Hearing Aid Signal Processing Research Articles

Relationships Between Hearing Status, Cognitive Abilities, and Reliance on Visual and Contextual Cues

Objectives: Visual and contextual cues facilitate speech recognition in suboptimal listening conditions (e.g., background noise, hearing loss, hearing aid signal processing). Moreover, successful speech recognition in challenging listening conditions is linked to cognitive abilities such as working memory and fluid intelligence. However, it is unclear which cognitive abilities facilitate the use of visual and contextual cues in individuals with normal hearing and hearing aid users. The first aim was to investigate whether individuals with hearing aid users rely on visual and contextual cues to a higher degree than individuals with normal hearing in a speech-in-noise recognition task. The second aim was to investigate whether working memory and fluid intelligence are associated with the use of visual and contextual cues in these groups. Design: Groups of participants with normal hearing and hearing aid users with bilateral, symmetrical mild to severe sensorineural hearing loss were included (n = 169 per group). The Samuelsson and Rönnberg task was administered to measure speech recognition in speech-shaped noise. The task consists of an equal number of sentences administered in the auditory and audiovisual modalities, as well as without and with contextual cues (visually presented word preceding the sentence, e.g.,: “Restaurant”). The signal to noise ratio was individually set to 1 dB below the level obtained for 50% correct speech recognition in the hearing-in-noise test administered in the auditory modality. The Reading Span test was used to measure working memory capacity and the Raven test was used to measure fluid intelligence. The data were analyzed using linear mixed-effects modeling. Results: Both groups exhibited significantly higher speech recognition performance when visual and contextual cues were available. Although the hearing aid users performed significantly worse compared to those with normal hearing in the auditory modality, both groups reached similar performance levels in the audiovisual modality. In addition, a significant positive relationship was found between the Raven test score and speech recognition performance only for the hearing aid users in the audiovisual modality. There was no significant relationship between Reading Span test score and performance. Conclusions: Both participants with normal hearing and hearing aid users benefitted from contextual cues, regardless of cognitive abilities. The hearing aid users relied on visual cues to compensate for the perceptual difficulties, reaching a similar performance level as the participants with normal hearing when visual cues were available, despite worse performance in the auditory modality. It is important to note that the hearing aid users who had higher fluid intelligence were able to capitalize on visual cues more successfully than those with poorer fluid intelligence, resulting in better speech-in-noise recognition performance.

Factors in the Effective Use of Hearing Aids among Subjects with Age-Related Hearing Loss: A Systematic Review.

Objectives: Investigate factors contributing to the effective management of age-related hearing loss (ARHL) rehabilitation. Methods: A systematic review was conducted following PRISMA guidelines. The protocol was registered in PROSPERO (CRD42022374811). Articles were identified through systematic searches in the Scopus, PubMed, Web of Science, and Cochrane databases in May 2024. Only articles published between January 2005 and May 2024 were included. Studies were assessed for eligibility by two independent researchers and evaluated using the Crowe Critical Appraisal Tool v1.4 (CCAT). Results: Of the 278 articles identified, 54 were included. Three factors explain effective HA use. First, hearing aid signal processing, with directional microphones and noise reduction, improves user comfort and understanding regarding noise. Second, there is hearing aid fitting, with the NAL prescription rules as the gold standard, and bilateral, high-level HA performance for spatial localization and noise comprehension. Third, there is a patient-centered approach, using patient-related outcome measures (PROMs), questionnaires, counseling, and regular follow-up to involve patients in their therapeutic rehabilitation. Conclusions: Reaching a consensus on acoustic parameters is challenging due to variability in audiological results. Involving patients in their rehabilitation, addressing their needs and expectations, and offering individualized care are crucial.

Chapter 6: What Else Can I Do with This Equipment?

AbstractIf there is sound in the ear canal, you can measure it with a probe microphone in the ear. The following are a few examples of how you might use your real-ear probe microphone measures beyond verifying hearing aid fittings, signal processing, and function of features. A process to simulate hearing loss to educate and support family members and patients is described.

Spatial Hearing in Children With and Without Hearing Loss: Where and What the Speech Is Matters for Local Speech Intelligibility.

