Speech understanding and extended high-frequency hearing sensitivity in blast-exposed veteransa).

Auditory difficulties reported by normal-hearing Veterans with a history of blast exposure are primarily thought to stem from processing deficits in the central nervous system. However, previous work on speech understanding in noise difficulties in this patient population have only considered peripheral hearing thresholds in the standard audiometric range. Recent research suggests that variability in extended high-frequency (EHF; >8 kHz) hearing sensitivity may contribute to speech understanding deficits in normal-hearing individuals. Therefore, this work was designed to identify the effects of blast exposure on several common clinical speech understanding measures and EHF hearing sensitivity. This work also aimed to determine whether variability in EHF hearing sensitivity contributes to speech understanding difficulties in normal-hearing blast-exposed Veterans. Data from 41 normal- or near-normal-hearing Veterans with a history of blast exposure and 31 normal- or near-normal-hearing control participants with no history of head injury were employed in this study. Analysis identified an effect of blast exposure on several speech understanding measures but showed no statistically significant differences in EHF thresholds between participant groups. Data showed that variability in EHF hearing sensitivity did not contribute to group-related differences in speech understanding, although study limitations impact interpretation of these results.

Oddball paradigm complexity in multi-token auditory evoked potentials.

We developed and tested a series of novel and increasingly complex multi-token electrophysiology paradigms for evoking the auditory P3 response. The primary goal was to evaluate the degree to which more complex discrimination tasks and listening environments - which are more likely to engage the types of neural processing used in real-world speech-in-noise situations - could still evoke a robust P3 response. If so, this opens the possibility of such a paradigm making up part of the toolkit for a brain-behavioral approach to improve understanding of speech processing. Fourteen normal-hearing adults were tested using four different auditory paradigms consisting of 5 tokens, 20 tokens, 160 tokens, or 160 tokens with background babble. Stimuli were naturally produced consonant-vowel tokens varying in consonant (/d/, /b/, /g/, /v/, and /ð/; all conditions), vowel (/ɑ/, /u/, /i/, and /ɜr/; 20- and 160-token conditions), and talker (4 female, 4 male; 160-token conditions only). All four conditions evoked robust neural responses, and all peaks had visible differences across conditions. However, the more exogenous auditory evoked potentials (N1 and P2) were primarily affected not by overall complexity but by the presence of background noise specifically, the presence of which was associated with longer latencies and smaller amplitudes. The more endogenous P3 peak, as well as the paradigm behavioral measures, revealed a more graded effect of overall paradigm complexity, rather than the background noise dominating the other factors. Our conclusion was that all four complex auditory paradigms, including the most complex (160 distinct consonant-vowel tokens presented in background babble), are viable means of stimulating N1-P2 and N2b-P3 auditory evoked responses and may therefore be useful in brain-behavioral approaches to understanding speech perception in noise.

Relating Suprathreshold Auditory Processing Abilities to Speech Understanding in Competition.

(1) Background: Difficulty hearing in noise is exacerbated in older adults. Older adults are more likely to have audiometric hearing loss, although some individuals with normal pure-tone audiograms also have difficulty perceiving speech in noise. Additional variables also likely account for speech understanding in noise. It has been suggested that one important class of variables is the ability to process auditory information once it has been detected. Here, we tested a set of these "suprathreshold" auditory processing abilities and related them to performance on a two-part test of speech understanding in competition with and without spatial separation of the target and masking speech. Testing was administered in the Portable Automated Rapid Testing (PART) application developed by our team; PART facilitates psychoacoustic assessments of auditory processing. (2) Methods: Forty-one individuals (average age 51 years), completed assessments of sensitivity to temporal fine structure (TFS) and spectrotemporal modulation (STM) detection via an iPad running the PART application. Statistical models were used to evaluate the strength of associations between performance on the auditory processing tasks and speech understanding in competition. Age and pure-tone-average (PTA) were also included as potential predictors. (3) Results: The model providing the best fit also included age and a measure of diotic frequency modulation (FM) detection but none of the other potential predictors. However, even the best fitting models accounted for 31% or less of the variance, supporting work suggesting that other variables (e.g., cognitive processing abilities) also contribute significantly to speech understanding in noise. (4) Conclusions: The results of the current study do not provide strong support for previous suggestions that suprathreshold processing abilities alone can be used to explain difficulties in speech understanding in competition among older adults. This discrepancy could be due to the speech tests used, the listeners tested, or the suprathreshold tests chosen. Future work with larger numbers of participants is warranted, including a range of cognitive tests and additional assessments of suprathreshold auditory processing abilities.

Training with an auditory perceptual learning game transfers to speech in competition.

