A simple method to estimate noise levels in the workplace based on self-reported speech communication effort in noise.

Objective: To validate a method using self-reported speech communication effort in noise to estimate occupational noise levels by comparing with measured noise levels. Design: A comparative observational study. Reported vocal effort to communicate with a person at a distance of 1.2 m during workplace-related tasks was used to provide an estimate of noise levels in the workplace. These estimated noise levels were compared against noise level measurements obtained using personal noise dosimetry badges for corresponding tasks undertaken by participants. Study sample: Participants (n = 168) aged 16-25 years were recruited from companies where workplace noise levels were at least 85 dB(A). Results: Estimated noise levels using speech communication ability were evenly distributed above and below the measured noise levels (n = 134), indicating a lack of systematic bias in the method. For 91% of participants, estimates of noise levels using speech communication were within ±6 dB of the measured levels, whilst 56% were within ±3 dB. Conclusions: Report of speech communication effort required in noise by employees is an effective method of estimating noise levels within the workplace. This can be used for retrospective noise level assessment where there are no recorded noise level measurements, such as for retrospective research studies or in medicolegal work.

Speech quality evaluation of a sparse coding shrinkage noise reduction algorithm with normal hearing and hearing impaired listeners.

Although there are numerous papers describing single-channel noise reduction strategies to improve speech perception in a noisy environment, few studies have comprehensively evaluated the effects of noise reduction algorithms on speech quality for hearing impaired (HI). A model-based sparse coding shrinkage (SCS) algorithm has been developed, and has shown previously (Sang et al., 2014) that it is as competitive as a state-of-the-art Wiener filter approach in speech intelligibility. Here, the analysis is extended to include subjective quality ratings and a method called Interpolated Paired Comparison Rating (IPCR) is adopted to quantitatively link the benefit of speech intelligibility and speech quality. The subjective quality tests are performed through IPCR to efficiently quantify noise reduction effects on speech quality. Objective measures including frequency-weighted segmental signal-to-noise ratio (fwsegSNR), perceptual evaluation of speech quality (PESQ) and hearing aid speech quality index (HASQI) are adopted to predict the noise reduction effects. Results show little difference in speech quality between the SCS and the Wiener filter algorithm but a difference in quality rating between the HI and NH listeners. HI listeners generally gave better quality ratings of noise reduction algorithms than NH listeners. However, SCS reduced the noise more efficiently at the cost of higher distortions that were detected by NH but not by the HI. SCS is a promising candidate for noise reduction algorithms for HI. In general, care needs to be taken when adopting algorithms that were originally developed for NH participants into hearing aid applications. An algorithm that is evaluated negatively with NH might still bring benefits for HI participants.

Simultaneous suppression of tone burst-evoked otoacoustic emissions: Two and three-tone burst combinations.

Previous investigations have shown that components of a tone burst-evoked otoacoustic emission (TBOAE) evoked by a 1 kHz tone burst (TB1) can be suppressed by the simultaneous presence of a 2 kHz tone burst (TB2) or a pair of tone bursts at 2 and 3 kHz (TB2 and TB3 respectively). No previous study has measured this "simultaneous suppression of TBOAEs" for both TB2 alone and TB2 and TB3 from the same ears, so that the effect of the additional presence of TB3 on suppression caused by TB2 is not known. In simple terms, three outcomes are possible; suppression increases, suppression is reduced or suppression is not affected. Comparison of previously reported simultaneous suppression data suggests TB3 causes a reduction in suppression, though it is not clear if this is a genuine effect or simply reflects methodological and ear differences between studies. This issue has implications for previously proposed mechanisms of simultaneous suppression of TBOAEs and the interpretation of clinical data, and is clarified by the present study. Simultaneous suppression of TBOAEs was measured for TB1 and TB2 as well as TB1, TB2 and TB3 at 50, 60 and 70 dB p.e. SPL from nine normal human ears. Results showed no significant difference between mean suppression obtained for the two and three-tone burst combinations, indicating the reduction of suppression inferred from comparison of previous data is likely a result of methodological and ear differences rather than a genuine effect.

Sparse Nonnegative Matrix Factorization Strategy for Cochlear Implants.