This study examined children's ability to perceive speech from multiple locations on the horizontal plane. Children with hearing loss were compared to normal-hearing peers while using amplification with and without advanced noise management. Participants were 21 children with normal hearing (9-15 years) and 12 children with moderate symmetrical hearing loss (11-15 years). Word recognition, nonword detection, and word recall were assessed. Stimuli were presented randomly from multiple discrete locations in multitalker noise. Children with hearing loss were fit with devices having separate omnidirectional and noise management programs. The noise management feature is designed to preserve audibility in noise by rapidly analyzing input from all locations and reducing the noise management when speech is detected from locations around the hearing aid user. Significant effects of left/right and front/back lateralization occurred as well as effects of hearing loss and hearing aid noise management. Children with normal hearing experienced a left-side advantage for word recognition and a right-side advantage for nonword detection. Children with hearing loss demonstrated poorer performance overall on all tasks with better word recognition from the back, and word recall from the right, in the omnidirectional condition. With noise management, performance improved from the front compared to the back for all three tasks and from the right for word recognition and word recall. The shape of children's local speech intelligibility on the horizontal plane is not omnidirectional. It is task dependent and shaped further by hearing loss and hearing aid signal processing. Front/back shifts in children with hearing loss are consistent with the behavior of hearing aid noise management, while the right-side biases observed in both groups are consistent with the effects of specialized speech processing in the left hemisphere of the brain.

The CogniAid trial. The impact of two hearing aid signal processing strategies on cognition

BackgroundUntreated hearing loss is a risk factor for age-related cognitive decline and hearing aids have been shown to slow cognitive decline in a population at risk for dementia. This double-blind multiple site randomized trial tested the hypothesis that for older adults with below-average cognition, a “Simple” hearing aid fitting strategy (based on linear amplification with output limiting compression signal processing) would improve hearing and cognition more than a “Standard” approach (adaptive compression-based processing).MethodsTwo hundred and fifty-six adults aged over 65 were screened for cognitive function using the NIH toolbox cognitive battery. Participants with below median age-adjusted fluid composite cognitive scores (<100) were eligible to participate (n = 104). Sixty-seven eligible participants proceeded to trial and were randomized 1:1 to a simple or standard hearing aid fitting. Participants in the Standard group were fitted with hearing aids matched to non-linear real-ear prescription targets (either NAL-NL1 or NL2), while participants in the Simple group were fitted with hearing aids matched to linear prescription targets (NAL-R). Participants and researchers not fitting the hearing aids were blinded to allocation.ResultsForty-eight participants completed assessments in 12 months. The Standard hearing aid group improved on measures of fluid cognition and hearing. There was a statistically significant difference in fluid cognition scores between groups. The fluid cognition composite score for participants receiving the Simple fitting changed by 3.5 points. Those with the Standard fitting improved by 10.3 points. Hearing outcomes for each group were improved by the same amount.ConclusionThis is the first study to show that hearing aid fitting strategies using markedly different signal processing result in significantly different cognitive outcomes after 12 months of use. The Standard fitting resulted in greater improvement in cognition than the Simpler fitting which was the opposite result to what had been hypothesized. The results reinforce findings indicating hearing aid benefits for the elderly and that they improve cognition.

Comparing outcomes with the cloud-based and portable versions of an open-source hearing aid

The open-source speech processing platform (OSP) is an open-source hearing aid (HA), developed to overcome proprietary restrictions of commercial HAs and pave the way for innovative HA technology through rigorous and reproducible research. This study evaluates portable and cloud-based platforms of the OSP that will enable a wide range of lab and field applications. The two platforms share common software applications for HA signal processing and objective outcome assessments (HO2). The cloud-based platform is hosted on a web server whereas the portable platform is accessed on a browser via a WiFi-enabled portable communication device. Listeners with mild to moderately severe hearing loss or normal hearing completed a word identification task (Modified Rhyme Test) in a 6-alternate forced choice paradigm using the HO2 app. Words were mixed with different levels of speech-shaped noise; presented via calibrated headphones or behind-the-ear receivers-in-the-canal for cloud-based and portable platforms, respectively. Signals were processed with individualized gain and compression ratios based on a clinically validated prescriptive formula. Results-to-date from four listeners show comparable range of word identification scores between platforms. The full dataset will also compare phoneme-level scores and response time measures generated from the HO2 app. Clinical research applications will be discussed. [Work supported by NIH-R44DC020406.]