Understanding speech in the presence of acoustical competition is a major complaint of those with hearing difficulties. Here, a novel perceptual learning game was tested for its effectiveness in reducing difficulties with hearing speech in competition. The game was designed to train a mixture of auditory processing skills thought to underlie speech in competition, such as spectral-temporal processing, sound localization, and auditory working memory. Training on these skills occurred both in quiet and in competition with noise. Thirty college-aged participants without any known hearing difficulties were assigned either to this mixed-training condition or an active control consisting of frequency discrimination training within the same gamified setting. To assess training effectiveness, tests of speech in competition (primary outcome), as well as basic supra-threshold auditory processing and cognitive processing abilities (secondary outcomes) were administered before and after training. Results suggest modest improvements on speech in competition tests in the mixed-training compared to the frequency-discrimination control condition (Cohen's d = 0.68). While the sample is small, and in normally hearing individuals, these data suggest promise of future study in populations with hearing difficulties. Supplementary Information: The online version contains supplementary material available at 10.1007/s41465-021-00224-5.

Age-Related Deficits in Electrophysiological and Behavioral Measures of Binaural Temporal Processing.

Binaural processing, particularly the processing of interaural phase differences, is important for sound localization and speech understanding in background noise. Age has been shown to impact the neural encoding and perception of these binaural temporal cues even in individuals with clinically normal hearing sensitivity. This work used a new electrophysiological response, called the interaural phase modulation-following response (IPM-FR), to examine the effects of age on the neural encoding of interaural phase difference cues. Relationships between neural recordings and performance on several behavioral measures of binaural processing were used to determine whether the IPM-FR is predictive of interaural phase difference sensitivity and functional speech understanding deficits. Behavioral binaural frequency modulation detection thresholds were measured to assess sensitivity to interaural phase differences while spatial release-from-masking thresholds were used to assess speech understanding abilities in spatialized noise. Thirty adults between the ages of 35 to 74 years with normal low-frequency hearing thresholds were used in this study. Data showed that older participants had weaker neural responses to the interaural phase difference cue and were less able to take advantage of binaural cues for speech understanding compared to younger participants. Results also showed that the IPM-FR was predictive of performance on the binaural frequency modulation detection task, but not on the spatial release-from-masking task after accounting the effects of age. These results confirm previous work that showed that the IPM-FR reflects age-related declines in binaural temporal processing and provide further evidence that this response may represent a useful objective tool for assessing binaural function. However, further research is needed to understand how the IPM-FR is related to speech understanding abilities.

A Questionnaire Survey of Current Rehabilitation Practices for Adults With Normal Hearing Sensitivity Who Experience Auditory Difficulties.

Purpose A questionnaire survey was conducted to collect information from clinical audiologists about rehabilitation options for adult patients who report significant auditory difficulties despite having normal or near-normal hearing sensitivity. This work aimed to provide more information about what audiologists are currently doing in the clinic to manage auditory difficulties in this patient population and their views on the efficacy of recommended rehabilitation methods. Method A questionnaire survey containing multiple-choice and open-ended questions was developed and disseminated online. Invitations to participate were delivered via e-mail listservs and through business cards provided at annual audiology conferences. All responses were anonymous at the time of data collection. Results Responses were collected from 209 participants. The majority of participants reported seeing at least one normal-hearing patient per month who reported significant communication difficulties. However, few respondents indicated that their location had specific protocols for the treatment of these patients. Counseling was reported as the most frequent rehabilitation method, but results revealed that audiologists across various work settings are also successfully starting to fit patients with mild-gain hearing aids. Responses indicated that patient compliance with computer-based auditory training methods was regarded as low, with patients generally preferring device-based rehabilitation options. Conclusions Results from this questionnaire survey strongly suggest that audiologists frequently see normal-hearing patients who report auditory difficulties, but that few clinicians are equipped with established protocols for diagnosis and management. While many feel that mild-gain hearing aids provide considerable benefit for these patients, very little research has been conducted to date to support the use of hearing aids or other rehabilitation options for this unique patient population. This study reveals the critical need for additional research to establish evidence-based practice guidelines that will empower clinicians to provide a high level of clinical care and effective rehabilitation strategies to these patients.

Investigating Influences of Medial Olivocochlear Efferent System on Central Auditory Processing and Listening in Noise: A Behavioral and Event-Related Potential Study.

