Advantages of Binaural Amplification to Acceptable Noise Level of Directional Hearing Aid Users

Objectives

The goal of the present study was to examine whether Acceptable Noise Levels (ANLs) would be lower (greater acceptance of noise) in binaural listening than in monaural listening condition and also whether meaningfulness of background speech noise would affect ANLs for directional microphone hearing aid users. In addition, any relationships between the individual binaural benefits on ANLs and the individuals'' demographic information were investigated.

Methods

Fourteen hearing aid users (mean age, 64 years) participated for experimental testing. For the ANL calculation, listeners'' most comfortable listening levels and background noise level were measured. Using Korean ANL material, ANLs of all participants were evaluated under monaural and binaural amplification with a counterbalanced order. The ANLs were also compared across five types of competing speech noises, consisting of 1- through 8-talker background speech maskers. Seven young normal-hearing listeners (mean age, 27 years) participated for the same measurements as a pilot testing.

Results

The results demonstrated that directional hearing aid users accepted more noise (lower ANLs) with binaural amplification than with monaural amplification, regardless of the type of competing speech. When the background speech noise became more meaningful, hearing-impaired listeners accepted less amount of noise (higher ANLs), revealing that ANL is dependent on the intelligibility of the competing speech. The individuals'' binaural advantages in ANLs were significantly greater for the listeners with longer experience of hearing aids, yet not related to their age or hearing thresholds.

Conclusion

Binaural directional microphone processing allowed hearing aid users to accept a greater amount of background noise, which may in turn improve listeners'' hearing aid success. Informational masking substantially influenced background noise acceptance. Given a significant association between ANLs and duration of hearing aid usage, ANL measurement can be useful for clinical counseling of binaural hearing aid candidates or unsuccessful users.     

Localisation of speech through similar and dissimilar binaural hearing aid listening modes

This paper compared the localisation abilities in the horizontal plane of 12 adults with bilateral asymmetrical sensorineural hearing impairment whilst listening to speech using each one of the following three binaural hearing aid listening modes: (a) binaural listening with two similar ear-level hearing aids, (b) binaural listening with two similar bodyworm hearing aids and, (c) binaural listening with two dissimilar hearing aids (one ear-level, one bodyworn). It was found that the differences in localisation ability between the three binaural hearing aid listening modes were small and none of them proved to be statistically significant. It was concluded that where possible binaural hearing aids should be of similar type and model, although in situations where this could not be achieved or was not indicated, the issuing of dissimilar binaural hearing aids should not be discouraged.     

可接受噪声级测试在单、双耳佩戴助听器效果评估中的应用

目的 通过比较双侧中重度听力损失患者在单、双耳助听下的可接受噪声级(acceptable noise level,ANL),探讨ANL对助听器验配及预测助听效果的作用.方法 选取15例双侧中重度听力损失患者,分别测得双耳未助听、左耳助听、右耳助听和双耳助听状态下的最舒适响度级(most comfortable levels,MCL)、最大背景噪声级(background noise level,BNL),并计算得到ANL值(ANL=MCL-BNL),对结果进行统计学分析.结果 15例受试者双耳未助听、左耳助听、右耳助听及双耳助听四种状态下测得的ANL值分别为18.87±5.26、12.60±2.47、12.00±2.90、5.13±1.25 dB S/N;MCL值分别为80.40±9.28、63.73±5.15、62.27±5.36、61.80±6.05 dB HL;BNL值分别为61.67±6.14、51.13±3.94、50.27±4.50、56.67±5.16 dB HL;左耳助听与右耳助听下的ANL值差异无统计学意义(P>0.05);单、双耳助听下与未助听的ANL值差异均具有统计学意义(P<0.05);双耳助听状态下ANL值显著低于单耳助听(P<0.05).结论 ANL值较低耳更利于助听器验配,佩戴助听器能有效提高听障患者对噪声的接受能力,并且双耳佩戴助听器的效果明显优于单耳.     

Comparison of monaural and binaural hearing aid use on a trial period basis

Thirty hearing-impaired patients compared monaural and binaural hearing aid use for a period of 4 weeks. Most of them preferred binaural hearing aids in quiet situations, but monaural hearing aids in noisy environments. Follow-up at 6 months revealed that 17 had purchased monaural hearing aids, 8 had purchased binaural hearing aids.     

