Tolerable hearing aid delays. I. Estimation of limits imposed by the auditory path alone using simulated hearing losses.

OBJECTIVE: When people who wear hearing aids speak, there are three paths by which they hear their own voices: 1) through the air and leakage around the earmold; 2) via the solid structures of their head; 3) through the air to the hearing aid microphone, and then through the aid circuitry. These paths involve different time delays. Digital processing introduces delays in path 3 from a few to several tens of milliseconds, which could lead to a range of disturbing effects. We examined one purely auditory effect, namely hearing speech through all three of these paths. Subjective disturbance was measured as a function of delay in path 3 using simulations of hearing loss and a simulated hearing aid. With increasing hearing loss, the loudness of sound heard via paths 1 and 2 decreases, and the aid user relies more on path 3. The disturbance produced by the delay then might be less perceptible. To test this idea, four different hearing losses were simulated, varying from mild to moderately severe. DESIGN: Each of two talkers was fitted with a closed earmold, and simultaneous above-ear and in-ear recordings were made of each talker reading prose. The above-ear signal was amplified using a simulated hearing aid with 4-channel full dynamic range compression; compression ratios and gains were selected using an algorithm based on the absolute thresholds used in the simulations of hearing loss. The resultant output was then mixed with the in-ear signal with one of five values of delay, and the combined signal was processed using the four simulations of hearing loss. The resulting stimuli simulated for normal-hearing listeners the experience of having a hearing impairment and listening through a hearing aid while talking, except that the talker's voice was not that of the listener. Twenty normally hearing subjects gave subjective ratings of the disturbance of the echo for each delay and each simulated hearing loss. RESULTS: Disturbance ratings generally increased monotonically with increasing delay. Average results show that delays are rated as "disturbing" for values between 20 and 30 msec for mild to moderate losses. For a moderately severe loss, the rating "disturbing" was not quite achieved at 40 msec. For moderate losses, a speaker with low fundamental frequency (f0)(70 to 140 Hz) was less disturbing than a speaker with a medium f0, (100 to 180 Hz). This effect reversed for the mildest loss for low values of delay. CONCLUSIONS: The auditory effects of delays between bone-conducted sound and aid-conducted sound are likely to become disturbing for delays exceeding 20 msec. Somewhat longer delays may be tolerable for moderate to severe hearing losses. These delays are smaller than the delays at which audio-visual integration is disrupted.     

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.     

Hearing aid evaluation for persons with postlingual hearing levels of 90 to 100 dB.

Of 20 subjects with profound (90 to 100 dB) hearing loss who underwent a careful hearing aid evaluation, 16 were able to benefit from hearing aid use. With the recommended aids, all subjects could detect speech at levels within the normal conversational range; 75% had some understanding of spondee words; and 56% successfully accomplished tasks in phoneme identification. Two subjects succeeded on a standard speech discrimination test. Ear-level instruments, five binaural, were recommended for 13 of the 16 subjects. Microphones were front-facing in the majority of instances; none were directional. Seven aids used amplitude compression. Subjects were encouraged to relate their subjective impressions, and home trial was an important part of the evaluation. In the majority of instances, lipreading scores were markedly better with hearing aid use than without.     

Relative benefits of linear analogue and advanced digital hearing aids

Speech recognition performance and self-reported benefit from linear analogue and advanced (digital) hearing aids were compared in 100 first-time hearing aid users with mild-to-moderate sensorineural hearing loss fitted monaurally with a behind-the-ear (BTE) hearing aid in a single-blind randomized crossover trial. Subjects used each aid for 5 weeks in turn, with aid order balanced across subjects. Three alternative models of digital hearing aid were assigned to subjects according to a balanced design. Aid type was disguised to keep subjects blind within practical limitations. Aided speech recognition performance in noise was measured at speech levels of 65 and 75dB at a speech-to-noise ratio (SNR) of +2dB for closed sets of single words. Self-rated benefit was measured using the Abbreviated Profile of Hearing Aid Benefit (APHAB) and the Glasgow Hearing Aid Benefit Profile (GHABP). Quality of life, hearing aid use and user preferences were also assessed. Speech recognition scores with the digital aids were significantly better at 75dB than with the analogue aids Self-reported benefit (APHAB, GHABP) and improvement in quality of life were generally not significantly different between analogue and digital aids, although aversiveness measured with the APHAB was significantly lower with digital aids, and satisfaction measured with the GHABP was greater. The digital aids were preferred significantly more often than the analogue aids, with 61 subjects choosing their digital aid, 26 choosing the analogue aid, and nine being equivocal. Overall, this study shows advantages for advanced digital over simple linear analogue aids in terms of both objective and subjective outcomes, although average differences are not large.     

