Hearing-impaired Listeners Research Articles

Auditory enhancement under forward masking in normal-hearing and hearing-impaired listeners.

A target within a spectrally notched masker can be enhanced by a preceding copy of the masker. Enhancement can also increase the effectiveness of the target as a forward masker. Enhancement has been reported in hearing-impaired listeners under simultaneous but not forward masking. However, previous studies of enhancement under forward masking did not fully assess the potential effect of differences in sensation level or spectral resolution between the normal-hearing and hearing-impaired listeners. This study measured enhancement via forward masking in hearing-impaired and age-matched normal-hearing listeners with different spectral notches in the masker, to account for potential differences in frequency selectivity, and with levels equated by adding a background masking noise to equate both sensation level and sound pressure level or by reducing the sound pressure level of the stimuli to equate sensation level. Hearing-impaired listeners showed no significant enhancement, regardless of spectral notch width. Normal-hearing listeners showed enhancement at high levels, but showed less enhancement when sensation levels were reduced to match those of the hearing-impaired group, either by reducing sound levels or by adding a masking noise. The results confirm a lack of forward-masked enhancement in hearing-impaired listeners but suggest this may be partly due to reduced sensation level.

Quality Evaluation of Speech Enhancement Algorithms for Normal and Hearing Loss Listeners

The subjective quality test of the enhanced speech from different enhancement algorithms for listeners with normal hearing (NH) capability as well as listeners with hearing impairment (HI) is reported. The subjective quality evaluation of speech enhancement methods in the literature survey is mostly done targeting NH listeners and fewer attempts are observed to subjectively evaluate for HI listeners. The algorithms evaluated are from four different classes: spectral subtraction class(SS), statistical model based class (minimum mean square error), subspace class(PKLT) and auditory class (ideal binary mask using STFT, ideal binary mask using gammatone filterbank and ideal binary mask using gammachirp filterbank). The algorithms are evaluated using four types of real world noises recorded in Indian scenarios namely cafeteria, traffic, station and train at -5, 0, 5 and 10 dB SNRs. The evaluation is being done as per ITU-T P.835 standard in terms of three parameters- speech signal alone, background noise and overall quality. The noisy speech database developed in Indian regional language, Marathi, at four SNRs -5, 0, 5 and 10 dB is used for evaluation. Significant improvement is observed in ideal binary mask algorithm in terms of overall quality and signal distortion ratings for NH and HI listeners. The performance of minimum mean square error is also observed comparable with the ideal binary mask algorithm in some cases.

Weak neural signatures of spatial selective auditory attention in hearing-impaired listeners.

Spatial attention may be used to select target speech in one location while suppressing irrelevant speech in another. However, if perceptual resolution of spatial cues is weak, spatially focused attention may work poorly, leading to difficulty communicating in noisy settings. In electroencephalography (EEG), the distribution of alpha (8–14 Hz) power over parietal sensors reflects the spatial focus of attention [Banerjee, Snyder, Molholm, and Foxe (2011). J. Neurosci. 31, 9923–9932; Foxe and Snyder (2011). Front. Psychol. 2, 154.] If spatial attention is degraded, however, alpha may not be modulated across parietal sensors. A previously published behavioral and EEG study found that, compared to normal-hearing (NH) listeners, hearing-impaired (HI) listeners often had higher interaural time difference thresholds, worse performance when asked to report the content of an acoustic stream from a particular location, and weaker attentional modulation of neural responses evoked by sounds in a mixture [Dai, Best, and Shinn-Cunningham (2018). Proc. Natl. Acad. Sci. U. S. A. 115, E3286]. This study explored whether these same HI listeners also showed weaker alpha lateralization during the previously reported task. In NH listeners, hemispheric parietal alpha power was greater when the ipsilateral location was attended; this lateralization was stronger when competing melodies were separated by a larger spatial difference. In HI listeners, however, alpha was not lateralized across parietal sensors, consistent with a degraded ability to use spatial features to selectively attend.

