Normal-hearing Listeners Research Articles

The Thomas More Lists: A Phonemically Balanced Dutch Monosyllabic Speech Audiometry Test.

Speech audiometry tests are a crucial tool in clinical care and research. In Dutch, the common practice is to use lists of monosyllabic words with a consonant-vowel-consonant (CVC) structure. However, there are relatively few lists, and they are short. Here, the goal is to develop an adult speech audiometry test for Dutch (Flemish) consisting of phonemically balanced lists of 25 CVC words. The ISO 8253-3:2012 norm was followed. From a pool of 689 well-known words, an initial set of 26 lists was recorded by a female speaker. The lists were optimized for perceptual balance by means of two studies with young normal hearing listeners (N1 = 24, N2 = 32). The final corpus contains 16 phonetically and perceptually balanced lists. In a last study (N3 = 25), the reference speech recognition curves in quiet and in speech-shaped noise were determined. Reference speech recognition threshold and slope values for phoneme scoring are respectively 20.3 dBSPL in quiet (slope 5.2%/dB) and −7.7 dBSNR (7.5%/dB) in noise, similar to existing materials. The lists may be a useful addition to the existing audiometric tests.

Parameter tuning of time-frequency masking algorithms for reverberant artifact removal within the cochlear implant stimulus

Cochlear implant recipients struggle to understand speech in reverberant environments. To restore speech perception, artifacts due to reverberant reflections can be removed from the cochlear implant stimulus by applying a matrix of gain values, a technique referred to as time-frequency masking. In this study, two common time-frequency masking strategies are implemented within cochlear implant processing, either introducing complete retention or deletion of stimulus components using a binary mask or continuous attenuation of stimulus components using a ratio mask. Parameters of each masking strategy control the level of attenuation imposed by the gain values. In this study, we perceptually tune the parameters of the masking strategy to determine a balance between speech retention and artifact removal. We measure the intelligibility of reverberant signals mitigated by each strategy with speech recognition testing in normal-hearing listeners using vocoding as a simulation of cochlear implant perception. For both masking strategies, we find parameterizations that maximize the intelligibility of the mitigated signals. At the best-performing parameterizations, binary-masked reverberant signals yield larger intelligibility improvements than ratio-masked signals. The results provide a perceptually optimized objective for the removal of reverberant artifacts from cochlear implant stimuli, facilitating improved speech recognition performance for cochlear implant recipients in reverberant environments.

Effect of wearing personal protective equipment on acoustic characteristics and speech perception during COVID-19

With the COVID-19 pandemic, the usage of personal protective equipment (PPE) has become ‘the new normal’. Both surgical masks and N95 masks with a face shield are widely used in healthcare settings to reduce virus transmission, but the use of these masks has a negative impact on speech perception. Therefore, transparent masks are recommended to solve this dilemma. However, there is a lack of quantitative studies regarding the effect of PPE on speech perception. This study aims to compare the effect on speech perception of different types of PPE (surgical masks, N95 masks with face shield and transparent masks) in healthcare settings, for listeners with normal hearing in the audiovisual or auditory-only modality. The Bamford–Kowal–Bench (BKB)-like Mandarin speech stimuli were digitally recorded by a G.R.A.S KEMAR manikin without and with masks (surgical masks, N95 masks with face shield and transparent masks). Two variants of video display were created (with or without visual cues) and tagged to the corresponding audio recordings. The speech recording and video were presented to listeners simultaneously in each of four conditions: unattenuated speech with visual cues (no mask); surgical mask attenuated speech without visual cues; N95 mask with face shield attenuated speech without visual cues; and transparent mask attenuated speech with visual cues. The signal-to-noise ratio for 50 % correct scores (SNR50) threshold in noise was measured for each condition in the presence of four-talker babble. Twenty-four subjects completed the experiment. Acoustic spectra obtained from all types of masks were primarily attenuated at high frequencies, beyond 3 kHz, but to different extents. The mean SNR50 thresholds of the two auditory-only conditions (surgical mask and N95 mask with face shield) were higher than those of the audiovisual conditions (no mask and transparent mask). SNR50 thresholds in the surgical-mask conditions were significantly lower than those for the N95 masks with face shield. No significant difference was observed between the two audiovisual conditions. The results confirm that wearing a surgical mask or an N95 mask with face shield has a negative impact on speech perception. However, wearing a transparent mask improved speech perception to a similar level as unmasked condition for young normal-hearing listeners.

