Effect of homolateral and contralateral routing of signals through Body-Worn hearing aids on the localization ability of Hearing-Impaired people

This investigation compared the localization abilities in the horizontal plane of 22 hearing-impaired adults (9 with symmetrical conductive and 13 with symmetrical sensorineural hearing impairment) whilst listening to speech through body-worn hearing aids in two different ways: (a) hearing-aid microphone placed on the same side as the stimulated ear (homolateral routing of signals); (b) hearing-aid microphone placed on the opposite side to the stimulated ear (contralateral routing of signals). It was found that the localization performances of all the subjects, especially when using binaural hearing aids, under homolateral routing of signals, were far superior to their respective localization performances achieved with contralateral routing of signals.

Résumé

Nous avons comparé la capacité de localiser des sons sur le plan horizontal chez 22 adultes atteints de surdité. Les sujets avaient des pertes bilatérales symétriques, soit surdités de transmission (9 sujets), soit surdités neuro-sensorielles (13 sujets). Les sujets devaient écouter des messages vocaux avec l'aide d'appareils de correction auditive portés sur le corps. Les appareils ont été utilisés de deux manières différentes: a) le microphone placé du méme côté que l'oreille stimulée (route homolatérale de stimulation); b) le microphone placé du côté opposé à l'oreille stimulée (route contralatérale de stimulation).

Nous avons constaté que la capacité de localiser des sons de tous les sujets, surtout quand ils portaient des appareils binauraux, était bien supérieure dans la condition de stimulation homolatérale aue dans la condition de stimulation controlatérale.     

Amplification in the rehabilitation of unilateral deafness: speech in noise and directional hearing effects with bone-anchored hearing and contralateral routing of signal amplification.

OBJECTIVE: Vibromechanical stimulation with a semi-implantable bone conductor (Entific BAHA device) overcomes some of the head-shadow effects in unilateral deafness. What specific rehabilitative benefits are observed when the functional ear exhibits normal hearing versus moderate sensorineural hearing loss (SNHL)? DESIGN: The authors conducted a prospective trial of subjects with unilateral deafness in a tertiary care center. PATIENTS: This study comprised adults with unilateral deafness (pure-tone average [PTA] > 90 dB; Sp.D. < 20%) and either normal monaural hearing (n = 18) or moderate SNHL (PTA = 25-50 dB: Sp.D. > 75%) in the contralateral functional ear (n = 5). INTERVENTIONS: Subjects were fit with contralateral routing of signal (CROS) devices for 1 month and tested before (mastoid) implantation, fitting, and testing with a bone-anchored hearing aid (BAHA). OUTCOME MEASURES: Outcome measures were: 1) subjective benefit; 2) source localization tests (Source Azimuth Identification in Noise Test [SAINT]); 3) speech discrimination in quiet and in noise assessed with Hearing In Noise Test (HINT) protocols. RESULTS: There was consistent satisfaction with BAHA amplification and poor acceptance of CROS amplification. General directional hearing decreased with CROS use and was unchanged by BAHA and directional microphone aids. Relative to baseline and CROS, BAHA produced significantly better speech recognition in noise. Twenty-two of 23 subjects followed up in this study continue to use their BAHA device over an average follow-up period of 30.24 months (range, 51-12 months). CONCLUSION: BAHA amplification on the side of a deaf ear yields greater benefit in subjects with monaural hearing than does CROS amplification. Advantages likely related to averting the interference of speech signals delivered to the better ear, as occurs with conventional CROS amplification, while alleviating the negative head-shadow effects of unilateral deafness. The advantages of head-shadow reduction in enhancing speech recognition with noise in the hearing ear outweigh disadvantages inherent in head-shadow reduction that can occur by introducing noise from the deaf side. The level of hearing impairment correlates with incremental benefit provided by the BAHA. Patients with a moderate SNHL in the functioning ear perceived greater increments in benefit, especially in background noise, and demonstrated greater improvements in speech understanding with BAHA amplification.     