A comparison between the Korean digits-in-noise test and Korean speech perception-in-noise test in normal-hearing and hearing-impaired listeners

The purpose of the present study was to determine whether the diagnostic efficacy of Korean version of the DIN (K-DIN) test is equivalent to that of the Korean speech perception-in-noise (K-SPIN) test, which is representative tool for speech-in-noise test. Twenty-seven subjects (15 normal-hearing listeners and 12 hearing-aid users) participated. 50 target digit triplets were presented at the most comfortable levels to each subject while presenting speech-shaped background noise at four levels of SNRs. K-SPIN test also was conducted at same procedure to the K-DIN test. The results of K-DIN and K-SPIN tests were compared by a Pearson-correlation test. The K-DIN test and the K-SPIN test were performed 74 times for each monaural and bilateral listening conditions. The results showed a statistically significant correlation between two tests in all listening conditions (left: r = 0.788, p < 0.001; right: r = 0.814, p < 0.001; bilateral: r = 0.727, p < 0.001). In the time consuming, the K-DIN test and the K-SPIN tests were about 5 minutes and 30 minutes, respectively. The current findings support that the K-DIN test is significantly correlated with the K-SPIN test in hearing-in-noise test performance, which implying that the K-DIN test can be used as a simpler and time-efficient hearing-in-noise test in Korea.

Preferences for digital noise reduction and microphone mode settings in hearing-impaired listeners with low and high tolerances for background noise

Objective: To examine whether people with low and high acceptable noise levels (ANLs) have different preferences for aggressiveness of noise reduction (NR) and microphone mode, and whether they get different noise tolerance benefit with these two features.Design: Participants completed laboratory tests of unaided ANL and aided modified ANLs (with speech fixed at two levels) and preferences (at two SNRs) while listening to four levels of NR, three microphone modes and four combinations of NR/directionality.Study sample: Twenty adults with hearing loss; 10 with low ANLs and 10 with high ANLs.Results: Seven individuals with low ANLs and 10 individuals with high ANLs preferred the maximum NR setting; the remaining three individuals with low ANLs had inconsistent preference for NR. Eight people in each ANL group preferred the maximum directional setting (broadband (BB) directionality), the remaining two people in each group had inconsistent preferences for microphone mode.Conclusions: Because most participants preferred the maximum NR and directionality settings, ANLs could not be used to differentially prescribe these hearing aid settings.

Personalization in Object-based Audio for Accessibility: A Review of Advancements for Hearing Impaired Listeners

Hearing loss is widespread and significantly impacts an individual’s ability to engage with broadcast media. Access can be improved through new object-based audio personalization methods. Utilizing the literature on hearing loss and intelligibility this paper develops three dimensions which are evidenced to improve intelligibility: spatial separation, speech to noise ratio and redundancy. These can be personalized, individually or concurrently, using object based audio. A systematic review of all work in object-based audio personalization is then undertaken. These dimensions are utilized to evaluate each project’s approach to personalisation, identifying successful approaches, commercial challenges and the next steps required to ensure continuing improvements to broadcast audio for hard of hearing individuals.

Contributions of lexical tone to Mandarin sentence recognition in hearing-impaired listeners under noisy conditions.

Mandarin sentence recognition using natural-tone and flat-tone sentences was tested in 22 subjects with sensorineural hearing loss (SNHL) and 25 listeners with normal hearing (NH) in quiet, speech-shaped noise, and two-talker-babble conditions. While little effects of flat tones on sentence recognition were seen in the NH listeners when the signal-to-noise ratio (SNR) was ≥0 dB, the SNHL listeners showed decreases in flat-tone-sentence recognition in quiet and at +5-dB SNR. Such declined performance was correlated with their degrees of hearing loss. Lexical tone contributes greatly to sentence recognition in hearing-impaired listeners in both quiet and in noise listening conditions.

The effect of F0 contour on the intelligibility of Mandarin Chinese for hearing-impaired listeners.

Dynamic F0 contour plays an important role in recognizing speech. The present work examined the effect of F0 contour on speech intelligibility for hearing-impaired listeners for Mandarin Chinese in quiet, in steady noise, and in two-talker competing speech. The intelligibility of two types of natural speech was measured: single-Tone speech with relatively flat F0 contours and multi-Tone speech with time-varying F0 contours. The speech rate and mean F0 of speech materials were carefully controlled to avoid effects other than F0 contour on the speech intelligibility. Results showed that intelligibility was significantly higher for speech with a flat F0 contour than that with a dynamic F0 contour at a low signal-to-masker ratio in both speech-spectrum noise and two-talker masker.

