Using hearing aid adaptive directional microphones to enhance cochlear implant performance

The goal of this study was to investigate whether adaptive microphone directionality could enhance cochlear implant performance. Speech stimuli were created by fitting a digital hearing aid with programmable omnidirectional (OM), fixed directional (FDM), or adaptive directional (ADM) microphones to KEMAR, and recording the hearing aid output in three noise conditions. The first condition simulated a diffused field with noise sources from five stationary locations, whereas the second and third condition represented one or three non-stationary locations in the back hemifield of KEMAR. Speech was always presented to 0° azimuth and the overall signal-to-noise ratio (SNR) was +5 dB in the sound field. Eighteen postlingually deafened cochlear implant users listened to the recorded test materials via the direct audio input of their speech processors. Their speech recognition ability and overall sound quality preferences were assessed and the correlation between the amount of noise reduction and the improvement in speech recognition were calculated. The results indicated that ADM yielded significantly better speech recognition scores and overall sound quality preference than FDM and OM in all three noise conditions and the improvement in speech recognition scores was highly correlated with the amount of noise reduction. Factors influencing the noise level are discussed.     

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.     

方向性麦克风技术在助听器中的应用

引言 目前，助听器的广泛使用已经使广大听力损失患者在很大程度上改善了他们的生活质量，但这些助听器用户在日常生活中还是会有一些聆听上的困难，尤其是在噪声环境下与人交谈。方向性麦克风系统（directional microphones system）也译为指向性麦克风，是用于提高助听器言语信噪比的一项重要技术，尤其能改善在噪声环境下的言语清晰度（可懂度）。本文通过介绍方向性麦克风的原理、作用以及实际应用方面等相关知识来帮助听力从业人员、技术人员和用户更好地了解和使用这项技术。     

Use of a loudness model for hearing aid fitting. V. On-line gain control in a digital hearing aid

Many researchers have proposed that hearing aids should process sounds so as to restore loudness perception to 'normal'. We describe how a model for predicting loudness for people with cochlear hearing loss can be implemented in a digital hearing aid so as to calculate the frequency-dependent gains that would be required to achieve that goal. It is assumed that the input signal is processed using brief segments or 'frames'. For each frame, the spectrum is calculated, usually via a fast Fourier transform (FFT). From the spectrum, an excitation pattern is calculated for a normal car and for the impaired ear of the patient. The loudness model is then used to calculate the gain required at the centre frequency of each channel in the aid, so as to match the specific loudness in the normal and impaired ears. The whole process is repeated for each successive frame, with overlap of frames and with smoothing of the gain changes across frames. We describe both an 'exact' model, which prescribes a 'curvilinear' compression characteristic at each frequency, and an approximation using 'straight' compression, which is computationally less intensive. Limitations of the present approach are described, and the approach is compared with more traditional approaches using multichannel compression, and with previous approaches using loudness models for fitting hearing aids.     

Comparison of performance on the hearing in noise test using directional microphones and digital noise reduction algorithms

PURPOSE: Difficulty understanding speech in background noise is one of the most common complaints of hearing aid users. In modern hearing aids, directional microphones (d-mics) are considered the method of choice in improving signal-to-noise ratio, with demonstrated improvement in speech-perception-in-noise tasks. On the other hand, digital noise reduction (DNR) algorithms, in commercially available products, are considered to provide comfort but not significant assistance in improving speech perception in noise. In practice, these 2 technologies are often used in conjunction, but few studies have evaluated their interaction and the resultant effect on speech perception in noise. The purpose of this study was to evaluate the effect on speech performance of using d-mics and DNR in isolation as well as in conjunction in the presence of background noise. METHOD: This study evaluates the performance of 16 experienced adult hearing aid users on the Hearing in Noise Test when each technology was activated independently and then simultaneously in 4 commercially available hearing aids. RESULT: Approximately 50% of our participants performed better with both d-mics and DNR activated in conjunction, while the other 50% performed best in the d-mic-only condition. When considering statistically significant differences in performance only, a reduction or improvement in performance was observed in 17% and 14% of the conditions, respectively. CONCLUSION: A direction for further research would be to identify predictive variables that could help the audiologist determine an individual's preference a priori.     