Relative benefits of linear analogue and advanced digital hearing aids

Speech recognition performance and self-reported benefitfrom linear analogue and advanced (digital) hearing aidswere compared in 100 first-time hearing aid users withmild-to-moderate sensorineural hearing loss fitted monaurally with a behind-the-ear (BTE) hearing aid in a single-blind randomized crossover trial. Subjects usedeach aid for 5 weeks in turn, with aid order balancedacross subjects. Three alternative models of digital hearing aid were assigned to subjects according to a balanceddesign. Aid type was disguised to keep subjects blind within practical limitations. Aided speech recognition performance in noise was measured at speech levels of 65 and 75 dB at a speech-to-noise ratio (SNR) of _2 dB forclosed sets of single words. Self-rated benefit was measured using the Abbreviated Profile of Hearing Aid Benefit (APHAB) and the Glasgow Hearing Aid Benefit Profile (GHABP). Quality of life, hearing aid use and user preferences were also assessed. Speech recognition scores with the digital aids were significantly better at 75 dB than with the analogue aids. Self-reported benefit (APHAB, GHABP) and improvement in quality of life were generally not significantly different between analogue and digital aids, although aversiveness measured with the APHAB was significantly lower with digital aids,and satisfaction measured with the GHABP was greater. The digital aids were preferred significantly more often than the analogue aids, with 61 subjects choosing their digital aid, 26 choosing the analogue aid, and nine being equivocal. Overall, this study shows advantages for advanced digital over simple linear analogue aids interms of both objective and subjective outcomes, although average differences are not large.     

Wirkung von Frequenzkompression in Hörgeräten auf das Sprachverstehen und das subjektive Klangempfinden der Nutzer

Background

The acceptance of hearing aids by users with high frequency hearing loss still represents a problem. Processing algorithms that shift high frequency signal components into an audible frequency range are proposed as a solution. We looked into the issue of whether frequency compression becomes more beneficial with increasing high frequency hearing loss or/and for users with cochlear dead regions (DR).

Subjects and methods

A total of 20 hearing aid candidates were assessed audiometrically and classified into two test groups in terms of their hearing loss and the presence of DR. The subjects then evaluated four hearing aid settings that differed solely in the degree of frequency compression. Speech recognition threshold measurements and subjective sound quality ratings were carried out for all four settings.

Results

Data showed that 15 of the 20 test subjects understood fricatives with a high frequency spectrum component better, since they were able to distinguish between the two logatomes“Afa” and“Asa”. No correlation was found between the beneficial effect of frequency compression and the degree of high frequency hearing loss or the presence of DR. Subjective sound quality ratings indicated no clear preference, but excessive frequency compression was generally deemed counterproductive.

Conclusion

Frequency compression may be appropriate for hearing aid users with high frequency hearing loss and can improve speech recognition. The degree of frequency compression required to achieve maximal benefit varies from case to case and has to be optimized on an individual basis.     

Low-frequency gain compensation in directional hearing aids

Hearing aids currently available on the market with both omnidirectional and directional microphone modes often have reduced amplification in the low frequencies when in directional microphone mode due to better phase matching. The effects of this low-frequency gain reduction for individuals with hearing loss in the low frequencies was of primary interest. Changes in sound quality for quiet listening environments following gain compensation in the low frequencies was of secondary interest. Thirty participants were fit with bilateral in-the-ear hearing aids, which were programmed in three ways while in directional microphone mode: no-gain compensation, adaptive-gain compensation, and full-gain compensation. All participants were tested with speech in noise tasks. Participants also made sound quality judgments based on monaural recordings made from the hearing aid. Results support a need for gain compensation for individuals with low-frequency hearing loss of greater than 40 dB HL.     

