Teresa Y. C. Ching

Speech recognition of hearing-impaired listeners: Predictions from audibility and the limited role of high-frequency amplification

Two experiments were conducted to examine the relationship between audibility and speech recognition for individuals with sensorineural hearing losses ranging from mild to profound degrees. Speech scores measured using filtered sentences were compared to predictions based on the Speech Intelligibility Index (SII). The SII greatly overpredicted performance at high sensation levels, and for many listeners, it underpredicted performance at low sensation levels. To improve predictive accuracy, the SII needed to be modified. Scaling the index by a multiplicative proficiency factor was found to be inappropriate, and alternative modifications were explored. The data were best fitted using a method that combined the standard level distortion factor (which accounted for decrease in speech intelligibility at high presentation levels based on measurements of normal-hearing people) with individual frequency-dependent proficiency. This method was evaluated using broadband sentences and nonsense syllables tests. Results indicate that audibility cannot adequately explain speech recognition of many hearing-impaired listeners. Considerable variations from audibility-based predictions remained, especially for people with severe losses listening at high sensation levels. The data suggest that, contrary to the basis of the SII, information contained in each frequency band is not strictly additive. The data also suggest that for people with severe or profound losses at the high frequencies, amplification should only achieve a low or zero sensation level at this region, contrary to the implications of the unmodified SII.

Binaural benefits for adults who use hearing aids and cochlear implants in opposite ears.

Objective This study aimed to investigate 1) how a hearing aid needs to be adjusted for an adult who uses a cochlear implant in the contralateral ear; 2) whether the use of a hearing aid with a cochlear implant leads to interference; and 3) whether adults derive binaural benefits from using a hearing aid with a cochlear implant for speech perception, localization, and functional performance in everyday life. Design Twenty-one adults (11 female and 10 male) who used either a Nucleus CI-22 (N = 3) or a Nucleus CI-24 (N = 18) cochlear implant system in one ear participated in this study. Twelve of the adults were experienced hearing aid and implant users, whereas nine did not use a hearing aid after implantation. The hearing aids were fitted using the NAL-NL1 prescription, and fine-tuned for each individual by using a paired-comparisons test to identify the frequency response that was best for understanding speech, and a loudness balancing test to find the hearing aid gain that gave the same overall loudness as that perceived in the ear with a cochlear implant. Effects from using a hearing aid with a cochlear implant (bimodal hearing) were assessed by three measures. These included speech perception in noise in diotic and dichotic listening conditions, horizontal localization, and functional performance in everyday life. Performance with cochlear implant and hearing aid (CIHA) was compared with that with cochlear implant alone (CI) and hearing aid alone (HA). Results The NAL-NL1 prescribed appropriate frequency response slope on average, and the mean gain needed for binaural loudness balance was 4 dB lower than the prescribed gain. Individual variations in preferences suggest that it is desirable to fine-tune the hearing aid response slope and gain according to individual needs. The speech test results indicated that the CIHA scores were significantly better than the CI or the HA scores. Localization test results showed that the adults made significantly less error when locating a sound source using CIHA compared with CI or HA. Functional performance questionnaire scores for CIHA were significantly higher than CI scores or HA scores. All adults showed binaural benefits in at least one performance measure. On average, those who derived greater speech benefits also made less localization error and functioned more effectively in real life. Conclusions The results clearly indicate that binaural advantages can be obtained from using a hearing aid with a cochlear implant in opposite ears. It is recommended that bimodal stimulation be standard practice for rehabilitation of adults who wear unilateral cochlear implants. A hearing aid should be fitted to the nonimplanted ear using the NAL-NL1 prescription as a starting point, and the frequency response slope and gain could be fine-tuned to suit individual needs.

Binaural-Bimodal Fitting or Bilateral Implantation for Managing Severe to Profound Deafness: A Review

There are now many recipients of unilateral cochlear implants who have usable residual hearing in the non-implanted ear. To avoid auditory deprivation and to provide binaural hearing, a hearing aid or a second cochlear implant can be fitted to that ear. This article addresses the question of whether better binaural hearing can be achieved with binaural/bimodal fitting (combining a cochlear implant and a hearing aid in opposite ears) or bilateral implantation. In the first part of this article, the rationale for providing binaural hearing is examined. In the second part, the literature on the relative efficacy of binaural/bimodal fitting and bilateral implantation is reviewed. Most studies on comparing either mode of bilateral stimulation with unilateral implantation reported some binaural benefits in some test conditions on average but revealed that some individuals benefited, whereas others did not. There were no controlled comparisons between binaural/bimodal fitting and bilateral implantation and no evidence to support the efficacy of one mode over the other. In the third part of the article, a crossover trial of two adults who had binaural/bimodal fitting and who subsequently received a second implant is reported. The findings at 6 and 12 months after they received their second implant indicated that binaural function developed over time, and the extent of benefit depended on which abilities were assessed for the individual. In the fourth and final parts of the article, clinical issues relating to candidacy for binaural/ bimodal fitting and strategies for bimodal fitting are discussed with implications for future research.