Pilot study on the effectiveness of the conventional CROS, the transcranial CROS and the BAHA transcranial CROS in adults with unilateral inner ear deafness

The objective of the present pilot study is to evaluate the effectiveness of three conventional contralateral routing of sound (CROS) hearing aids in adults with unilateral inner ear deafness. The study included tertiary referral center. Ten patients with unilateral inner ear deafness and normal hearing in the contralateral ear were selected to evaluate three different methods of amplification: the CROS hearing aid, the completely in the canal hearing aid and the bone-anchored hearing aid CROS (BAHA). Each of the three hearing aids was tried in a random order for a period of 8 weeks. Audiometric performance, including speech-in-noise, directional hearing and subjective benefit were measured after each trial period, using the APHAB, SSQ and single-sided deafness questionnaire. Sound localization performance was essentially at chance level in all four conditions. Mixed results were seen on the other patient outcome measures that alternated in favor of one of the three CROS devices. After the trial, three patients chose to be fitted with the BAHA CROS and one with the conventional CROS. In conclusion, most of the patients experienced some degree of benefit with each of the three hearing aids. Preference for one of the three hearing aids was independent of the order in which they were tried. It would be worthwhile to formulate selection criteria; still, we recommend that all patients with unilateral inner ear deafness should be offered a trial with at least the BAHA CROS.     

Directivity of different hearing aid microphone locations

In this study, we present a new method to derive a single-number measure of the directivity of hearing aids. The method is an extension of the conventional directivity index (DI), and is called overall directivity index (ODI). The directivities of five different hearing aid styles were compared with that of the open ear. The behind-the-ear (BTE) style showed the lowest directionality compared to the other hearing aid styles and the open ear. There were only minor differences in directivity between any of the four different hearing aid styles placed in the ear and of the open ear canal. The conventional measure of DI is less suitable for hearing aids, because it ignores sound coming from other than the frontal direction. To quantify directionality of a hearing aid in a real-life situation, we suggest the single-number ODI, weighted with the articulation index and related to a listening segment of 0-30 degrees. An application of the data is shown for a BTE with a directional microphone.     

Large vestibular aqueduct syndrome: a case study

A 23-month-old female was referred for hearing aid fitting after failing newborn hearing screening and being diagnosed with significant hearing loss through subsequent diagnostic testing. Auditory brainstem response (ABR) and behavioral testing revealed a moderate-to-severe bilateral mixed hearing loss. Prior to the hearing aid evaluation, tympanostomy tubes had been placed bilaterally with little or no apparent change in hearing sensitivity. Initial testing during the hearing aid fitting confirmed earlier findings, but abnormal middle ear results were observed, requiring referral for additional otologic management. Following medical clearance, binaural digital programmable hearing aids were fit using Desired Sensation Level parameters. Behavioral testing and probe microphone measures showed significant improvements in audibility. Decrease in hearing sensitivity was observed six months following hearing aid fitting. Radiological studies, ordered due to the mixed component and decreased hearing sensitivity, revealed large vestibular aqueduct syndrome (LVAS). Based on the diagnosis of LVAS, a cochlear implant was placed on the right ear; almost immediate speech-language gains were observed.     

Directivity quantification in hearing aids: fitting and measurement effects

OBJECTIVE: To evaluate the impact of venting, microphone port orientation, and compression on the electroacoustically measured directivity of directional and omnidirectional behind-the-ear hearing aids. In addition, the average directivity provided across three brands of directional and omnidirectional behind-the-ear hearing aids was compared with that provided by the open ear. DESIGN: Three groups of hearing aids (four instruments in each group) representing three commercial models (a total of 12) were selected for electroacoustic evaluation of directivity. Polar directivity patterns were measured and directivity index was calculated across four different venting configurations, and for five different microphone port angles. All measurements were made for instruments in directional and omnidirectional modes. Single source traditional, and two-source modified front-to-back ratios were also measured with the hearing aids in linear and compression modes. RESULTS: The directivity provided by the open (Knowles Electronics Manikin for Acoustic Research) ear was superior to that of the omnidirectional hearing aids in this study. Although the directivity measured for directional hearing aids was significantly better than that of omnidirectional models, significant variability was measured both within and across the tested models both on average and at specific test frequencies. Both venting and microphone port orientation affected the measured directivity. Although compression reduced the magnitude of traditionally measured front-to-back ratios, no difference from linear amplification was noted using a modified methodology. CONCLUSIONS: The variation in the measured directivity both within and across the directional microphone hearing aid brands suggests that manufacturer's specification of directivity may not provide an accurate index of the actual performance of all individual instruments. The significant impact of venting and microphone port orientation on directivity indicate that these variables must be addressed when fitting directional hearing aids on hearing-impaired listeners. Modified front-to-back ratio results suggest that compression does not affect the directivity of hearing aids, if it is assumed that the signal of interest from one azimuth, and the competing signal from a different azimuth, occur at the same time.     