Current cochlear implant (CI) strategies carry speech information via the waveform envelope in frequency subbands. CIs require efficient speech processing to maximize information transfer to the brain, especially in background noise, where the speech envelope is not robust to noise interference. In such conditions, the envelope, after decomposition into frequency bands, may be enhanced by sparse transformations, such as nonnegative matrix factorization (NMF). Here, a novel CI processing algorithm is described, which works by applying NMF to the envelope matrix (envelopogram) of 22 frequency channels in order to improve performance in noisy environments. It is evaluated for speech in eight-talker babble noise. The critical sparsity constraint parameter was first tuned using objective measures and then evaluated with subjective speech perception experiments for both normal hearing and CI subjects. Results from vocoder simulations with 10 normal hearing subjects showed that the algorithm significantly enhances speech intelligibility with the selected sparsity constraints. Results from eight CI subjects showed no significant overall improvement compared with the standard advanced combination encoder algorithm, but a trend toward improvement of word identification of about 10 percentage points at +15 dB signal-to-noise ratio (SNR) was observed in the eight CI subjects. Additionally, a considerable reduction of the spread of speech perception performance from 40% to 93% for advanced combination encoder to 80% to 100% for the suggested NMF coding strategy was observed.

Further tests of the local nonlinear interaction-based mechanism for simultaneous suppression of tone burst-evoked otoacoustic emissions.

Tone burst-evoked otoacoustic emission (TBOAE) components measured in response to a 1 kHz tone burst (TB1) are suppressed by the simultaneous presence of an additional tone burst (TB2). This "simultaneous suppression of TBOAEs" has been explained in terms of a mechanism based on local nonlinear interactions between the basilar membrane (BM) travelling waves caused by TB1 and TB2. A test of this local nonlinear interaction (LNI)-based mechanism, as a function of the frequency separation (Δf, expressed in kHz) between TB1 and TB2, has previously been reported by Killan et al. (2012) using a simple mathematical model [Killan et al., Hear. Res. 285, 58-64 (2012)]. The two experiments described in this paper add additional data on the extent to which the LNI-based mechanism can account for simultaneous suppression, by testing two further hypotheses derived from the model predictions. Experiment I tested the hypothesis that TBOAE suppression is directly linked to TBOAE amplitude nonlinearity where ears that exhibit a higher degree of amplitude nonlinearity yield greater suppression than more linear ears, and this relationship varies systematically as a function of Δf. In order to test this hypothesis simultaneous suppression at a range of values of Δf at 60 dB peak-equivalent sound pressure level (p.e. SPL) and TBOAE amplitude nonlinearity from normal human ears was measured. In Experiment II the hypothesis that suppression will also increase progressively as a function of increasing tone burst level was tested by measuring suppression for a range of Δf and tone burst levels at 40, 50, 60 and 70 dB p.e. SPL. The majority of the findings from both experiments provide support for the LNI-based mechanism being primarily responsible for simultaneous suppression. However, some data were inconsistent with this view. Specifically, a breakdown in the relationship between suppression and TBOAE amplitude nonlinearity at Δf = 1 (i.e. when TB2 was reasonably well separated from, and had a higher frequency than TB1) and unexpected level-dependence, most notably at Δf = 1, but also where Δf = -0.5, was observed. Either the LNI model is too simple or an alternative explanation, involving response components generated at basal regions of the basilar membrane, is required to account for these findings.

Evaluation of the sparse coding shrinkage noise reduction algorithm in normal hearing and hearing impaired listeners.