Should children who use cochlear implants wear hearing aids in the opposite ear

Objective The aim of this study was to investigate 1) whether a hearing aid needs to be adjusted differently depending on whether a child wears a cochlear implant or another hearing aid in the contralateral ear; 2) whether the use of a hearing aid and a cochlear implant in opposite ears leads to binaural interference; and 3) whether the use of a hearing aid and a cochlear implant in opposite ears leads to binaural benefits in speech perception, localization, and communicative functioning in real life. Design Sixteen children participated in this study. All children used a Nucleus 22 or Nucleus 24 cochlear implant system programmed with the SPEAK strategy in one ear. The hearing aid amplification requirements in the nonimplanted ear of these children were determined using two procedures. A paired comparison technique was used to identify the frequency response that was best for speech intelligibility in quiet, and a loudness balancing technique was used to match the loudness of speech in the ear with a hearing aid to that with a cochlear implant. Eleven of the 16 children participated in the investigation of binaural effects. Performance in speech perception, localization, and communicative functioning was assessed under four aided conditions: cochlear implant with hearing aid as worn, cochlear implant alone, hearing aid alone, and cochlear implant with hearing aid adjusted according to individual requirements. Results Fifteen of the 16 children whose amplification requirements were determined preferred a hearing aid frequency response that was within ±6 dB/octave of the NAL-RP prescription. On average, the children required 6 dB more gain than prescribed to balance the loudness of the implanted ear for a speech signal presented at 65 dB SPL. For all 11 children whose performance was evaluated for investigating binaural effects, there was no indication of significantly poorer performance under bilaterally aided conditions compared with unilaterally aided conditions. On average, there were significant benefits in speech perception, localization, and aural/oral function when the children used cochlear implants with adjusted hearing aids than when they used cochlear implants alone. All individuals showed benefits in at least one of the measures. Conclusions Hearing aids for children who also use cochlear implants can be selected using the NAL-RP prescription. Adjustment of hearing aid gain to match loudness in the implanted ear can facilitate integration of signals from both ears, leading to better speech perception. Given that there are binaural advantages from using cochlear implants with hearing aids in opposite ears, clinicians should advise parents and other professionals about these potential advantages, and facilitate bilateral amplification by adjusting hearing aids after stable cochlear implant MAPs are established.

Outcomes of early- and late-identified children at 3 years of age: findings from a prospective population-based study.

Objective: To address the question of whether, on a population level, early detection and amplification improve outcomes of children with hearing impairment. Design: All families of children who were born between 2002 and 2007, and who presented for hearing services below 3 years of age at Australian Hearing pediatric centers in New South Wales, Victoria, and Southern Queensland were invited to participate in a prospective study on outcomes. Children’s speech, language, functional, and social outcomes were assessed at 3 years of age, using a battery of age-appropriate tests. Demographic information relating to the child, family, and educational intervention was solicited through the use of custom-designed questionnaires. Audiological data were collected from the national database of Australian Hearing and records held at educational intervention agencies for children. Regression analysis was used to investigate the effects of each of 15 predictor variables, including age of amplification, on outcomes. Results: Four hundred and fifty-one children enrolled in the study, 56% of whom received their first hearing aid fitting before 6 months of age. On the basis of clinical records, 44 children (10%) were diagnosed with auditory neuropathy spectrum disorder. There were 107 children (24%) reported to have additional disabilities. At 3 years of age, 317 children (70%) were hearing aid users and 134 children (30%) used cochlear implants. On the basis of parent reports, about 71% used an aural/oral mode of communication, and about 79% used English as the spoken language at home. Children’s performance scores on standardized tests administered at 3 years of age were used in a factor analysis to derive a global development factor score. On average, the global score of hearing-impaired children was more than 1 SD below the mean of normal-hearing children at the same age. Regression analysis revealed that five factors, including female gender, absence of additional disabilities, less severe hearing loss, higher maternal education, and (for children with cochlear implants) earlier age of switch-on were associated with better outcomes at the 5% significance level. Whereas the effect of age of hearing aid fitting on child outcomes was weak, a younger age at cochlear implant switch-on was significantly associated with better outcomes for children with cochlear implants at 3 years of age. Conclusions: Fifty-six percent of the 451 children were fitted with hearing aids before 6 months of age. At 3 years of age, 134 children used cochlear implants and the remaining children used hearing aids. On average, outcomes were well below population norms. Significant predictors of child outcomes include: presence/absence of additional disabilities, severity of hearing loss, gender, maternal education, together with age of switch-on for children with cochlear implants.

