Objective: This study was aimed at evaluating improvements in speech-in-noise recognition ability as measured by signal-to-noise ratio (SNR) with the use of wireless remote microphone technology. These microphones transmit digital signals via radio frequency directly to hearing aids and may be a valuable assistive listening device for the hearing-impaired population of Mandarin speakers in China.Methods: Twenty-three adults (aged 19–80 years old) and fourteen children (aged 8–17 years old) with bilateral sensorineural hearing loss were recruited. The Mandarin Hearing in Noise Test was used to test speech recognition ability in adult subjects, and the Mandarin Hearing in Noise Test for Children was used for children. The subjects’ perceived SNR was measured using sentence recognition ability at three different listening distances of 1.5, 3, and 6 m. At each distance, SNR was obtained under three device settings: hearing aid microphone alone, wireless remote microphone alone, and hearing aid microphone and wireless remote microphone simultaneously.Results: At each test distance, for both adult and pediatric groups, speech-in-noise recognition thresholds were significantly lower with the use of the wireless remote microphone in comparison with the hearing aid microphones alone (P < 0.05), indicating better SNR performance with the wireless remote microphone. Moreover, when the wireless remote microphone was used, test distance had no effect on speech-in-noise recognition for either adults or children.Conclusion: Wireless remote microphone technology can significantly improve speech recognition performance in challenging listening environments for Mandarin speaking hearing aid users in China.

scholarly journals Psychometric Comparison of the Hearing in Noise Test and the American English Matrix Test

2019 ◽  
Vol 30 (04) ◽  
pp. 315-326 ◽  
Author(s):  
Jumana Harianawala ◽  
Jason Galster ◽  
Benjamin Hornsby
Keyword(s):  
Speech Recognition ◽  
Hearing Aids ◽  
Repeated Measures ◽  
American English ◽  
Hearing Aid ◽  
Speech Corpus ◽  
Speech In Noise ◽  
Hearing In Noise ◽  
Noise Test ◽  
Intensity Functions

AbstractThe hearing in noise test (HINT) is the most popular adaptive test used to evaluate speech in noise performance, especially in context of hearing aid features. However, the number of conditions that can be tested on the HINT is limited by a small speech corpus. The American English Matrix test (AEMT) is a new alternative adaptive speech in noise test with a larger speech corpus. The study examined the relationships between the performance of hearing aid wearers on the HINT and the AEMT.To examine whether there was a difference in performance of hearing aid wearers on the HINT and the AEMT. A secondary purpose, given the AEMT’s steep performance-intensity function, was to determine whether the AEMT is more sensitive to changes in speech recognition resulting from directional (DIR) microphone processing in hearing aids.A repeated measures design was used in this study. Multiple measurements were made on each subject. Each measurement involved a different experimental condition.Ten adults with hearing loss participated in this study.All participants completed the AEMT and HINT, using adaptive and fixed test formats while wearing hearing aids. Speech recognition was assessed in two hearing aid microphone settings—omnidirectional and fixed DIR. All testing was conducted via sound field presentation. Performance on HINT and AEMT were systematically compared across all test conditions using a linear model with repeated measures.The results of this study revealed that adult hearing aid users perform differently on the HINT and AEMT, with adaptive AEMT testing yielding significantly better (more negative) thresholds than the HINT. Slopes of performance intensity functions obtained by testing at multiple fixed signal-to-noise ratios, revealed a somewhat steeper slope for the HINT compared with the AEMT. Despite this steeper slope, the benefit provided by DIR microphones was not significantly different between the two speech tests.The observation of similar DIR benefits of the HINT and AEMT suggests that the HINT and AEMT are equally sensitive to changes in speech recognition thresholds following intervention. Therefore, the decision to use the AEMT or the HINT will depend on the purpose of the study and/or the technology being investigated. Other test related factors such as available sentence corpus, learning effects and test time will also influence test selection.

