Heightened OAEs in young adult musicians: Influence of current noise exposure and training recency.

Otoacoustic emissions (OAEs) are a non-invasive metric of cochlear function. Studies of OAEs in musicians have yielded mixed results, ranging from evidence of diminished OAEs in musicians-suggesting noise-induced hearing loss-to no difference when compared to non-musicians, or even a trend for stronger OAEs in musicians. The goal of this study was to use a large sample of college students with normal hearing (n = 160) to compare OAE SNRs in musicians and non-musicians and to explore potential effects of training recency and noise exposure on OAEs in these cohorts. The musician cohort included both active musicians (who at the time of enrollment practiced at least weekly) and past musicians (who had at least 6 years of training). All participants completed a questionnaire about recent noise exposure (previous 12 months), and a subset of participants (71 musicians and 15 non-musicians) wore a personal noise dosimeter for one week to obtain a more nuanced and objective measure of exposure to assess how different exposure levels may affect OAEs before the emergence of a clinically significant hearing loss. OAEs were tested using both transient-evoked OAEs (TEOAEs) and distortion-product OAEs (DPOAEs). As predicted from the literature, musicians experienced significantly higher noise levels than non-musicians based on both subjective (self-reported) and objective measures. Yet we found stronger TEOAEs and DPOAEs in musicians compared to non-musicians in the ∼1-5 kHz range. Comparisons between past and active musicians suggest that enhanced cochlear function in young adult musicians does not require active, ongoing musical practice. Although there were no significant relations between OAEs and noise exposure as measured by dosimetry or questionnaire, active musicians had weaker DPOAEs than past musicians when the entire DPOAE frequency range was considered (up to ∼16 kHz), consistent with a subclinical noise-induced hearing loss that only becomes apparent when active musicians are contrasted with a cohort of individuals with comparable training but without the ongoing risks of noise exposure. Our findings suggest, therefore, that separate norms should be developed for musicians for earlier detection of incipient hearing loss. Potential explanations for enhanced cochlear function in musicians include pre-existing (inborn or demographic) differences, training-related enhancements of cochlear function (e.g., upregulation of prestin, stronger efferent feedback mechanisms), or a combination thereof. Further studies are needed to determine if OAE enhancements offer musicians protection against damage caused by noise exposure.

A high-density EEG and structural MRI source analysis of the frequency following response to missing fundamental stimuli reveals subcortical and cortical activation to low and high frequency stimuli.

Pitch is a perceptual rather than physical phenomenon, important for spoken language use, musical communication, and other aspects of everyday life. Auditory stimuli can be designed to probe the relationship between perception and physiological responses to pitch-evoking stimuli. One technique for measuring physiological responses to pitch-evoking stimuli is the frequency following response (FFR). The FFR is an electroencephalographic (EEG) response to periodic auditory stimuli. The FFR contains nonlinearities not present in the stimuli, including correlates of the amplitude envelope of the stimulus; however, these nonlinearities remain undercharacterized. The FFR is a composite response reflecting multiple neural and peripheral generators, and their contributions to the scalp-recorded FFR vary in ill-understood ways depending on the electrode montage, stimulus, and imaging technique. The FFR is typically assumed to be generated in the auditory brainstem; there is also evidence both for and against a cortical contribution to the FFR. Here a methodology is used to examine the FFR correlates of pitch and the generators of the FFR to stimuli with different pitches. Stimuli were designed to tease apart biological correlates of pitch and amplitude envelope. FFRs were recorded with 256-electrode EEG nets, in contrast to a typical FFR setup which only contains a single active electrode. Structural MRI scans were obtained for each participant to co-register with the electrode locations and constrain a source localization algorithm. The results of this localization shed light on the generating mechanisms of the FFR, including providing evidence for both cortical and subcortical auditory sources.

Cultural differences in auditory ecology.

Demographic differences in acoustic environments are usually studied using geographic area monitoring. This approach, however, may miss valuable information differentiating cultures. This motivated the current study, which used wearable sound recorders to measure noise levels and speech-to-noise ratios (SNRs) in the immediate acoustic environment of Latinx and European-American college students. Latinx experienced higher noise levels (64.8 dBC) and lower SNRs (3.7 dB) compared to European-Americans (noise levels, 63 dB; SNRs, 5.4 dB). This work provides a framework for a larger study on the impact of culture on auditory ecology.

