Acoustical feedback associated with the use of post aural hearing aids for profoundly deaf children

The feedback properties of 29 ears fitted with post aural hearing aids and hard acrylic earmoulds, have been investigated for a group of profoundly deaf children. Complex loop gain has been measured, and maximum hearing aid gain before instability has been calculated from the measurement results. Guidelines for prediction of maximum hearing loss, which can be managed, are stated, and a suitable hearing aid frequency response for profoundly deaf children is proposed. This response ensures that acoustical feedback above approximately 1 kHz does not limit the low frequency gain, which is assumed to be very important for the speech recognition.     

Maximum real-ear gain of in-the-ear hearing aids

Three hearing aid manufacturers provided custom full-shell in-the-ear hearing aids for each of 3 hearing-impaired subjects. Each manufacturer was instructed that the hearing aids should provide the maximum possible acoustic gain within the limits of hearing aid shell size and available components. Coupler gain, insertion gain, and functional gain were measured for each hearing aid. Gain measures were made with the volume control at either the full-on setting or the highest setting possible before the onset of acoustical feedback. Full-on coupler gain curves were similar across all nine hearing aids. Individual differences in concha/ear canal size and in the fit of the hearing aids produced substantial variance in insertion gain across hearing aids. Peak insertion gain varied from 41 to 58 dB. If 10 dB reserve gain is allowed, the range of estimated peak use gain from these maximum-gain in-the-ear hearing aids is 31-48 dB.     

Real-world performance of a reverse-horn vent

The present study compared differences in subjective and objective performance in completely-in-the-canal (CIC) hearing aids with conventional uniform 1.5 mm parallel vents and another with a reverse horn vent where the diameter increased from 1.5 mm on the lateral faceplate to 3 mm on the medial opening of the hearing aid. Nine hearing-impaired persons with a high-frequency hearing loss participated. The test battery included unaided in situ thresholds, amount of available gain before feedback, speech in quiet, speech in noise (HINT), subjective ratings of hollowness and tolerance, objective measures of the occlusion effect, and real-ear aided response. Results showed less available gain before feedback but less occlusion effect for subjective ratings and objective measures with the reverse horn vent. This type of vent design may be useful to increase the effective vent diameter of custom (including CIC) hearing aids.     

Speech understanding and directional hearing for hearing-impaired subjects with in-the-ear and behind-the-ear hearing aids

With respect to acoustical properties, in-the-ear (ITE) aids should give better understanding and directional hearing than behind-the-ear (BTE) aids. Also hearing-impaired subjects often prefer ITEs. A study was performed to assess objectively the improvement in speech understanding and directional hearing afforded by ITE aids versus BTEs. In 28 hearing-impaired subjects, who visited our Centre for a check-up of their ITEs, the following parameters were measured: (a) thresholds for third-octave bandpass noises between 0.25 and 4 kHz, (b) speech reception thresholds for short Dutch sentences in quiet and with background noise, (c) directional hearing. All three experiments were done binaurally with the subjects wearing their ITEs, BTEs, and no hearing aid. With the 2-cc coupler, the gain used by the subject was measured. The SRT values for the ITE were significantly lower than those for BTE. More gain at 2 and 4 kHz in the ITE proved to be a responsible factor for this improvement. Directional hearing was not improved by wearing an ITE. Large interindividual differences were found between functional gain and the 2-cc coupler measurements. The mean functional gain at 4 kHz for an ITE is higher than the gain measured in a 2-cc coupler. For a BTE, the functional gain at 2 and 4 kHz is lower than the 2-cc coupler gain.     

Factors affecting the use and perceived benefit of ITE and BTE hearing aids.

The aim of the present study was to investigate factors that might affect hearing aid use, satisfaction and perceived benefit. A further aim was to look at which variables affect the choice of hearing aid, in particular, an in-the-ear (ITE) versus a behind-the-ear (BTE) device. Twenty-nine elderly hearing-impaired people with a mild-to-moderate hearing loss were fitted with both an ITE and a BTE hearing aid with similar electroacoustic performance. Both hearing aids were linear with output compression limiting and were fitted in a randomized order. After wearing each device for a six-week period, subj ets were asked to select the hearing aid they preferred. Variables significantly related to hearing aid choice, use and perceived benefit included ease of management, accuracy with which the NAL-R insertion gain target was achieved, earmould comfort and the type of hearing aid the client preferred initially.     