The Effects of Changes in Head Angle on Auditory and Visual Input for Omnidirectional and Directional Microphone Hearing Aids

2003 ◽  
Vol 12 (1) ◽  
pp. 41-51 ◽  
Author(s):  
Paula Henry ◽  
Todd Ricketts
Keyword(s):  
Hearing Loss ◽  
Speech Recognition ◽  
Hearing Aids ◽  
Visual Cues ◽  
Signal To Noise Ratio ◽  
Hearing Aid ◽  
Recognition Performance ◽  
Binaural Hearing ◽  
Increase Signal Intensity ◽  
Visual Mode

Improving the signal-to-noise ratio (SNR) for individuals with hearing loss who are listening to speech in noise provides an obvious benefit. Although binaural hearing provides the greatest advantage over monaural hearing in noise, some individuals with symmetrical hearing loss choose to wear only one hearing aid. The present study tested the hypothesis that individuals with symmetrical hearing loss fit with one hearing aid would demonstrate improved speech recognition in background noise with increases in head turn. Fourteen individuals were fit monaurally with a Starkey Gemini in-the-ear (ITE) hearing aid with directional and omnidirectional microphone modes. Speech recognition performance in noise was tested using the audiovisual version of the Connected Speech Test (CST v.3). The test was administered in auditory-only conditions as well as with the addition of visual cues for each of three head angles: 0°, 20°, and 40°. Results indicated improvement in speech recognition performance with changes in head angle for the auditory-only presentation mode at the 20° and 40° head angles when compared to 0°. Improvement in speech recognition performance for the auditory + visual mode was noted for the 20° head angle when compared to 0°. Additionally, a decrement in speech recognition performance for the auditory + visual mode was noted for the 40° head angle when compared to 0°. These results support a speech recognition advantage for listeners fit with one ITE hearing aid listening in a close listener-to-speaker distance when they turn their head slightly in order to increase signal intensity.

Are Two Ears Not Better Than One?

2012 ◽  
Vol 23 (03) ◽  
pp. 171-181 ◽  
Author(s):  
Rachel A. McArdle ◽  
Mead Killion ◽  
Monica A. Mennite ◽  
Theresa H. Chisolm
Keyword(s):  
Hearing Loss ◽  
Speech Recognition ◽  
Hearing Aids ◽  
Repeated Measures ◽  
Signal To Noise Ratio ◽  
Hearing Aid ◽  
Binaural Hearing ◽  
Analysis Experiment ◽  
Insert Earphones ◽  
Speech Recognition In Noise

Background: The decision to fit one or two hearing aids in individuals with binaural hearing loss has been debated for years. Although some 78% of U.S. hearing aid fittings are binaural (Kochkin , 2010), Walden and Walden (2005) presented data showing that 82% (23 of 28 patients) of their sample obtained significantly better speech recognition in noise scores when wearing one hearing aid as opposed to two. Purpose: To conduct two new experiments to fuel the monaural/binaural debate. The first experiment was a replication of Walden and Walden (2005), whereas the second experiment examined the use of binaural cues to improve speech recognition in noise. Research Design: A repeated measures experimental design. Study Sample: Twenty veterans (aged 59–85 yr), with mild to moderately severe binaurally symmetrical hearing loss who wore binaural hearing aids were recruited from the Audiology Department at the Bay Pines VA Healthcare System. Data Collection and Analysis: Experiment 1 followed the procedures of the Walden and Walden study, where signal-to-noise ratio (SNR) loss was measured using the Quick Speech-in-Noise (QuickSIN) test on participants who were aided with their current hearing aids. Signal and noise were presented in the sound booth at 0° azimuth under five test conditions: (1) right ear aided, (2) left ear aided, (3) both ears aided, (4) right ear aided, left ear plugged, and (5) unaided. The opposite ear in (1) and (2) was left open. In Experiment 2, binaural Knowles Electronics Manikin for Acoustic Research (KEMAR) manikin recordings made in Lou Malnati's pizza restaurant during a busy period provided a typical real-world noise, while prerecorded target sentences were presented through a small loudspeaker located in front of the KEMAR manikin. Subjects listened to the resulting binaural recordings through insert earphones under the following four conditions: (1) binaural, (2) diotic, (3) monaural left, and (4) monaural right. Results: Results of repeated measures ANOVAs demonstrated that the best speech recognition in noise performance was obtained by most participants with both ears aided in Experiment 1 and in the binaural condition in Experiment 2. Conclusions: In both experiments, only 20% of our subjects did better in noise with a single ear, roughly similar to the earlier Jerger et al (1993) finding that 8–10% of elderly hearing aid users preferred one hearing aid.