Comparison of three hearing aid fittings using the Speech Intelligibility Rating (SIR) Test

This study compared the effects of three different hearing aids on subjective ratings of speech intelligibility. Insertion gain measurements on KEMAR indicated that the hearing aid fittings differed primarily in midfrequency gain. The test passages of the Speech Intelligibility Rating Test (SIR) were recorded onto tape through each hearing aid. The processed passages were presented monaurally to 13 subjects with hearing loss limited to frequencies above 2000 Hz. They rated five passages through each frequency responses (FR) in a randomized order. Each subject was retested within 2 or 3 days to assess test-retest reliability. Results indicated that the FR with the most midfrequency amplification did not differ significantly from the aid with the least amount of midfrequency gain. However, the FR with intermediate midfrequency gain received significantly lower ratings than did FR with most gain. Examination of the data from individual subjects indicated that the SIR results did not show differences among the FRs for the majority of subjects.     

Relative effects of low-frequency amplification on syllable recognition and speech quality

A moderate-bandwidth master hearing aid was used to study the relationships among low-frequency response, syllable recognition scores, and perceived speech quality. As measured on KEMAR, this hearing aid provided true high-frequency emphasis in all conditions, with three degrees of relative low-frequency de-emphasis. Subjects were 12 listeners with gradually sloping sensorineural hearing loss bilaterally. Contrary to common expectations, increased low-frequency response yielded a substantial enhancement in speech quality under both quiet and babble conditions, as well as a modest improvement in syllable recognition in quiet. Furthermore, low-frequency amplification, as used in this study, resulted in no observable degradation in syllable recognition in the presence of multitalker babble. The findings have clinical implications in the evaluation and selection of hearing aids when optimization of speech quality is desired.     

Technology, expectations, and adjustment to hearing loss: predictors of hearing aid outcome

This study examined the influence of technology, demographic factors, and prefitting expectations, attitudes, and adjustment to hearing loss on hearing aid outcome. Clients obtaining new hearing aids completed questionnaires measuring personal adjustment to hearing loss, expectations of and attitudes toward hearing aids, and hearing aid benefit. Eighty-one percent of the 200 subjects completing the prefitting questionnaires returned questionnaires evaluating hearing aid outcome. Factors affecting hearing aid use, overall satisfaction, and benefit were investigated using regression analyses. Higher use time was associated with higher prefitting expectations and greater acceptance of hearing loss. Greater benefit in easy and difficult listening situations was predicted by higher prefitting expectations. Multiple-memory hearing aids produced higher satisfaction. Benefit was greater for multiple-memory, multiple-channel, and wide dynamic range compression aids. Findings were consistent with previous studies showing positive outcomes for newer technologies but also showed that two subjective factors, prefitting hearing aid expectations and acceptance of hearing loss, significantly influenced hearing aid outcome.     

A multi-center,double blind clinical trial comparing benefit from three commonly used hearing aid circuits

OBJECTIVE: Although numerous studies have demonstrated that hearing aids provide significant benefit, carefully controlled, multi-center clinical trials have not been conducted. A multi-center clinical trial was conducted to compare the efficacy of three commonly used hearing aid circuits: peak clipping, compression limiting, and wide dynamic range compression. DESIGN: Patients (N = 360) with bilateral, sensorineural hearing loss were studied using a double blind, three-period, three-treatment crossover design. The patients were fit with each of three programmable hearing aid circuits. Outcome tests were administered in the unaided condition at baseline and then after 3 mo usage of each circuit, the tests were administered in both aided and unaided conditions. The outcome test battery included tests of speech recognition, sound quality and subjective scales of hearing aid benefit, including patients' overall rank-order rating of the three circuits. RESULTS: Each hearing aid circuit improved speech recognition markedly, with greater improvement observed for soft and conversationally loud speech in both quiet and noisy listening conditions. In addition, a significant reduction in the problems encountered in communication was observed. Some tests suggested that the two compression hearing aids provided a better listening experience than the peak clipping hearing aid. In the rank-order ratings, patients preferred the compression limiting hearing aid more frequently than the other two hearing aids. CONCLUSIONS: The three hearing aid circuits studied provide significant benefit both in quiet and in noisy listening situations. The two compression hearing aids appear to provide superior benefits compared to the linear circuit, although the differences between the hearing aids were smaller than the differences between unaided and aided conditions.     