阻尼位置对耳背式助听器频响特性影响的研究

目的 探究阻尼置于耳模不同位置时对耳背式助听器输出频响曲线的影响.方法 将阻尼分别放置在近耳钩处、近出声孔处、两者中间点或不放置,并且检测各种情况下耳背式助听器的输出频响曲线.结果 阻尼对耳背式助听器频响曲线中各频率的增益均会产生衰减作用,其中以0.5、1、4 kHz为甚;且当阻尼每向耳模出声孔处靠近一个位置,增益衰减越大.结论 阻尼可以明显平滑耳背式助听器输出频响曲线上瞬时不稳定的共振峰,使得输出频响曲线更加圆滑,并且随着阻尼位置的变化,衰减频率区间和衰减量都可呈规律性变化.     

Classification of steady state gain reduction produced by amplitude modulation based noise reduction in digital hearing aids

Digital noise reduction systems in modern digital hearing aids aim to improve either speech intelligibility or listening comfort. Little is known, however, about the actual gain reduction produced by different noise reduction systems. The aim of this study is to compare the gain reduction of different noise reduction systems.

We applied a systematic variation of different presentation levels of the input signal, different signal-to-noise ratios, and different target hearing loss configurations. The gain reduction of 12 different hearing aids was compared both qualitatively and quantitatively by means of principal value decomposition.

The results show that these hearing aids differ considerably in their responses. These differences are presented qualitatively by plotting contour maps that give the gain reduction as function of signal-to-noise-ratio and frequency. The quantitative analysis shows that the gain reduction produced by most hearing aids can be characterized by two transfer functions. The most important being an overall gain reduction. In addition to this, the frequency response is tilted to achieve either more low-frequency reduction and less high-frequency reduction, or the opposite.     

Vibrant Sound Bridge System. A new kind hearing prosthesis for patients with sensorineural hearing loss. 2. Audiological results

OBJECTIVE: Implantable hearing aids present a new treatment modality for patients suffering from sensorineural hearing loss. The functional gain obtained with the partially implantable Symphonix soundbridge system was evaluated in a clinical study. The audiological results achieved with n = 34 patients over a period of up to three years are presented in this second part of the publication. PATIENTS AND METHODS: 34 patients have received the Symphonix Vibrant soundbridge system since February 1997. The average age at implantation was 47.2 years (minimum: 18.9 years; maximum: 80.3 years). All patients have had several years of experience with hearing aids, which, however, provided insufficient functional gain or could not be fitted with a conventional hearing aid for medical reasons (such as auditory ear canal problems). All patients fulfilled the audiological selection criteria as they had bilateral moderate to severe sensorineural hearing loss. As a rule, the ear with poorer performance was implanted. All patients were fitted with the audio processor eight weeks after the implantation. The pure tone thresholds, the functional gain, the monosyllable and sentence understanding (G?ttinger Sentence Test in quiet and noise) were preoperatively and postoperatively assessed. Standardized self-assessment questionnaires were used to evaluate the subjective benefit (PHAB) and the quality of hearing (HDSS) as compared to the preoperative situation. Further hearing tests were performed after four weeks, three, six, nine, twelve, eighteen, twenty-four and thirty-six months postoperatively. During the observation period of up to three years the audioprocessor was updated several times, most recently with the fully digital three-channel-system Vibrant D. The results obtained were documented. RESULTS: Postoperatively, the pure tone threshold with the soundbridge system switched off did not change significantly in the implanted ear. All patients had a functional gain that was either comparable to the gain achieved with hearing aids or better. In particular speech-related frequencies showed improved amplification. The free field speech recognition tests revealed higher scores in quiet and in noise. The patients commended the natural sound quality, the lack of feedback, the absence of occlusion and distortion, the improved speech understanding in noise and the favourable cosmetic appeal. Only two patients failed to achieve better results as compared to their performance with conventional hearing aids. No complications, such as a deterioration of hearing due to inner ear damage or a conductive hearing loss, were observed in the long-term. CONCLUSIONS: The Symphonix Vibrant Soundbridge is a new and promising treatment modality for patients suffering from moderate to severe sensorineural hearing loss. Further improvement of the good results can be expected with improved coupling of the transducer to the ossicular chain and further development of signal processing.     