Speech Tracking in Complex Auditory Scenes with Differentiated In- and Out-Field-Of-View Processing in Hearing Aids.

In naturalistic auditory scenes, relevant information is rarely concentrated at a single location, but rather unpredictably scattered in- and out-field-of-view (in-/out-FOV). Although the parsing of a complex auditory scene is a fairly simple job for a healthy human auditory system, the uncertainty represents a major issue in the development of effective hearing aid (HA) processing strategies. Whereas traditional omnidirectional microphones (OM) amplify the complete auditory scene without enhancing signal-to-noise-ratio (SNR) between in- and out-FOV streams, directional microphones (DM) may greatly increase SNR at the cost of preventing HA users to perceive out-FOV information. The present study compares the conventional OM and DM HA settings to a split processing (SP) scheme differentiating between in- and out-FOV processing. We recorded electroencephalographic data of ten young, normal-hearing listeners who solved a cocktail-party-scenario-paradigm with continuous auditory streams and analyzed neural tracking of speech with a stimulus reconstruction (SR) approach. While results for all settings exhibited significantly higher SR accuracies for attended in-FOV than unattended out-FOV streams, there were distinct differences between settings. In-FOV SR performance was dominated by DM and SP and out-FOV SR accuracies were significantly higher for SP compared to OM and DM. Our results demonstrate the potential of a SP approach to combine the advantages of traditional OM and DM settings without introduction of significant compromises.

Cortical Entrainment to Speech Produced by Cochlear Implant Users and Normal-Hearing Talkers.

The perceived sound quality of speech produced by hard-of-hearing individuals greatly depends on the degree and configuration of their hearing loss. A cochlear implant (CI) may provide some compensation and auditory feedback to monitor/control speech production. However, to date, the speech produced by CI users is still different in quality from that produced by normal-hearing (NH) talkers. In this study, we attempted to address this difference by examining the cortical activity of NH listeners when listening to continuous speech produced by 8 CI talkers and 8 NH talkers. We utilized a discriminative model to decode and reconstruct the speech envelope from the single-trial electroencephalogram (EEG) recorded from scalp electrode in NH listeners when listening to continuous speech. The correlation coefficient between the reconstructed envelope and original speech envelope was computed as a metric to quantify the difference in response to the speech produced by CI and NH talkers. The same listeners were asked to rate the perceived sound quality of the speech as a behavioral sound quality assessment. Both behavioral perceived sound quality ratings and the cortical entrainment to speech envelope were higher for the speech set produced by NH talkers than for the speech set produced by CI talkers.

Cross-Frequency Coupling in Cortical Processing of Speech.

This study examines power-power cross-frequency coupling (CFC) between different frequency bands of cortical activity in normal-hearing (NH) listeners and its association to the processing temporal envelope (ENV) and temporal fine structure (TFS) of speech. CFC between alpha and theta bands and between gamma and theta bands was investigated when only ENV or TFS or the original speech itself were processed. Comparing the cortical activity in response to ENV and original speech, there was an increase in alpha-theta CFC and in gamma-theta CFC when listening to ENV alone. However, when comparing the response when to listening TFS alone, there was a reduction in gamma-theta CFC compared to the original speech and the alpha-theta CFC was comparable to the equivalent observed with original speech. The increase in CFC may suggest that there is more synchrony across different bands of cortical activity in processing ENV than TFS. These measures can serve as indicators when either ENV or TFS is perceived.