Efficacy of a Cochlear Implant Simultaneous Analog Stimulation Strategy Coupled with a Monopolar Electrode Configuration

2005 ◽  
Vol 114 (11) ◽  
pp. 886-893 ◽  
Author(s):  
Li Xu ◽  
Teresa A. Zwolan ◽  
Catherine S. Thompson ◽  
Bryan E. Pfingst
Keyword(s):  
Speech Recognition ◽  
Cochlear Implant ◽  
Speech Processing ◽  
Dynamic Range ◽  
Recognition Performance ◽  
Electrode Configuration ◽  
Processing Strategy ◽  
Open Set ◽  
Hearing In Noise ◽  
Noise Test

Objectives: The present study was performed to evaluate the efficacy and clinical feasibility of using monopolar stimulation with the Clarion Simultaneous Analog Stimulation (SAS) strategy in patients with cochlear implants. Methods: Speech recognition by 10 Clarion cochlear implant users was evaluated by means of 4 different speech processing strategy/electrode configuration combinations; ie, SAS and Continuous Interleaved Sampling (CIS) strategies were each used with monopolar (MP) and bipolar (BP) electrode configurations. The test measures included consonants, vowels, consonant-nucleus-consonant words, and Hearing in Noise Test sentences with a +10 dB signal-to-noise ratio. Additionally, subjective judgments of sound quality were obtained for each strategy/configuration combination. Results: All subjects but 1 demonstrated open-set speech recognition with the SAS/MP combination. The group mean Hearing in Noise Test sentence score for the SAS/MP combination was 31.6% (range, 0% to 92%) correct, as compared to 25.0%, 46.7%, and 37.8% correct for the CIS/BP, CIS/MP, and SAS/BP combinations, respectively. Intersubject variability was high, and there were no significant differences in mean speech recognition scores or mean preference ratings among the 4 strategy/configuration combinations tested. Individually, the best speech recognition performance was with the subject's everyday strategy/configuration combination in 72% of the applicable cases. If the everyday strategy was excluded from the analysis, the subjects performed best with the SAS/MP combination in 37.5% of the remaining cases. Conclusions: The SAS processing strategy with an MP electrode configuration gave reasonable speech recognition in most subjects, even though subjects had minimal previous experience with this strategy/configuration combination. The SAS/MP combination might be particularly appropriate for patients for whom a full dynamic range of electrical hearing could not be achieved with a BP configuration.

scholarly journals An Evaluation of Hearing Aid Beamforming Microphone Arrays in a Noisy Laboratory Setting

2019 ◽  
Vol 30 (02) ◽  
pp. 131-144 ◽  
Author(s):  
Erin M. Picou ◽  
Todd A. Ricketts
Keyword(s):  
Hearing Loss ◽  
Speech Recognition ◽  
Hearing Aids ◽  
Linear Models ◽  
Hearing Aid ◽  
Recognition Performance ◽  
Microphone Arrays ◽  
Laboratory Setting ◽  
Subjective Ratings ◽  
Sentence Recognition