Acceptance of noise with monaural and binaural amplification

The present study investigated the effects of monaural and binaural amplification on speech understanding in noise and acceptance of noise for 39 listeners with hearing impairment. Results demonstrated that speech understanding in noise improved with binaural amplification; however, acceptance of noise was not dependent on monaural or binaural amplification for most listeners. These results suggest that although two hearing aids maximize speech understanding ability in noise, most individuals' acceptance of noise, which is directly related to hearing aid use, may not be affected by the use of binaural amplification. It should be noted that monaural amplification resulted in greater acceptance of noise for some listeners, indicating that binaural amplification may negatively affect some individuals' willingness to wear hearing aids. It should also be noted that interaural differences in acceptance of noise might exist for some listeners; therefore, if only one hearing aid is fitted, monaural ANLs should be measured.     

Listeners who prefer monaural to binaural hearing aids

Four patients who preferred monaural as compared with binaural amplification were evaluated. For these patients, audiometric data, recognition performance on a dichotic digit task, and monaural and binaural hearing aid performance using four amplification strategies (National Acoustic Laboratories-Revised, a speech in noise algorithm, multiple-microphone arrays, and frequency modulated [FM]) are described. The results of dichotic testing using a one-, two-, and three-pair dichotic digit task in free- and directed-recall conditions indicated a left-ear deficit for all subjects that could not be explained by peripheral auditory findings or by a cognitive-based deficit. The results of soundfield testing using a speech in multitalker babble paradigm indicated that when listening in noise, there was little difference between aided and unaided word-recognition performance, suggesting that the binaural hearing aids originally fit for each patient were not providing substantial benefit when listening in a competing babble background. Word-recognition performance when aided monaurally in the right ear was superior to performance when aided monaurally in the left ear and when aided binaurally. The only successful binaural amplification strategy was the FM system. The results indicate that listeners with an auditory-based deficit in dichotic listening may function better with a monaural hearing aid fitting or with an assistive listening device such as an FM system. The findings also suggest that a test of dichotic listening is an important component in the evaluation of patients being considered for amplification.     

Improved Horizontal Directional Hearing in Bone Conduction Device Users with Acquired Unilateral Conductive Hearing Loss

We examined horizontal directional hearing in patients with acquired severe unilateral conductive hearing loss (UCHL). All patients (n = 12) had been fitted with a bone conduction device (BCD) to restore bilateral hearing. The patients were tested in the unaided (monaural) and aided (binaural) hearing condition. Five listeners without hearing loss were tested as a control group while listening with a monaural plug and earmuff, or with both ears (binaural). We randomly varied stimulus presentation levels to assess whether listeners relied on the acoustic head-shadow effect (HSE) for horizontal (azimuth) localization. Moreover, to prevent sound localization on the basis of monaural spectral shape cues from head and pinna, subjects were exposed to narrow band (1/3 octave) noises. We demonstrate that the BCD significantly improved sound localization in 8/12 of the UCHL patients. Interestingly, under monaural hearing (BCD off), we observed fairly good unaided azimuth localization performance in 4/12 of the patients. Our multiple regression analysis shows that all patients relied on the ambiguous HSE for localization. In contrast, acutely plugged control listeners did not employ the HSE. Our data confirm and further extend results of recent studies on the use of sound localization cues in chronic and acute monaural listening.     

Towards a Unifying Basis of Auditory Thresholds: Binaural Summation

Absolute auditory threshold decreases with increasing sound duration, a phenomenon explainable by the assumptions that the sound evokes neural events whose probabilities of occurrence are proportional to the sound’s amplitude raised to an exponent of about 3 and that a constant number of events are required for threshold (Heil and Neubauer, Proc Natl Acad Sci USA 100:6151–6156, 2003). Based on this probabilistic model and on the assumption of perfect binaural summation, an equation is derived here that provides an explicit expression of the binaural threshold as a function of the two monaural thresholds, irrespective of whether they are equal or unequal, and of the exponent in the model. For exponents >0, the predicted binaural advantage is largest when the two monaural thresholds are equal and decreases towards zero as the monaural threshold difference increases. This equation is tested and the exponent derived by comparing binaural thresholds with those predicted on the basis of the two monaural thresholds for different values of the exponent. The thresholds, measured in a large sample of human subjects with equal and unequal monaural thresholds and for stimuli with different temporal envelopes, are compatible only with an exponent close to 3. An exponent of 3 predicts a binaural advantage of 2 dB when the two ears are equally sensitive. Thus, listening with two (equally sensitive) ears rather than one has the same effect on absolute threshold as doubling duration. The data suggest that perfect binaural summation occurs at threshold and that peripheral neural signals are governed by an exponent close to 3. They might also shed new light on mechanisms underlying binaural summation of loudness.     