Trial of a two-channel hearing aid (low-frequency compression-high-frequency linear amplification) with school age children.

OBJECTIVE: The study was designed to investigate the efficacy of a 2-channel hearing aid with low-frequency compression and high-frequency linear amplification on a group of school-age hearing aid wearers. DESIGN: The study was a single-center, 2-way crossover design in which 25 children (age 6 to 15 yr) were fitted with 2-channel hearing aids for 12 wk and with their own (single-channel) hearing aids for 12 wk, refitted according to published protocols. Speech perception in quiet and in noise was measured at the end of each 12 wk period; in addition, questionnaires were given to teachers, parents, and children. RESULTS: Two-channel hearing aids showed significantly higher mean scores for speech perception in noise and significantly higher composite questionnaire scores (reflecting aspects of satisfaction and benefit). Final choice of hearing aids at the end of the study by parents and children also favored the 2-channel device. CONCLUSIONS: The 2-channel hearing aids appear to be an acceptable management option for audiometrically suitable children. The results provide support for the 2-channel design rationale and suggest the need for further trials.     

Comparison of the electroacoustic characteristics of five hearing aids

This paper describes a comparison of the electroacoustic characteristics of five hearing aids: (1) a linear BTE aid of the type dispensed under the UK National Health Service (NHS), the BE19; (2) an analogue programmable BTE aid incorporating two-channel wide dynamic range compression, the ReSound BT2; (3) and (4) two digital BTE aids incorporating multi-channel wide dynamic range compression, the Phonak Claro and the Danavox Danalogic; (5) a disposable ITE hearing aid with single-channel compression, the Songbird. Measurements of frequency response using a 2 cc coupler showed that the NHS aid had a distinct undesired peak around 1 kHz. The response rolled off at low and high frequencies, and no gain was applied above about 4000 Hz. The BT2 and Claro both showed somewhat irregular responses with effective upper frequency limits of 5000-6000 Hz. The Danalogic had a reasonably smooth response and provided gain up to 6000 Hz. The Songbird had a smooth response and provided gain up to about 7000 Hz. All aids showed reasonably low harmonic and intermodulation distortion (probably below audible levels for hearing-impaired listeners), the Phonak Claro being the best in this respect. Measures of the effective input noise were obtained using two new methods. The NHS aid had the highest (worst) effective input noise, whereas the Songbird had the lowest, especially at low frequencies. The BT2 and the two digital aids had similar noise levels on one measure, but the BT2 was superior on the other measure. The compression circuits were characterized by measuring attack and release times and by using a method described by Stone and Moore (1992). The aids varied markedly in the extent to which they compressed amplitude modulation at the rates typically occurring in speech (2-10 Hz), the Claro providing the least compression and the Danalogic and Songbird aids providing the most. Overall, the results indicate that the NHS aid performed more poorly in several respects than the other aids. There were no great differences in electroacoustic characteristics between the remaining analogue aids and the digital aids, although the Songbird had a somewhat wider frequency range and lower effective input noise than the other aids.     

Preferred insertion gain of hearing aids in listening and reading-aloud situations

Nine hearing-impaired subjects with primarily high-frequency hearing loss (Group A) and 8 hearing-impaired subjects with hearing loss in both the high- and low-frequency regions (Group B) participated in the experiment. Subjects wore binaural programmable multimemory hearing aids and selected the preferred amount of insertion gain while they listened to discourse passages read by a male speaker (listen). Subjects also selected the preferred amount of gain while they listened to themselves as they were reading the same passages (read-aloud). Subjects' word-recognition performances and their subjective impressions of the hearing aids determined in listen and read-aloud conditions were examined on subsequent listening and reading tasks. Hearing-impaired subjects preferred more insertion gain in the listen condition than in the read-aloud condition. Different insertion gains led to different objective and subjective performances. Hearing-aid responses selected for a particular condition (listening vs. reading aloud) yielded the best performance in that condition. Assuming the primary purpose of a hearing aid is for amplifying the speech of others, these findings suggest that one should not adjust the gain of a hearing aid using one's own voice as the reference. In addition, one should be careful in soliciting subjective comments from hearing-impaired patients during hearing-aid fittings to avoid underamplifying those individuals in the low frequencies. Multimemory hearing aids may be necessary for some hearing-impaired patients to use their hearing aids satisfactorily in listening and speaking conditions.     