Unaided and aided performance with a directional open-fit hearing aid

Differences in performance between unaided and aided performance (omnidirectional and directional) were measured using an open-fit behind-the-ear (BTE) hearing aid. Twenty-six subjects without prior experience with amplification were fitted bilaterally using the manufacturer's recommended procedure. After wearing the hearing aids for one week, the fitting parameters were fine-tuned, based on subjective comments. Four weeks later, differences in performance between unaided and aided (omnidirectional and directional) were assessed by measuring reception thresholds for sentences (RTS in dB), using HINT sentences presented at 0 degrees with R-Space restaurant noise held constant at 65dBA and presented via eight loudspeakers set 45 degrees apart. In addition, the APHAB was administered to assess subjective impressions of the experimental aid. Results revealed that significant differences in RTS (in dB) were present between directional and omnidirectional performance, as well as directional and unaided performance. Aided omnidirectional performance, however, was not significantly different from unaided performance. These findings suggest for the hearing aids and experimental condition used in this study, a patient would require directional microphones in order to perform significantly better than unaided or aided with omnidirectional microphones, and that performance with an omnidirectional microphone would not be significantly better than unaided. Finally, the APHAB-aided scores were significantly better than unaided scores for the EC, BN, RV, and AV subscales indicating the subjects, on average, perceived the experimental aid to provide significantly better performance than unaided, and that aided performance was more aversive than unaided.     

Unaided and aided performance with a directional open-fit hearing aid

Differences in performance between unaided and aided performance (omnidirectional and directional) were measured using an open-fit behind-the-ear (BTE) hearing aid. Twenty-six subjects without prior experience with amplification were fitted bilaterally using the manufacturer's recommended procedure. After wearing the hearing aids for one week, the fitting parameters were fine-tuned, based on subjective comments. Four weeks later, differences in performance between unaided and aided (omnidirectional and directional) were assessed by measuring reception thresholds for sentences (RTS in dB), using HINT sentences presented at 0° with R-Space^TM restaurant noise held constant at 65dBA and presented via eight loudspeakers set 45° apart. In addition, the APHAB was administered to assess subjective impressions of the experimental aid.

Results revealed that significant differences in RTS (in dB) were present between directional and omnidirectional performance, as well as directional and unaided performance. Aided omnidirectional performance, however, was not significantly different from unaided performance. These findings suggest for the hearing aids and experimental condition used in this study, a patient would require directional microphones in order to perform significantly better than unaided or aided with omnidirectional microphones, and that performance with an omnidirectional microphone would not be significantly better than unaided. Finally, the APHAB-aided scores were significantly better than unaided scores for the EC, BN, RV, and AV subscales indicating the subjects, on average, perceived the experimental aid to provide significantly better performance than unaided, and that aided performance was more aversive than unaided.     

Performance of directional microphones for hearing aids: real-world versus simulation

The purpose of this study was to assess the accuracy of clinical and laboratory measures of directional microphone benefit. Three methods of simulating a noisy restaurant listening situation ([1] a multimicrophone/multiloudspeaker simulation, the R-SPACE, [2] a single noise source behind the listener, and [3] a single noise source above the listener) were evaluated and compared to the "live" condition. Performance with three directional microphone systems differing in polar pattern (omnidirectional, supercardioid, and hypercardioid array) and directivity indices (0.34, 4.20, and 7.71) was assessed using a modified version of the Hearing in Noise Test (HINT). The evaluation revealed that the three microphones could be ordered with regard to the benefit obtained using any of the simulation techniques. However, the absolute performance obtained with each microphone type differed among simulations. Only the R-SPACE simulation yielded accurate estimates of the absolute performance of all three microphones in the live condition. Performance in the R-SPACE condition was not significantly different from performance in the "live restaurant" condition. Neither of the single noise source simulations provided accurate predictions of real-world (live) performance for all three microphones.     

Evaluation of an adaptive directional system in a DSP hearing aid

The effectiveness of an adaptive directional microphone design, as implemented in the Phonak Claro behind-the-ear hearing aid, is evaluated. Participants were fit bilaterally and tested in 2 environments, an anechoic chamber and a moderately reverberant classroom, with the microphones in the fixed (cardioid) setting and the adaptive setting. Five speakers were placed between 110 degrees and 250 degrees azimuth around the listener. Speech-weighted noise was presented from those speakers at an overall level (OAL) of 65 dB (A). Noise was increased by 8 dB from 1 speaker at a time, using 2-s modulation and random assignment, while the output from the other speakers was reduced to maintain the constant OAL. Results of 2 speech perception tasks used as outcome measures indicated that the adaptive system was not able to follow the dominant noise source in the presence of lower level noise sources. Self-report measures obtained after blinded home trials were consistent with laboratory findings that the participants did not perceive this adaptive microphone design to be more effective than the default fixed-microphone option.     