AbstractPeople with hearing loss experience difficulty understanding speech in noisy environments. Beamforming microphone arrays in hearing aids can improve the signal-to-noise ratio (SNR) and thus also speech recognition and subjective ratings. Unilateral beamformer arrays, also known as directional microphones, accomplish this improvement using two microphones in one hearing aid. Bilateral beamformer arrays, which combine information across four microphones in a bilateral fitting, further improve the SNR. Early bilateral beamformers were static with fixed attenuation patterns. Recently adaptive, bilateral beamformers have been introduced in commercial hearing aids.The purpose of this article was to evaluate the potential benefits of adaptive unilateral and bilateral beamformers for improving sentence recognition and subjective ratings in a laboratory setting. A secondary purpose was to identify potential participant factors that explain some of the variability in beamformer benefit.Participants were fitted with study hearing aids equipped with commercially available adaptive unilateral and bilateral beamformers. Participants completed sentence recognition testing in background noise using three hearing aid settings (omnidirectional, unilateral beamformer, bilateral beamformer) and two noise source configurations (surround, side). After each condition, participants made subjective ratings of their perceived work, desire to control the situation, willingness to give up, and tiredness.Eighteen adults (50–80 yr, M = 66.2, σ = 8.6) with symmetrical mild sloping to severe hearing loss participated.Sentence recognition scores and subjective ratings were analyzed separately using generalized linear models with two within-subject factors (hearing aid microphone and noise configuration). Two benefit scores were calculated: (1) unilateral beamformer benefit (relative to performance with omnidirectional) and (2) additional bilateral beamformer benefit (relative to performance with unilateral beamformer). Hierarchical multiple linear regression was used to determine if beamformer benefit was associated with participant factors (age, degree of hearing loss, unaided speech in noise ability, spatial release from masking, and performance in omnidirectional).Sentence recognition and subjective ratings of work, control, and tiredness were better with both types of beamformers relative to the omnidirectional conditions. In addition, the bilateral beamformer offered small additional improvements relative to the unilateral beamformer in terms of sentence recognition and subjective ratings of tiredness. Speech recognition performance and subjective ratings were generally independent of noise configuration. Performance in the omnidirectional setting and pure-tone average were independently related to unilateral beamformer benefits. Those with the lowest performance or the largest degree of hearing loss benefited the most. No factors were significantly related to additional bilateral beamformer benefit.Adaptive bilateral beamformers offer additional advantages over adaptive unilateral beamformers in hearing aids. The small additional advantages with the adaptive beamformer are comparable to those reported in the literature with static beamformers. Although the additional benefits are small, they positively affected subjective ratings of tiredness. These data suggest that adaptive bilateral beamformers have the potential to improve listening in difficult situations for hearing aid users. In addition, patients who struggle the most without beamforming microphones may also benefit the most from the technology.

Effects of Adaptive Hearing Aid Directionality and Noise Reduction on Masked Speech Recognition for Children Who Are Hard of Hearing

2019 ◽  
Vol 28 (1) ◽  
pp. 101-113 ◽  
Author(s):  
Jenna M. Browning ◽  
Emily Buss ◽  
Mary Flaherty ◽  
Tim Vallier ◽  
Lori J. Leibold
Keyword(s):  
Speech Recognition ◽  
Hearing Aids ◽  
Hard Of Hearing ◽  
Signal To Noise Ratio ◽  
Hearing Aid ◽  
Normal Hearing ◽  
Signal To Noise ◽  
Open Set ◽  
Fully Adaptive ◽  
Noise Ratio

Purpose The purpose of this study was to evaluate speech-in-noise and speech-in-speech recognition associated with activation of a fully adaptive directional hearing aid algorithm in children with mild to severe bilateral sensory/neural hearing loss. Method Fourteen children (5–14 years old) who are hard of hearing participated in this study. Participants wore laboratory hearing aids. Open-set word recognition thresholds were measured adaptively for 2 hearing aid settings: (a) omnidirectional (OMNI) and (b) fully adaptive directionality. Each hearing aid setting was evaluated in 3 listening conditions. Fourteen children with normal hearing served as age-matched controls. Results Children who are hard of hearing required a more advantageous signal-to-noise ratio than children with normal hearing to achieve comparable performance in all 3 conditions. For children who are hard of hearing, the average improvement in signal-to-noise ratio when comparing fully adaptive directionality to OMNI was 4.0 dB in noise, regardless of target location. Children performed similarly with fully adaptive directionality and OMNI settings in the presence of the speech maskers. Conclusions Compared to OMNI, fully adaptive directionality improved speech recognition in steady noise for children who are hard of hearing, even when they were not facing the target source. This algorithm did not affect speech recognition when the background noise was speech. Although the use of hearing aids with fully adaptive directionality is not proposed as a substitute for remote microphone systems, it appears to offer several advantages over fixed directionality, because it does not depend on children facing the target talker and provides access to multiple talkers within the environment. Additional experiments are required to further evaluate children's performance under a variety of spatial configurations in the presence of both noise and speech maskers.