Noise reduction hearing aids: release from masking and release from distortion.

Automatic frequency response (AFR) hearing aids usually reduce their low-frequency gain in the presence of noise; several investigators have reported improved recognition of high-frequency speech information in low-frequency band-limited noise with AFR versus non-AFR hearing aids. In this work, masking patterns (masked threshold for frequency-modulated probe tones as a function of probe frequency) were obtained for a narrowband low-frequency noise. Speech recognition threshold for a set of high-frequency loaded monosyllables also was obtained in the presence of the same noise. Aided speech and masking pattern data for one normal and two hearing-impaired subjects wearing a master hearing aid incorporating a commercially available AFR circuit showed modest AFR effects. Moreover, masking noise spectra measured in ear canals of subjects wearing the master hearing aid showed evidence of substantial hearing aid-generated distortion products in the AFR-off condition. Results obtained from the normal subject listening with a low-distortion laboratory simulation of an AFR hearing aid showed greater release from masking for the same low-frequency attenuation as provided by the hearing aid. Improvements of speech recognition in noise observed with AFR hearing aids may result from some combination of release from upward spread of masking and reduction of distortion products generated by the hearing aid in the non-AFR setting.     

Allowing for real ear venting effects when selecting the coupler gain of hearing aids.

Vents in hearing aids have two major effects on the insertion gain of a hearing aid: they let low-frequency sound in without amplification, and they reduce the low-frequency gain of sound transmitted through the hearing aid. Their net effect on low-frequency gain can thus be either negative or positive. This paper shows how to allow for both of these effects. One of the results is that for many hearing-impaired clients, there is a range of coupler gain curves which will result in the required insertion gain. The tables in this article are arranged to enable the user to specify a desired vent, and then determine the allowable range of coupler gains that will achieve a desired insertion gain to within a specified tolerance. The results of various studies comparing coupler gain and insertion gain are also compared and combined. The calculation method outlined in this paper can predict low-frequency real ear insertion gain for the individual subject with a prediction accuracy (root-mean-square-error) of 3.6 dB.     

Evaluation of a frequency transposition algorithm using wearable hearing aids

Transposition of acoustic information from higher to lower frequencies may help people with severe or profound high-frequency hearing loss, especially when a ‘dead region’ is present. Previously, we (Robinson et al, ) evaluated the benefit of an FFT-based transposition algorithm in a laboratory study. Although results were promising, we hypothesized that further training and exposure would be needed to gain the full benefit. This was tested here by implementing the algorithm in wearable digital hearing aids. Five subjects with high-frequency dead regions used the aids for five weeks. Performance on the transposing and control conditions was compared objectively using speech tests (vowel-consonant-vowel, ‘s’ detection, and speech in noise) and subjectively using questionnaires. Overall, the results showed no benefit with the transposition even after experience. Subjective preference was generally for the control condition.     

Insertion gain measurements using two low-powered analogue hearing aids

Differences between insertion gain measurements and coupler measurements were investigated using two different hearing aids, to assess the accuracy of hearing aid fitting methods which involve the use of real-ear-to-coupler differences (RECDs). The hearing aids used were the NHS BE19 and the Lavis X11. They were allocated alternately to 80 new adult hearing aid users, and insertion gain measurement was carried out with the allocated aid on all subjects, and with both hearing aids on 36 subjects. Coupler measurements were also carried out with both hearing aids, at two different gain settings. Comparison of the coupler measurements and the insertion gain measurements suggests that the differences in insertion gain produced by different hearing aids cannot be predicted accurately from the differences in coupler gain measurements produced by the same aids. Although the use of RECDs measured using insert earphones may accurately predict the real-ear performance of some models of hearing aid, this method may not produce equally satisfactory results with other models.     