Cochlear Implant Facilitates the Use of Talker Sex and Spatial Cues to Segregate Competing Speech in Unilaterally Deaf Listeners.

Talker sex and spatial cues can facilitate segregation of competing speech. However, the spectrotemporal degradation associated with cochlear implants (CIs) can limit the benefit of talker sex and spatial cues. Acoustic hearing in the nonimplanted ear can improve access to talker sex cues in CI users. However, it's unclear whether the CI can improve segregation of competing speech when maskers are symmetrically placed around the target (i.e., when spatial cues are available), compared with acoustic hearing alone. The aim of this study was to investigate whether a CI can improve segregation of competing speech by individuals with unilateral hearing loss. Speech recognition thresholds (SRTs) for competing speech were measured in 16 normal-hearing (NH) adults and 16 unilaterally deaf CI users. All participants were native speakers of Mandarin Chinese. CI users were divided into two groups according to thresholds in the nonimplanted ear: (1) single-sided deaf (SSD); pure-tone thresholds <25 dB HL at all audiometric frequencies, and (2) Asymmetric hearing loss (AHL; one or more thresholds > 25 dB HL). SRTs were measured for target sentences produced by a male talker in the presence of two masker talkers (different male or female talkers). The target sentence was always presented via loudspeaker directly in front of the listener (0°), and the maskers were either colocated with the target (0°) or spatially separated from the target at ±90°. Three segregation cue conditions were tested to measure masking release (MR) relative to the baseline condition: (1) Talker sex, (2) Spatial, and (3) Talker sex + Spatial. For CI users, SRTs were measured with the CI on or off. Binaural MR was significantly better for the NH group than for the AHL or SSD groups ( P < 0.001 in all cases). For the NH group, mean MR was largest with the Talker sex + spatial cues (18.8 dB) and smallest for the Talker sex cues (10.7 dB). In contrast, mean MR for the SSD group was largest with the Talker sex + spatial cues (14.7 dB), and smallest with the Spatial cues (4.8 dB). For the AHL group, mean MR was largest with the Talker sex + spatial cues (7.8 dB) and smallest with the Talker sex (4.8 dB) and the Spatial cues (4.8 dB). MR was significantly better with the CI on than off for both the AHL ( P = 0.014) and SSD groups ( P < 0.001). Across all unilaterally deaf CI users, monaural (acoustic ear alone) and binaural MR were significantly correlated with unaided pure-tone average thresholds in the nonimplanted ear for the Talker sex and Talker sex + spatial conditions ( P < 0.001 in both cases) but not for the Spatial condition. Although the CI benefitted unilaterally deaf listeners' segregation of competing speech, MR was much poorer than that observed in NH listeners. Different from previous findings with steady noise maskers, the CI benefit for segregation of competing speech from a different talker sex was greater in the SSD group than in the AHL group.

The P300 Auditory Event-Related Potential May Predict Segregation of Competing Speech by Bimodal Cochlear Implant Listeners.

Compared to normal-hearing (NH) listeners, cochlear implant (CI) listeners have greater difficulty segregating competing speech. Neurophysiological studies have largely investigated the neural foundations for CI listeners' speech recognition in quiet, mainly using the P300 component of event-related potentials (ERPs). P300 is closely related to cognitive processes involving auditory discrimination, selective attention, and working memory. Different from speech perception in quiet, little is known about the neurophysiological foundations for segregation of competing speech by CI listeners. In this study, ERPs were measured for a 1 vs. 2 kHz contrast in 11 Mandarin-speaking bimodal CI listeners and 11 NH listeners. Speech reception thresholds (SRTs) for a male target talker were measured in steady noise or with a male or female masker. Results showed that P300 amplitudes were significantly larger and latencies were significantly shorter for the NH than for the CI group. Similarly, SRTs were significantly better for the NH than for the CI group. Across all participants, P300 amplitude was significantly correlated with SRTs in steady noise (r = −0.65, p = 0.001) and with the competing male (r = −0.62, p = 0.002) and female maskers (r = −0.60, p = 0.003). Within the CI group, there was a significant correlation between P300 amplitude and SRTs with the male masker (r = −0.78, p = 0.005), which produced the most informational masking. The results suggest that P300 amplitude may be a clinically useful neural correlate of central auditory processing capabilities (e.g., susceptibility to informational masking) in bimodal CI patients.