A Comparison of Personal Sound Amplification Products and Hearing Aids in Ecologically Relevant Test Environments

2018 ◽  
Vol 27 (4) ◽  
pp. 581-593 ◽  
Author(s):  
Lisa Brody ◽  
Yu-Hsiang Wu ◽  
Elizabeth Stangl
Keyword(s):  
Speech Recognition ◽  
Hearing Aids ◽  
Speech Intelligibility ◽  
Best Practice ◽  
Hearing Aid ◽  
Recognition Performance ◽  
Sound Quality ◽  
Listening Effort ◽  
Speech Intelligibility Index ◽  
Sound Amplification

Purpose The aim of this study was to compare the benefit of self-adjusted personal sound amplification products (PSAPs) to audiologist-fitted hearing aids based on speech recognition, listening effort, and sound quality in ecologically relevant test conditions to estimate real-world effectiveness. Method Twenty-five older adults with bilateral mild-to-moderate hearing loss completed the single-blinded, crossover study. Participants underwent aided testing using 3 PSAPs and a traditional hearing aid, as well as unaided testing. PSAPs were adjusted based on participant preference, whereas the hearing aid was configured using best-practice verification protocols. Audibility provided by the devices was quantified using the Speech Intelligibility Index (American National Standards Institute, 2012). Outcome measures assessing speech recognition, listening effort, and sound quality were administered in ecologically relevant laboratory conditions designed to represent real-world speech listening situations. Results All devices significantly improved Speech Intelligibility Index compared to unaided listening, with the hearing aid providing more audibility than all PSAPs. Results further revealed that, in general, the hearing aid improved speech recognition performance and reduced listening effort significantly more than all PSAPs. Few differences in sound quality were observed between devices. All PSAPs improved speech recognition and listening effort compared to unaided testing. Conclusions Hearing aids fitted using best-practice verification protocols were capable of providing more aided audibility, better speech recognition performance, and lower listening effort compared to the PSAPs tested in the current study. Differences in sound quality between the devices were minimal. However, because all PSAPs tested in the study significantly improved participants' speech recognition performance and reduced listening effort compared to unaided listening, PSAPs could serve as a budget-friendly option for those who cannot afford traditional amplification.

Digital processing technology for bone-anchored hearing aids: randomised comparison of two devices in hearing aid users with mixed or conductive hearing loss

2014 ◽  
Vol 128 (2) ◽  
pp. 119-127 ◽  
Author(s):  
P Hill-Feltham ◽  
S A Roberts ◽  
R Gladdis
Keyword(s):  
Hearing Aids ◽  
Speech Processing ◽  
Signal To Noise Ratio ◽  
Hearing Aid ◽  
Digital Processing ◽  
New Device ◽  
Digital Devices ◽  
Speech In Noise ◽  
Bone Anchored Hearing Aid ◽  
Conductive Hearing

AbstractObjective:This study compared the performance of two new bone-anchored hearing aids with older bone-anchored hearing aids that were not fully digital.Methods:Fourteen experienced bone-anchored hearing aid users participated in this cross-over study. Performance of their existing bone-anchored hearing aid was assessed using speech-in-noise testing and questionnaires. Participants were then fitted with either a Ponto Pro or a BP100 device. After four weeks of use with each new device, the same assessments were repeated.Results:Speech-in-noise testing for the 50 per cent signal-to-noise ratio (the ratio at which 50 per cent of responses were correct) showed no significant differences between the Ponto Pro and the BP100 devices (p = 0.1) However, both devices showed significant improvement compared with the participants' previous bone-anchored hearing aid devices (p < 0.001). There were no significant differences between the two new devices in the questionnaire data.Conclusion:Both fully digital bone-anchored hearing aids demonstrated superior speech processing compared with the previous generation of devices. There were no substantial differences between the two digital devices in either objective or subjective tests.