Evaluation of wideband frequency responses and non-linear frequency compression for children with mild to moderate high-frequency hearing loss

Objective: To evaluate wideband amplification and non-linear frequency compression (NLFC) as a means to improve speech recognition for children with mild/moderate hearing loss. Design: Randomized within-subject design with repeated measures across test conditions. Study sample: Eleven children with mild to moderate hearing loss were evaluated with: (1) Phonak BTE without NLFC, (2) Phonak BTE with NLFC, and (3) Oticon BTE with wideband response extending to 8000 Hz. Results: Use of NLFC provided better detection and recognition of high-frequency stimuli (e.g. /sh/ and /s/). No difference in performance between conditions was observed for speech recognition when measured with the University of Western Ontario (UWO) plurals test and the UWO distinctive features difference test. Finally, there were no differences between conditions on the BKB-SIN test. Conclusions: Children with mild to moderate hearing loss have good access to high-frequency phonemes presented at fixed levels (e.g. 50 to 60 dBA) with both wideband and NLFC technology. Similarly, sentence recognition in noise was similar with wideband and NLFC. Adaptive test procedures that probe performance at lower input levels showed small but significant improvements in the detection and recognition of the phonemes /s/ and /sh/ with NLFC condition when compared to the NLFC Off and wideband conditions.     

Perceptual consequence of vents in hearing aids

The perceptual consequence of venting an earmould while maintaining the insertion gain at a preferred listening level was examined on nine hearing-impaired individuals with bilaterally symmetrical sloping sensorineural hearing loss. Subjects wore binaural programmable hearing aids and selected their preferred insertion gain while the hearing aids were coupled to vented (2.2 mm parallel vent) and unvented earmoulds. A modified Simplex procedure with discourse passages presented in quiet was used to determine preferred insertion gain. The results showed that venting enhanced subjects' quality rating of the hearing aids during listening and vocalization tasks, but did not change subjects' word recognition scores. These results suggest that vented earmoulds should be used to achieve target insertion gain in order to maximize patients' acceptance of hearing aids.     

Predicted and measured speech recognition performance in noise with linear amplification

OBJECTIVE: The purpose of this study was to investigate the applicability of the Speech Intelligibility Index (SII) in hearing aid fitting. It was hypothesized that estimated speech intelligibility, based on the SII, could be a more reliable measure than real speech recognition results for comparing hearing aid characteristics. DESIGN: The test subjects were 29 elderly persons (66 to 80 yr) with mild-to-moderate hearing loss, who were using monaurally fitted linear hearing aids. They were selected from the files at Sahlgrenska hearing clinic. Speech recognition scores were obtained at fixed speech-to-noise ratios with Phonemically Balanced (PB) words in speech-weighted noise and in low-frequency noise. A Just-Follow-Conversation (JFC) test was performed with connected speech presented in the same background noises. The subjects were tested without hearing aid and with their hearing aids set at three different frequency responses. Predicted speech recognition scores were calculated for each condition based on the SII, complemented with a correction for sensorineural hearing impairment. The calculations involved speech and noise spectra, pure tone thresholds and insertion gain responses. RESULTS: For each condition, the measured speech recognition scores were, on average, well predicted by the calculated scores. The intra-individual standard deviation of the predicted scores was estimated to be about one percent unit. The group results of the JFC test were in agreement with the word recognition results for the aided conditions, but a floor effect was observed for the unaided conditions. CONCLUSIONS: Speech intelligibility prediction based on the modified SII is a valid estimate of speech recognition performance of hearing-impaired persons with mild-to-moderate hearing loss. Estimated intelligibility based on the SII is more reliable than actually measured speech recognition performance, for comparing amplification conditions within subjects.     

Effect of hearing aids on speech perception in noisy situations.

Hearing-impaired people often complain about poor speech intelligibility when they are in noisy surroundings. Several authors have published data suggesting that hearing aids add distortion to the signal and thus make speech less intelligible. Given the tendency of people to speak louder in competing noise, it means that some patients might understand better in such circumstances without an aid than with an aid. The present study investigated the effect of modern commercial hearing aids on the ability of patients to understand speech monaurally in noisy circumstances. The results in general showed speech to be equally understandable with and without an aid if the effects of presentation level (amplification) are excluded. The results, however, varied considerably between patients. Statistical analysis showed that the variance could be explained primarily by the degree of high-frequency loss and the slope of the audiogram. Patients with steep sloping audiograms understand better and patients with a conductive hearing loss component understand less in noisy circumstances with a hearing aid. Speech intelligibility in noisy situations did not correlate at all with the hearing loss averaged over the mid-frequencies (500, 1,000 and 2,000 Hz) but it did correlate with the high-frequency hearing loss (2,000 and 4,000 Hz) and the slope of the audiogram, indicating the importance of high-frequency emphasis in hearing aids.