Age-related declines to serum prestin levels in humans.

Measurement of the motor protein prestin offers a novel approach to assessing outer hair cell (OHC) status using serological techniques. Motivated by our prior work showing reduced serum prestin levels in healthy young adults at-risk for noise damage, the current study examined serum prestin levels, measured from circulating blood, across the age span from 18 to 82 years old. Results suggest that serum prestin levels negatively correlate with age, with young adults having higher levels of circulating serum in the blood than older adults. Group-level analyses showed minimal differences in prestin levels between 18 and 29, 30-39, and 40-49 year olds, but significant reductions in the 50+ years-old age group compared to the three younger groups, even though all groups significantly differed from each other in audiometric thresholds and distortion product otoacoustic emissions signal-to-noise ratio. Serum prestin levels declined with increasing levels of hearing loss, with a statistically significant relationship emerging between prestin and low-frequency hearing thresholds (0.25-2 kHz) but a weaker non-significant relationship for high-frequency hearing thresholds (3-8 kHz). This differential pattern between low- and high- frequency thresholds is consistent with the basal-to-apical progression of OHC loss with age. Findings support the idea that serum prestin is the product of residual OHCs in the less age-affected apical regions. Moreover, when entered in a regression model with audiometric thresholds, age was a stronger predictor than pure tone hearing threshold level for predicting serum prestin levels.

A Home-Based Approach to Auditory Brainstem Response Measurement: Proof-of-Concept and Practical Guidelines.

Broad-scale neuroscientific investigations of diverse human populations are difficult to implement. This is because the primary neuroimaging methods (magnetic resonance imaging, electroencephalography [EEG]) historically have not been portable, and participants may be unable or unwilling to travel to test sites. Miniaturization of EEG technologies has now opened the door to neuroscientific fieldwork, allowing for easier access to under-represented populations. Recent efforts to conduct auditory neuroscience outside a laboratory setting are reviewed and then an in-home technique for recording auditory brainstem responses (ABRs) and frequency-following responses (FFRs) in a home setting is introduced. As a proof of concept, we have conducted two in-home electrophysiological studies: one in 27 children aged 6 to 16 years (13 with autism spectrum disorder) and another in 12 young adults aged 18 to 27 years, using portable electrophysiological equipment to record ABRs and FFRs to click and speech stimuli, spanning rural and urban and multiple homes and testers. We validate our fieldwork approach by presenting waveforms and data on latencies and signal-to-noise ratio. Our findings demonstrate the feasibility and utility of home-based ABR/FFR techniques, paving the course for larger fieldwork investigations of populations that are difficult to test or recruit. We conclude this tutorial with practical tips and guidelines for recording ABRs and FFRs in the field and discuss possible clinical and research applications of this approach.

Evidence for a Musician Speech-Perception-in-Noise Advantage in School-Age Children.

PURPOSE: The objective of this study was to evaluate whether child musicians are better at listening to speech in noise (SPIN) than nonmusicians of the same age. In addition, we aimed to explore whether the musician SPIN advantage in children was related to general intelligence (IQ). METHOD: Fifty-one children aged 8.2-11.8 years and with different levels of music training participated in the study. A between-group design and correlational analyses were used to determine differences in SPIN skills as they relate to music training. IQ was used as a covariate to explore the relationship between intelligence and SPIN ability. RESULTS: More years of music training were associated with better SPIN skills than fewer years of music training. Furthermore, this difference in SPIN skills remained even when accounting for IQ. These results were found at the group level and also when years of instrument training was treated as a continuous variable (i.e., correlational analyses). CONCLUSIONS: We confirmed results from previous studies in which child musicians outperformed nonmusicians in SPIN skills. We also showed that this effect was not related to differences in IQ between the musicians and nonmusicians for this cohort of children. However, confirmation of this finding with a cohort of children from more diverse socioeconomic statuses and cognitive profiles is warranted.

Automatic sound encoding is sensitive to language familiarity: Evidence from English monolinguals and Spanish-English bilinguals.

