Wouter A. Dreschler

ICRA Noises: Artificial Noise Signals with Speech-like Spectral and Temporal Properties for Hearing Instrument Assessment: Ruidos ICRA: Señates de ruido artificial con espectro similar al habla y propiedades temporales para pruebas de instrumentos auditivos

Current standards involving technical specification of hearing aids provide limited possibilities for assessing the influence of the spectral and temporal characteristics of the input signal, and these characteristics have a significant effect on the output signal of many recent types of hearing aids. This is particularly true of digital hearing instruments, which typically include non-linear amplification in multiple channels. Furthermore, these instruments often incorporate additional non-linear functions such as “noise reduction” and “feedback cancellation”. The output signal produced by a non-linear hearing instrument relates to the characteristics of the input signal in a complex manner. Therefore, the choice of input signal significantly influences the outcome of any acoustic or psychophysical assessment of a non-linear hearing instrument. For this reason, the International Collegium for Rehabilitative Audiology (ICRA) has introduced a collection of noise signals that can be used for hearing aid testing (including real-ear measurements) and psychophysical evaluation. This paper describes the design criteria, the realisation process, and the final selection of nine test signals on a CD. Also, the spectral and temporal characteristics of these signals are documented. The ICRA noises provide a well-specified set of speech-like noises with spectra shaped according to gender and vocal effort, and with different amounts of speech modulation simulating one or more speakers. These noises can be applied as well-specified background noise in psychophysical experiments. They can also serve as test signals for the evaluation of digital hearing aids with noise reduction. It is demonstrated that the ICRA noises show the effectiveness of the noise reduction schemes. Based on these initial measurements, some initial steps are proposed to develop a standard method of technical specification of noise reduction based on the modulation characteristics. For this purpose, the sensitivity of different noise reduction schemes is compared by measurements with ICRA noises with a varying ratio between unmodulated and modulated test signals: a modulated-unmodulated ratio. It can be anticipated that this information is important to understand the differences between the different implementations of noise reduction schemes in different hearing aid models and makes. Los estándares actuales de las especificaciones técnicas de los auxiliares auditivos proporcionan posibilidades limitadas para conocer la influencia de las characterísticas temporales y espectrales de la señal de entrada y estas caracteristicas tienen un efecto significativo en la señal de salida de muchos tipos actuales de auxiliares auditivos. Esto es particularmente cierto en el caso de los instrumentos digitales, que típicamente presentan una amplification no lineal en canales multiples. Incluso, estos instrumentos a menudo incorporan funciones no lineales adicionales como la “reduction de ruido” y la “cancelatión de la retroalimentación”. La señal de salida producida por un instrumento no lineal se relaciona en una forma muy compleja con la señal de entrada, por lo que la selectión de la señal de entrada influye significativamente en la salida de cualquier prueba acustica o psicoaciistica de un instrumento auditivo. Por esta razón el Colegio International de Audiología Rehabilitatoria (ICRA) ha introducido una serie de señales de ruido que pueden ser utilizadas en las pruebas de auxiliares auditivos (incluyendo mediciones in-situ) y evaluaciones psicoacusticas. Este trabajo describe los criterios de diseño, el proceso de realizatión y la selectión final de 9 señales de prueba en un CD. También se describen las characterísticas espectrales y temporales de estas señales. Los ruidos ICRA son un conjunto muy específico de sonidos vocales con forma espectral acorde al género y el esfuerzo vocal y con diversas dosis de modulation vocal que simulan uno o más hablantes. Estos ruidos pueden ser utilizados como ruidos de fondo muy especificos en experimentos psicoacsticos. Tambien pueden servir como señales de prueba para evaluar auxiliares auditivos digitales con reductión de ruido. Se demuestra que los ruidos ICRA tienen la efectividad de los esquemas de reductión de ruido. Con base en estas mediciones iniciales, se proponen algunos pasos iniciales para desarrollar métodos estándar de las especificaciones técnicas de reductión de ruido tomando en cuenta las characterísticas de modulation. Para ello se compara la sensibilidad de diferentes esquemas de reductión de ruido mediante las mediciones de ruidos ICRA con un rango de variation entre senales de prueba modulares y no modulares. Se puede anticipar que esta informatión es importante para comprender las diferencias al implementar diferentes esquemas de reductión de ruido en diferentes modelos y tipos de auxiliares auditivos.