Although there are numerous single-channel noise reduction strategies to improve speech perception in noise, most of them improve speech quality but do not improve speech intelligibility, in circumstances where the noise and speech have similar frequency spectra. Current exceptions that may improve speech intelligibility are those that require a priori knowledge of the speech or noise statistics, which limits practical application. Hearing impaired (HI) listeners suffer more in speech intelligibility than normal hearing listeners (NH) in the same noisy environment, so developing better single-channel noise reduction algorithms for HI listeners is justified. Our model-based "sparse coding shrinkage" (SCS) algorithm extracts key speech information in noisy speech. We evaluate it by comparison with a state-of-the-art Wiener filtering approach using speech intelligibility tests with NH and HI listeners. The model-based SCS algorithm relies only on statistical signal information without prior information. Results show that the SCS algorithm improves speech intelligibility in stationary noise and is comparable to the Wiener filtering algorithm. Both algorithms improve intelligibility for HI listeners but not for NH listeners. Improvement is less in fluctuating (babble) noise than in stationary noise. Both noise reduction algorithms perform better at higher input signal-to-noise ratios (SNR) where HI listeners can benefit but where NH listeners have already reached ceiling performance. The difference between NH and HI subjects in intelligibility gain depends fundamentally on the input SNR rather than the hearing loss level. We conclude that HI listeners need different signal processing algorithms from NH subjects and that the SCS algorithm offers a promising alternative to Wiener filtering. Performance of all noise reduction algorithms is likely to vary according to extent of hearing loss and algorithms that show little benefit for listeners with moderate hearing loss may be more beneficial for listeners with more severe hearing loss.

Top-down influences of the medial olivocochlear efferent system in speech perception in noise.

One of the putative functions of the medial olivocochlear (MOC) system is to enhance signal detection in noise. The objective of this study was to elucidate the role of the MOC system in speech perception in noise. In normal-hearing human listeners, we examined (1) the association between magnitude of MOC inhibition and speech-in-noise performance, and (2) the association between MOC inhibition and the amount of contralateral acoustic stimulation (CAS)-induced shift in speech-in-noise acuity. MOC reflex measurements in this study considered critical measurement issues overlooked in past work by: recording relatively low-level, linear click-evoked otoacoustic emissions (CEOAEs), adopting 6 dB signal-to-noise ratio (SNR) criteria, and computing normalized CEOAE differences. We found normalized index to be a stable measure of MOC inhibition (mean = 17.21%). MOC inhibition was not related to speech-in-noise performance measured without CAS. However, CAS in a speech-in-noise task caused an SNRSP enhancement (mean = 2.45 dB), and this improvement in speech-in-noise acuity was directly related to their MOC reflex assayed by CEOAEs. Individuals do not necessarily use the available MOC-unmasking characteristic while listening to speech in noise, or do not utilize unmasking to the extent that can be shown by artificial MOC activation. It may be the case that the MOC is not actually used under natural listening conditions and the higher auditory centers recruit MOC-mediated mechanisms only in specific listening conditions-those conditions remain to be investigated.

Repeatability of click-evoked otoacoustic emission-based medial olivocochlear efferent assay.

OBJECTIVES: Otoacoustic emissions-based efferent assays are evolving to become a part of auditory diagnostics. The wide range of clinical applications, such as assessment of auditory neuropathy, auditory processing disorders, learning disability, monitoring success in auditory intervention and others illustrate the significance of this measurement. Defining the procedure's test-retest repeatability is of critical importance, to allow for distinction between measurement deviations and true physiological or pathological changes. The purpose of this study was to assess the repeatability of a click-evoked otoacoustic emission-based (CEOAE) test of the medial olivocochlear (MOC) reflex in normal-hearing (NH) adults. DESIGN: Test-retest data were collected from 35 NH young adults in two distinct test sessions separated by 1 to 4 days. CEOAEs were recorded without and with contralateral acoustic stimulation (CAS; 35 dB SL). Three indices of the MOC reflex were computed: CAS-induced (a) absolute changes in CEOAE amplitude, (b) normalized changes in CEOAE amplitude, and (c) changes in CEOAE input-output functions. Repeatability of these indices was assessed by a three-layered approach, which consisted of Bland-Altman plots, coefficient of reliability (Cronbach's α), and analysis of variance. RESULTS: Analyses indicated good repeatability of three CEOAE-based MOC reflex indices. A two-way analysis of variance of the indices demonstrated no significant difference between test and retest. Normalized index showed similar repeatability as other indices. CEOAE signal to noise ratio did not seem to vary between test sessions. Notably, CAS caused a decrease in CEOAE input-output functions slope in a majority of participants (n = 29). CONCLUSIONS: The present study is the first to elucidate the intrasubject variability of absolute and normalized indices of the MOC inhibitory effect. Although the measurements were conducted under realistic conditions resembling the clinical setting, repeatability was generally good in NH adults. For MOC reflex test, the signal to noise ratio of 6 dB for recording CEOAEs seems to be a recommendable criterion when considering practicability and measurement quality in clinical conditions. The present findings exemplify the suitability of CEOAE-based MOC assay as a monitoring tool of medial efferent status over time. The data are intended to assist clinicians and scientists alike in the accurate interpretation of CAS-induced CEOAE changes in the test-retest situation.