Maximizing effective audibility in hearing aid fitting

Objective This paper examines why more audibility is not always better than less audibility if hearing-impaired people are to best understand speech. Design We used speech perception data from 14 normally hearing and 40 hearing-impaired people to quantify the contribution of audibility to speech intelligibility. The quantification revealed that the effectiveness of audibility decreased with hearing loss, and the decrement was greater at high frequencies than at lower frequencies. To apply the Speech Intelligibility Index (SII) model to predict speech intelligibility for hearing-impaired people, we modified the model to take account of effective audibility rather than physical audibility. Results The modified SII model provided an adequate description of speech performance of people with a wide range of hearing threshold levels. We applied the model to the evaluation of two prescriptions for a sloping audiogram at prescribed levels and at equated loudness levels to demonstrate the necessity of considering loudness and effective audibility in prescribing amplification. Effective audibility is defined as audibility corrected for the effects of level distortion and hearing loss desensitization, and this paper proposes a method of estimating effective audibility from hearing threshold level at different frequencies. Conclusions The practical implication of considering effective audibility in prescribing hearing aids is that for a given listening level, less gain is provided at frequencies where the hearing is most impaired to allow more gain at frequencies where audibility is most useful. In developing the NAL-NL1 prescription for nonlinear hearing aids, we adopted the modified SII model together with a loudness model to derive optimal gain-frequency response characteristics that maximize predicted speech intelligibility for people with different degrees of hearing losses.

An Overview of Binaural Advantages for Children and Adults Who Use Binaural/Bimodal Hearing Devices

Aim: The aim of this paper was to summarize the binaural advantages for sentence perception in noise and sound localization obtained by children and adults who wore a cochlear implant (CI) and a hearing aid in opposite ears (bimodal hearing devices). Patients and Methods: We evaluated the speech perception and sound localization ability of 29 children and 21 adults who received a Nucleus CI system in one ear and wore a hearing aid in the other ear. All subjects used hearing aids that were adjusted systematically to complement their CIs. Performance with a CI and a hearing aid was compared with that with a CI alone. Results: On average, both children and adults derived binaural advantages relating to binaural redundancy and head shadow for sentence perception in noise. Neither the degree of hearing loss nor the duration of use of bimodal hearing devices was significantly related to the amount of binaural speech benefits. Both groups also located sounds better with CI and a hearing aid than with CI alone. Conclusions: The evidence supports the implementation of binaural/bimodal fittings as the standard management of children and adults who receive a unilateral CI and who have residual hearing in the nonimplanted ear.

Binaural redundancy and inter-aural time difference cues for patients wearing a cochlear implant and a hearing aid in opposite ears.

We investigated speech perception advantages arising from the use of inter-aural time difference cues, and from the provision of redundant information by the use of a hearing aid contralateral to a cochlear implant (bimodal hearing devices). Thirty-eight subjects (14 normally hearing and 23 hearing-impaired) participated in this study. The effect of binaural redundancy was assessed by comparing the signal-to-noise ratio (SNR) required for 50% correct identification of sentences in noise when listening monaurally to that when listening binaurally. The use of inter-aural time difference cues was determined by comparing the binaural SNRs obtained with or without a noise delay of 700 µs between ears. Results indicated adults who used bimodal hearing devices benefited from binaural redundancy, but children did not. Whereas normally hearing subjects used inter-aural time difference cues to improve speech perception in noise, neither adults nor children who used bimodal hearing devices were able to do so.