We investigated whether language familiarity has a modulatory effect on automatic sound encoding in the auditory brainstem by measuring frequency-following responses (FFRs) to repeating speech syllables that played in the background while monolingual English speakers and Spanish-English bilingual speakers watched cartoon videos in English and Spanish. For the English monolinguals, we found that the FFR signal quality was different between the two language conditions, with higher signal to noise ratios emerging for the Spanish compared to the English condition. For the Spanish-English bilinguals, the FFR signal quality was overall higher than the monolinguals, but there no effect of language condition on the FFR. Thus, both language familiarity of the environment and bilingual language experience, may modulate automatic sound encoding.

Noise exposure levels predict blood levels of the inner ear protein prestin.

Serological biomarkers of inner ear proteins are a promising new approach for studying human hearing. Here, we focus on the serological measurement of prestin, a protein integral to a human's highly sensitive hearing, expressed in cochlear outer hair cells (OHCs). Building from recent nonhuman studies that associated noise-induced OHC trauma with reduced serum prestin levels, and studies suggesting subclinical hearing damage in humans regularly engaging in noisy activities, we investigated the relation between serum prestin levels and environmental noise levels in young adults with normal clinical audiograms. We measured prestin protein levels from circulating blood and collected noise level data multiple times over the course of the experiment using body-worn sound recorders. Results indicate that serum prestin levels have a negative relation with noise exposure: individuals with higher routine noise exposure levels tended to have lower prestin levels. Moreover, when grouping participants based on their risk for a clinically-significant noise-induced hearing loss, we found that prestin levels differed significantly between groups, even though behavioral hearing thresholds were similar. We discuss possible interpretations for our findings including whether lower serum levels may reflect subclinical levels of OHC damage, or possibly an adaptive, protective mechanism in which prestin expression is downregulated in response to loud environments.

Auditory Cortical Changes Precede Brainstem Changes During Rapid Implicit Learning: Evidence From Human EEG.

The auditory system is sensitive to stimulus regularities such as frequently occurring sounds and sound combinations. Evidence of regularity detection can be seen in how neurons across the auditory network, from brainstem to cortex, respond to the statistical properties of the soundscape, and in the rapid learning of recurring patterns in their environment by children and adults. Although rapid auditory learning is presumed to involve functional changes to the auditory network, the chronology and directionality of changes are not well understood. To study the mechanisms by which this learning occurs, auditory brainstem and cortical activity was simultaneously recorded via electroencephalogram (EEG) while young adults listened to novel sound streams containing recurring patterns. Neurophysiological responses were compared between easier and harder learning conditions. Collectively, the behavioral and neurophysiological findings suggest that cortical and subcortical structures each provide distinct contributions to auditory pattern learning, but that cortical sensitivity to stimulus patterns likely precedes subcortical sensitivity.

Auditory Temporal Processing in Dancers.

While many studies have examined the auditory abilities of musicians, this study uniquely asks whether dance training, a similar yet understudied type of early-life training, also benefits auditory abilities. We focused this investigation on temporal resolution, given the importance of subtle temporal cues in synchronizing movement. We found that, compared to untrained controls, novice adult dancers who have trained continuously since childhood had enhanced temporal resolution, measured with a gap detection task. In an analysis involving current and former dancers, total years of training was a significant predictor of temporal resolution thresholds. The association between dance experience and improved auditory skills has implications for current theories of experience-dependent auditory plasticity and the design of sound-based educational and rehabilitation activities.

Reliability of Serological Prestin Levels in Humans and its Relation to Otoacoustic Emissions, a Functional Measure of Outer Hair Cells.