This electrophysiological study investigated the role of the medial olivocochlear (MOC) efferents in listening in noise. Both ears of eleven normal-hearing adult participants were tested. The physiological tests consisted of transient-evoked otoacoustic emission (TEOAE) inhibition and the measurement of cortical event-related potentials (ERPs). The mismatch negativity (MMN) and P300 responses were obtained in passive and active listening tasks, respectively. Behavioral responses for the word recognition in noise test were also analyzed. Consistent with previous findings, the TEOAE data showed significant inhibition in the presence of contralateral acoustic stimulation. However, performance in the word recognition in noise test was comparable for the two conditions (i.e., without contralateral stimulation and with contralateral stimulation). Peak latencies and peak amplitudes of MMN and P300 did not show changes with contralateral stimulation. Behavioral performance was also maintained in the P300 task. Together, the results show that the peripheral auditory efferent effects captured via otoacoustic emission (OAE) inhibition might not necessarily be reflected in measures of central cortical processing and behavioral performance. As the MOC effects may not play a role in all listening situations in adults, the functional significance of the cochlear effects of the medial olivocochlear efferents and the optimal conditions conducive to corresponding effects in behavioral and cortical responses remain to be elucidated.

Differential effects of hearing impairment and age on electrophysiological and behavioral measures of speech in noise.

Understanding speech in background noise is difficult for many listeners with and without hearing impairment (HI). This study investigated the effects of HI on speech discrimination and recognition measures as well as speech-evoked cortical N1-P2 and MMN auditory event-related potentials (AERPs) in background noise. We aimed to determine which AERP components can predict the effects of HI on speech perception in noise across adult listeners with and without HI. The data were collected from 18 participants with hearing thresholds ranging from within normal limits to bilateral moderate-to-severe sensorineural hearing loss. Linear mixed effects models were employed to examine how hearing impairment, age, stimulus type, and SNR listening condition affected neural and behavioral responses and what AERP components were correlated with effects of HI on speech-in-noise perception across participants. Significant effects of age were found on the N1-P2 but not on MMN, and significant effects of HI were observed on the MMN and behavioral measures. The results suggest that neural responses reflecting later cognitive processing of stimulus discrimination may be more susceptible to the effects of HI on the processing of speech in noise than earlier components that signal the sensory encoding of acoustic stimulus features. Objective AERP responses were also potential neural predictors of speech perception in noise across participants with and without HI, which has implications for the use of AERPs as a potential clinical tool for assessing speech perception in noise.

Neural indices of phonemic discrimination and sentence-level speech intelligibility in quiet and noise: A P3 study.

This study examined how speech babble noise differentially affected the auditory P3 responses and the associated neural oscillatory activities for consonant and vowel discrimination in relation to segmental- and sentence-level speech perception in noise. The data were collected from 16 normal-hearing participants in a double-oddball paradigm that contained a consonant (/ba/ to /da/) and vowel (/ba/ to /bu/) change in quiet and noise (speech-babble background at a -3 dB signal-to-noise ratio) conditions. Time-frequency analysis was applied to obtain inter-trial phase coherence (ITPC) and event-related spectral perturbation (ERSP) measures in delta, theta, and alpha frequency bands for the P3 response. Behavioral measures included percent correct phoneme detection and reaction time as well as percent correct IEEE sentence recognition in quiet and in noise. Linear mixed-effects models were applied to determine possible brain-behavior correlates. A significant noise-induced reduction in P3 amplitude was found, accompanied by significantly longer P3 latency and decreases in ITPC across all frequency bands of interest. There was a differential effect of noise on consonant discrimination and vowel discrimination in both ERP and behavioral measures, such that noise impacted the detection of the consonant change more than the vowel change. The P3 amplitude and some of the ITPC and ERSP measures were significant predictors of speech perception at segmental- and sentence-levels across listening conditions and stimuli. These data demonstrate that the P3 response with its associated cortical oscillations represents a potential neurophysiological marker for speech perception in noise.

Application of Linear Mixed-Effects Models in Human Neuroscience Research: A Comparison with Pearson Correlation in Two Auditory Electrophysiology Studies.

Neurophysiological studies are often designed to examine relationships between measures from different testing conditions, time points, or analysis techniques within the same group of participants. Appropriate statistical techniques that can take into account repeated measures and multivariate predictor variables are integral and essential to successful data analysis and interpretation. This work implements and compares conventional Pearson correlations and linear mixed-effects (LME) regression models using data from two recently published auditory electrophysiology studies. For the specific research questions in both studies, the Pearson correlation test is inappropriate for determining strengths between the behavioral responses for speech-in-noise recognition and the multiple neurophysiological measures as the neural responses across listening conditions were simply treated as independent measures. In contrast, the LME models allow a systematic approach to incorporate both fixed-effect and random-effect terms to deal with the categorical grouping factor of listening conditions, between-subject baseline differences in the multiple measures, and the correlational structure among the predictor variables. Together, the comparative data demonstrate the advantages as well as the necessity to apply mixed-effects models to properly account for the built-in relationships among the multiple predictor variables, which has important implications for proper statistical modeling and interpretation of human behavior in terms of neural correlates and biomarkers.

Perceptual Temporal Asymmetry Associated with Distinct ON and OFF Responses to Time-Varying Sounds with Rising versus Falling Intensity: A Magnetoencephalography Study.