Acoustic Feedback Noise Cancellation in Hearing Aids Using Adaptive Filter

To enhance speech intelligibility for people with hearing loss, hearing aids will amplify speech using gains derived from evidence-based prescriptive methods, in addition to other advanced signal processing mechanisms. While the evidence supports the use of hearing aid signal processing for speech intelligibility, these signal processing adjustments can also be detrimental to hearing aid sound quality, with poor hearing aid sound quality cited as a barrier to device adoption. In general, an uncontrolled environment may contain degradation components like background noise, speech from other speakers etc. along with required speech components. In this paper, we implement adaptive filtering design for acoustic feedback noise cancellation in hearing aids. The adaptive filter architecture has been designed using normalized least mean square algorithm. By using adaptive filters both filter input coefficients are changeable during run-time and reduce noise in hearing aids. The proposed design is implemented in matlab and the simulations shows that the proposed architecture produces good quality of speech, accuracy, maintain stable steady state. The proposed design is validated with parameters like Noise Distortion, Perceptual Evaluation of Speech Quality, Signal to Noise Ratio, and Speech Distortion. The feedback canceller is implemented in MATLAB 9.4 simulink version release name of R2018a is used for validation with Echo Return Loss Enhancement (ERLE). The ERLE of the NMLS is reduced when the filter order is increases.Around 10% of the power spectrum density (PSD) is less when compared with existing designs.

Exploring the need for language-specific hearing aid signal processing

Speech phonemes in higher frequencies have varying acoustic characteristics in different languages. For example, /s/ and /ʃ/, fricatives commonly used in English, have spectral peaks at higher frequencies than /ʂ/ and /x/, fricatives commonly used in Mandarin. Data on the relationship between the acoustic characteristics of a listener’s native language and their hearing aid signal prescription requirements could provide important clinical guidance. Non-linear frequency compression is a digital signal processing tool that compresses auditory information above a pre-determined cutoff frequency. In hearing aids, this compression is applied with the intention of making higher-frequency speech sounds more audible to listeners with high-frequency hearing loss. Here, we studied the effect of different frequency compression settings on fricative perception between Mandarin and English listeners. Normal-hearing participants between age 18 to 50 years were presented with fricative identification and fricative discrimination tasks under various frequency compression settings. Participants were grouped between those with exclusive English language background birth to 6 years to those with exclusive Mandarin language background during the same period. Results display different responses for presented phonemes and frequency compression settings, suggesting that language specificity could be considered for hearing aid signal prescription.

Feasibility of Tablet-Based Remote Data Collection Method for Measuring Hearing Aid Preference.

The purpose of this study was to determine the feasibility of a tablet-based remote data collection method for measuring preference for hearing aid signal processing features. Participants were nine individuals with bilateral mild to moderately severe sensorineural hearing loss. Stimuli were spatialized low-context sentences mixed with six-talker babble at two realistic signal-to-noise ratios (3 and 8 dB) and processed through a hearing aid simulator. Preference for full factorial combinations of three common hearing aid processing features (two levels each) was elicited using a paired-comparison task. Participants completed two versions of the experiment: The lab version was completed in a sound-treated booth using a custom MATLAB application on a desktop computer; the remote version was completed in a quiet room in the participant's home, using a custom MATLAB executable application on a tablet. Both versions used the same calibrated headphones. Strict infection control protocols were followed. McNemar's test showed no association between preference and data collection method for the majority of the conditions. Percentage agreement and kappa scores were moderate/fair across most conditions. The results indicated that the remote versus lab versions did not have a systematic effect on preference. However, the relatively low agreement and kappa scores suggested within-subject variability in the outcome (preference). The tablet-based version of remote experimentation was comparable to the lab-based version for eliciting preference for hearing aid signal processing features.

Preference for Combinations of Hearing Aid Signal Processing.