关于学龄听障儿童听觉言语康复训练的思考

基于家庭的经济状况和家长的文化程度及对残疾子女的重视程度等原因,欠发达地区听障儿童的入学往往偏迟。如何对这些有一定残余听力却错过语言发展关键期的学龄听障儿童进行科学、系统、有效的听觉言语康复训练,使他们更快、更好地发展语言,值得广大特教工作者深思。     

Nonlinear digital hearing aid with near-instantaneous amplitude compression

We designed a new type of nonlinear digital hearing aid (TD-1) with near-instantaneous amplitude compression for sensorineural hearing-impaired people. The amplification method utilized by the TD-1 normalizes the signal waveforms within a time window bounded by two adjacent positive going zero-crossing points. The signals within this window are amplified so that the maximum amplitude reaches a preset value, thus allowing a consistent peak amplitude to be maintained. To test this, we examined the efficacy of the TD-1 device in 31 patients with sensorineural hearing loss. When tested for recognition of Japanese sentences in a quiet environment, 7 of 25 (28.0%) subjects wearing the TD-1 showed a 20% or greater increase in the maximum intelligibility score than that obtained when wearing their own linear hearing aids. In addition, 7 of 31 (22.6%) subjects showed the same increase with the TD-1 relative to that obtained when they wore HA70 or HA73 devices (Rion Co., Ltd., Tokyo, Japan), which are conventional analogue hearing aids. These results indicate that TD-1 can be effective for patients with sensorineural hearing loss. Received: 27 March 2001 / Accepted: 29 June 2001     

Impact of compression and hearing aid style on directional hearing aid benefit and performance.

OBJECTIVE: To evaluate the impact of low-threshold compression and hearing aid style (in-the-ear [ITE] versus behind-the-ear [BTE]) on the directional benefit and performance of commercially available directional hearing aids. DESIGN: Forty-seven adult listeners with mild-to-moderate sensorineural hearing loss were fit bilaterally with one BTE and four different ITE hearing aids. Speech recognition performance was measured through the Connected Speech Test (CST) and Hearing in Noise Test (HINT) for a simulated noisy restaurant environment. RESULTS: For both the HINT and CST, speech recognition performance was significantly greater for subjects fit with directional in comparison with omnidirectional microphone hearing aids. Performance was significantly poorer for the BTE instrument in comparison with the ITE hearing aids when using omnidirectional microphones. No differences were found for directional benefit between compression and linear fitting schemes. CONCLUSIONS: No systematic relationship was found between the relative directional benefit and hearing aid style; however, the speech recognition performance of the subjects was somewhat predictable based on Directivity Index measures of the individual hearing aid models. The fact that compression did not interact significantly with microphone type agrees well with previously reported electroacoustic data.     

Evaluation of a hearing screening questionnaire for use with Ecuadorian school-aged children

Objective: The purpose of this study was to evaluate the accuracy of a teacher-administered hearing screening questionnaire to detect hearing loss among first-grade Ecuadorian children in public schools. Design: A cross-sectional design was used to compare screening results from the teacher-administered questionnaire and pure-tone audiometry. Study sample: Children were randomly selected from 117 schools. The study was conducted in two phases to accommodate different school calendars in the country. Data for both screening methods were available for 4616 children. Results: For Phase 1, almost 90% who failed the questionnaire passed audiometry; and, 85% who failed audiometry passed the questionnaire. A revised questionnaire was used for Phase 2 and 70% who failed the questionnaire passed audiometry; and 85% who failed audiometry, passed the questionnaire. Of the 27 children identified in Phase 2 as having hearing loss at the time screening was done, 88.9% failed audiometry, but only 22.2% failed the questionnaire. Conclusions: Because there was little agreement between the questionnaire and the audiometry, it was recommended that the questionnaire not be used to screen Ecuadorian children for hearing loss. The results of this evaluation of the school hearing screening program provided the Ecuadorian government with important information to guide policy decisions.     