Subjective measures of hearing aid benefit in the NIDCD/VA Clinical Trial

OBJECTIVE: Subjective measures of performance were assessed on three different hearing aid circuits as part of a large clinical trial. These measurements included the Profile of Hearing Aid Performance and a subjective ranking of individual preference. DESIGN: A multi-center, double-masked clinical trial of hearing aids was conducted at eight VA Medical Centers. Three hearing aid circuits, a linear peak-clipper, a linear compression limiter and a wide dynamic range compressor, were investigated. The experimental design was a three-period, three-treatment crossover design. Subjects (N = 360) were stratified by site and randomized to one of six sequences for the hearing aid circuits. All fittings were binaural and involved a 3-mo trial with each of the three circuits. All subjective measures were administered for unaided and aided conditions at the end of each trial period. RESULTS: While all of the circuits resulted in improved scores on the aided versus the unaided PHAP, there were few conditions in which one circuit outperformed the others. An exception was the aversiveness of sound subscale where the peak clipper frequently scored worse than either the compression limiter or the wide dynamic range compressor. In the subjective ranking scale the compression limiter received more first place rankings than the other two circuits, especially for one subgroup of patients with moderate flat hearing loss. CONCLUSIONS: All circuits were perceived as beneficial by these subjects in most situations. The peak clipper scored worse on aversiveness of sound than did the other two circuits for most subjects, while the compression limiter seemed to have a slight advantage in subjective rankings. Most subjects perceived considerable aided benefit in situations involving background noise and reverberation, situations where hearing aid benefit is often questioned.     

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.     

Disturbance caused by varying propagation delay in non-occluding hearing aid fittings

The disturbance caused by various short propagation delays to the perception of external sounds and own voice for a non-occluding hearing aid was investigated. Ten normal-hearing and 10 mildly hearing-impaired individuals listened to external sounds and their own voice while wearing non-occluding devices providing 10dB of linear gain. Participants rated the disturbance caused by delays of 2, 4 and 10ms to music, running speech, and their own voices. The results indicated greater disturbance for the longest delay for both subject groups when judging own voice, with the ratings of the hearing-impaired participants being lowest. Normal-hearing participants also judged the 10-ms delay as more disturbing for the external sounds. Owing to the listening conditions with constant gain from 800Hz and above, the results apply directly only to this experiment. Disturbance ratings for all delays were low, which suggests that any of those tested would be acceptable for this application.     

Disturbance caused by varying propagation delay in non-occluding hearing aid fittings

The disturbance caused by various short propagation delays to the perception of external sounds and own voice for a non-occluding hearing aid was investigated. Ten normal-hearing and 10 mildly hearing-impaired individuals listened to external sounds and their own voice while wearing non-occluding devices providing 10dB of linear gain. Participants rated the disturbance caused by delays of 2, 4 and 10ms to music, running speech, and their own voices. The results indicated greater disturbance for the longest delay for both subject groups when judging own voice, with the ratings of the hearing-impaired participants being lowest. Normal-hearing participants also judged the 10-ms delay as more disturbing for the external sounds. Owing to the listening conditions with constant gain from 800Hz and above, the results apply directly only to this experiment. Disturbance ratings for all delays were low, which suggests that any of those tested would be acceptable for this application.     

A "virtual hearing aid" for comparing hearing aids in children: a double-blind crossover study.

In this study, a "virtual hearing aid" was used to compare different types of hearing aids. A digital hearing aid (Oticon DigiFocus Compact) and an analogue, automatic reference hearing aid were compared in a group of 17 schoolchildren (median age: 10 years) with moderate to severe, symmetrical, sensorineural hearing loss. Differences in performance were assessed using routine diagnostic methods (speech recognition performance tests, loudness scaling), subjective assessments (questionnaires) and the "virtual hearing aid". Guaranteeing double-blind testing conditions, the "virtual hearing aid" offers the possibility to directly compare individual in-situ recordings of different hearing aids. In contrast to the clear subjective preferences for the digital hearing aid, we could not obtain any significant results with routine diagnostic methods. Using the "virtual hearing aid", the subjective comparison and speech recognition performance tasks yielded significant differences. The "virtual hearing aid" proved to be suitable for directly comparing different hearing aids under double-blind testing conditions.