The purpose of this study was to determine how multiple types of signal processing activated together influence listeners' preferences. Participants were adults with mild to moderately severe sensorineural hearing loss. Stimuli were spatialized low-context sentences mixed with six-talker babble at 3 and 8 dB signal-to-noise ratios (SNRs). Stimuli were processed with three common hearing aid processing algorithms: wide dynamic range compression (WDRC), frequency compression (FC), and digital noise reduction (DNR). A full-factorial design with two levels for each algorithm (WDRC & DNR: mild versus strong; FC: ON versus OFF; clinically relevant ranges) was evaluated. Preference was measured using a paired-comparison task within a choice-based conjoint analysis framework. Remote data collection methods were used. A signal fidelity metric quantified the acoustic effects across conditions. At 3 dB SNR, participants preferred a combination of Slow WDRC and Mild DNR, although the mean preference was small (odds ratio close to 1). At both SNRs when Strong DNR was used, Fast WDRC was preferred over Slow WDRC. This may be related to signal fidelity, which was lower for the combination of Fast WDRC and Mild DNR and higher for the combination of Slow WDRC and either Mild DNR or Strong DNR. There was no effect of FC on preference or signal fidelity. WDRC and DNR together influenced both listeners' preferences and signal fidelity in the investigated listening conditions. On average, the small effect sizes suggest that minor fine-tuning adjustments to hearing aid algorithms may not result in a substantial change in clinical outcomes.

The Effect of Multichannel and Channel-Free Hearing Aids on Spectral-Temporal Resolution and Speech Understanding in Noise.

Identifying and understanding speech is difficult for individuals with sensorineural hearing loss, especially in noisy environments. Possible causes include less audibility of the signal, impaired temporal resolution, and low selectivity of frequency. The hearing aid is the most common option used to minimize the problems faced by individuals with sensorineural hearing loss. This article investigates the effects of multichannel and channel-free hearing aid signal processing techniques on spectral-temporal resolution and speech understanding in noise. An experimental study was used in which the determined tests were applied to the participants. Thirty-four individuals with bilateral symmetrical sensorineural hearing loss between the ages of 18 and 70 were included in our study. Spectral-temporally modulated ripple test, random gap detection test (RGDT), and Turkish matrix test were applied to the participants using multichannel and channel-free hearing aids. All the data obtained were compared statistically in terms of the performances of the hearing aids. There was no significant difference between multichannel and channel-free hearing aids for spectral resolution and speech understanding in noise tests (p > 0.05). While there was no significant difference between the two hearing aids for 500 and 4,000 Hz RGDT in temporal resolution measurement (p > 0.05), for 1,000 Hz (p = 0.045), 2,000 Hz (p = 0.046), and composite RGDT (p = 0.001), statistically significant better performances were obtained with the channel-free hearing aids. It is thought that faster processing of the incoming signal in the channel-free hearing aids improves the temporal resolution performance. It is predicted that our study findings might help to determine the signal processing technique that will maximize the communication skills of the patients in various conditions.

Susceptibility to signal distortion in older listeners with hearing loss

Older adults show significant individual variability in hearing aid benefit. Our recent work has identified factors contributing to this individual variability including age, degree of hearing loss, and working memory. Specifically, older adults with greater hearing loss and poorer working memory are disadvantaged (poorer speech recognition) by signal distortions arising from adverse listening conditions and aggressive hearing aid signal processing settings. In this presentation, we focus on the range of signal distortions (quantified by a cepstral correlation metric) due to hearing aid signal processing such as amplitude compression, frequency lowering, and digital noise reduction, combined with different amounts and types of background noise. Across studies, we characterized individual susceptibility to signal distortions with a comprehensive set of conditions ranging from laboratory simulations to realistic listening conditions. Earlier studies considered omnidirectional settings and co-located speech and noise conditions, whereas recent work has focused on clinically realistic conditions such as wearable hearing aids, microphone directionality, and spatially-separated speech and multi-talker babble. We will discuss the clinical implications of these findings, particularly the impact on customizing hearing aid fittings to maximize benefit for older individuals. [Work is funded by NIDCD.]

Comparison of laboratory and clinical computational metrics of acoustic measures of hearing-aid processed speech

Computational auditory metrics are used to characterize hearing-aid fittings in the laboratory and the clinic. The purpose of this study is to compare the speech intelligibility index (SII) as a clinical metric to the laboratory based SII and the hearing-aid speech perception index (HASPI) and hearing-aid speech quality index (HASQI) laboratory metrics. These comparisons are drawn from a comprehensive dataset of hearing-aid fittings for 120 hearing-aid recipients from a hospital-based audiology clinic. Hearing-aid devices are drawn from multiple manufacturers and multiple technology levels, and a total of nine hearing-aid devices are included. Acoustic recordings are made with the hearing-aids positioned on the KEMAR manikin and include multiple hearing-aid settings for each patient (manufacturer’s recommended fit, first fit by the audiologist, and the final fitting selected by the patient). Metric values are computed for each of the settings, and these metric comparisons highlight the advantages and challenges of each metric in characterizing hearing-aid signal processing. In addition, the results provide insight regarding hearing-aid fittings from the manufacturer’s fitting versus clinician/patient driven fittings. [Work supported by NIH R01 DC012289, NIH NRSA T32DC012280, and GN Hearing OCG6790B.]