Acceptable noise level as a measure of directional hearing aid benefit

An acceptable noise level (ANL) procedure for measuring hearing aid directional benefit was compared with masked speech reception threshold (SRT) and front-to-back ratio (FBR) procedures. ANL is the difference between the most comfortable listening level and the maximum accepted background noise level while listening to speech. Forty adult subjects wearing their own binaural hearing aids were evaluated in omnidirectional and directional modes. The subjects were fitted with a variety of hearing aids by clinical audiologists, independent of the study. For each procedure, speech and noise were presented through loudspeakers located at 0 degrees and 180 degrees azimuth, respectively. Mean ANL (3.5 dB), SRT (3.7 dB), and FBR (2.9 dB) directional benefits were not significantly different. The ANL and masked SRT benefits were significantly correlated. The ANL appears to be a quick, clinician/user friendly procedure for measuring hearing aid directional benefit.     

Predicting directional hearing aid benefit for individual listeners

The fitting of directional microphone hearing aids is becoming increasingly more routine, and this fitting option has proven to be a successful method to improve speech intelligibility in many noisy listening environments. Data suggest, however, that some hearing-impaired listeners receive significantly more directional benefit than others. It is of interest, therefore, to determine if directional benefit is predictable from identifiable audiologic factors. In this report, we examined whether the slope of audiometric configuration, amount of high-frequency hearing loss, and/or the aided omnidirectional performance for a speech-in-noise intelligibility task could be used to predict the magnitude of directional hearing aid benefit. Overall results obtained from three separate investigations revealed no significant correlation between the slope of audiometric configuration or amount of high-frequency hearing loss and the benefit obtained from directional microphone hearing instruments. Although there was a significant, negative relationship between aided omnidirectional performance and the directional benefit obtained in one study, there was considerable variability among individual participants, and nearly all of the listeners with the best omnidirectional hearing aid performance still received significant additional benefit from directional amplification. These results suggest that audiologists should consider the use of directional amplification for patients regardless of audiogram slope, high-frequency hearing loss, or omnidirectional speech intelligibility score.     

Apparent change of masking functions with compression-type digital hearing aid

Signal perception ability under conditions of a narrow band masker in subjects with hearing aids was examined using a theoretical model of the auditory nerve fibre (ANF) with a deteriorated tuning curve in addition to measurements of actual masking function in subjects wearing hearing aids. The results obtained indicate that the apparent masking function could be affected by the frequency-gain character as well as by the degree of compression. Usually, the compression-type of amplification with flat and/or high-frequency weighted characteristics improves not only the apparent thresholds but also the apparent masked thresholds under conditions of lower frequency masking. On the other hand, a low-frequency masker amplified by a higher gain with low-frequency weighted amplification could cause larger upward-masking effects on the signal perception of the higher frequency signal in some conditions. The present study may contribute to our understanding of the underlying mechanisms of the effects of different amplification by the aid.     

How directional microphones affect speech recognition,listening effort and localisation for listeners with moderate-to-severe hearing loss

Objective: The purpose of this study was to evaluate the effects of directional microphone use on laboratory measures of sentence recognition, listening effort and localisation. An additional purpose of this study was to evaluate the effects of asymmetric directional microphone use on the same laboratory measures. Design: Three hearing aid conditions were evaluated: (1) bilateral omnidirectional microphones, (2) bilateral directional microphones and (3) asymmetric microphones (directional microphone for only one hearing aid). Sentence recognition performance was evaluated using a connected speech test. Listening effort was evaluated using a dual-task paradigm with a response time-based secondary task requiring word categorisation. Localisation was examined using a complex task requiring localisation and recall of speech originating from one of four loudspeakers in the horizontal plane (?60°, ?45°,?+45°,?+60°). Study sample: Eighteen adults (M?=?61.8 years) with symmetrical, moderate-to-severe hearing loss participated. Results: Performance on each task was analysed separately using a repeated measures analysis of variance. Results revealed directional benefits for sentence recognition and listening effort, but microphone setting did not affect localisation. Performance was equivalent with symmetric and asymmetric directional configurations. Conclusions: Bilateral and asymmetric directional microphone configurations equally improved sentence recognition and listening effort; neither affected localisation or recall.     

One year follow-up of users of a digital hearing aid.

A follow-up study has been performed on 29 of 33 original subjects who participated in a clinical trial of the digital hearing aid Oticon DigiFocus. The follow-up was performed after one year's use. Use of hearing instruments was assessed and questionnaires on hearing aid benefit, and hearing impairment and handicap were administered. Ratings of sound quality and measurements of speech recognition in noise were also performed. The results indicated almost doubled daily use of hearing aids as compared to that stated for the subjects' previous analogue aids one year earlier. Further, we found statistically significant improvements in speech recognition in noise one year post-fitting as compared to after one month. Other test results were essentially unchanged over time: no measure showed a significantly poorer rating or performance.