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.     

Auditory localization under conditions of unilateral fitting of different hearing aid systems.

The spatial localization function of hearing-impaired listeners, usually fitted bilaterally with BTE, ITE or ITC devices, was tested under conditions of unilateral fitting of each of their own hearing aids, and unilateral fitting of stock versions of each of the other types. For the BTE wearers average localization accuracy and individual variability were not greatly changed when wearing only their left ear device, compared with bilateral aided performance. In ITE wearers, unilateral fitting in either ear led to somewhat poorer performance than bilateral. In the ITC wearers unilateral fitting produced inconsistent outcomes. Both BTE and ITE wearers fared poorly when fitted unilaterally with stock forms of devices 'foreign' to them, whereas ITC wearers did not show such a contrasting outcome. A group of non-impaired listeners showed severe disruption of localization under unilateral BTE and ITC hearing aid conditions, and to a lesser extent with ITEs. Results for the hearing-impaired listeners are interpreted in terms of adaptation to different usage patterns, with BTE wearers suggested as having adapted to their own systems unilaterally as well as bilaterally.     

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.     

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.     

Directivity and noise reduction in hearing aids: speech perception and benefit

Hearing aid.AimTo compare the performance, benefit and satisfaction of users of ITE, CIC and BTE digital hearing aid with noise reduction and omnidirectional and directional microphones.Method34 users of hearing aid were evaluated by means of speech perception in noise tests and APHAB and IOI self assessment questionnaires. Prospective study.ResultsBetter results were obtained by users of ITE, CIC and directional hearing aids, however, no statistical significance was found between the groups.ConclusionDirectivity improved speech perception in noise and benefit in daily life situations.     

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.     

Speech recognition with in-the-ear and behind-the-ear dual-microphone hearing instruments

The primary purpose of this study was to compare the overall listening benefit in diffuse noise provided by dual-microphone technology in an in-the-ear (ITE) hearing instrument to that provided by dual-microphone technology in a behind-the-ear (BTE) hearing instrument. Further, the study was designed to determine whether the use of the dual-microphone + the manufacturer's party response algorithm in the ITE and BTE hearing instruments provided listening benefit in diffuse noise over their respective omnidirectional microphone modes. Twenty-four adults with mild to moderately severe sensorineural hearing loss were evaluated while wearing binaural BTE and ITE hearing instruments. The results indicated that the dual-microphone + party response mode did provide significant benefit in diffuse noise for both the ITE (3.27 dB signal-to-noise ratio [SNR] improvement) and BTE (5.77 dB SNR improvement) hearing instruments relative to their respective conventional omnidirectional microphones. No significant difference in performance was found between the ITE and BTE hearing instruments when each device was in the dual-microphone + party response mode. It is concluded that the use of dual-microphone technology in both ITE and BTE hearing instruments can improve speech recognition in diffuse noise.     

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.     

Can maximum comfortable loudness levels in hearing impaired listeners be predicted from ipsilateral acoustic reflex thresholds recorded with high frequency probes?

This study was designed to test the effectiveness of the ipsilateral acoustic reflex thresholds measured with low and high frequency probes in predicting the maximum comfortable loudness levels (MaxCLs) in hearing-impaired subjects using recently available sophisticated procedures for acoustic reflex and loudness measures. Loudness growth functions were measured in hearing-impaired subjects at .5, 1 and 2 kHz using a computerized procedure. The maximum level among those sound pressure levels judged as 'comfortable' was designated as the MaxCL. Acoustic reflex thresholds were measured for .5, 1 and 2 kHz activator signals using 226, 678 and 1000 Hz probes. Regression analyses suggested that acoustic reflex thresholds recorded with the 678 and 1000 Hz probes could provide an objective estimate of the MaxCLs for 1 and 2 kHz. Thus, acoustic reflex thresholds may be useful in fitting hearing aids for those subjects in whom reliable measures of MaxCLs cannot be obtained.     