The effect of auditory experience on speech perception, localization, and functional performance of children who use a cochlear implant and a hearing aid in opposite ears

This study was aimed at determining the effect of auditory experience on binaural benefits from using a cochlear implant and a hearing aid in opposite ears. Eighteen children were evaluated using tests of speech perception, horizontal localization, and functional performance when they used either a cochlear implant alone (CI) or a cochlear implant with a hearing aid (CIHA). Eight were experienced CIHA users, whereas ten had not worn a hearing aid in the non-implanted ear for up to eight years prior to participation. All children were fitted with a hearing aid in the non-implanted ear using the NAL–RP prescription, and the hearing aids were fine-tuned individually using a paired-comparisons procedure and a loudness balancing test. Evaluation results indicated that performance for all measures was significantly better with CIHA than with CI for both groups of children. We conclude that children who receive a unilateral cochlear implant should be encouraged to wear a hearing aid in the opposite ear where there is usable residual hearing. Sumario El propósito de este estudio fue determinar el efecto de la experiencia auditiva sobre los beneficios binaurales al utilizar un implante coclear y un auxiliar auditivo en oídos opuestos. Se evaluó a dieciocho niños por medio de pruebas de percepción del lenguaje, de localización horizontal, y de desempeño funcional cuando utilizaban el implante coclear (CI) aisladamente, o un implante coclear con un auxiliar auditivo (CIHA). Ocho eran usuarios con experiencia en CIHA, mientras que ocho nunca había usado un auxiliar auditivo en el oído no implantado hasta 8 años antes de su participación. A todos los niños se les adaptó un auxiliar auditivo en el oído no implantado usando la prescripción NAL-RP, y éste fue configurado individualmente utilizando un procedimiento de comparaciones pareadas y una prueba de balance de la sonoridad. Los resultados de las evaluaciones indicaron que el desempeño en todas las medidas fue significativamente mejor con CIHA que con el CI para ambos grupos de niños. Concluimos que los niños que reciben un implante coclear unilateral deben ser motivados a usar un auxiliar auditivo en el oído opuesto cuando exista una audición residual utilizable.

A cross-over, double-blind comparison of the NAL-NL1 and the DSL v4.1 prescriptions for children with mild to moderately severe hearing loss

Abstract The relative effectiveness of the NAL-NL1 and the DSL4.1 prescriptions for 48 children with mild to moderately severe hearing loss was studied using a double-blind, four-period, two-treatment cross-over design in Australia and in Canada. Evaluations included speech perception tests, loudness ratings, reports from parents and teachers on functional performance in real life, childrens self-reports, paired-comparison judgements of intelligibility, and childrens preferences in real-world environments. Electroacoustic measures of hearing aids revealed that gain differences dominated the comparison. Across trials and measures, individual Australian children consistently preferred either the NAL-NL1 or the DSL v.4.1 prescription. An overall figure of merit (FOM), calculated by averaging the standardized difference scores between prescriptions for all measures, revealed that the strongest prescription-related differences were found in Australia. On average, an advantage and preference for the NAL-NL1 prescription was associated with lesser degrees of hearing loss. This research provides evidence on the effectiveness of the NAL-NL1 and DSL v.4.1 prescriptions, and highlights the need for evaluating and fine-tuning amplification to meet the diverse needs of individual children in real life. Sumario Se estudió la relativa efectividad de las prescripciones NAL-NL1 y DSL 4.1 en 48 niños con pérdidas auditivas de leves a moderadamente severas, usando un estudio doble ciego, en cuatro períodos y con un diseño cruzado de dos tratamientos en Australia y en Canadá. Las evaluaciones incluyeron pruebas de percepción de la palabra, tasas de reclutamiento, auto-reportes de los niños, juicios de inteligibilidad comparados por pares y preferencias de los niños en ambientes de mundo real. Las mediciones electroacústicas de los auxiliares auditivos revelaron que las diferencias en ganancia dominaron la comparación. En todas las pruebas y mediciones, los niños Australianos individualmente prefirieron de manera consistente tanto la prescripción NAL-NL1 como la DSL v.4.1. Una figura global de mérito (FOM), calculada al promediar las puntuaciones de diferencias estandarizadas entre prescripciones de todas las medidas, revelaron que las diferencias más fuertemente relacionadas con la prescripción, se encontraron en Australia. En promedio, la ventaja y preferencias hacia la prescripción NAL-NL1 se asoció con grados menores de pérdida auditiva. Esta investigación proporciona evidencia de la efectividad de las prescripciones NAL-NL1 y DSL v.4.1 y pone de relieve la necesidad de evaluar y de afinar la amplificación para alcanzar las diversas necesi-dades individuales de los niños en la vida real.