Evaluation of the preliminary auditory profile test battery in an international multi-centre study.

OBJECTIVE: This paper describes the composition and international multi-centre evaluation of a battery of tests termed the preliminary auditory profile. It includes measures of loudness perception, listening effort, speech perception, spectral and temporal resolution, spatial hearing, self-reported disability and handicap, and cognition. Clinical applicability and comparability across different centres are investigated. DESIGN: Headphone tests were conducted in five centres divided over four countries. Effects of test-retest, ear, and centre were investigated. Results for normally-hearing (NH) and hearing-impaired (HI) listeners are presented. STUDY SAMPLE: Thirty NH listeners aged 19-39 years, and 72 HI listeners aged 22-91 years with a broad range of hearing losses were included. RESULTS: Test-retest reliability was generally good and there were very few right/left ear effects. Results of all tests were comparable across centres for NH listeners after baseline correction to account for necessary differences between test materials. For HI listeners, results were comparable across centres for the language-independent tests. CONCLUSIONS: The auditory profile forms a clinical test battery that is applicable in four different languages. Even after baseline correction, differences between test materials have to be taken into account when interpreting results of language-dependent tests in HI listeners.

A mechanism for simultaneous suppression of tone burst-evoked otoacoustic emissions.

Tone burst-evoked otoacoustic emission (TBOAE) components in response to a 1 kHz tone burst are suppressed by the simultaneous presence of tone bursts at higher frequencies. To date, the underlying cause of this "simultaneous suppression" of TBOAEs is unclear. This paper describes a potential mechanism based on local nonlinear interactions between basilar membrane (BM) travelling waves, and tests the extent to which it is able to account for this specific suppression phenomenon. A simple mathematical model based on local nonlinear interactions was developed, and its predictions for a range of tone burst pairs were compared to corresponding TBOAE suppression data recorded from fourteen normally hearing human ears at a level of 60 dB p.e. SPL. Model predictions and mean TBOAE suppression data showed close agreement for all pairs of tone bursts. These results suggest that simultaneous suppression of TBOAEs can be explained solely in terms of the local nonlinear interaction-based mechanism. However, the involvement of other mechanisms, involving components generated at places basal to their characteristic place along the BM, cannot be excluded.

Relationship between speech recognition in noise and sparseness.

OBJECTIVE: Established methods for predicting speech recognition in noise require knowledge of clean speech signals, placing limitations on their application. The study evaluates an alternative approach based on characteristics of noisy speech, specifically its sparseness as represented by the statistic kurtosis. DESIGN: Experiments 1 and 2 involved acoustic analysis of vowel-consonant-vowel (VCV) syllables in babble noise, comparing kurtosis, glimpsing areas, and extended speech intelligibility index (ESII) of noisy speech signals with one another and with pre-existing speech recognition scores. Experiment 3 manipulated kurtosis of VCV syllables and investigated effects on speech recognition scores in normal-hearing listeners. STUDY SAMPLE: Pre-existing speech recognition data for Experiments 1 and 2; seven normal-hearing participants for Experiment 3. RESULTS: Experiments 1 and 2 demonstrated that kurtosis calculated in the time-domain from noisy speech is highly correlated (r > 0.98) with established prediction models: glimpsing and ESII. All three measures predicted speech recognition scores well. The final experiment showed a clear monotonic relationship between speech recognition scores and kurtosis. CONCLUSIONS: Speech recognition performance in noise is closely related to the sparseness (kurtosis) of the noisy speech signal, at least for the types of speech and noise used here and for listeners with normal hearing.

Measuring real-ear signal-to-noise ratio: application to directional hearing aids.

