Bilateral Fitting Research Articles

New research findings cast doubt on advantage of bilateral fittings in noise

Although the benefits of bilateral fittings have long been accepted, some recent research findings are challenging established views that two hearing aids are generally better than one in noise. A report on this important issue.

A survey of public health policy on bilateral fittings and comparison with market trends: The evidence-base required to frame policy

This report presents a review of the situation in a number of countries with respect to public health policy for funding of hearing aid services in general and support to bilateral fittings in particular. The data show considerable variations among the countries studied in number of hearing aids fitted per 1000 inhabitants, differing by a factor of 6 between the extremes. Also the percentage of bilateral fittings differs with an average estimated to be of the order of 50%. For hearing-impaired children, bilateral fittings are given full financial support in most countries studied. The data presented indicate the need for a reliable, scientifically valid evidence-base regarding bilateral hearing aid fitting.

Fitting strategies and candidature criteria for unilateral and bilateral hearing aid fittings

In this paper, hearing aid fitting strategies are reviewed and candidature criteria for unilateral and bilateral fittings are discussed. Fitting strategies are primarily governed by the objectives of hearing aid fitting that can be set in different ways. Based on common goals, fitting strategies can be broken down into three stages: (1) basic fitting, (2) fine-tuning and (3) verification and validation. A fine-tuning concept basing on so-called meta-controllers is described and the issue of bilateral fitting strategies is discussed. In a first order approach, bilateral hearing aids can be fitted in parallel as unilateral aids, followed by bilateral fine-tuning, making sure that loudness is balanced and overall loudness is accepted. Parallel fitting of bilateral aids is more favourable than sequential fitting to avoid rejection because of a negative experience with unilateral amplification due to difficulties in disadvantageous listening situations. Candidature criteria are presented by means of a flow chart structuring the decision making process and arriving at the conclusion that bilateral fitting should be considered the normal case. If there is any doubt about the benefit of bilateral fitting, a trial with bilateral aids should be performed.

Bilateral hearing aids: A review of self-reports of benefit in comparison with unilateral fitting

The literature on self-assessed outcomes from bilateral and unilateral hearing aid fitting is reviewed. The nature, aims, and design of different studies are quite varied, and limitations attend many of them. Nonetheless, certain indications can be extracted from the pattern of reported results. Thus, greater measured impairment, greater self-rated disability, and/or more critical contexts of listening emerge as candidate predictors of preference for, or persistence with, a bilateral fitting profile. Two matters are briefly critiqued regarding one vs two hearing aids: 1) the analogue with binocular optical correction; 2) the unaided ear (“deprivation”) effect. Questions are raised about the adequacy of the range of hearing functions addressed by previous investigations of bilateral vs. unilateral fitting—and a broadened range of functions is outlined. A recent self-report-based comparison of one versus two hearing aids (Noble & Gatehouse, International Journal of Audiology, 2006) reveals that the benefit of two lies in contexts of more demanding and dynamic listening and in reduced listening effort.

Rehabilitation approaches to promote successful unilateral and bilateral fittings and avoid inappropriate prescription

Successful hearing aid fitting occurs when the person fitted wears the aid/s on a regular basis and reports benefit when the aid/s is used. A significant number of people fitted with unilateral or bilateral hearing aids for the first time do not continue to use one or both aids in the long term. In this paper, factors consistently found in previous research to be associated with unsuccessful fitting are explored; in particular, the negative attitudes of some clients towards hearing aids, their lack of motivation for seeking help, inability to identify goals for rehabilitation, and problems with the management of the devices. It is argued here that success in hearing aid fitting involves the same dynamics as found with other assistive technologies (e.g., wheelchairs, walking frames), and is dependent on a match between the characteristics of a prospective user, the technology itself, and the environments of use (Scherer, ). It is recommended that for clients who identify concerns about hearing aids, or who are unsure about when they would use them, and/or are likely to have problems with aid management, only one aid be fitted in the first instance, if hearing aid fitting is to proceed at all. Rehabilitation approaches to promote successful fitting are discussed in light of results obtained from a survey of clients who experienced both successful and unsuccessful aid fitting.