This magnetoencephalography (MEG) study investigated evoked ON and OFF responses to ramped and damped sounds in normal-hearing human adults. Two pairs of stimuli that differed in spectral complexity were used in a passive listening task; each pair contained identical acoustical properties except for the intensity envelope. Behavioral duration judgment was conducted in separate sessions, which replicated the perceptual bias in favour of the ramped sounds and the effect of spectral complexity on perceived duration asymmetry. MEG results showed similar cortical sites for the ON and OFF responses. There was a dominant ON response with stronger phase-locking factor (PLF) in the alpha (8-14 Hz) and theta (4-8 Hz) bands for the damped sounds. In contrast, the OFF response for sounds with rising intensity was associated with stronger PLF in the gamma band (30-70 Hz). Exploratory correlation analysis showed that the OFF response in the left auditory cortex was a good predictor of the perceived temporal asymmetry for the spectrally simpler pair. The results indicate distinct asymmetry in ON and OFF responses and neural oscillation patterns associated with the dynamic intensity changes, which provides important preliminary data for future studies to examine how the auditory system develops such an asymmetry as a function of age and learning experience and whether the absence of asymmetry or abnormal ON and OFF responses can be taken as a biomarker for certain neurological conditions associated with auditory processing deficits.

Neural indices of phonemic discrimination and sentence-level speech intelligibility in quiet and noise: A mismatch negativity study.

Successful speech communication requires the extraction of important acoustic cues from irrelevant background noise. In order to better understand this process, this study examined the effects of background noise on mismatch negativity (MMN) latency, amplitude, and spectral power measures as well as behavioral speech intelligibility tasks. Auditory event-related potentials (AERPs) were obtained from 15 normal-hearing participants to determine whether pre-attentive MMN measures recorded in response to a consonant (from /ba/ to /bu/) and vowel change (from /ba/ to /da/) in a double-oddball paradigm can predict sentence-level speech perception. The results showed that background noise increased MMN latencies and decreased MMN amplitudes with a reduction in the theta frequency band power. Differential noise-induced effects were observed for the pre-attentive processing of consonant and vowel changes due to different degrees of signal degradation by noise. Linear mixed-effects models further revealed significant correlations between the MMN measures and speech intelligibility scores across conditions and stimuli. These results confirm the utility of MMN as an objective neural marker for understanding noise-induced variations as well as individual differences in speech perception, which has important implications for potential clinical applications.

Effects of background noise on inter-trial phase coherence and auditory N1-P2 responses to speech stimuli.

This study investigated the effects of a speech-babble background noise on inter-trial phase coherence (ITPC, also referred to as phase locking value (PLV)) and auditory event-related responses (AERP) to speech sounds. Specifically, we analyzed EEG data from 11 normal hearing subjects to examine whether ITPC can predict noise-induced variations in the obligatory N1-P2 complex response. N1-P2 amplitude and latency data were obtained for the /bu/syllable in quiet and noise listening conditions. ITPC data in delta, theta, and alpha frequency bands were calculated for the N1-P2 responses in the two passive listening conditions. Consistent with previous studies, background noise produced significant amplitude reduction and latency increase in N1 and P2, which were accompanied by significant ITPC decreases in all the three frequency bands. Correlation analyses further revealed that variations in ITPC were able to predict the amplitude and latency variations in N1-P2. The results suggest that trial-by-trial analysis of cortical neural synchrony is a valuable tool in understanding the modulatory effects of background noise on AERP measures.

Effective identification of functional hearing loss using behavioral threshold measures.

PURPOSE: Four functional hearing loss protocols were evaluated. METHOD: For each protocol, 30 participants feigned a hearing loss first on an audiogram and then for a screening test that began a threshold search from extreme levels (-10 or 90 dB HL). Two-tone and 3-tone protocols compared thresholds for ascending and descending tones for 2 (0.5 and 1.0 kHz) and 3 (0.5, 1.0, and 2.0 kHz) frequencies, respectively. A noise-band protocol compared an ascending noise-band threshold with that for 2 descending tones (0.5 and 1.0 kHz). A spondee protocol compared an ascending spondee threshold with that for 2 descending tones (0.5 and 1.0 kHz). These measures were repeated without the participants feigning losses. RESULTS: With nonfeigning participants, ascending and descending threshold differences were minimal for all protocols. When the participants feigned a loss, the spondee protocol produced the largest average threshold difference (30.8 dB), whereas the other protocols produced smaller differences (19.6-22.2 dB). CONCLUSIONS: Using both the screening test and a comparison of the initial audiogram with the screening test, the spondee and 3-tone protocols resulted in 100% true positives and 0% false positives for functional hearing loss. Either of these protocols could be used clinically or in occupational hearing conservation programs.