Predicting speech intelligibility in hearing-impaired listeners using a physiologically inspired auditory model

This study presents a major update and full evaluation of a speech intelligibility (SI) prediction model previously introduced by Scheidiger, Carney, Dau, and Zaar [(2018), Acta Acust. United Ac. 104, 914-917]. The model predicts SI in speech-in-noise conditions via comparison of the noisy speech and the noise-alone reference. The two signals are processed through a physiologically inspired nonlinear model of the auditory periphery, for a range of characteristic frequencies (CFs), followed by a modulation analysis in the range of the fundamental frequency of speech. The decision metric of the model is the mean of a series of short-term, across-CF correlations between population responses to noisy speech and noise alone, with a sensitivity-limitation process imposed. The decision metric is assumed to be inversely related to SI and is converted to a percent-correct score using a single data-based fitting function. The model performance was evaluated in conditions of stationary, fluctuating, and speech-like interferers using sentence-based speech-reception thresholds (SRTs) previously obtained in 5 normal-hearing (NH) and 13 hearing-impaired (HI) listeners. For the NH listener group, the model accurately predicted SRTs across the different acoustic conditions (apart from a slight overestimation of the masking release observed for fluctuating maskers), as well as plausible effects in response to changes in presentation level. For HI listeners, the model was adjusted to account for the individual audiograms using standard assumptions concerning the amount of HI attributed to inner-hair-cell (IHC) and outer-hair-cell (OHC) impairment. HI model results accounted remarkably well for elevated individual SRTs and reduced masking release. Furthermore, plausible predictions of worsened SI were obtained when the relative contribution of IHC impairment to HI was increased. Overall, the present model provides a useful tool to accurately predict speech-in-noise outcomes in NH and HI listeners, and may yield important insights into auditory processes that are crucial for speech understanding.

AzBio Sentence test in Hebrew (HeBio): development, preliminary validation, and the effect of noise

Objective The AzBio sentence test is widely used to assess speech perception pre- and post-cochlear implantation. This study created and validated a Hebrew version of AzBio (HeBio) and tested its intelligibility amidst background noise. Methods In Experiment 1, 1,000 recorded Hebrew sentences were presented via five-channel vocoder to 10 normal hearing (NH) listeners for intelligibility testing. In Experiment 2, HeBio lists were presented to 25 post-lingual cochlear implant (CI) users amidst four-talker babble noise (4TBN) or in quiet, along with one-syllable word test. In Experiment 3, 20 NH listeners were presented with eight HeBio lists in two noise conditions [4TBN, speech shaped noise (SSN)] and four SNRs (+3, 0 dB, −3 dB, −6 dB). Results HeBio lists (33) produced 82% average understanding, no inter-list intelligibility differences among NH, and equal intelligibility for CI users. One-syllable words predicted 67% of the variance in HeBio among CI users. Higher intelligibility was found for SSN than for 4TBN, and the mean speech receptive threshold (SRT) was more negative for SSN than for 4TBN. Conclusions HeBio results were similar to AzBio. Results obtained with two noise types were as expected. HeBio is recommended for evaluation of different populations in quiet and noise.