OBJECTIVES: Serological biomarkers, common to many areas of medicine, have the potential to inform on the health of the human body and to give early warning of risk of compromised function or illness before symptoms are experienced. Serological measurement of prestin, a motor protein uniquely produced and expressed in outer hair cells, has recently been identified as a potential biomarker to inform on the health of the cochlea. Before any test can be introduced into the clinical toolkit, the reproducibility of the measurement when repeated in the same subject must be considered. The primary objective of this study is to outline the test-retest reliability estimates and normative ranges for serological prestin in healthy young adults with normal hearing. In addition, we examine the relation between serum prestin levels and otoacoustic emissions (OAEs) to compare this OHC-specific protein to the most common measure of OHC function currently used in hearing assessments. DESIGN: We measured prestin levels serologically from circulating blood in 34 young adults (18 to 24 years old) with clinically normal pure-tone audiometric averages at five different timepoints up to six months apart (average intervals between measurements ranged from <1 week to 7 weeks apart). To guide future studies of clinical populations, we present the standard error of the measurement, reference normative values, and multiple measures of reliability. Additionally, we measured transient evoked OAEs at the same five timepoints and used correlation coefficients to examine the relation between OAEs and prestin levels (pg/mL). RESULTS: Serum prestin levels demonstrated good to excellent reliability between and across the five different time points, with correlation coefficients and intraclass correlations >0.8. Across sessions, the average serum prestin level was 250.20 pg/mL, with a standard error of measurement of 7.28 pg/mL. Moreover, positive correlations (generally weak to moderate) were found between prestin levels and OAE magnitudes and signal-to-noise ratios. CONCLUSIONS: Findings characterize serum prestin in healthy young adults with normal hearing and provide initial normative data that may be critical to interpreting results from individuals with sensorineural hearing loss. Our results demonstrate reliability of serum prestin levels in a sample of normal-hearing young adults across five test sessions up to 6 months apart, paving the way for testing larger samples to more accurately estimate test-retest standards for clinical protocols, including those involving serial monitoring. The positive correlations between serum prestin and OAE levels, although weak to moderate, reinforce that the source of serum prestin is likely the outer hair cells in the inner ear, but also that serum prestin and OAEs each may also index aspects of biologic function not common to the other.

Multi-Voiced Music Bypasses Attentional Limitations in the Brain.

Attentional limits make it difficult to comprehend concurrent speech streams. However, multiple musical streams are processed comparatively easily. Coherence may be a key difference between music and stimuli like speech, which does not rely on the integration of multiple streams for comprehension. The musical organization between melodies in a composition may provide a cognitive scaffold to overcome attentional limitations when perceiving multiple lines of music concurrently. We investigated how listeners attend to multi-voiced music, examining biological indices associated with processing structured versus unstructured music. We predicted that musical structure provides coherence across distinct musical lines, allowing listeners to attend to simultaneous melodies, and that a lack of organization causes simultaneous melodies to be heard as separate streams. Musician participants attended to melodies in a Coherent music condition featuring flute duets and a Jumbled condition where those duets were manipulated to eliminate coherence between the parts. Auditory-evoked cortical potentials were collected to a tone probe. Analysis focused on the N100 response which is primarily generated within the auditory cortex and is larger for attended versus ignored stimuli. Results suggest that participants did not attend to one line over the other when listening to Coherent music, instead perceptually integrating the streams. Yet, for the Jumbled music, effects indicate that participants attended to one line while ignoring the other, abandoning their integration. Our findings lend support for the theory that musical organization aids attention when perceiving multi-voiced music.

Baseline, retest, and post-injury profiles of auditory neural function in collegiate football players.

OBJECTIVES: Recent retrospective studies report differences in auditory neurophysiology between concussed athletes and uninjured controls using the frequency-following response (FFR). Adopting a prospective design in college football players, we compared FFRs before and after a concussion and evaluated test-retest reliability in non-concussed teammates. DESIGN: Testing took place in a locker room. We analysed the FFR to the fundamental frequency (F0) (FFR-F0) of a speech stimulus, previously identified as a potential concussion biomarker. Baseline FFRs were obtained during the football pre-season. In athletes diagnosed with concussions during the season, FFRs were measured days after injury and compared to pre-season baseline. In uninjured controls, comparisons were made between pre- and post-season. STUDY SAMPLE: Participants were Tulane University football athletes (n = 65). RESULTS: In concussed athletes, there was a significant group-level decrease in FFR-F0 from baseline (26% decrease on average). By contrast, the control group's change from baseline was not statistically significant, and comparisons of pre- and post-season had good repeatability (intraclass correlation coefficient = 0.75). CONCLUSIONS: Results converge with previous work to evince suppressed neural function to the FFR-F0 following concussion. This preliminary study paves the way for larger-scale clinical evaluation of the specificity and reliability of the FFR as a concussion diagnostic.HighlightsThis prospective study reveals suppressed neural responses to sound in concussed athletes compared to baseline.Neural responses to sound show good repeatability in uninjured athletes tested in a locker-room setting.Results support the feasibility of recording frequency-following responses in non-laboratory conditions.