Bone-anchored hearing aids in unilateral inner ear deafness

In nine patients with unilateral deafness and normal hearing in the contralateral ear, measurements of sound localization and speech perception were obtained before intervention, with a conventional contralateral routing of sound (CROS) hearing aid and later with a bone-anchored hearing aid (BAHA) implanted in the deaf ear. Sound localization did not show any differences between the three conditions. Speech perception using short, everyday sentences showed a reduction in the head-shadow effect of 2 dB for both the conventional CROS hearing aid and the BAHA in comparison to the unaided condition. Patients' real-life experiences of the three conditions were evaluated using the Abbreviated Profile of Hearing Aid Benefit (APHAB) questionnaire. The results showed a significant benefit with the BAHA in situations involving background noise and reverberation and a reduced aversion to loud sounds in comparison to the unaided and conventional CROS conditions.     

Bone-anchored Hearing Aids in Unilateral Inner Ear Deafness

In nine patients with unilateral deafness and normal hearing in the contralateral ear, measurements of sound localization and speech perception were obtained before intervention, with a conventional contralateral routing of sound (CROS) hearing aid and later with a bone-anchored hearing aid (BAHA) implanted in the deaf ear. Sound localization did not show any differences between the three conditions. Speech perception using short, everyday sentences showed a reduction in the head-shadow effect of 2 dB for both the conventional CROS hearing aid and the BAHA in comparison to the unaided condition. Patients' real-life experiences of the three conditions were evaluated using the Abbreviated Profile of Hearing Aid Benefit (APHAB) questionnaire. The results showed a significant benefit with the BAHA in situations involving background noise and reverberation and a reduced aversion to loud sounds in comparison to the unaided and conventional CROS conditions.     

听障儿童双耳双模式配戴的声源定位能力初探*

目的探讨双耳双模式配戴能否帮助听障儿童改善声源定位能力以及哪些因素可能影响双耳双模式声源定位优势的发挥。方法采用强迫二选一任务,比较16名听障儿童在不同助听模式及不同声源角度下的声源定位能力。结果声源位于90°/270°时,38%的被试体现出双耳双模式的声源定位优势;位于45°/315°时,优势比例下降到25%。进一步分析表明,人工耳蜗麦克风的位置以及术前双耳配戴助听器的经验与双耳双模式声源定位优势的发挥密切相关。结论声源定位能力是听障儿童日常生活中的难点,即使双耳双模式配戴,也仅在声源位于左右方时,比单侧耳蜗状态体现出一定优势,随着声源角度的减小,双耳强度差和时间差线索减弱,双耳双模式的声源定位优势也随之减小。人工耳蜗的麦克风须放置在正确位置,否则会影响声源定位能力。此外,术前助听器配戴经验可能会影响听障儿童利用双耳线索的能力。     

Recording and classification of the acoustic environment of hearing aid users

This article investigates the different acoustic signals that hearing aid users are exposed to in their everyday environment. Binaural microphone signals from recording positions close to the microphone locations of behind-the-ear hearing aids were recorded by 20 hearing aid users during daily life. The recorded signals were acoustically analyzed with regard to narrowband short-term level distributions. The subjects also performed subjective assessments of their own recordings in the laboratory using several questions from the Glasgow Hearing Aid Benefit Profile (GHABP) questionnaire. Both the questionnaire and the acoustic analysis data show that the importance, problems, and hearing aid benefit as well as the acoustic characteristics of the individual situations vary a lot across subjects. Therefore, in addition to a nonlinear hearing aid fitting, further signal classification and signal/situation-adaptive features are highly desirable inside modern hearing aids. These should be compatible with the variability of the individual sound environments of hearing-impaired listeners.     