Side-of-Implantation Effect on Functional Asymmetry in the Auditory Cortex of Single-Sided Deaf Cochlear-Implant Users

Cochlear implants (CIs) allow to restore the hearing function in profoundly deaf individuals. Due to the degradation of the stimulus by CI signal processing, implanted individuals with single-sided deafness (SSD) have the specific challenge that the input highly differs between their ears. The present study compared normal-hearing (NH) listeners (N = 10) and left- and right-ear implanted SSD CI users (N = 10 left, N = 9 right), to evaluate cortical speech processing between CI- and NH-ears and to explore for side-of-implantation effects. The participants performed a two-deviant oddball task, separately with the left and the right ear. Auditory event-related potentials (ERPs) in response to syllables were compared between proficient and non-proficient CI users, as well as between CI and NH ears. The effect of the side of implantation was analysed on the sensor and the source level. CI proficiency could be distinguished based on the ERP amplitudes of the N1 and the P3b. Moreover, syllable processing via the CI ear, when compared to the NH ear, resulted in attenuated and delayed ERPs. In addition, the left-ear implanted SSD CI users revealed an enhanced functional asymmetry in the auditory cortex than right-ear implanted SSD CI users, regardless of whether the syllables were perceived via the CI or the NH ear. Our findings reveal that speech-discrimination proficiency in SSD CI users can be assessed by N1 and P3b ERPs. The results contribute to a better understanding of the rehabilitation success in SSD CI users by showing that cortical speech processing in SSD CI users is affected by CI-related stimulus degradation and experience-related functional changes in the auditory cortex.

Differing Bilateral Benefits for Spatial Release From Masking and Sound Localization Accuracy Using Bone Conduction Devices.

Objectives:Normal binaural hearing facilitates spatial hearing and therefore many everyday listening tasks, such as understanding speech against a backdrop of competing sounds originating from various locations, and localization of sounds. For stimulation with bone conduction hearing devices (BCD), used to alleviate conductive hearing losses, limited transcranial attenuation results in cross-stimulation so that both cochleae are stimulated from the position of the bone conduction transducer. As such, interaural time and level differences, hallmarks of binaural hearing, are unpredictable at the level of the inner ears. The aim of this study was to compare spatial hearing by unilateral and bilateral BCD stimulation in normal-hearing listeners with simulated bilateral conductive hearing loss.Design:Bilateral conductive hearing loss was reversibly induced in 25 subjects (mean age = 28.5 years) with air conduction and bone conduction (BC) pure-tone averages across 0.5, 1, 2, and 4 kHz (PTA4) <5 dB HL. The mean (SD) PTA4 for the simulated conductive hearing loss was 48.2 dB (3.8 dB). Subjects participated in a speech-in-speech task and a horizontal sound localization task in a within-subject repeated measures design (unilateral and bilateral bone conduction stimulation) using Baha 5 clinical sound processors on a softband. For the speech-in-speech task, the main outcome measure was the threshold for 40% correct speech recognition when masking speech and target speech were both colocated (0°) and spatially and symmetrically separated (target 0°, maskers ±30° and ±150°). Spatial release from masking was quantified as the difference between colocated and separated masking and target speech thresholds. For the localization task, the main outcome measure was the overall variance in localization accuracy quantified as an error index (0.0 = perfect performance; 1.0 = random performance). Four stimuli providing various spatial cues were used in the sound localization task.Results:The bilateral BCD benefit for recognition thresholds of speech in competing speech was statistically significant but small regardless if the masking speech signals were colocated with, or spatially and symmetrically separated from, the target speech. Spatial release from masking was identical for unilateral and bilateral conditions, and significantly different from zero. A distinct bilateral BCD sound localization benefit existed but varied in magnitude across stimuli. The smallest benefit occurred for a low-frequency stimulus (octave-filtered noise, CF = 0.5 kHz), and the largest benefit occurred for unmodulated broadband and narrowband (octave-filtered noise, CF = 4.0 kHz) stimuli. Sound localization by unilateral BCD was poor across stimuli.Conclusions:Results suggest that the well-known transcranial transmission of BC sound affects bilateral BCD benefits for spatial processing of sound in differing ways. Results further suggest that patients with bilateral conductive hearing loss and BC thresholds within the normal range may benefit from a bilateral fitting of BCD, particularly for horizontal localization of sounds.