Relations between psychophysical data and speech perception for hearing‐impaired subjects. II

Twenty-one sensorineurally hearing-impaired adolescents were studied with an extensive battery of tone-perception, phoneme-perception, and speech-perception tests. Tests on loudness perception, frequency selectivity, and temporal resolution at the test frequencies of 500, 1000, and 2000 Hz were included. The mean values and the gradient across frequencies were used in further analysis. Phoneme-perception data were gathered by means of similarity judgments and phonemic confusions. Speech-reception thresholds were determined in quiet and in noise for unfiltered speech material, and with additional low-pass and high-pass filtering in noise. The results show that hearing loss for speech is related to both the frequency resolving power and temporal processing by the ear. Phoneme-perception parameters proved to be more related to the filtered-speech thresholds than to the thresholds for unfiltered speech. This finding may indicate that phoneme-perception parameters play only a secondary role, and for that reason their bridging function between tone perception and speech perception is only limited.

Extended speech intelligibility index for the prediction of the speech reception threshold in fluctuating noise

The extension to the speech intelligibility index (SII; ANSI S3.5-1997 (1997)) proposed by Rhebergen and Versfeld [Rhebergen, K.S., and Versfeld, N.J. (2005). J. Acoust. Soc. Am. 117(4), 2181-2192] is able to predict for normal-hearing listeners the speech intelligibility in both stationary and fluctuating noise maskers with reasonable accuracy. The extended SII model was validated with speech reception threshold (SRT) data from the literature. However, further validation is required and the present paper describes SRT experiments with nonstationary noise conditions that are critical to the extended model. From these data, it can be concluded that the extended SII model is able to predict the SRTs for the majority of conditions, but that predictions are better when the extended SII model includes a function to account for forward masking.

The relationship between the intelligibility of time-compressed speech and speech in noise in young and elderly listeners

A conventional measure to determine the ability to understand speech in noisy backgrounds is the so-called speech reception threshold (SRT) for sentences. It yields the signal-to-noise ratio (in dB) for which half of the sentences are correctly perceived. The SRT defines to what degree speech must be audible to a listener in order to become just intelligible. There are indications that elderly listeners have greater difficulty in understanding speech in adverse listening conditions than young listeners. This may be partly due to the differences in hearing sensitivity (presbycusis), hence audibility, but other factors, such as temporal acuity, may also play a significant role. A potential measure for the temporal acuity may be the threshold to which speech can be accelerated, or compressed in time. A new test is introduced where the speech rate is varied adaptively. In analogy to the SRT, the time-compression threshold (or TCT) then is defined as the speech rate (expressed in syllables per second) for which half of the sentences are correctly perceived. In experiment I, the TCT test is introduced and normative data are provided. In experiment II, four groups of subjects (young and elderly normal-hearing and hearing-impaired subjects) participated, and the SRTs in stationary and fluctuating speech-shaped noise were determined, as well as the TCT. The results show that the SRT in fluctuating noise and the TCT are highly correlated. All tests indicate that, even after correction for the hearing loss, elderly normal-hearing subjects perform worse than young normal-hearing subjects. The results indicate that the use of the TCT test or the SRT test in fluctuating noise is preferred over the SRT test in stationary noise.

High Frequency Audiometry in Prospective Clinical Research of Ototoxicity Due to Platinum Derivatives

The results of clinical use of routine high frequency audiometry in monitoring the ototoxic side effects of platinum and its derivatives are described in this prospective study. After demonstrating the reproducibility of the technique, we discuss the first results of an analysis of ototoxic side effects in 75 patients (150 ears). Significant differences in the pattern of hearing loss were registered for the different platinum treatment groups (cisplatin 20 mg/m2, cisplatin 50 mg/m2, and carboplatin 350 mg/m2). In the groups receiving cisplatin 50 mg/m2 and carboplatin 350 mg/m2, 42% and 25%, respectively, of the investigated ears proved to be undamaged, versus 9% undamaged in the group receiving cisplatin 20 mg/m2 (p< .01). Ototoxic hearing loss started mainly (46% to 70%) in the higher frequencies (10,000 to 18,000 Hz) and developed into a broader-range hearing loss (1,000 to 18,000 Hz) during treatment in 13% to 43% (p< .01). The onset of hearing damage was influenced by the patients age (p< .001) and the existence of a troubled otologic history (p< .05). The study demonstrates the important role of high frequency audiometry in early detection and monitoring of ototoxic damage.