Predictive measures of directional benefit part 1: estimating the directivity index on a manikin

OBJECTIVE: In this investigation, a method for computing a directivity index (DI) on a manikin for directional microphones in hearing aids was proposed and evaluated comparatively to other conventional methods. DESIGN: Test devices included first- and second-order directional microphones. Signal presentation, implemented in an anechoic chamber, involved a single noise source rotated completely around the directional microphone in a hearing aid, in free field and on a manikin, at a defined radius. The area covered was equivalent to the approximate surface area of a sphere. It was anticipated that an equal angular resolution of 10 degrees (elevation and azimuth) would effectively estimate the DI of first-, second-, and higher-order directional microphone systems located in a hearing aid on a manikin. A total of 450 spatially varied presentation points were analyzed, each weighted in reference to direction of arrival on the directional microphone. RESULTS: Empiric differences between the DI derived from the 3D-DI method proposed in this investigation and the conventionally derived 2D-DI method DI on a manikin were as large as 3.8 dB in the higher frequencies, depending on the device under test. CONCLUSIONS: The magnitude of these differences was dependent on the device under test microphone location. The further the microphone was placed into the ear of the manikin, the larger the empiric differences.     

The evidence base for the application of contralateral bone anchored hearing aids in acquired unilateral sensorineural hearing loss in adults

? Acquired unilateral sensorineural hearing loss reduces the ability to localize sounds and to discriminate in background noise. ? Four controlled trials attempt to determine the benefit of contralateral bone anchored hearing aids over contralateral routing of signal (CROS) hearing aids and over the unaided condition. All found no significant improvement in auditory localization with either aid. Speech discrimination in noise and subjective questionnaire measures of auditory abilities showed an advantage for bone anchored hearing aid (BAHA) > CROS > unaided conditions. ? All four studies have material shortfalls: (i) the BAHA was always trialled after the CROS aid; (ii) CROS aids were only trialled for 4 weeks; (iii) none used any measure of hearing handicap when selecting subjects; (iv) two studies have a bias in terms of patient selection; (v) all studies were underpowered (vi) double reporting of patients occurred. ? There is a paucity of evidence to support the efficacy of BAHA in the treatment of acquired unilateral sensorineural hearing loss. Clinicians should proceed with caution and perhaps await a larger randomized trial. ? It is perhaps only appropriate to insert a BAHA peg at the time of vestibular schwanoma tumour excision in patients with good preoperative hearing, as their hearing handicap increases most.     

The Effects of Microphone Spacing on Auditory Localization

The localization ability of 10 normally hearing adults was determined under varying microphone separations and varying sound source azimuths. The stimuli (white noise bursts) were prerecorded, after being transduced through 'body' hearing aids and then played to the subjects over headphones. Results indicated that there was an improvement in localization ability for all azimuth conditions when the microphones were spaced wider than 12.7 cm apart (15.2–30.5 cm). The smaller the separations (5.5–12.7 cm), the poorer the localization. Localization was always poorer at 30° azimuth (the smallest used) than at any of the other azimuths (0°, 30°, 60°, 90° right and left), regardless of microphone spacing. Implications are made about the relation of these findings to the use of binaural body aids on infants and young children.     

New perspectives on assessing amplification effects

Clinicians have long been aware of the range of performance variability with hearing aids. Despite improvements in technology, there remain many instances of well-selected and appropriately fitted hearing aids whereby the user reports minimal improvement in speech understanding. This review presents a multistage framework for understanding how a hearing aid affects performance. Six stages are considered: (1) acoustic content of the signal, (2) modification of the signal by the hearing aid, (3) interaction between sound at the output of the hearing aid and the listener's ear, (4) integrity of the auditory system, (5) coding of available acoustic cues by the listener's auditory system, and (6) correct identification of the speech sound. Within this framework, this review describes methodology and research on 2 new assessment techniques: acoustic analysis of speech measured at the output of the hearing aid and auditory evoked potentials recorded while the listener wears hearing aids. Acoustic analysis topics include the relationship between conventional probe microphone tests and probe microphone measurements using speech, appropriate procedures for such tests, and assessment of signal-processing effects on speech acoustics and recognition. Auditory evoked potential topics include an overview of physiologic measures of speech processing and the effect of hearing loss and hearing aids on cortical auditory evoked potential measurements in response to speech. Finally, the clinical utility of these procedures is discussed.     