Influence of Audibility and Distortion on Recognition of Reverberant Speech for Children and Adults with Hearing Aid Amplification.

Adults and children with sensorineural hearing loss (SNHL) have trouble understanding speech in rooms with reverberation when using hearing aid amplification. While the use of amplitude compression signal processing in hearing aids may contribute to this difficulty, there is conflicting evidence on the effects of amplitude compression settings on speech recognition. Less clear is the effect of a fast release time for adults and children with SNHL when using compression ratios derived from a prescriptive procedure. The aim of the study is to determine whether release time impacts speech recognition in reverberation for children and adults with SNHL and to determine if these effects of release time and reverberation can be predicted using indices of audibility or temporal and spectral distortion. This is a quasi-experimental cohort study. Participants used a hearing aid simulator set to the Desired Sensation Level algorithm m[i/o] for three different amplitude compression release times. Reverberation was simulated using three different reverberation times. Participants were 20 children and 16 adults with SNHL. Participants were seated in a sound-attenuating booth and then nonsense syllable recognition was measured. Predictions of speech recognition were made using indices of audibility, temporal distortion, and spectral distortion and the effects of release time and reverberation were analyzed using linear mixed models. While nonsense syllable recognition decreased in reverberation release time did not significantly affect nonsense syllable recognition. Participants with lower audibility were more susceptible to the negative effect of reverberation on nonsense syllable recognition. We have extended previous work on the effects of reverberation on aided speech recognition to children with SNHL. Variations in release time did not impact the understanding of speech. An index of audibility best predicted nonsense syllable recognition in reverberation and, clinically, these results suggest that patients with less audibility are more susceptible to nonsense syllable recognition in reverberation.

Hearing-Aid Directionality Improves Neural Speech Tracking in Older Hearing-Impaired Listeners.

In recent years, a growing body of literature has explored the effect of hearing impairment on the neural processing of speech, particularly related to the neural tracking of speech envelopes. However, only limited work has focused on the potential usage of the method for evaluating the effect of hearing aids designed to amplify and process the auditory input provided to hearing-impaired listeners. The current study investigates how directional sound processing in hearing-aids, denoted directionality, affects the neural tracking and encoding of speech in EEG recorded from 11 older hearing-impaired listeners. Behaviorally, the task performance improved when directionality was applied, while subjective ratings of listening effort were not affected. The reconstruction of the to-be-attended speech envelopes improved significantly when applying directionality, as well as when removing the background noise altogether. When inspecting the modelled response of the neural encoding of speech, a faster transition was observed between the early bottom-up response and the later top-down attentional-driven responses when directionality was applied. In summary, hearing-aid directionality affects both the neural speech tracking and neural encoding of to-be-attended speech. This result shows that hearing-aid signal processing impacts the neural processing of sounds and that neural speech tracking is indicative of the benefits associated with applying hearing-aid processing algorithms.

Binaural filterbank hearing aid simulation V5

In this presentation, we describe the Binaural Filterbank Hearing Aid Simulation (BFHAS) which is a MATLAB-based package that simulates commonly available hearing aid signal processing. This package allows the user to process custom audio signals (e.g., noisy speech; music) with a suite of hearing aid algorithms. Linear or non-linear fitting prescription fitting formulae can be used for gain compensation. The hearing-aid algorithms include spectral-subtraction noise suppression, wide dynamic-range compression (WDRC), and frequency compression based on sinusoidal modeling of the high frequencies of the signal. Users can vary signal processing settings like number of bands; add/modify spectral subtraction; gains, knee points, attack and release times for WDRC; compression ratios and cutoffs for frequency compression etc. The simulation provides the processed hearing aid output that includes the compensation and hearing aid quality and intelligibility metrics for the input stimuli. Future updates will include the room-simulations and built-in noise generators to simulate different levels of signal degradation. We also provide a user guide and examples illustrating the use of different package modules. This package will be made available for download. [Work supported by NIH R01 DC012289 and by a grant from GN ReSound to University of Colorado.]