Hearing Aid Technology to Improve Speech Intelligibility in Noise: Increasing the Effectiveness of Hearing Aid Directional Microphones

Directionality is the only hearing aid technology — in addition to amplification — proven to help hearing aid users hear better in noise. Hearing aid directionality has been documented to improve speech intelligibility in multiple laboratory studies. In contrast, real-world studies have shown a disconnect between the potential of the technology and what hearing aid users experience in their daily life. This article describes the real-world studies that inspired ReSound to take a different approach to applying directional microphone technology. This approach is based on the idea that hearing aid directionality can leverage natural binaural hearing and inherent listening strategies. The directional strategy includes three listening modes that will be explained. These are the Spatial Cue Preservation mode, the Binaural Listening mode, and the Speech Intelligibility mode. The strategy and the advantages it provides in terms of sound quality, spatial hearing, and improved signal-to-noise ratio with maintained awareness of surroundings are explained.     

A comparison of sound quality judgments for monaural and binaural hearing aid processed stimuli.

Fifteen adults with bilaterally symmetrical mild and/or moderate sensorineural hearing loss completed a paired-comparison task designed to elicit sound quality preference judgments for monaural/binaural hearing aid processed signals. Three stimuli (speech-in-quiet, speech-in-noise, and music) were recorded separately in three listening environments (audiometric test booth, living room, and a music/lecture hall) through hearing aids placed on a Knowles Electronics Manikin for Acoustics Research. Judgments were made on eight separate sound quality dimensions (brightness, clarity, fullness, loudness, nearness, overall impression, smoothness, and spaciousness) for each of the three stimuli in three listening environments. Results revealed a distinct binaural preference for all eight sound quality dimensions independent of listening environment. Binaural preferences were strongest for overall impression, fullness, and spaciousness. Stimulus type effect was significant only for fullness and spaciousness, where binaural preferences were strongest for speech-in-quiet. After binaural preference data were obtained, subjects ranked each sound quality dimension with respect to its importance for binaural listening relative to monaural. Clarity was ranked highest in importance and brightness was ranked least important. The key to demonstration of improved binaural hearing aid sound quality may be the use of a paired-comparison format.     

Advantages of directional hearing aid microphones related to room acoustics.

In this study, two types of hearing aids were used. Both aids had the same frequency characteristics for frontal sound, but one employed an omnidirectional microphone and the other a directional microphone. The frequency characteristics of both hearing aids were measured for five azimuths on KEMAR and in situ in 12 normal-hearing subjects. For these subjects we also determined the speech reception threshold (SRT) with background noise in two rooms with different reverberation times. The direction of the speech stimuli was always frontal; the direction of the noise was varied. Additionally, directional hearing was measured with short noise bursts from eight loudspeakers surrounding the subject. In the less reverberant room, sounds coming from behind were less amplified by the hearing aid with the directional microphone than by the one with the omnidirectional microphone. In this room the monaural SRT values were largely determined by the level of the background noise. For the directional hearing aids there was an extra binaural advantage which depended on the direction of the background noise. Only for low-frequency noise bursts was directional hearing better with directional hearing aids. In the more reverberant room, no distinct differences between the frequency characteristics of the two hearing aid types were measured. However, a systematic difference between monaural SRT values measured through the two hearing aids was found. This difference was independent of noise azimuth. In conclusion, hearing aid(s) with a directional microphone showed no disadvantages and clear advantages under specific conditions.     

The effect of asymmetrical signal degradation on binaural speech recognition in children and adults.