Due to individual characteristics such as head size, earmould type, and earmould venting, the directional benefit that an individual will obtain from a hearing aid cannot be predicted from average data. It is therefore desirable to measure real ear directional benefit. This paper demonstrates a method to measure real ear hearing aid directivity based on a general approach to measure the broadband output signal-to-noise ratio of a hearing aid. Errors arising from non-linearity were tested in simulation and found to be low for typical hearing aid compression ratios. Next, the efficacy of the method to estimate directional benefit was demonstrated on KEMAR. Finally the variability of directional benefit was explored in real-ears. Significant differences in signal-to-noise ratio between directional and omnidirectional microphone settings were demonstrated at most azimuths. Articulation-Index-weighted directional benefit varied by more than 7 dB across ears at some azimuths. Such individual variation in directional benefit has implications when fitting hearing aids: it should not be assumed that all users will receive similar directional benefit from the same hearing aid.

Absence of short-term effects of UMTS exposure on the human auditory system.

The aim of this study, which was performed in the framework of the European project EMFnEAR, was to investigate the potential effects of Universal Mobile Telecommunications System (UMTS, also known as 3G) exposure at a high specific absorption rate (SAR) on the human auditory system. Participants were healthy young adults with no hearing or ear disorders. Auditory function was assessed immediately before and after exposure to radiofrequency (RF) radiation, and only the exposed ear was tested. Tests for the assessment of auditory function were hearing threshold level (HTL), distortion product otoacoustic emissions (DPOAE), contralateral suppression of transiently evoked otoacoustic emission (CAS effect on TEOAE), and auditory evoked potentials (AEP). The exposure consisted of speech at a typical conversational level delivered via an earphone to one ear, plus genuine or sham RF-radiation exposure obtained by an exposure system based on a patch antenna and controlled by software. Results from 73 participants did not show any consistent pattern of effects on the auditory system after a 20-min UMTS exposure at 1947 MHz at a maximum SAR over 1 g of 1.75 W/kg at a position equivalent to the cochlea. Analysis entailed a double-blind comparison of genuine and sham exposure. It is concluded that short-term UMTS exposure at this relatively high SAR does not cause measurable immediate effects on the human auditory system.

Effects of UMTS cellular phones on human hearing: results of the European project EMFnEAR.

Abstract The European project EMFnEAR was undertaken to assess potential changes in human auditory function after a short-term exposure to radiofrequency (RF) radiation produced by UMTS (Universal Mobile Telecommunication System) mobile phones. Participants were healthy young adults with no hearing or ear disorders. Auditory function was assessed immediately before and after exposure to radiofrequency radiation, and only the exposed ear was tested. Tests for the assessment of auditory function were hearing threshold level (HTL), distortion product otoacoustic emissions (DPOAE), contralateral suppression of transiently evoked otoacoustic emission (CAS effect on TEOAE), and auditory evoked potentials (AEP). The exposure consisted of speech at a typical conversational level delivered via an earphone to one ear, plus genuine or sham RF-radiation exposure produced by a commercial phone controlled by a personal computer. Results from 134 participants did not show any consistent pattern of effects on the auditory system after a 20-min UMTS exposure at the maximum output of the phone with 69 mW/kg SAR in the cochlea region in a double blind comparison of genuine and sham exposure. An isolated effect on the hearing threshold at high frequencies was identified, but this was statistically nonsignificant after correction for multiple comparisons. It is concluded that UMTS short-term exposure at the maximum output of consumer mobile phones does not cause measurable immediate effects on the human auditory system.

Measuring outcome from vestibular rehabilitation, part II: refinement and validation of a new self-report measure.

A prototype self-report measure of vestibular rehabilitation outcome is described in a previous paper. The objectives of the present work were to identify the most useful items and assess their psychometric properties. Stage 1: One hundred fifty-five participants completed a prototype 36-item Vestibular Rehabilitation Benefit Questionnaire (VRBQ). Statistical analysis demonstrated its subscale structure and identified redundant items. Stage 2: One hundred twenty-four participants completed a refined 22-item VRBQ and three established questionnaires (Dizziness Handicap Inventory, DHI; Vertigo Symptom Scale short form, VSS-sf; Medical Outcomes Study short form 36, SF-36) in a longitudinal study. Statistical analysis revealed four internally consistent subscales of the VRBQ: Dizziness, Anxiety, Motion-Provoked Dizziness, and Quality of Life. Correlations with the DHI, VSS-sf, and SF-36 support the validity of the VRBQ, and effect size estimates suggest that the VRBQ is more responsive than comparable questionnaires. Twenty participants completed the VRBQ twice in a 24-hour period, indicating excellent test-retest reliability. The VRBQ appears to be a concise and psychometrically robust questionnaire that addresses the main aspects of dizziness impact.