Influence of hearing aid compression speed and channels on measures of psychophysical tuning curves

While much work has been completed on spectral resolution in listeners with SNHL, little attention has been paid to the impact of hearing-aid signal processing on access to spectral information. In this study, we hypothesized that increasing the hearing aid compression speed and number of compression channels would improve access to spectral information by providing better audibility across frequency. However, limited outer hair cell function or inhibition could curtail the benefit of improved audibility on spectral resolution. In this experiment, psychophysical tuning curves were measured for 25 participants with hearing loss. Both an excitation and phenomenological model of the auditory system were used to examine potential mechanisms that contributed to the observed results. The provision of amplification improved the measured sharpness of tuning for the low-frequency side. While decreasing the compression speed did not have a systematic effect on the measured psychophysical tuning curves, the low frequency side improved as the number of compression channels was increased. Threshold estimates from the excitation and phenomenological models were able to account for some of these observed trends in the psychophysical tuning curves, but the threshold estimates from the phenomenological model were more consistent with the measured thresholds.

Binaural Signal Processing in Hearing Aids.

For many years, clinicians have understood the advantages of listening with two ears compared with one. In addition to improved speech intelligibility in quiet, noisy, and reverberant environments, binaural versus monaural listening improves perceived sound quality and decreases the effort listeners must expend to understand a target voice of interest or to monitor a multitude of potential target voices. For most individuals with bilateral hearing impairment, the body of evidence collected across decades of research has also found that the provision of two compared with one hearing aid yields significant benefit for the user. This article briefly summarizes the major advantages of binaural compared with monaural hearing, followed by a detailed description of the related technological advances in modern hearing aids. Aspects related to the communication and exchange of data between the left and right hearing aids are discussed together with typical algorithmic approaches implemented in modern hearing aids.

Improving Speech Understanding and Monitoring Health with Hearing Aids Using Artificial Intelligence and Embedded Sensors.

This article details ways that machine learning and artificial intelligence technologies are being integrated in modern hearing aids to improve speech understanding in background noise and provide a gateway to overall health and wellness. Discussion focuses on how Starkey incorporates automatic and user-driven optimization of speech intelligibility with onboard hearing aid signal processing and machine learning algorithms, smartphone-based deep neural network processing, and wireless hearing aid accessories. The article will conclude with a review of health and wellness tracking capabilities that are enabled by embedded sensors and artificial intelligence.

Cognitive Hearing Science: Three Memory Systems, Two Approaches, and the Ease of Language Understanding Model.

Purpose The purpose of this study was to conceptualize the subtle balancing act between language input and prediction (cognitive priming of future input) to achieve understanding of communicated content. When understanding fails, reconstructive postdiction is initiated. Three memory systems play important roles: working memory (WM), episodic long-term memory (ELTM), and semantic long-term memory (SLTM). The axiom of the Ease of Language Understanding (ELU) model is that explicit WM resources are invoked by a mismatch between language input-in the form of rapid automatic multimodal binding of phonology-and multimodal phonological and lexical representations in SLTM. However, if there is a match between rapid automatic multimodal binding of phonology output and SLTM/ELTM representations, language processing continues rapidly and implicitly. Method and Results In our first ELU approach, we focused on experimental manipulations of signal processing in hearing aids and background noise to cause a mismatch with LTM representations; both resulted in increased dependence on WM. Our second-and main approach relevant for this review article-focuses on the relative effects of age-related hearing loss on the three memory systems. According to the ELU, WM is predicted to be frequently occupied with reconstruction of what was actually heard, resulting in a relative disuse of phonological/lexical representations in the ELTM and SLTM systems. The prediction and results do not depend on test modality per se but rather on the particular memory system. This will be further discussed. Conclusions Related to the literature on ELTM decline as precursors of dementia and the fact that the risk for Alzheimer's disease increases substantially over time due to hearing loss, there is a possibility that lowered ELTM due to hearing loss and disuse may be part of the causal chain linking hearing loss and dementia. Future ELU research will focus on this possibility.