Johannes Zaar

Purpose: This study presents an experimental method for measuring speech intelligibility using connected speech in a competing-talker paradigm. Method: Short target sentences from a well-established speech intelligibility test were embedded in excerpts of connected speech spoken by the same talker and presented to the listener in the presence of an interfering signal consisting of connected speech spoken by a different talker of the same sex. The method was evaluated in normal-hearing (NH) and hearing-impaired (HI) listeners. Speech-intelligibility scores for short sentences embedded in connected speech were compared with the intelligibility of the same short sentences not embedded in connected speech, using the same type of masker. Results: No average difference in speech intelligibility was found between the two presentation modes for NH or HI listeners. Large variability was observed across listeners, especially across HI listeners, suggesting individual benefits in one of the two presentation modes. Conclusion: The proposed method enables speech-intelligibility testing using connected speech and thus provides an experimental tool for measuring how speech perception is influenced by signal characteristics and signal-processing algorithms that require a relatively long time window to yield perceptual effects.

Preferences for advanced hearing aid (HA) noise management features, such as directionality and noise reduction (DIR + NR), differ significantly among users. Due to the lack of standardized clinical guidelines for fine-tuning these features, audiologists often rely on individual user preferences. However, this approach doesn’t always ensure optimal hearing outcomes. The goal of this study was to examine how users respond to these advanced features in everyday acoustic environments, with two main goals: to assess how sensitive users are to changes in DIR + NR settings compared to subtle gain adjustments, and to identify the factors influencing DIR + NR preferences in various situations. A total of 123 individuals using bilateral HAs participated in the study, conducted at two locations in Germany and Japan. Over six testing periods (half a year), participants were provided with two listening programs that differed either in the strength of their DIR + NR settings or in gain levels for high-frequency and soft sounds. Participants documented their preferences via self-initiated questionnaires, reporting experiences with the different settings in real-life listening scenarios. Most participants preferred modest adaptive DIR + NR settings and participants generally expressed higher preference strength for small gain changes than for variations in DIR + NR. Preferences could not be reliably predicted from audiologic or environmental factors, apart from a minor influence of subjective noisiness. These findings suggest that clinicians can guide the initial fitting of DIR + NR settings to optimize speech-in-noise performance, as adaptive DIR + NR configurations are broadly acceptable. User preferences remain important, particularly during gain fine-tuning, as small adjustments can be noticeable.

Objective: Previous studies have demonstrated that the speech reception threshold (SRT) can be estimated using scalp electroencephalography (EEG), referred to as SRTneuro. The present study assesses the feasibility of using ear-EEG, which allows for discreet measurement of neural activity from in and around the ear, to estimate the SRTneuro. Approach: Twenty young normal-hearing participants listened to audiobook excerpts at varying signal-to-noise ratios (SNRs) whilst wearing a 66-channel EEG cap and 12 ear-EEG electrodes. A linear decoder was trained on different electrode configurations to estimate the envelope of the audio excerpts from the EEG recordings. The reconstruction accuracy was determined by calculating the Pearson’s correlation between the actual and the estimated envelope. A sigmoid function was then fitted to the reconstruction-accuracy-vs-SNR data points, with the midpoint of the sigmoid serving as the SRTneuro estimate for each participant. Main results: Using only in-ear electrodes , the estimated SRTneuro was within 3 dB of the behaviorally measured SRT (SRTbeh) for 6 out of 20 participants (30%). With electrodes placed both in and around the ear, the SRTneuro was within 3 dB of the SRTbeh for 19 out of 20 participants (95%) and thus on par with the reference estimate obtained from full-scalp EEG. Using only electrodes in and around the ear from the right side of the head, the SRTneuro remained within 3 dB of the SRTbeh for 19 out of 20 participants.

Previous studies have demonstrated the feasibility of estimating the speech reception threshold (SRT) based on electroencephalography (EEG), termed SRT _neuro , in younger normal-hearing (YNH) participants. This method may support speech perception in hearing-aid users through continuous adaptation of noise-reduction algorithms. The prevalence of hearing impairment and thereby hearing-aid use increases with age. The SRT _neuro estimation is based on envelope reconstruction accuracy, which has also been shown to increase with age, possibly due to excitatory/inhibitory imbalance or recruitment of additional cortical regions. This could affect the estimated SRT _neuro . This study investigated the age-related changes in the temporal response function (TRF) and the feasibility of SRT _neuro estimation across age. Twenty YNH and 22 older normal-hearing (ONH) participants listened to audiobook excerpts at various signal-to-noise ratios (SNRs) while EEG was recorded using 66 scalp electrodes and 12 in-ear-EEG electrodes. A linear decoder reconstructed the speech envelope, and the Pearson's correlation was calculated between the reconstructed and speech-stimulus envelopes. A sigmoid function was fitted to the reconstruction-accuracy-versus-SNR data points, and the midpoint was used as the estimated SRT _neuro . The results show that the SRT _neuro can be estimated with similar precision in both age groups, whether using all scalp electrodes or only those in and around the ear. This consistency across age groups was observed despite physiological differences, with the ONH participants showing higher reconstruction accuracies and greater TRF amplitudes. Overall, these findings demonstrate the robustness of the SRT _neuro method in older individuals and highlight its potential for applications in age-related hearing loss and hearing-aid technology.