Temporal integration contributes to the masking release by amplitude modulation

Modulated maskers produce less amount of masking than unmodulated maskers, an effect referred to as masking release (MR). Both listening in the temporal dips and fast cochlear compression have been suggested as underlying mechanisms. We addressed the role of dip listening by measuring temporal integration in simultaneous masking using Schroeder-phase harmonic complexes (SPHC) with various phase curvatures. In an experiment with six normal-hearing listeners, SPHC masker and pure-tone target stimuli were covaried in duration at a high masker level. The MR increased with stimulus duration, suggesting integration of target information across multiple masker dips. The duration dependence of the MR was predicted by a physiology-inspired model based on the temporal envelope modulation strength in the auditory periphery. The modeling analysis suggested that listeners detect the presence of the target by a reduction in fluctuation strength that results primarily from a decline of F0-based response peaks, an effect known as synchrony capture. The detailed pattern of masked thresholds across various masker phase curvatures was not predicted by the model, suggesting that its phase response does not well fit the human phase response. Overall, temporal integration across neural envelope features associated with the masker dips seems to contribute to the MR with SPHCs.

Music Appreciation of Cochlear Implant Users versus Normal Hearing Individuals.

Introduction:Cochlear implants (CI) provide speech perception for patients with sensorineural hearing impairment; nonetheless, listening to music is a daunting challenge for them. The present study aimed to compare Iranian CI users and normal hearing (NH) controls in terms of musical habits and appreciation and investigate the possible effect of background variables.Materials and Methods:A total of 37 CI users who underwent surgery at least 18 months before the study and 59 NH listeners were enrolled in this study. The participants were assigned to two age groups: group A (patients ≥15 years old) and group B (patients <15 years old). They were asked to complete the questionnaires to assess their music engagement.Results:In group A, the mean score of music importance was significantly higher in CI users (8.7±2.1), as compared to that in NH subjects (5.8±2.3) (P=0.005). Participation in professional musical training and singing with music was not significantly different between the groups. In group B, the mean score of desire for music was not significantly different between CI users (8.2±1.8) and NH subjects (7.7±2.0). They participated in professional musical training and had a reaction to music almost equally. Singing with music was significantly less common in the CI group (CI 16[61.5%], NH (40[85.1%]) (P=0.023). Selected background variables had no significant effect on the music tendency and habits of CI users.Conclusions:Iranian CI users tended to have a high level of music appreciation in both adult and children groups. Moreover, CI users and NH controls did not significantly differ in the importance of music, devoted time, participation in musical activities, and musical habits.

Effects of degraded speech processing and binaural unmasking investigated using functional near-infrared spectroscopy (fNIRS).

The present study aimed to investigate the effects of degraded speech perception and binaural unmasking using functional near-infrared spectroscopy (fNIRS). Normal hearing listeners were tested when attending to unprocessed or vocoded speech, presented to the left ear at two speech-to-noise ratios (SNRs). Additionally, by comparing monaural versus diotic masker noise, we measured binaural unmasking. Our primary research question was whether the prefrontal cortex and temporal cortex responded differently to varying listening configurations. Our a priori regions of interest (ROIs) were located at the left dorsolateral prefrontal cortex (DLPFC) and auditory cortex (AC). The left DLPFC has been reported to be involved in attentional processes when listening to degraded speech and in spatial hearing processing, while the AC has been reported to be sensitive to speech intelligibility. Comparisons of cortical activity between these two ROIs revealed significantly different fNIRS response patterns. Further, we showed a significant and positive correlation between self-reported task difficulty levels and fNIRS responses in the DLPFC, with a negative but non-significant correlation for the left AC, suggesting that the two ROIs played different roles in effortful speech perception. Our secondary question was whether activity within three sub-regions of the lateral PFC (LPFC) including the DLPFC was differentially affected by varying speech-noise configurations. We found significant effects of spectral degradation and SNR, and significant differences in fNIRS response amplitudes between the three regions, but no significant interaction between ROI and speech type, or between ROI and SNR. When attending to speech with monaural and diotic noises, participants reported the latter conditions being easier; however, no significant main effect of masker condition on cortical activity was observed. For cortical responses in the LPFC, a significant interaction between SNR and masker condition was observed. These findings suggest that binaural unmasking affects cortical activity through improving speech reception threshold in noise, rather than by reducing effort exerted.