A Systematic Review for Auditory Training Effect Based on Korean Database

Auditory training should be necessary to improve listeners’ performance in auditory tasks in terms of active listening. Many clinicians, thus, believe that it is a potential intervention and an important component of the effective rehabilitation for hearing-impaired listeners. In the present paper, we reviewed articles of the auditory training based on the Korean database which accumulated over 20 years and scrutinized their training effects. Using key terms ‘auditory training,’ ‘aural rehabilitation’ from four Korean electronic databases, 258 articles were systematically found from 1998 to present. Among them, 21 articles met our inclusion criteria which followed a procedure of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses flow diagram. Then, their study quality was evaluated using ten pre-defined scientific and intervention-specific measures. Unfortunately, meta-analysis technically failed to confirm due to heterogeneity among the sample data. The average scores of qualitative evaluations for 21 articles were 9.62 (± 2.40), while showing a large difference in the quality. Only 7 out of 21 articles statistically supported that the hearing-impaired listeners had a significant improvement after conducting the auditory training. Regardless, most of the articles analyzed couldn’t include systematic standards for the auditory training effect to be concluded comprehensively. Our findings demonstrate that published evidence for efficacy of the auditory training in the hearing-impaired listeners isn’t robust and thus can’t be reliably used to guide intervention at this time. When highly-qualitied evidence provides its efficacy for people with hearing loss in many following studies, it will suggest appropriate research direction on the auditory training program for the clinical application in Korea. Key Words: Auditory training effect, Systematic review, Participants-Intervention-Control-Outcomes-Study design, Study quality 중심 단어: ì²­ëŠ¥í›ˆë ¨ 효과, ì²´ê³„ì  문헌 ê³ ì°°, 피코스(PICOS), 연구의 질

Age-related hearing loss increases full-brain connectivity while reversing directed signaling within the dorsal-ventral pathway for speech.

Speech comprehension difficulties are ubiquitous to aging and hearing loss, particularly in noisy environments. Older adults' poorer speech-in-noise (SIN) comprehension has been related to abnormal neural representations within various nodes (regions) of the speech network, but how senescent changes in hearing alter the transmission of brain signals remains unspecified. We measured electroencephalograms in older adults with and without mild hearing loss during a SIN identification task. Using functional connectivity and graph-theoretic analyses, we show that hearing-impaired (HI) listeners have more extended (less integrated) communication pathways and less efficient information exchange among widespread brain regions (larger network eccentricity) than their normal-hearing (NH) peers. Parameter optimized support vector machine classifiers applied to EEG connectivity data showed hearing status could be decoded (> 85% accuracy) solely using network-level descriptions of brain activity, but classification was particularly robust using left hemisphere connections. Notably, we found a reversal in directed neural signaling in left hemisphere dependent on hearing status among specific connections within the dorsal-ventral speech pathways. NH listeners showed an overall net "bottom-up" signaling directed from auditory cortex (A1) to inferior frontal gyrus (IFG; Broca's area), whereas the HI group showed the reverse signal (i.e., "top-down" Broca's → A1). A similar flow reversal was noted between left IFG and motor cortex. Our full-brain connectivity results demonstrate that even mild forms of hearing loss alter how the brain routes information within the auditory-linguistic-motor loop.

Subjective evaluation of single microphone noise reduction with different time constants

Objective: Previous studies on single microphone noise reduction (NR) in hearing aids (HAs) have shown that some NR algorithms provide beneficial effects in terms of listener preference. To improve HA user satisfaction, we are interested in characteristics that determine preferences for NR, and in the inter-individual variability. The aim of this study was to test if dynamic properties of NR influence listener preference.Design: The gain reduction at speech offsets of a NR algorithm was slowed down by applying temporal exponential smoothing. At speech onsets the gain recovery was left unchanged. Test signals consisted of speech in continuous and modulated speech-shaped background noise, processed with three time constants: 0, 100, and 200 ms.Study sample: 16 Normal hearing (NH) and 16 hearing impaired (HI) subjects participated in a paired-comparison listening test.Results: NH subjects as a group had a significant preference for NR with time constants of 100, or 200 ms (slower acting NR). HI listeners as a group preferred NR over no NR, but had no clear preference for fast or slow NR. Patterns of preference differed between individual listeners.Conclusions: NR dynamics had an impact on individual listener preference and should be considered when optimising HAs.