Nonlinear hearing AIDS and verification of fitting targets

This paper addresses the issue of initial verification of hearing aid gain and output for nonlinear hearing aids. Specifically, "urban legend" has it that nonlinear hearing aids with digital noise reduction circuitry may not be accurately measured using functional gain and/or probe microphone measures. Discussed are the advantages and disadvantages of both measurement strategies, and how they may be used to "acoustically match" hearing aids to individual patients. An evaluation protocol that employs both optimal aided thresholds and probe microphone measurements to assess gain, output, and audibility in hearing-impaired patients.     

Cochlear implant in patients with residual hearing

Objective: The postoperative speech perception abilities of severely hearing-impaired patients with multi-channel cochlear implant were compared with preoperative speech perception performance with conventional hearing aids. Methods: Cochlear implantation was performed in six severely to profoundly hearing-impaired patients. They had unaided pure-tone thresholds of 70–100-dB HL and aided thresholds of 35–90-dB HL in the better ear, but were not able to perceive speech sounds well with hearing aids. Results: Postoperatively, all the patients had significantly improved speech perception performance, exceeded the average skills of profoundly deaf cochlear implant users, and were able to communicate without writing. Conclusion: These results imply that cochlear implant may be indicated for severely to profoundly deaf subjects, if they receive little or no benefit from conventional hearing aids.     

The impact of head angle on monaural and binaural performance with directional and omnidirectional hearing aids

OBJECTIVE: To evaluate the impact of head turn and monaural and binaural fittings on the sentence reception thresholds of hearing-impaired listeners wearing directional and omnidirectional hearing aids. DESIGN: Sentence reception thresholds were measured for 20 listeners fit monaurally and binaurally with behind-the-ear hearing aids set in both directional and omnidirectional modes. All listeners exhibited symmetrical, sloping, sensorineural hearing loss. The aided performance across these four fittings was evaluated for three different head and body angles. The three angles reflected body turns of 0 degrees, 15 degrees, and 30 degrees as measured relative to the primary sound source, with 0 degrees denoting the listener directly facing the sound source. Listeners were instructed to keep their heads in a fixed horizontal position and turn their heads and bodies to face visual targets at the three test angles. Sentences from the Hearing in Noise Test presented with a background of five, spatially separated, uncorrelated samples of cafeteria noise served as test material. All testing was performed in a moderately reverberant (Rt = 631 msec) "living room" environment. RESULTS: Participants generally performed significantly better when fit with directional versus omnidirectional hearing aids, and when fit binaurally versus monaurally across test conditions. The measured "binaural advantage" was reduced with increasing head angle. Participants performed significantly better with a 30 degree head angle than when directly facing the primary speaker. This "head turn advantage" was most prominent for monaural (versus binaural) conditions. Binaural and head turn advantages were not significantly different across directional and omnidirectional modes. CONCLUSIONS: These data provide additional support for the use of directional hearing aids and binaural amplification to improve speech intelligibility in noisy environments. The magnitude of these advantages was similar to that reported in previous investigations. The data also showed that hearing aid wearers achieved significantly better speech intelligibility in noise by turning their heads and bodies to a position in which they were not directly facing the sound source. This head turn advantage was in good agreement with the increase in Directivity Index with head turn and reflected the fact that hearing aids are generally most sensitive to sounds arriving from angles other than directly in front of the hearing aid wearer. Although these data suggest that many monaural hearing aid wearers may significantly improve speech intelligibility in noise through the use of head turn, the interaction between this advantage and the potential loss of visual cues with head turn is unknown.     