Comparisons of Auditory Brainstem Responses Between a Laboratory and Simulated Home Environment.

Purpose Miniaturization of digital technologies has created new opportunities for remote health care and neuroscientific fieldwork. The current study assesses comparisons between in-home auditory brainstem response (ABR) recordings and recordings obtained in a traditional lab setting. Method Click-evoked and speech-evoked ABRs were recorded in 12 normal-hearing, young adult participants over three test sessions in (a) a shielded sound booth within a research lab, (b) a simulated home environment, and (c) the research lab once more. The same single-family house was used for all home testing. Results Analyses of ABR latencies, a common clinical metric, showed high repeatability between the home and lab environments across both the click-evoked and speech-evoked ABRs. Like ABR latencies, response consistency and signal-to-noise ratio (SNR) were robust both in the lab and in the home and did not show significant differences between locations, although variability between the home and lab was higher than latencies, with two participants influencing this lower repeatability between locations. Response consistency and SNR also patterned together, with a trend for higher SNRs to pair with more consistent responses in both the home and lab environments. Conclusions Our findings demonstrate the feasibility of obtaining high-quality ABR recordings within a simulated home environment that closely approximate those recorded in a more traditional recording environment. This line of work may open doors to greater accessibility to underserved clinical and research populations.

Phonetic discrimination mediates the relationship between auditory brainstem response stability and syntactic performance.

Syntactic, lexical, and phonological/phonetic knowledge are vital aspects of macro level language ability. Prior research has predominantly focused on environmental or cortical sources of individual differences in these areas; however, a growing literature suggests an auditory brainstem contribution to language performance in both typically developing (TD) populations and children with autism spectrum disorder (ASD). This study investigates whether one aspect of auditory brainstem responses (ABRs), neural response stability, which is a metric reflecting trial-by-trial consistency in the neural encoding of sound, can predict syntactic, lexical, and phonetic performance in TD and ASD school-aged children. Pooling across children with ASD and TD, results showed that higher neural stability in response to the syllable /da/ was associated with better phonetic discrimination, and with better syntactic performance on a standardized measure. Furthermore, phonetic discrimination was a successful mediator of the relationship between neural stability and syntactic performance. This study supports the growing body of literature that stable subcortical neural encoding of sound is important for successful language performance.

Evolving perspectives on the sources of the frequency-following response.

The auditory frequency-following response (FFR) is a non-invasive index of the fidelity of sound encoding in the brain, and is used to study the integrity, plasticity, and behavioral relevance of the neural encoding of sound. In this Perspective, we review recent evidence suggesting that, in humans, the FFR arises from multiple cortical and subcortical sources, not just subcortically as previously believed, and we illustrate how the FFR to complex sounds can enhance the wider field of auditory neuroscience. Far from being of use only to study basic auditory processes, the FFR is an uncommonly multifaceted response yielding a wealth of information, with much yet to be tapped.

Noise Exposure and Background Noise Tolerance in Listeners With Normal Audiograms.

Purpose Tolerance for background noise when listening to speech has been found to vary greatly between individuals, despite clinically similar audiograms. Recent work suggests that listeners at risk for noise-induced hearing loss (NIHL) self-report greater annoyance of background sounds compared with listeners at lower risk for NIHL. To date, the relationship between noise exposure levels and background noise tolerance has not been studied using objective noise exposure level measurements and quantitative (i.e., not questionnaire-based) background noise tolerance measures. Method Acceptable Noise Level (ANL; Nabelek, Tucker, & Letowski, 1991) scores and week-long noise dosimetry measurements were obtained for 56 normal-hearing college students, 22 of whom were routinely exposed to levels of noise that exceed recommended exposure limits (higher risk). The remaining 34 participants did not exceed recommended exposure limits (lower risk). Results The lower risk group's average daily noise dose was 26%, whereas the higher risk group accrued an average daily noise dose of 461%. The lower risk group was found to be more tolerant of background noise than the higher risk group, with mean ANL scores of 3.1 dB and 5.4 dB signal-to-noise ratio, respectively. A small but statistically significant relationship between ANL and noise dose was found, indicating that higher levels of noise exposure were associated with lower background noise tolerance. Conclusions Results suggest that young adults at higher risk for NIHL based on objective noise exposure data have a slightly lower tolerance for background noise when listening to speech. These findings open avenues for future work on background noise tolerance in more diverse noise-exposed populations.