Acquisition of Subcortical Auditory Potentials With Around-the-Ear cEEGrid Technology in Normal and Hearing Impaired Listeners.

Even though the principles of recording brain electrical activity remain unchanged since their discovery, their acquisition has seen major improvements. The cEEGrid, a recently developed flex-printed multi-channel sensory array, can be placed around the ear and successfully record well-known cortical electrophysiological potentials such as late auditory evoked potentials (AEPs) or the P300. Due to its fast and easy application as well as its long-lasting signal recording window, the cEEGrid technology offers great potential as a flexible and ‘wearable’ solution for the acquisition of neural correlates of hearing. Early potentials of auditory processing such as the auditory brainstem response (ABR) are already used in clinical assessment of sensorineural hearing disorders and envelope following responses (EFR) have shown promising results in the diagnosis of suprathreshold hearing deficits. This study evaluates the suitability of the cEEGrid electrode configuration to capture these AEPs. cEEGrid potentials were recorded and compared to cap-EEG potentials for young normal-hearing listeners and older listeners with high-frequency sloping audiograms to assess whether the recordings are adequately sensitive for hearing diagnostics. ABRs were elicited by presenting clicks (70 and 100-dB peSPL) and stimulation for the EFRs consisted of 120 Hz amplitude-modulated white noise carriers presented at 70-dB SPL. Data from nine bipolar cEEGrid channels and one classical cap-EEG montage (earlobes to vertex) were analysed and outcome measures were compared. Results show that the cEEGrid is able to record ABRs and EFRs with comparable shape to those recorded using a conventional cap-EEG recording montage and the same amplifier. Signal strength is lower but can still produce responses above the individual neural electrophysiological noise floor. This study shows that the application of the cEEGrid can be extended to the acquisition of early auditory evoked potentials.

Sound Quality Effects of an Adaptive Nonlinear Frequency Compression Processor with Normal-Hearing and Hearing-Impaired Listeners.

Frequency lowering (FL) technology offers a means of improving audibility of high-frequency sounds. For some listeners, the benefit of such technology can be accompanied by a perceived degradation in sound quality, depending on the strength of the FL setting. The studies presented in this article investigate the effect of a new type of FL signal processing for hearing aids, adaptive nonlinear frequency compression (ANFC), on subjective speech quality. Listener ratings of sound quality were collected for speech stimuli processed with systematically varied fitting parameters. Study 1 included 40 normal-hearing (NH) adult and child listeners. Study 2 included 11 hearing-impaired (HI) adult and child listeners. HI listeners were fitted with laboratory-worn hearing aids for use during listening tasks. Speech quality ratings were assessed across test conditions consisting of various strengths of static nonlinear frequency compression (NFC) and ANFC speech. Test conditions included those that were fine-tuned on an individual basis per hearing aid fitting and conditions that were modified to intentionally alter the sound quality of the signal. Listeners rated speech quality using the MUlti Stimulus test with Hidden Reference and Anchor (MUSHRA) test paradigm. Ratings were analyzed for reliability and to compare results across conditions. Results show that interrater reliability is high for both studies, indicating that NH and HI listeners from both adult and child age groups can reliably complete the MUSHRA task. Results comparing sound quality ratings across experimental conditions suggest that both the NH and HI listener groups rate the stimuli intended to have poor sound quality (e.g., anchors and the strongest available parameter settings) as having below-average sound quality ratings. A different trend in the results is reported when considering the other experimental conditions across the listener groups in the studies. Speech quality ratings measured with NH listeners improve as the strength of ANFC decreases, with a range of bad to good ratings reported, on average. Speech quality ratings measured with HI listeners are similar and above-average for many of the experimental stimuli, including those with fine-tuned NFC and ANFC parameters. Overall, HI listeners provide similar sound quality ratings when comparing static and adaptive forms of frequency compression, especially when considering the individualized parameter settings. These findings suggest that a range in settings may result in above-average sound quality for adults and children with hearing impairment. Furthermore, the fitter should fine-tune FL parameters for each individual listener, regardless of type of FL technology.