Two-eared listening in dynamic situations

Reports of hearing disabilities, particularly those acoustically and perceptually dynamic circumstances, are associated with compromised binaural capacities. Those disabilities that are compromised largely correspond to the areas where benefits of bilateral fitting over unilateral fitting emerge. The singular exception is for disabilities in “Sound quality and naturalness”. When binaural capacities are measured by traditional static masking level difference paradigms, relationships between compromised binaural capacity and self-reports of disability are largely absent. However, when masking level differences are assessed using dynamic parameters that are more representative of the conditions experienced in everyday living then significant associations between binaural capacities and self-reports of disability do emerge. We contend that, for both the self-report domain and the psychoacoustical domain, procedures should be more properly representative of the dynamic environments that listeners are routinely exposed to.

Physiological aspects regarding bilateral fitting of BAHAs

Normally, when we hear a sound, the sound is transmitted through the outer and middle ear to the inner ear where the sound energy is converted to nerve impulses. These impulses are transmitted further to the cochlear nucleus and superior olivary complex where information from both ears is mixed, compared and analysed. It is here the binaural process occur which allows us to determine the direction of the sound source as well as improve hearing in noise when the useful sound source and noise source is spatially separated. Hence, a patient with a bilateral hearing loss and fitted with airconduction (AC) hearing aids generally benefits from binaural fitting compared with monaural fitting. When a bone-anchored hearing aid (BAHA) is used, the sound is transmitted via bone conduction (BC) to the inner ear. The difference between the stimulation level of the contralateral and ipsilateral cochlea, often referred to as the transcranial attenuation, is normally in the range of 0–20 dB for frequencies up to 10 kHz. Hence, the side-specific stimulation of the inner ears is less with BC than with AC, which affects the binaural effect of the hearing. Due to the overhearing between the cochleae with BC, it is questionable whether binaural hearing is possible using BC stimulation and, consequently, BAHAs. Proceedings of the 4th International Symposium on Electronic Implants in Otology 83

Physiological aspects regarding bilateral fitting of BAHAs

Normally, when we hear a sound, the sound is transmitted through the outer and middle ear to the inner ear where the sound energy is converted to nerve impulses. These impulses are transmitted further to the cochlear nucleus and superior olivary complex where information from both ears is mixed, compared and analysed. It is here the binaural process occur which allows us to determine the direction of the sound source as well as improve hearing in noise when the useful sound source and noise source is spatially separated. Hence, a patient with a bilateral hearing loss and fitted with airconduction (AC) hearing aids generally benefits from binaural fitting compared with monaural fitting. When a bone-anchored hearing aid (BAHA) is used, the sound is transmitted via bone conduction (BC) to the inner ear. The difference between the stimulation level of the contralateral and ipsilateral cochlea, often referred to as the transcranial attenuation, is normally in the range of 0–20 dB for frequencies up to 10 kHz. Hence, the side-specific stimulation of the inner ears is less with BC than with AC, which affects the binaural effect of the hearing. Due to the overhearing between the cochleae with BC, it is questionable whether binaural hearing is possible using BC stimulation and, consequently, BAHAs. Proceedings of the 4th International Symposium on Electronic Implants in Otology 83

Bilateral fitting of BAHAs and BAHA® fitted in unilateral deaf persons: Acoustical aspectsAdaptación bilateral de BAHA y adaptación de BAHA en sorderas unilaterales: Aspectos acústicos

The benefit of a bone-anchored hearing aid (BAHA) to a patient fitted bilaterally; and the benefit of a BAHA®to a unilaterally deaf person was estimated by four acoustical measurements: directional sensitivity of a BAHA® placed at the skull, vibration transmission in the skull, gain, and estimated transcranial attenuation of bone conducted sound. Provided a patient has a similar bone conduction hearing ability at both cochlea, it was found that a patient should, theoretically, benefit from bilateral fitting of BAHAs in terms of better hearing thresholds from the front, and better overall hearing ability from the surround. The data indicates further, that bilateral fitting facilitates extraction of interaural cues, which should lead to greater ability to determine the direction of a sound source, as well as better hearing in noise. However, due to the cross-hearing of bone conducted sound, the binaural processing for the patient fitted bilaterally with BAHAs is less than for normal binaural air conduction hearing. Finally, the data showed that the benefit of fitting a BAHA® in a unilaterally deaf person, depends on that person's transcranial attenuation.