Odontoma of the middle ear: case report with 25-year follow-up

We report the 25-year follow-up on the first reported case of odontoma in the middle ear. Diagnosis of odontoma had been made on the basis of radiography films that showed a middle ear mass with multiple toothlike areas of radiopacity. No clinical intervention was recommended. At 25-year follow-up, audiometry showed progressive mixed hearing loss on the affected side and mild ipsilateral sensorineural hearing loss. Computed tomography better characterized the discrete mass, which was shaped similar to a dental crown. To avoid jeopardizing cochlear and facial nerve function, no surgical intervention was pursued, and we recommended use of a BiCROS (bilateral contralateral routing of signal) hearing aid.     

Binaurality in middle ear implant recipients using contralateral digital hearing AIDS.

OBJECTIVE: For some patients, conventional hearing aids might have disadvantages that clearly limit the benefit of using them. The middle ear implant, Vibrant Soundbridge hearing prosthesis offers an approach to help such patients. Our study's objective was to identify the binaurality in a well-fitted digital hearing aid worn in the contralateral ear in recipients experienced with use of the Vibrant Soundbridge middle ear implant device. STUDY DESIGN: In a prospective study, warble-tone thresholds and stereophony were evaluated for the following conditions: (1) binaural unaided-with the middle ear implant inactive and the behind-the-ear hearing aid removed; (2) middle ear implant alone-middle ear implant active, behind-the-ear hearing aid removed; (3) middle ear implant plus behind-the-ear omnidirectional-middle ear implant active, behind-the-ear active; and (4) behind-the-ear omnidirectional alone-middle ear implant inactive, behind-the-ear omnidirectional active. Behind-the-ear omnidirectional and behind-the-ear is defined as the behind-the-ear active in the omnidirectional or directional response, respectively. Behind-the-ear is a contralateral digital hearing aid to the middle ear implant. Benefits such as improved sound detection, speech perception in quiet and in noise, and sound quality were investigated. The evaluation of subjective hearing benefit was based on the Abbreviated Profile of Hearing Aid Benefit (APHAB) test. Paired t tests (subject) were used to analyze the differences between mean thresholds for the different test conditions. SETTING: Tertiary referral center. PATIENTS: Eight adults (aged 45-68 yr) had undergone implantation with a single Vibrant Soundbridge at least 12 months before starting the study. These eight subjects presented no contraindication for contralateral hearing aid use. Patients were fitted 5 weeks before testing with a Siemens Signia digital behind-the-ear hearing aid in the side contralateral to the Vibrant Soundbridge. RESULTS: Five weeks after use of the contralateral hearing aid together with the middle ear implant, mean differences in warble-tone thresholds between Conditions 2 and 3 and between Conditions 3 and 4 were both statistically significant. The mean differences in speech reception thresholds were in line with the mean differences in average warble-tone thresholds. The mean speech reception threshold for the middle ear implant plus behind-the-ear omnidirectional condition was slightly worse (3 dB) than that for the middle ear implant alone condition; however, this difference was not statistically significant. Whereas speech reception threshold difference between Condition 1 and Condition 4 was not statistically significant (60 dB and 61 dB, respectively). The mean difference for the 0-degree azimuth alone was statistically significant (p < 0.05) for the conditions middle ear implant alone and middle ear implant plus behind-the-ear omnidirectional. The middle ear implant alone appears to give good sensitivity at 2 kHz for any direction. Increasing scores indicate greater percentages of problems. Percentages of problems were on average lower for the middle ear implant when used with the contralateral digital hearing aid based on the global score. CONCLUSION: The use of a middle ear implant Vibrant Soundbridge together with a contralateral digital hearing aid improved functional gain and speech perception thresholds in quiet, especially for the sound coming from the front of the patient. The use of a middle ear implant together with a contralateral digital hearing did not significantly improve hearing in noise.     

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.