The effect of perceived sound quality of speech in noisy speech perception by normal hearing and hearing impaired listeners.

Most noise reduction algorithms in current assistive hearing devices were designed to reduce noise to achieve the best signal to noise ratio (SNR) possible, presuming that the perceived quality of speech can be compromised as long as the level of noise is relatively much lower than the level of speech. In this study, we investigated and compared various factors other than SNR that may possibly affect the quality rating pattern of normal hearing (NH), cochlear implant (CI) and hearing aid (HA) subjects. In one of the comparisons, we found that the perceived sound quality ratings of noisy sentences at the same SNR were dependent on the level of speech present in the sentences rather than the noise. Noisy sentences with a higher level of speech were rated higher in perceived sound quality by NH subjects. However, in a similar comparison, CI subjects rated higher in perceived sound quality when the level of speech present was lower, but HA subjects do not show any clear trend with their perceived sound quality ratings on the same sentences.

Brainstem encoding of frequency-modulated sweeps is relevant to Mandarin concurrent-vowels identification for normal-hearing and hearing-impaired listeners

F0 contours convey the primary information of lexical Tones for Mandarin Chinese, and the processing of time-varying F0 contours is important for Mandarin concurrent-vowels identification (MCVI). In this work, we examined the relationship between frequency modulation (FM) detection of auditory system and MCVI in both normal-hearing (NH) and hearing-impaired (HI) listeners. Three experiments were conducted with the same subjects to measure their MCVI, FM detection limen (FMDL), and frequency following responses (FFRs) evoked by FM sweeps, respectively. To ensure that F0 contour was the primary cue utilized, mean F0s and durations were equalized among all test vowels in the MCVI experiment. To simulate the pattern of F0 contours of Mandarin vowels, linearly FM sweeps were used as stimuli in the FMDL and FFRs experiments. The results confirmed that the performance of HI listeners was significantly worse than that of NH listeners in all of the three measurements. Besides, FFRs evoked by FM sweeps had significantly lower tracking accuracy than those evoked by steady tones only for HI listeners. The correlation analysis further revealed that any two of the three measured indices were significantly correlated when the effects of age and absolute threshold were partialed out (|r| ≥ 0.502, p ≤ 0.017). These results suggested an association between the poor performance of HI listeners in the MCVI task and their degraded auditory function on FM detection, and such a behavioral degradation has emerged in the phase-locking activity at the brainstem level.

The optimal threshold for removing noise from speech is similar across normal and impaired hearing-a time-frequency masking study.

Hearing-impaired listeners' intolerance to background noise during speech perception is well known. The current study employed speech materials free of ceiling effects to reveal the optimal trade-off between rejecting noise and retaining speech during time-frequency masking. This relative criterion value (-7 dB) was found to hold across noise types that differ in acoustic spectro-temporal complexity. It was also found that listeners with hearing impairment and those with normal hearing performed optimally at this same value, suggesting no true noise intolerance once time-frequency units containing speech are extracted.

Integrating a remote microphone with hearing-aid processing

A remote microphone (RM) links a talker's microphone to a listener's hearing aids (HAs). The RM improves intelligibility in noise and reverberation, but the binaural cues necessary for externalization are lost. Augmenting the RM signal with synthesized binaural cues and early reflections enhances externalization, but interactions of the RM signal with the HA processing could reduce its effectiveness. These potential interactions were evaluated using RM plus HA processing in a realistic listening simulation. The HA input was the RM alone, the augmented RM signal, the acoustic inputs at the HA microphones, including reverberation measured using a dummy head, or a mixture of the augmented RM and acoustic input signals. The HA simulation implemented linear amplification or independent dynamic-range compression at the two ears and incorporated the acoustic effects of vented earmolds. Hearing-impaired listeners scored sentence stimuli for intelligibility and rated clarity, overall quality, externalization, and apparent source width. Using the RM improved intelligibility but reduced the spatial impression. Increasing the vent diameter reduced clarity and increased the spatial impression. Listener ratings reflect a trade-off between the attributes of clarity and overall quality and the attributes of externalization and source width that can be explained using the interaural cross correlation.