Sound Source Localization by Cochlear Implant Recipients with Normal Hearing in the Contralateral Ear: Effects of Spectral Content and Duration of Listening Experience

Introduction: Cochlear implant (CI) recipients with normal hearing (NH) in the contralateral ear experience a significant improvement in sound source localization when listening with the CI in combination with their NH-ear (CI + NH) as compared to with the NH-ear alone. The improvement in localization is primarily due to sensitivity to interaural level differences (ILDs). Sensitivity to interaural timing differences (ITDs) may be limited by auditory aging, frequency-to-place mismatches, the signal coding strategy, and duration of CI use. The present report assessed the sensitivity of ILD and ITD cues in CI + NH listeners who were recipients of long electrode arrays that provide minimal frequency-to-place mismatches and were mapped with a coding strategy that presents fine structure cues on apical channels. Methods: Sensitivity to ILDs and ITDs for localization was assessed using broadband noise (BBN), as well as high-pass (HP) and low-pass (LP) filtered noise for adult CI + NH listeners. Stimuli were 200-ms noise bursts presented from 11 speakers spaced evenly over an 180° arc. Performance was quantified in root-mean-squared error and response patterns were analyzed to evaluate the consistency, accuracy, and side bias of the responses. Fifteen listeners completed the task at the 2-year post-activation visit; seven listeners repeated the task at a later annual visit. Results: Performance at the 2-year visit was best with the BBN and HP stimuli and poorer with the LP stimulus. Responses to the BBN and HP stimuli were significantly correlated, consistent with the idea that CI + NH listeners primarily use ILD cues for localization. For the LP stimulus, some listeners responded consistently and accurately and with limited side bias, which may indicate sensitivity to ITD cues. Two of the 7 listeners who repeated the task at a later annual visit experienced a significant improvement in performance with the LP stimulus, which may indicate that sensitivity to ITD cues may improve with long-term CI use. Conclusions: CI recipients with a NH-ear primarily use ILD cues for sound source localization, though some may use ITD cues as well. Sensitivity to ITD cues may improve with long-term CI listening experience.

Comparing the monaural effects of reverberation on speech intelligibility in noise for hearing-impaired and normal-hearing listeners

Reverberation has several detrimental effects on speech intelligibility in noise. They have been extensively studied with normal-hearing listeners. These effects are often simultaneous, and it is hard to disentangle the corresponding difficulties experienced by hearing-impaired listeners in noisy reverberant rooms. In this study, two monaural effects of reverberation were investigated for normal-hearing and hearing-impaired listeners with linear amplification (NAL-RP) to compensate for audibility. One is the temporal smearing of the target speech, which makes it less intelligible. The other is the temporal smearing of the noise masker, which decreases the dip listening benefit associated with envelope modulations in the noise. These two effects were studied separately and in combination, by applying reverberation either on the target speech, on the noise masker or on both. The results were analyzed using Bayesian ANOVAs and t-tests. Overall, the detrimental influence of reverberation was found similar for the hearing-impaired and normal-hearing listeners, indicating that a linear amplification of the signals seemed sufficient to compensate for the potential differences experienced by normal-hearing and hearing-impaired listeners.