The "hearing aid effect" 2005: a rigorous test of the visibility of new hearing aid styles

PURPOSE: The visibility of open ear (OE) styles of hearing instruments was rigorously investigated for their potential to reduce the stigma of wearing hearing aids. METHOD: Three groups of 50 young adults (150 total) rated the visibility of 6 hearing aid styles-OE, invisible completely-in-the-canal (CIC), mini in-the-canal (m-ITC), half- and full-shell in-the-ear (ITE), and behind-the-ear (BTE)-worn by a peer model with revealing hairstyle, photographed from 2 ft and at 3 different angles (45 degrees, 90 degrees, and 135 degrees). RESULTS: CIC was rated significantly most "invisible" at 45 degrees and 90 degrees, OE and m-ITC were next at those angles, and OE and BTE were least invisible at 135 degrees. CONCLUSIONS: The findings have implications for counseling potential users who are reluctant to try hearing aids for cosmetic reasons.     

A study of the application of a frequency transposition hearing system in children

The aim of this retrospective study was to investigate the use of the frequency transposition Transonic FT 40 system in a group of 36 children with profound sensorineural hearing loss. The group comprised 36 children (11 boys, 25 girls) aged between 2.8 and 15.6 years (mean 7.6 years) at fitting of the FT 40 device. At 48 months post-FT 40 fitting, only 11 children (30%) were still wearing the device. The children discontinued wearing the FT 40 for the following reasons: ergonomic (11%); no perceived benefit from the system (11%); cosmetic (17%); and subsequent cochlear implantation (30%). The performance of the long-term FT 40 users was investigated using the following outcome measures: aided soundfield hearing thresholds: closed set speech tests (the E2L toy test and the Manchester Picture Test discrimination test) and a speech intelligibility rating score. The 11 long-term FT 40 users (three boys, eight girls) were aged from 5.3 to 12.9 years (mean 7.2 years) at the time of initial fitting of the FT 40 device. At time of fitting, the aided soundfield thresholds with the FT 40 were significantly better at 500 Hz (p<0.04), 1 kHz (p<0.019), 2 kHz (p<0.001) and 4 kHz (p <0.001) compared to thresholds with conventional hearing aids. Six of 11 children did not show any change in performance on the closed set speech tests and two children had intelligible speech at 48 months' follow-up. A small subgroup of good performers was identified. These children were younger at age of fitting (mean 6.2 years compared to a mean of 7.7 years for the remainder of the group), were predominantly oral communicators and had identified aetiologies for their deafness. The present study suggests that there is a small subgroup of hearing-impaired children who benefit from frequency transposition hearing systems, and future suggested fitting criteria and outcome measures are listed.     

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.     

Gain and feedback problems when fitting behind-the-ear hearing aids to profoundly hearing-impaired children

Previous laboratory studies with severely and profoundly hearing-impaired persons aided with behind-the-ear (BTE) hearing aids have resulted in prediction rules for insertion gain and maximum gain without occurrence of acoustic feedback. The practicability of these findings was investigated in the present field trial with 21 profoundly deaf children fitted with power BTE hearing aids. In dialogue situations without background noise, the gain control settings were in accordance with the insertion gain prediction rule, whereas preferred gain may be 10 dB lower in the presence of noise. Consistent with the prediction rule for maximum gain without feedback and the gain response of the present test hearing aid, we observed oscillation in the high-frequency range in which the children had no remaining hearing. When the high-frequency gain was reduced, sufficient low-frequency gain could be provided without feedback problems.     

A comparison of different binaural hearing aid systems for sound localization in the horizontal and vertical planes

Three groups of hearing-impaired listeners who had been fitted binaurally with behind-the-ear (BTE), in-the-ear (ITE), or in-the-ear-canal (ITC) hearing aids were tested on spatial localization function for sources in the frontal horizontal and vertical planes. No significant differences in unaided performance were observed between the groups, nor between that and aided performance in the BTE and ITE wearers. ITC wearers, by contrast, showed a deterioration in aided over unaided performance. From observations of performance when each group wore temporary fittings of the other two types of system, and from the performance of a non-impaired control group, it appears that the performance decrement for the ITC wearers was due to their own particular systems although specific reasons for this decrement could not be identified. In all conditions, aided and unaided, vertical plane localization was markedly disrupted in all the hearing impaired groups. It was also disrupted, to a lesser but still substantial extent, in aided conditions for the non-impaired listeners.     

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.