Investigating the Effect of Cochlear Synaptopathy on Envelope Following Responses Using a Model of the Auditory Nerve

The healthy auditory system enables communication in challenging situations with high levels of background noise. Yet, despite normal sensitivity to pure tones, many listeners complain about having difficulties in such situations. Recent animal studies demonstrated that noise overexposure that produces temporary threshold shifts can cause the loss of auditory nerve (AN) fiber synapses (i.e., cochlear synaptopathy, CS), which appears to predominantly affect medium- and low-spontaneous rate (SR) fibers. In the present study, envelope following response (EFR) magnitude-level functions were recorded in normal hearing (NH) threshold and mildly hearing-impaired (HI) listeners with thresholds elevated above 2 kHz. EFRs were elicited by sinusoidally amplitude modulated (SAM) tones presented in quiet with a carrier frequency of 2 kHz, modulated at 93 Hz, and modulation depths of 0.85 (deep) and 0.25 (shallow). While EFR magnitude-level functions for deeply modulated tones were similar for all listeners, EFR magnitudes for shallowly modulated tones were reduced at medium stimulation levels in some NH threshold listeners and saturated in all HI listeners for the whole level range. A phenomenological model of the AN was used to investigate the extent to which hair-cell dysfunction and/or CS could explain the trends observed in the EFR data. Hair-cell dysfunction alone, including postulated elevated hearing thresholds at extended high frequencies (EHF) beyond 8 kHz, could not account for the recorded EFR data. Postulated CS led to simulations generally consistent with the recorded data, but a loss of all types of AN fibers was required within the model framework. The effects of off-frequency contributions (i.e., away from the characteristic place of the stimulus) and the differential loss of different AN fiber types on EFR magnitude-level functions were analyzed. When using SAM tones in quiet as the stimulus, model simulations suggested that (1) EFRs are dominated by the activity of high-SR fibers at all stimulus intensities, and (2) EFRs at medium-to-high stimulus levels are dominated by off-frequency contributions.

Development and validation of the FrBio, an international French adaptation of the AzBio sentence lists

Objectives: The goal of this work was to develop and normalise an international French version of the AzBio sentence test.Design: A corpus of 1000 sentences was generated. These sentences were recorded with four talkers and processed through a four-channel cochlear implant simulation. The mean intelligibility for each sentence achieved by 16 normal-hearing listeners was computed. The consecutively ordered 165 sentences from each talker rendering an average score of 85% were sequentially assigned to 33 lists of 20 sentences. All lists were presented to 30 normal-hearing and 25 hearing-impaired listeners in order to verify their equivalency. Thirty normal-hearing adults were also recruited to assess the test’s psychometrics and define norms.Results: The results of the list equivalency validation study showed no significant differences in percent correct scores for 30 sentence lists. A binomial distribution model was used to estimate the 95% critical differences for each potential percentage score. Normalization data showed an average performance between 96% and 99% with a very low standard deviation.Conclusions: With a set of 30 lists, researchers and clinicians can use the FrBio to evaluate a large number of experimental conditions; changes in performance over time or across conditions can then be tracked.

Speaker-independent auditory attention decoding without access to clean speech sources.

Speech perception in crowded environments is challenging for hearing-impaired listeners. Assistive hearing devices cannot lower interfering speakers without knowing which speaker the listener is focusing on. One possible solution is auditory attention decoding in which the brainwaves of listeners are compared with sound sources to determine the attended source, which can then be amplified to facilitate hearing. In realistic situations, however, only mixed audio is available. We utilize a novel speech separation algorithm to automatically separate speakers in mixed audio, with no need for the speakers to have prior training. Our results show that auditory attention decoding with automatically separated speakers is as accurate and fast as using clean speech sounds. The proposed method significantly improves the subjective and objective quality of the attended speaker. Our study addresses a major obstacle in actualization of auditory attention decoding that can assist hearing-impaired listeners and reduce listening effort for normal-hearing subjects.