The effectiveness of bilateral cochlear implants for severe-to-profound deafness in children: a systematic review.

Objective: To assess the clinical effectiveness of bilateral cochlear implantation compared with unilateral cochlear implantation alone or with a contralateral hearing aid (bimodal stimulation), in children with severe-to-profound hearing loss. Recently, the National Institute for Health and Clinical Excellence (NICE) in the U.K. has conducted a systematic review on cochlear implantation. We decided to update the pediatric part of the NICE review. Data Sources: The electronic databases MEDLINE and Embase were searched for European, North American, and Australasian studies published between October 2006 and June 2009. Reference lists of the included articles were also searched for relevant articles. Study Selection: Studies were included if they comprised data on comparisons between bilateral cochlear implantation and unilateral cochlear implantation and/or bilateral cochlear implantation and bimodal stimulation, in children with severe-to-profound sensorineural hearing loss. The following outcome measures were analyzed: audiological, speech perception, speech production, functional capacities, health-related quality of life, and/or educational outcomes. Data Extraction: Characteristics of the participants, interventions, outcomes, and methodological comments were entered into data extraction forms and the level of evidence was assessed. Data Synthesis: Results were standardized for each outcome measure by calculating a standardized mean difference (effect size). Conclusion: Effect sizes could not be pooled because of the heterogeneity of the studies. Therefore, we presented the results qualitatively. Although the level of evidence was low, the advantages of bilateral cochlear implants corresponded with the primary benefits of bilateral hearing, that is, improved speech perception in quiet and noise. Localization results were less consistent. No data on audiologic, speech production, or educational outcomes were available.

International Outcome Inventory for Hearing Aids (IOI-HA): results from The Netherlands

This paper presents data on the Dutch translation of the International Outcome Inventory for Hearing Aids (IOI-HA). The inventory was used as an additional postal tool in a nationwide study on the benefits of bilateral hearing aid fitting. Responses of 505 hearing aid users were analysed. Descriptive statistics and inter-item correlations are reported. Factor analysis resulted in the extraction of two factors. Cronbachs alpha coefficients and corrected item total correlations showed high internal consistency of the scales. Significant correlations were found between IOI Factor 2 and the Hearing Handicap and Disability Inventory and subscales of the Amsterdam Invcntory for Hearing Disability and Handicap. Sumario Este trabajo presenta los datos de la traducciócute;n al holandés del Inventario Internacional de Resultados para Auxiliares Auditivos (IOI-HA). El inventario fue usado como un instrumento postal adicional en un estudio nacional acerca de los beneficios de la adaptatiócute;n bilateral de auxiliares auditivos. Se analizaron las respuestas de 505 usuarios de auxiliares auditivos. Se reportan los datos estadisticos descriptivos y las correlaciones entre los items. El factor de analisis finalìzócute; en la extractiócute;n de dos factores. Los coeficientes alpha de Cronbach y las correlaciones totales de los items corregidos mostraron una alta consistencia interna de las escalas. Se encontraron correlaciones significativas entre el factor2 IOI, el Inventario de desventaja y discapacidad auditiva y las subescalas del Inventario Amsterdam para discapacidad y desventaja auditiva.This paper presents data on the Dutch translation of the International Outcome Inventory for Hearing Aids (IOI-HA). The inventory was used as an additional postal tool in a nationwide study on the benefits of bilateral hearing aid fitting. Responses of 505 hearing aid users were analysed. Descriptive statistics and inter-item correlations are reported. Factor analysis resulted in the extraction of two factors. Cronbachs alpha coefficients and corrected item total correlations showed high internal consistency of the scales. Significant correlations were found between IOI Factor 2 and the Hearing Handicap and Disability Inventory and subscales of the Amsterdam Inventory for Hearing Disability and Handicap.