To determine the effect of asymmetrical signal degradation on binaural speech recognition, 28 children and 14 adults were administered a sentence recognition task amidst multitalker babble. There were 3 listening conditions: (a) monaural, with mild degradation in 1 ear; (b) binaural, with mild degradation in both ears (symmetric degradation); and (c) binaural, with mild degradation in one ear and severe degradation in the other ear (asymmetric degradation). Sentences and babble were degraded digitally to simulate mild and severe cochlear hearing loss. All participants demonstrated significant binaural advantage (average of 7 dB) when listening to symmetrically degraded signals as compared to when listening monaurally. In contrast, adults and children achieved little or no binaural benefit, on average, when listening to asymmetrically degraded signals. Moreover, overall performance of the adults was significantly worse when listening to binaural asymmetrically degraded signals than when listening to monaural signals, thus demonstrating evidence of binaural interference. In contrast to our original speculations, however, children did not show an overall demonstration of binaural interference. Relative performance in the binaural-asymmetric and the monaural conditions was not influenced by which ear (right or left) received the more degraded signal.     

Binaural benefit--when and how much?

Subjective ratings of aided hearing ability on a five point scale in ten hypothetical listening situations were obtained from 150 binaural hearing aid users, and from 296 monaural hearing aid users. Ratings of unaided hearing ability in nine of the same situations were obtained from 125 persons with self-defined normal hearing. The results indicated that in situations where signal-to-noise ratio was low, hearing aid users rated their listening much below the performance of normal hearing persons, binaural users indicating no advantage over monaural users. In the other hypothetical situations the binaural users rated their ability higher than did the monaural aid users. In some situations, where the sound was presented from a single source, binaural aid users rated their ability on a par with the normal hearing individuals. Age and hearing loss had small effects on the ratings, but the magnitudes of these effects were considerably less than that attributable to the type of aid provision, that is, whether monaural or binaural. These findings lend support to the benefits of binaural amplification in many listening situations.     

Changing systems of amplification

This paper reports on the changing systems of amplification used by hearing-impaired children in the last decade (1977 to 1987). The major changes noted were in terms of ear-level v. body-worn hearing aids, monaural v. binaural hearing aids and FM-wireless v. hardwire group hearing aids (GHAs). There was an increase in the use of ear-level hearing aids, binaural hearing aids and FM-wireless hearing aids with a corresponding decrease in the use of body-worn hearing aids and hardwire GHAs.     

Hearing Aid Technology to Improve Speech Intelligibility in Noise: Motion Sensors in Automatic Steering of Hearing Aids

A requirement for modern hearing aids is to evaluate a listening environment for the user and automatically apply appropriate gain and feature settings for optimal hearing in that listening environment. This has been predominantly achieved by the hearing aids'' acoustic sensors, which measure acoustic characteristics such as the amplitude and modulation of the incoming sound sources. However, acoustic information alone is not always sufficient for providing a clear indication of the soundscape and user''s listening needs. User activity such as being stationary or being in motion can drastically change these listening needs. Recently, hearing aids have begun utilizing integrated motion sensors to provide further information to the hearing aid''s decision-making process when determining the listening environment. Specifically, accelerometer technology has proven to be an appropriate solution for motion sensor integration in hearing aids. Recent investigations have shown benefits with integrated motion sensors for both laboratory and real-world ecological momentary assessment measurements. The combination of acoustic and motion sensors provides the hearing aids with data to better optimize the hearing aid features in anticipation of the hearing aid user''s listening needs.     

Monaural versus binaural hearing: ease of listening, word recognition, and attentional effort.

Forty-eight normal-hearing subjects performed ease of listening, word recognition, and attentional effort tasks for speech in noise under binaural and two simulated unilateral conductive hearing loss (monaural) conditions. The two monaural conditions differed as a function of unoccluded ear orientation to the primary signal (monaural-near and monaural-far). Ease of listening ratings and word recognition scores were significantly poorer during monaural listening and significantly affected by ear orientation to the speech signal. Attentional effort was not significantly affected by changing from binaural to monaural-near listening, but was significantly poorer in the monaural-far condition than in either of the other listening conditions. There was a significant correlation between ease of listening ratings and word recognition, but no correlation between attentional effort and either ease of listening or word recognition.     

Aging and the binaural advantage in reverberation and noise.

The consonant identification ability of younger normal-hearing adults and older adults with little or no peripheral hearing loss was assessed using monaural and binaural presentation in four listening conditions: quiet, noise, reverberation, and reverberation + noise. Performance was examined in terms of identification accuracy and amount of binaural advantage. Results suggest that the small amount of hearing loss in the older subjects limited their perception of distorted consonants. Neither age nor peripheral hearing loss was related strongly to the amount of benefit obtained from binaural presentation.