Bilateral amplification and sound localization: Then and now

This article is concerned with the evolution and pros and cons of bilateral amplification. Determining whether a bilateral hearing aid fitting is superior to that of a monaural hearing aid is a long-standing question; for this reason, the trend toward bilateral amplification has been slow. However, it is now assumed that bilateral amplification has significant advantages over monaural amplification in most cases, a view that is supported by our localization results. In this article, we will address the advantages of bilateral hearing aids and reveal some new localization data that show that most listeners with bilateral amplification, when tested unaided, as well as normal-hearing listeners manifested very high degrees of symmetry in their judgments of perceived angle while listeners who routinely use monaural amplification and those with asymmetric hearing loss had relatively large asymmetries. These data show that asymmetry in localization judgments is a much more sensitive indicator of abnormal localization ability than the magnitude of localization errors.

Cochlear implantation in Waardenburg's syndrome

Conclusions. Children with Waardenburg's syndrome (WS) derive significant benefit from cochlear implantation (CI) and do so to an extent that is comparable to that of the general population of implanted children. Although we report on a relatively small cohort, our data are useful for counseling the parents of children with WS considering CI. Objective. To present our experience with CI in patients with WS. Material and methods. A retrospective record review was conducted for five children who underwent CI in our department between 1993 and 2004. Results. Children with WS comprised 1.9% of our entire pediatric CI population: four girls had a familial history of WS and the phenotype of WS Type I, and one boy met the criteria for WS Type II. They were all diagnosed as having bilateral profound sensorineural hearing loss 4–24 weeks after birth. Rehabilitation was initiated immediately and included bilateral fitting of hearing aids and intensive speech and language therapy. Otoscopic and temporal bone high-resolution CT findings were normal in all patients. At surgery, all children were found to have a patent cochlea, and the electrodes were implanted into the scala tympani without difficulty. After 1.3–10.2 years of implant use all children achieved open-set recognition of 2-syllable words, with an average score of 81%. Four of the 5 children achieved open-set recognition of monosyllabic words (average score 40%) and 3 achieved open-set recognition of words in sentences (average score 81%).

Time–intensity trading in bilateral congenital aural atresia patients

In an effort to examine the rules by which information of bilaterally applied bone-conducted signals arising from interaural time differences (ITD) and interaural intensity differences (IID) is combined, data were measured for continuous 500 Hz narrow band noise at 65–70 dB HL in 11 patients with bilateral congenital aural atresia. Time–intensity trading functions were obtained by shifting the sound image towards one side using ITD, and shifting back to a centered sound image by varying the IID in the same ear (auditory midline task). ITD values were varied from −600 to +600 μs at 200 μs steps, where negative values indicate delays to the right ear. The results indicate that time–intensity trading is present in patients with bilateral aural atresia. The gross response properties of time–intensity trading in response to bone-conducted signals were comparable in patients with bilateral aural atresia and normal-hearing subjects, though there was a larger inter-subject variability and higher discrimination thresholds across IIDs in the atresia group. These results suggest that the mature auditory brainstem has a potential to employ binaural cues later in life, although to a restricted degree. A binaural fitting of a bone-conducted hearing aid might optimize binaural hearing and improve sound lateralization, and we recommend now systematically bilateral fitting in aural atresia patients.

Bilateral bone-anchored hearing aids (BAHAs): an audiometric evaluation.

Since the technique to implant bone-anchored hearing aids (BAHAs) with the use of osseointegrated implants was developed in 1977, more than 15,000 patients have been fitted with BAHAs worldwide. Although the majority have bilateral hearing loss, they are primarily fitted unilaterally. The main objective of this study was to reveal benefits and drawbacks of bilateral fitting of BAHAs in patients with symmetric or slight asymmetric bone-conduction thresholds. The possible effects were divided into three categories: hearing thresholds, directional hearing, and binaural hearing. Prospective study of 12 patients with bilateral BAHAs. Baseline audiometry, directional hearing, speech reception thresholds in quiet and in noise, and binaural masking level difference were tested when BAHAs were fitted unilaterally and bilaterally. Eleven of the 12 patients used bilateral BAHAs on a daily basis. Tests performed in the study show a significant improvement in sound localization with bilateral BAHAs; the results with unilateral fitting were close to the chance level. Furthermore, with bilateral application, the improvement of the speech reception threshold in quiet was 5.4 dB. An improvement with bilateral fitting was also found for speech reception in noise. Overall, the results with bilateral fitted BAHAs were better than with unilaterally fitted BAHA; the benefit is not only caused simply by bilateral stimulation but also, to some extent, by binaural hearing. Bilateral BAHAs should be considered for patients with bilateral hearing loss otherwise suitable for BAHAs.