The Role of High-Frequency Audiometry in Early Detection of Ototoxicity

Ototoxicity is one of the unwanted side-effects of a number of medical drugs. As ototoxicity appears to be most pronounced in the higher frequencies, it can be assessed at an earlier stage by using high-frequency audiometry from 8 to 20 kHz. We have investigated the precision of these measurements. In spite of inaccuracies of headphone positioning, which may influence especially the high-frequency thresholds, standard deviations for frequencies above 8 kHz were obtained that were nearly as small as for audiometry up to 8 kHz. Age-related reference curves for the higher frequencies are presented. The results on 100 ears of patients treated with platinum-derivatives show the importance of high-frequency audiometry for the early detection of ototoxicity.

Field Trials Using a Digital Hearing Aid with Active Noise Reduction and Dual-Microphone Directionality: Estudios de campo utilizando un audifono digital con reduccion activa del ruido y micrófono de direccionalidad dual

In this study, we measured the effects of a digital hearing aid on speech recognition or reception in noise for two noise reduction concepts: active noise reduction by speech-sensitive processing (SSP) and improved directionality by a dual- or so-called twin-microphone system (TMS). This was conducted in a well-controlled clinical field trial in 16 hearing-aid users, using a single-blind crossover design. The hearing aid fitting was controlled by insertion gain measurements and measurements with loudness scaling. This study combined laboratory experiments with three consecutive field trials of 4 weeks each. We used performance measurements (speech recognition tests in background noise), paired comparisons, and self-report measurements (questionnaires). The speech recognition or reception tests were performed before and after each field trial, the paired comparisons were performed in weeks 4 and 12, and the questionnaires were administered after each field trial. For all subjects, results were obtained for three different settings: no noise reduction, SSP alone, and TMS alone. In the last week, we also performed speech recognition or reception tests in background noise with both noise reduction concepts combined. Three types of results have been reported: “objective” results from the critical signal to noise ratios for speech recognition or reception in different background noises for different settings and “subjective” results: paired comparisons and questionnaires. The subjective scores show the same trend as the objective scores. The effects of TMS were clearly positive, especially for the speech reception threshold tests and for the paired comparisons. The effects of SSP were much smaller but showed significant benefits with respect to aversive-ness and speech perception or reception in noise foi specific acoustical environments. There was no extra benefit from the combined effect of SSP and TMS relative to TMS alone.

Clinical evaluation of a full-digital in-the-ear hearing instrument.

In this study we measured the efficacy of a digital hearing aid with compression and noise reduction in a well-controlled clinical field trial in two independent centres. The experiments focused on a number of aspects of the application of the digital hearing aids. The study combines a field test of 2x4 weeks with laboratory experiments. We used objective measurements (speech perception tests in background noise, loudness scaling) and subjective assessments (questionnaires). The measurements were performed before and after the field test. The questionnaires were collected after each field test. The results of the digital hearing aids were compared to the results of similar tests with newly fitted analogue reference aids. The study involved 27 sensorineural hearing-impaired subjects, wearing new hearing aids. They comprised a representative sample of in-the-ear users. We used a crossover design in which the subjects used successively digital hearing aids and analogue reference aids in a randomized order. On average, the subjective data are more positive than the objective data. In the end, 20 out of 27 subjects had an overall preference for the digital hearing aid. The financial implications were not taken into consideration. However, objective data do not support this strong subjective preference. A reason could be that the method of analysis (short sentences in a short-duration background noise) is not suited for the digital hearing aid; the testing procedure does not allow the noise-reduction algorithm to adapt to the background noise. There was a striking difference between the results for the two centres. This difference can, to at least a certain extent, be attributed to the timing of speech relative to the background noise in the objective tests. This illustrates that the test conditions are critical in modern non-linear signal-processing hearing aids with long time constants. New evaluation techniques should be developed for this new generation of active non-linear hearing aids.