Measuring outcome from Vestibular Rehabilitation, Part I: Qualitative development of a new self-report measure.

Research suggests that Vestibular Rehabilitation (VR) is an effective treatment for dizziness, but there is currently no measure specifically designed to assess treatment outcome. A review of existing self-report measures of dizziness indicates that no measure has been designed for longitudinal application and all suffer from limitations which restrict their usefulness in measuring VR outcome. A need for a psychometrically robust patient-oriented measure of quality of life benefit from VR is identified. The aim of the present study was to explore dimensions relevant to VR with a view to developing a measure of outcome. Eighteen adults receiving VR participated in interviews about the quality of life impact of dizziness. Qualitative analysis revealed 64 themes describing self-perceived quality of life impact. Themes were developed into potential questionnaire items and 35 were selected to represent the quality of life impact of dizziness in a prototype questionnaire. A quarter of items in the prototype questionnaire refer to issues not addressed by existing measures; the remaining items draw together issues covered by the range of questionnaires currently in use.

Effects of GSM cellular phones on human hearing: the European project "GUARD".

The European multicenter project named GUARD involved nine centers and aimed to assess potential changes in auditory function as a consequence of exposure to low-intensity electromagnetic fields (EMFs) produced by GSM cellular phones. Participants were healthy young adults without any evidence of hearing or ear disorders. Auditory function was assessed immediately before and after exposure to EMFs, and only the exposed ear was tested. The procedure was conducted twice in a double blinded design, once with a genuine EMF exposure and once with a sham exposure (at least 24 h apart). Tests for assessment of auditory function were hearing threshold level (HTL), transient otoacoustic emissions (TEOAE), distortion product otoacoustic emissions (DPOAE), and auditory brainstem response (ABR). The exposure consisted of speech at a typical conversational level delivered via an earphone to one ear, plus genuine or sham EMF exposure. The EMF exposure used the output of a software-controlled consumer cellular phone at full power for 10 min. A system of phone positioning that allowed participants to freely move their heads without affecting exposure was used. Analysis of the data showed there were no effects of exposure to GSM mobile phone signals on the main measures of the status of the auditory system.

Transient evoked otoacoustic emission input-output function variation in a large sample of neonates and implications for hearing screening.

We performed a retrospective analysis of TEOAEs from 1415 neonatal ears to investigate whether the application of linear averaging techniques may provide greater screening specificity than conventional nonlinear averaging techniques. Pass criteria were based on correlations between replicate averages, and pass rates were compared between linear and nonlinear averaging techniques. The linear averaging technique gave a higher pass rate as hypothesized, so that 35% of ears that passed using the linear method failed using the nonlinear method. In addition, lack of saturation was more evident for the short-latency components of the TEOAE. These results, from a large sample of recordings obtained under field conditions, indicate that there is potential to improve specificity of neonatal TEOAE screening using linear averaging techniques. A combination of linear and nonlinear techniques for the long and short latency components of the TEOAE, respectively, may offer further advantages.

Learning to discriminate interaural time differences at low and high frequencies.

This study investigated learning, in normal-hearing adults, associated with training (i.e. repeated practice) on the discrimination of ongoing interaural time difference (ITD). Specifically, the study addressed an apparent disparity in the conclusions of previous studies, which reported training-induced learning at high frequencies but not at low frequencies. Twenty normal-hearing adults were trained with either low- or high-frequency stimuli, associated with comparable asymptotic thresholds, or served as untrained controls. Overall, trained listeners learnt more than controls and over multiple sessions. The magnitudes and time-courses of learning with the low- and high-frequency stimuli were similar. While this is inconsistent with the conclusion of a previous study with low-frequency ITD, this previous conclusion may not be justified by the results reported. Generalization of learning across frequency was found, although more detailed investigations of stimulus-specific learning are warranted. Overall, the results are consistent with the notion that ongoing ITD processing is functionally uniform across frequency. These results may have implications for clinical populations, such as users of bilateral cochlear implants.