The combination of directional microphones (DIR) and spectral noise reduction (NR) is a common technique in hearing aid signal processing, for improving speech intelligibility in spatial acoustic scenarios. The benefit from DIR + NR varies considerably across individuals, which impedes prescribing the optimal strength of such processing during hearing aid fitting. The goal of this study was to investigate the correlation of four audiological factors with the benefit of speech reception thresholds (SRTs) from DIR + NR: the closedness of the acoustic coupling in the ear canal, audible contrast thresholds test (ACT™), the audiogram, and age. As part of a larger field study, 123 experienced hearing aid users in two centers in Germany and Japan were fitted bilaterally with the same hearing aids. SRTs were obtained with and without strong DIR + NR in a spatial speech-in-noise scenario before and after the field trials. Closedness of acoustic coupling was found to have the strongest correlation with SRT benefit from DIR + NR (most likely dominated by DIR rather than NR processing), followed by audible contrast thresholds (ACT) and the audiogram, both with the same significantly weaker correlation. Age was not correlated with the benefit from DIR + NR. The results suggest fitting hearing aid users irrespective of age with as-closed-as-possible acoustic coupling to maximize the benefit of DIR + NR. Furthermore, the closedness of acoustic coupling in combination with ACT or the audiogram may serve audiologists in predicting individual speech intelligibility benefits from strong DIR + NR for better guidance to set its strength during hearing aid fitting.

The perception of amplitude modulation (AM), characterized by a frequency-selective process in the modulation domain, is considered critical for speech intelligibility. Previous literature has provided evidence of an age-related decline in AM frequency selectivity. Additionally, a notable sharpening of AM tuning with hearing loss has been observed, which was proposed to be related to a perceptual advantage resulting from peripheral compression loss. This study explores whether such changes in AM tuning with age and hearing loss contribute to the speech intelligibility challenges older listeners often face in noisy environments. Young (n = 10, aged 22–28 years) and older (n = 9, aged 57–77 years) listeners with normal hearing as well as older listeners with hearing impairment (n = 9, aged 64–77 years) participated in the study. All had previously taken part in studies on AM tuning. Speech-reception thresholds (SRTs) were collected under conditions including stationary, fluctuating, and competing-speech maskers. The results revealed an age-related increase in SRTs, with an additional negative impact of hearing loss. Beyond age and audibility, a measure of AM tuning significantly contributed to explaining the variance in SRTs across listeners for specific maskers. These findings motivate further exploration of the relationship between AM frequency selectivity and speech intelligibility in noise.

Objective: Previous studies have demonstrated that the speech reception threshold (SRT) can be estimated using scalp electroencephalography (EEG), referred to as SRTneuro. The present study assesses the feasibility of using ear-EEG, which allows for discreet measurement of neural activity from in and around the ear, to estimate the SRTneuro. Such an estimate can be highly useful e.g. for continuously adjusting noise-reduction algorithms in hearing aids or for logging the SRT in the user's natural environment. Approach: Twenty young normal-hearing participants listened to audiobook excerpts at varying signal-to-noise ratios (SNRs) whilst wearing a 66-channel EEG cap and 12 ear-EEG electrodes. A linear decoder was trained on different electrode configurations to estimate the envelope of the audio excerpts from the EEG recordings. The reconstruction accuracy was determined by calculating the Pearson's correlation between the actual and the estimated envelope. A sigmoid function was then fitted to the reconstruction-accuracy-vs-SNR data points, with the midpoint of the sigmoid serving as the SRTneuro estimate for each participant. Main results: Using only in-ear electrodes, the estimated SRTneuro was within 3 dB of the behaviorally measured SRT (SRTbeh) for 6 out of 20 participants (30%). With electrodes placed both in and around the ear, the SRTneuro was within 3 dB of the SRTbeh for 19 out of 20 participants (95%) and thus on par with the reference estimate obtained from full-scalp EEG. Using only electrodes in and around the ear from the right side of the head, the SRTneuro remained within 3 dB of the SRTbeh for 19 out of 20 participants. Significance: These findings suggest that the SRTneuro can be reliably estimated using ear-EEG, especially when combining in-ear electrodes and around-the-ear electrodes.

The processing and perception of amplitude modulation (AM) in the auditory system reflect a frequency-selective process, often described as a modulation filterbank. Previous studies on perceptual AM masking reported similar results for older listeners with hearing impairment (HI listeners) and young listeners with normal hearing (NH listeners), suggesting no effects of age or hearing loss on AM frequency selectivity. However, recent evidence has shown that age, independently of hearing loss, adversely affects AM frequency selectivity. Hence, this study aimed to disentangle the effects of hearing loss and age. A simultaneous AM masking paradigm was employed, using a sinusoidal carrier at 2.8 kHz, narrowband noise modulation maskers, and target modulation frequencies of 4, 16, 64, and 128 Hz. The results obtained from young (n = 3, 24–30 years of age) and older (n = 10, 63–77 years of age) HI listeners were compared to previously obtained data from young and older NH listeners. Notably, the HI listeners generally exhibited lower (unmasked) AM detection thresholds and greater AM frequency selectivity than their NH counterparts in both age groups. Overall, the results suggest that age negatively affects AM frequency selectivity for both NH and HI listeners, whereas hearing loss improves AM detection and AM selectivity, likely due to the loss of peripheral compression.