Comparison of three procedures for initial fitting of compression hearing aids. II. Experienced users, fitted unilaterally

This paper is the second in a series comparing three procedures for the initial fitting of multichannel compression hearing aids. The first paper reported the results for a group of 10 experienced hearing aid users fitted bilaterally. This paper reports the results for a different group of 10 experienced hearing aid users fitted unilaterally. The three procedures were: (1) CAMEQ, which aims to amplify speech so as to give equal loudness per critical band over the frequency range 500-5000 Hz, and to give similar overall loudness to normal over a wide range of speech levels; (2) CAMREST, which aims to amplify speech so as to restore normal specific loudness patterns, over a wide range of speech levels; and (3) DSL [i/o], which aims to map the dynamic range of normalhearing people into the reduced dynamic range of hearingimpaired people, with full restoration of audibility. Each subject was fitted with one Danalogic 163D digital hearing aid, using each of the three fitting procedures in turn; the order was counter-balanced across subjects. Prescribed insertion gains for 55 and 80 dB SPL input levels were verified using real-ear measurements. Immediately after fitting with a given procedure, and 1 week after fitting, the gains were adjusted, when required, by the minimum amount necessary to achieve acceptable fittings. On average, the adjustments were smallest for the CAMREST procedure, slightly larger for the CAMEQ procedure, and largest of all for DSL [i/o]. For the DSL [i/o] the gain changes were mostly negative, especially for high frequencies and the higher input level. After these gain adjustments, users wore the aids for at least 3 weeks before speech reception thresholds (SRTs) for sentences in quiet and in steady and fluctuating background noise were measured. The APHAB questionnaire was also administered. The hearing aids were then refitted with the next procedure. SRTs and APHAB scores did not differ significantly between the three procedures. We conclude that the CAMEQ and CAMREST procedures provide a more appropriate initial fitting than DSL [i/o] for unilaterally experienced hearing aid wearers. Comparison with our earlier study based on bilateral fittings suggests that the preferred gains are similar for unilateral and bilateral fittings.

BAHA®: The Direct Bone Conductor.

The BAHA® device uses the principle of direct bone conduction (DBC) to overcome several of the drawbacks of conventional air-conduction (AC) and bone-conduction (BC) hearing aids for patients with conductive or mixed hearing loss. Recent developments of the BAHA system have made it more user friendly and the device has been further miniaturized. The FDA has cleared the device for both adults and pediatrics (from age 5 and up) and also for bilateral fitting. With the BAHA system, a vibrating transducer is directly connected to the skull bone, of which the cochlea is an integrated part. This principle of DBC provides a more or less direct and clear transmission pathway to the cochlea. The BAHA surgery is, however, a minor surgical procedure and does not in any way interfere with the hearing organ so there are no risks of damaging the ear or the residual hearing. Scientific papers about BAHA from around the world report high performance, safety, and patient satisfaction. (Tjellstrom and Granstrom, 1995; Powell et al., 1996; Hartland et al., 1996; Papsin et al., 1997; Tietze et al., 2001; Tjellstrom and Hakansson, 2001; Snik et al., 2001; Lustig et al., 2001). Today, more than 9000 patients around the world have been treated with BAHA.

Opting for two hearing aids: a predictor of long-term use among adult patients fitted after screening: La opcion de dos auxiliares auditivos: una prediccion del uso a largo plazo en adultos con auxiliares adaptados despues de un programa de tamiz