Bilingualism and Speech Understanding in Noise: Auditory and Linguistic Factors.

BACKGROUND: Bilingual speakers often have difficulty understanding speech in noisy and acoustically degraded conditions. PURPOSE: The first aim was to examine the potential source(s) of the difficulties that English-proficient bilingual listeners experience when hearing English speech in noise. The second aim was to assess how bilingual listeners perform on a battery of central auditory processing tests. RESEARCH DESIGN: A mixed design was used in this study. STUDY SAMPLE: Normal-hearing college students (n = 24) participated in this study. The bilingual participants (n = 12) self-reported that they learned a second language before age 9 and the monolingual participants reported that they only knew American English. All participants considered themselves to be native speakers of American English. DATA COLLECTION AND ANALYSIS: Participants were administered the Revised Speech Perception in Noise (R-SPIN) test to assess whether bilingual listeners' speech understanding in noise reflects auditory factors, linguistic factors, or a combination of the two. To minimize the influence of short-term memory and motor movements, only the final word of a sentence is repeated for this test. Sentence-final words were presented in two linguistic contexts: in the high-predictability condition, the final word can be deduced from the context created by the preceding words, and in the low-predictability condition, it cannot. The R-SPIN test was administered at two signal-to-noise ratios (SNRs) (0 and 3 dB). In addition, the participants were given a reading comprehension test to measure their ability to use context when linguistic stimuli are delivered to the visual, not auditory, modality. The central auditory test battery consisted of three tests: Competing Sentences, Dichotic Digits, and NU-6 Time-Compressed Speech with Reverberation. All test materials were given in American English. RESULTS: The bilingual and monolingual groups performed similarly in the low-context condition of the R-SPIN test. However, in comparison to the age-matched monolingual group, the bilingual group did not derive the same level of benefit from contextual cues, as seen by a smaller improvement in performance between the low- and high-predictability R-SPIN conditions. The bilingual and monolingual groups showed a similar decrement in performance when the SNR dropped. In addition, bilingual individuals underperformed on the Competing Sentences test when instructed to attend to the left ear. However, the bilingual and monolingual groups performed equally well on the reading comprehension test, as well as on the Time-Compressed Speech with Reverberation and Dichotic Digits tests. CONCLUSIONS: We show that individuals who are exposed to two languages from an early age, and self-report as having a high level of proficiency in English, perform like their monolingual counterparts in acoustically degraded conditions where context is not facilitative, but they underperform in conditions where sentence-level linguistic context is facilitative to understanding. We conclude that deficits observed in noise are likely not due to a perceptual deficit or a lack of linguistic competence, but instead reflect a linguistic system that performs inefficiently in noise. In addition, we do not find evidence of an auditory processing weakness or advantage in our bilingual cohort; however, the use of speech materials to assess auditory processing is a confound.

Noise Exposure May Diminish the Musician Advantage for Perceiving Speech in Noise.

OBJECTIVE: Although numerous studies have shown that musicians have better speech perception in noise (SPIN) compared to nonmusicians, other studies have not replicated the "musician advantage for SPIN." One factor that has not been adequately addressed in previous studies is how musicians' SPIN is affected by routine exposure to high levels of sound. We hypothesized that such exposure diminishes the musician advantage for SPIN. DESIGN: Environmental sound levels were measured continuously for 1 week via body-worn noise dosimeters in 56 college students with diverse musical backgrounds and clinically normal pure-tone audiometric averages. SPIN was measured using the Quick Speech in Noise Test (QuickSIN). Multiple linear regression modeling was used to examine how music practice (years of playing a musical instrument) and routine noise exposure predict QuickSIN scores. RESULTS: Noise exposure and music practice were both significant predictors of QuickSIN, but they had opposing influences, with more years of music practice predicting better QuickSIN scores and greater routine noise exposure predicting worse QuickSIN scores. Moreover, mediation analysis suggests that noise exposure suppresses the relationship between music practice and QuickSIN scores. CONCLUSIONS: Our findings suggest a beneficial relationship between music practice and SPIN that is suppressed by noise exposure.