Spectral weighting functions for localization of complex sound: Effects of sensorineural hearing loss

When localization cues are distributed across the spectrum of a complex sound, listeners with normal hearing (NH) utilize cues near the 600-800 Hz “ITD dominance region” [Bilsen and Raatgever, Acustica 28, 131–132 (1973)]. Recent work has quantified this pattern using spectral weighting functions (SWFs) [Folkerts and Stecker, ARO 42, 505 (2018)] in NH listeners. However, the salience of the ITD dominance region in listeners with sensorineural hearing loss (SNHL) remains unexamined. Folkerts and Stecker [ARO 45, 171 (2022)] used simulated SNHL in NH listeners to measure impacts of elevated hearing thresholds, loudness recruitment, and reduced high-frequency ITD sensitivity [Steinberg and Gardener, J Acoust. Soc Am 9, 11–23 (1937)] on SWFs. The current study measured SWFs in listeners with bilateral sloping high-frequency SNHL. Direct comparisons to SWFs measured with simulated SNHL test the hypothesis that reduced audibility of high-frequency components shifts the ITD dominance region to lower frequencies (i.e., 400–600 Hz). Individual SWFs measured in listeners with SNHL are compared to their headphone and free field thresholds to assess whether audibility can account for weighting changes. [Work supported by NIH R01-DC016643.]

A novel paradigm to define functional spatial boundaries

One approach to studying an individual’s binaural function is to measure speech reception ability for spatially separated compared to co-located competing speech streams. This spatial-release-from-masking (SRM) task has been widely adopted due to its capacity to detect abnormal binaural function, but it has its limitations in interpreting individual spatial abilities. Here, we introduce a modified SRM task that directly measures the needed spatial separation between target and maskers to achieve a specific SRM. Stimuli were presented from 24 speakers in the free field using an equal power panning method. Normal-hearing listeners (n = 10) were tasked with identifying digits in a target stream of monosyllabic words always presented from the front. Initial measures were made using the classic SRM paradigm in which two opposite-gender masker streams were either presented from the front (co-located), or symmetrically from 30° (fixed-separation), to determine a speech reception threshold (SRT; in dB target-to-masker ratio). Based on the co-located SRT, the task then adaptively tracked the separation angle needed to achieve 6-dB SRM. Results showed for most listeners, a 10-dB SRM at 30° separation and an average spatial boundary less than 30 degrees when fixed at 6-dB SRM. [Work supported by NIH NIDCD R21DC017832 to EJO.]

The impact of temporally coherent visual and vibrotactile cues on speech perception in noise performance

The inputs delivered to different sensory organs provide us with complementary information about the environment. Our recent study demonstrated that presenting abstract visual information of speech envelopes substantially improves speech perception ability in normal-hearing (NH), listeners [Yuan et al., J. Acoust. Soc. Am. (2020)]. The purpose of this study was to expand this audiovisual speech perception to the tactile domain. Twenty adults participated in sentence recognition threshold measurements in four different sensory modalities (AO: auditory-only; AV: auditory-visual; AT: audio-tactile; and AVT: audio-visual-tactile). The target sentence [CRM speech corpus, Bolia et al., J. Acoust. Soc. Am. (2000)] level was fixed at 60 dBA, and the masker (speech-shaped noise) levels were adaptively varied to find masked thresholds. The amplitudes of both visual and vibrotactile stimuli were temporally synchronized and non-synchronized with the target speech envelope for comparison. Results show that temporally coherent multi-modal stimulation (AV, AT, and AVT) significantly improves speech perception ability when compared to audio-only (AO) stimulation. These multisensory speech perception benefits were reduced when the cross-modal temporal coherence characteristics were eliminated. These findings suggest that multisensory interactions are fundamentally important for speech perception ability in NH listeners. The outcome of this multisensory speech processing highly depends on temporal coherence characteristics between multi-modal sensory inputs.