This study is a follow-up of patients fitted with one or two hearing aids, approximately 10 years previously. Our patients were identified through population screening for hearing difficulties when they were aged 50–65 years. At the time, they had a trial of unilateral and bilateral fittings, and then they made their own choice to keep one or two aids. We found that 10 of the 12 who had opted for two aids and were available for follow-up 10 years later continued using at least one aid (83%, 95% CI 55–95). Six of the 17 who opted for unilateral fitting and were available for follow-up used a hearing aid in the long term (35%, 95% CI: 17–59%). Therefore, this study suggests that people who are identified through population screening, are bilaterally impaired, are willing to try bilateral fitting, and choose to continue with two aids, are likely to become long-term users of (one or two) hearing aids. Those who choose to continue with one aid after a trial of bilateral fitting are at high risk of rejecting the aid in the long term. Our sample is small, and we took a number of steps in the analysis in order to clarify whether these findings are reliable. We could not identify any confounding factors. The patients' preference for continuing with bilateral or unilateral aids after fitting was the only predictor of long-term use in our sample. Remarkably, bilateral preference was a better predictor of long-term use than the degree of hearing impairment. We discuss how this study provides useful information for planning population screening for hearing difficulties in middle age.Sumario: En este estudio se realiza un seguimiento de pacientes con adaptación de uno o dos auxiliares auditivos, aproximadamente 10 años antes. Nuestros pacientes fueron identificados a través de un estudio de tamiz poblacional para dificultades auditivas, cuando tenian edades entre los 50 y los 65 años. En aquel momento, se les realizaron pruebas para adaptación unilateral y bilateral, para que luego ellos hicieran su propia elección de si mantenian uno o dos auxiliares auditivos. Encontramos que 10 de los 12 sujetos que optaron por dos auxiliares auditivos y que estuvieron disponibles para la evaluación hasta 10 años después, continuaron utilizando al menos uno de ellos (83%, 95%; IC55–95%). Seis de los 17 que optaron por una adaptación unilateral y que estuvieron disponibles para el seguimiento, continuaron usando un auxiliar auditivo a largo plazo (35%, 95%; IC17–59%). Por lo tanto, este estudio sugiere que las personas identificadas por medio de pruebas de tamiz poblacional, que tienen un compromiso bilateral, que están dispuesta a intentar una adaptación bilateral y que escogen continuar usando dos auxiliares auditivos, muy probablemente se convertirán en usuarios a largo plazo de (uno o dos) auxiliares auditivos. Aquellos que escogen continuar con sólo uno, luego de una prueba de adaptación bilateral, enfrentan un alto riesgo de rechazarlo a largo plazo. Nuestra muestra es pequeña, y nosotros seguimos una serie de pasos en el análisis para aclarar si estos hallazgos eran confiables. No pudimos indentificar ningún factor de confusión. La preferencia de los pacientes de continuar con auxiliares auditivos uni o bilateralmente después de la adaptación, fue el único elemento de predicción a largo plazo en nuestra muestra. Interesantemente, la preferencia bilateral fue un mejor criterio de predicción a largo plazo, que el grado de trastorno auditivo. Discutimos aquí cómo este estudio aporta información valiosa para la planificación de estudios de identificatión de dificultades auditivas en sujetos de edad media.

Horizontal localization and speech intelligibility with bilateral and unilateral hearing aid amplification: Localización horizontal y discriminación del lenguaje con adaptación unilateral y bilateral de auxiliares auditivos

Speech intelligibility and horizontal localization of 19 subjects with mild-to-moderate hearing loss were studied in order to evaluate the advantages and disadvantages of bilateral and unilateral hearing aid (HA) fittings. Eight loudspeakers were arranged in a circular array covering the horizontal plane around the subjects. Speech signals of a sentence test were delivered by one, randomly chosen, loudspeaker. At the same time, the other seven loudspeakers emitted noise with the same long-term average spectrum as the speech signals. The subjects were asked to repeat the speech signal and to point out the corresponding loudspeaker. Speech intelligibility was significantly improved by HAs, bilateral amplification being superior to unilateral. Horizontal localization could not be improved by HA amplification. However, bilateral HAs preserved the subjects' horizontal localization, whereas unilateral amplification decreased their horizontal localization abilities. Front-back confusions were common in the horizontal localization test. The results indicate that bilateral HA amplification has advantages compared with unilateral amplification.SumarioSe estudió la inteligibilidad y la localización sonora horizontal en 19 sujetos con hipoacusia de nivel superficial a medio, para evaluar las ventajas y desventajas de la adaptación bilateral y unilateral de auxiliares auditivos (HA). Se colocaron en circulo ocho bocinas que cubrian el piano horizontal de los sujetos. A través de una bocina seleccionada al azar, se trasmitieron señales lingüisticas contenidas en una prueba de frases. Simultáneamente las otras siete bocinas emitian ruido del mismo espectro de duración que la señal lingüistica. Se les pidió a los sujetos que repitieran la señal lingüistica escuchada y que señalaran la bocina que la emitía. La inteligibilidad del lenguaje fue mucho mejor con la adaptación binaural de auxiliares auditivos que con la unilateral. No hubo mejoria en la localización horizontal con la adaptación de auxiliares auditivos. Sin embargo, la adaptación binaural preservó la localización horizontal, mientras que la adaptación unilateral disminuyó esa habilidad. La confusión entre frente y detrás es común en la prueba de localización horizontal. El resultado indica que la adaptación bilateral de auxiliares tiene ventajas sobre la adaptación unilateral.