An Evaluation of Several Rationales for Selecting Hearing Aid Gain

1986 ◽  
Vol 51 (3) ◽  
pp. 272-281 ◽  
Author(s):  
Larry E. Humes
Keyword(s):  
Hearing Loss ◽  
Speech Recognition ◽  
Hearing Aids ◽  
Hearing Aid ◽  
Recognition Performance ◽  
Second Phase ◽  
Selection Procedures ◽  
Relative Gain ◽  
Typical Range ◽  
Selection Of

The present study evaluates the rationales underlying several hearing aid selection procedures. The first portion of the evaluation confirms that the gain-selection rationales result in the selection of different hearing aids for a given patient. Nine different audiometric configurations representing varying degrees of fiat, sloping, and rising sensorineural hearing loss were considered. The second phase of the evaluation considered how well each procedure achieved the goal of maximizing speech recognition. This analysis made use of the Articulation Index and was applied to each of the nine audiometric configurations. The results of this analysis suggested that, given the ability to adjust the overall gain over a typical range available through most volume controls, any of the procedures could produce optimal aided speech recognition performance. The final portion of the evaluation examined the ability of each procedure to prescribe absolute gain and relative gain (frequency response) that corresponded to that preferred by hearing aid wearers. The data for preferred insertion gain came from a recent investigation by Leijon, Eriksson-Mangold, an d Beck-Karlsen (1984). The results of this evaluation suggested that some procedures prescribe gain values closer to those preferred by listeners than others. More data are needed on preferred gain values for a variety of configurations, however, before any one procedure can be recommended over another.

scholarly journals The Effect of Hearing Aid Technologies on Listening in an Automobile

2013 ◽  
Vol 24 (06) ◽  
pp. 474-485 ◽  
Author(s):  
Yu-Hsiang Wu ◽  
Elizabeth Stangl ◽  
Ruth A. Bentler ◽  
Rachel W. Stanziola
Keyword(s):  
Signal Processing ◽  
Speech Recognition ◽  
Hearing Aids ◽  
Hearing Aid ◽  
Recognition Performance ◽  
Road Noise ◽  
Processing Scheme ◽  
Repeated Measures Design ◽  
Directional Microphone ◽  
Omnidirectional Microphones

Background: Communication while traveling in an automobile often is very difficult for hearing aid users. This is because the automobile/road noise level is usually high, and listeners/drivers often do not have access to visual cues. Since the talker of interest usually is not located in front of the listener/driver, conventional directional processing that places the directivity beam toward the listener's front may not be helpful and, in fact, could have a negative impact on speech recognition (when compared to omnidirectional processing). Recently, technologies have become available in commercial hearing aids that are designed to improve speech recognition and/or listening effort in noisy conditions where talkers are located behind or beside the listener. These technologies include (1) a directional microphone system that uses a backward-facing directivity pattern (Back-DIR processing), (2) a technology that transmits audio signals from the ear with the better signal-to-noise ratio (SNR) to the ear with the poorer SNR (Side-Transmission processing), and (3) a signal processing scheme that suppresses the noise at the ear with the poorer SNR (Side-Suppression processing). Purpose: The purpose of the current study was to determine the effect of (1) conventional directional microphones and (2) newer signal processing schemes (Back-DIR, Side-Transmission, and Side-Suppression) on listener's speech recognition performance and preference for communication in a traveling automobile. Research Design: A single-blinded, repeated-measures design was used. Study Sample: Twenty-five adults with bilateral symmetrical sensorineural hearing loss aged 44 through 84 yr participated in the study. Data Collection and Analysis: The automobile/road noise and sentences of the Connected Speech Test (CST) were recorded through hearing aids in a standard van moving at a speed of 70 mph on a paved highway. The hearing aids were programmed to omnidirectional microphone, conventional adaptive directional microphone, and the three newer schemes. CST sentences were presented from the side and back of the hearing aids, which were placed on the ears of a manikin. The recorded stimuli were presented to listeners via earphones in a sound-treated booth to assess speech recognition performance and preference with each programmed condition. Results: Compared to omnidirectional microphones, conventional adaptive directional processing had a detrimental effect on speech recognition when speech was presented from the back or side of the listener. Back-DIR and Side-Transmission processing improved speech recognition performance (relative to both omnidirectional and adaptive directional processing) when speech was from the back and side, respectively. The performance with Side-Suppression processing was better than with adaptive directional processing when speech was from the side. The participants' preferences for a given processing scheme were generally consistent with speech recognition results. Conclusions: The finding that performance with adaptive directional processing was poorer than with omnidirectional microphones demonstrates the importance of selecting the correct microphone technology for different listening situations. The results also suggest the feasibility of using hearing aid technologies to provide a better listening experience for hearing aid users in automobiles.

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