Verifying loudness perception after hearing aid fitting.

During the verification phase of a hearing aid fitting, clinicians often want to assess the extent to which loudness perceptions for amplified sounds are similar to those typical of normal hearers. This type of verification calls for a criterion for "normal" loudness perception of sounds presented in a sound field. This research sought to answer several questions about the parameters of a valid "normal" criterion for a verification procedure using the Contour test of loudness perception. Loudness data were obtained from 30 listeners with normal hearing. Results indicated that a loudness growth function obtained with earphone listening is not an appropriate normative reference for hearing aid fitting verification. Instead, the normative data should be based on sound field listening. Results also indicated that the same normative function could be used to assess both unilateral and bilateral fittings. Further, it is likely that the same normative function can be used for most frequency responses that are likely to be used in feasible fittings. Finally, it was found that a previously published normative function obtained using an automated test procedure was not faithfully replicated using a carefully executed fully manual test procedure. We concluded that, until a replicable normative function is established, practitioners will need to generate their own local norms to perform postfitting verification of loudness normalization.

Effect of Spectral Shaping and Content on Loudness Discomfort

The purpose of this investigation was to study the impact of spectral shape and content on thresholds of discomfort (TD) for listeners with normal hearing and listeners with hearing loss. Secondary to that purpose was to quantify binaural summation at high intensities across complex stimulus conditions for both groups of listeners. Forty subjects (20 with normal hearing, 20 with hearing loss) participated. Complex acoustic stimuli (multitone and continuous discourse) were filtered to have four spectral shapes: (1) flat spectrum, (2) long-term average speech spectrum, (3) reverse long-term average speech spectrum, and (4) the TD contour derived for each subject from pure-tone TD obtained with eight pure tones from 250 to 4000 Hz. The results suggest that (1) TD for complex stimuli are lower for subjects with hearing loss compared with those with normal hearing, suggesting increased loudness summation with this population; (2) binaural summation of approximately 6 dB (independent of stimulus type, filter shape, or spectral content), indicating that a correction of similar magnitude for bilateral hearing aid fittings is appropriate; and (3) TD obtained at 750, 1500, and 3000 Hz accounted for approximately 60 percent of the variance in the complex TD measures, suggesting that TD at these frequencies be used to set the output obtained from a hearing aid with a 90-dB pure-tone sweep as the input stimulus.

Audiometric Evaluation of Bilaterally Fitted Bone-anchored Hearing Aids: Evaluatión audíométrica de auxiliares auditivos tipo vibrador óseo bilateral

Bilateral fittings of bone-anchored hearing aids (BAHA) were evaluated in 25 patients with at least 3 months experience with using two BAHAs. For all patients, air conduction hearing aids were contraindicated due to either recurrent otorrhoea or otitis externa (19 cases) or to congenital aural atresia (six cases). Candidacy for bilateral fitting was primarily based on symmetry of bone conduction thresholds. For all patients, measurements comprised sound localisation, speech recognition in quiet and in noise. In addition, in a subgroup of nine patients, release from masking for pure-tone stimuli in noise with interaural phase differences (binaural masking level difference, BMLD) was measured. The percentage of correct localisation judgments with 500-Hz and 2-kHz noise bursts increased significantly (p<0.01) from 22.2 per cent and 24.3 per cent for unilateral fittings to 41.8 per cent and 45.3 per cent for bilateral fittings, respectively. With unilateral fittings sound localisation judgments appeared to be...