Musical experience sharpens human cochlear tuning

Musical training is not associated with spectral context effects in instrument sound categorization

Musicians display a variety of auditory perceptual benefits relative to people with little or no musical training; these benefits are collectively referred to as the "musician advantage." Importantly, musicians consistently outperform nonmusicians for tasks relating to pitch, but there are mixed reports as to musicians outperforming nonmusicians for timbre-related tasks. Due to their experience manipulating the timbre of their instrument or voice in performance, we hypothesized that musicians would be more sensitive to acoustic context effects stemming from the spectral changes in timbre across a musical context passage (played by a string quintet then filtered) and a target instrument sound (French horn or tenor saxophone; Experiment 1). Additionally, we investigated the role of a musician's primary instrument of instruction by recruiting French horn and tenor saxophone players to also complete this task (Experiment 2). Consistent with the musician advantage literature, musicians exhibited superior pitch discrimination to nonmusicians. Contrary to our main hypothesis, there was no difference between musicians and nonmusicians in how spectral context effects shaped instrument sound categorization. Thus, musicians may only outperform nonmusicians for some auditory skills relevant to music (e.g., pitch perception) but not others (e.g., timbre perception via spectral differences).

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.

Attention, Musicality, and Familiarity Shape Cortical Speech Tracking at the Musical Cocktail Party

The "cocktail party problem" challenges our ability to understand speech in noisy environments, which often include background music. Here, we explored the role of background music in speech-in-noise listening. Participants listened to an audiobook in familiar and unfamiliar music while tracking keywords in either speech or song lyrics. We used EEG to measure neural tracking of the audiobook. When speech was masked by music, the modeled peak latency at 50 ms (P1TRF) was prolonged compared to unmasked. Additionally, P1TRF amplitude was larger in unfamiliar background music, suggesting improved speech tracking. We observed prolonged latencies at 100 ms (N1TRF) when speech was not the attended stimulus, though only in less musical listeners. Our results suggest early neural representations of speech are enhanced with both attention and concurrent unfamiliar music, indicating familiar music is more distracting. One's ability to perceptually filter "musical noise" at the cocktail party depends on objective musical abilities.

Opposite effects of rapid auditory stimulation on tetanized and non-tetanized tone of adjacent frequency: Mismatch negativity study

Our study describes the effects of sensory tetanization on neurophysiological and behavioral measures in humans linking cellular studies of long-term potentiation with high-level brain processes. Rapid (every 75ms) presentation of pure tone (1020 Hz, 50ms) for 2 minutes was preceded and followed by oddball blocks that contained the same stimulus presented as deviant (probability of 5-10%) interspersed with standard (80-90%) and deviant tones (5-10%) of adjacent frequencies (1000 and 980Hz, respectively). Mismatch negativity (MMN) component in response to tetanized tone (1020Hz), while being similar to MMN for non-tetanized tone before tetanization, became larger than that after tetanization, pointing to the increase in cortical differentiation of these tones. However, this differentiation was partially due to the MMN decrease after tetanization for tones adjacent to tetanized frequency, suggesting the influence of lateral inhibition to this effect. Although MMN correlated with tone discriminability in a psychophysical task, the behavioral improvement after tetanization was not statistically detectable. To conclude, short-term auditory tetanization affects cortical representation of tones that are not limited to the tetanized stimuli.

Evidence of cortical thickness increases in bilateral auditory brain structures following piano learning in older adults

Morphological differences in the auditory brain of musicians compared to nonmusicians are often associated with life-long musical activity. Cross-sectional studies, however, do not allow for any causal inferences, and most experimental studies testing music-driven adaptations investigated children. Although the importance of the age at which musical training begins is widely recognized to impact neuroplasticity, there have been few longitudinal studies examining music-related changes in the brains of older adults. Using magnetic resonance imaging, we measured cortical thickness (CT) of 12 auditory-related regions of interest before and after 6 months of musical instruction in 134 healthy, right-handed, normal-hearing, musically-naive older adults (64-76 years old). Prior to the study, all participants were randomly assigned to either piano training or to a musical culture/music listening group. In five regions-left Heschl's gyrus, left planum polare, bilateral superior temporal sulcus, and right Heschl's sulcus-we found an increase in CT in the piano training group compared with the musical culture group. Furthermore, CT of the right Heschl's gyrus could be identified as a morphological substrate supporting speech in noise perception. The results support the conclusion that playing an instrument is an effective stimulator for cortical plasticity, even in older adults.

Rapid Enhancement of Subcortical Neural Responses to Sine-Wave Speech

The efferent auditory nervous system may be a potent force in shaping how the brain responds to behaviorally significant sounds. Previous human experiments using the frequency following response (FFR) have shown efferent-induced modulation of subcortical auditory function online and over short- and long-term time scales; however, a contemporary understanding of FFR generation presents new questions about whether previous effects were constrained solely to the auditory subcortex. The present experiment used sine-wave speech (SWS), an acoustically-sparse stimulus in which dynamic pure tones represent speech formant contours, to evoke FFR_SWS. Due to the higher stimulus frequencies used in SWS, this approach biased neural responses toward brainstem generators and allowed for three stimuli (/bɔ/, /bu/, and /bo/) to be used to evoke FFR_SWSbefore and after listeners in a training group were made aware that they were hearing a degraded speech stimulus. All SWS stimuli were rapidly perceived as speech when presented with a SWS carrier phrase, and average token identification reached ceiling performance during a perceptual training phase. Compared to a control group which remained naïve throughout the experiment, training group FFR_SWS amplitudes were enhanced post-training for each stimulus. Further, linear support vector machine classification of training group FFR_SWS significantly improved post-training compared to the control group, indicating that training-induced neural enhancements were sufficient to bolster machine learning classification accuracy. These results suggest that the efferent auditory system may rapidly modulate auditory brainstem representation of sounds depending on their context and perception as non-speech or speech.

Human Auditory-Frequency Tuning Is Sensitive to Tonal Language Experience

Purpose The aim of this study is to investigate whether human auditory frequency tuning can be influenced by tonal language experience. Method Perceptual tuning measured via psychophysical tuning curves and cochlear tuning derived via stimulus-frequency otoacoustic emission suppression tuning curves in 14 native speakers of a tonal language (Mandarin) were compared to those of 14 native speakers of a nontonal language (English) at 1 and 4 kHz. Results Group comparisons of both psychophysical tuning curves (p = .046) and stimulus-frequency otoacoustic emission suppression tuning curves (p = .007) in the 4-kHz region indicated sharper frequency tuning in the Mandarin-speaking group relative to the English-speaking group. The auditory tuning was better at the higher (4 kHz) than the lower (1 kHz) probe frequencies (p < .001). Conclusions The sharper auditory tuning in the 4-kHz cochlear region is associated with long-term tonal language (i.e., Mandarin) experience. Experience-dependent plasticity of tonal language may occur before the sound signal reaches central neural stages, as peripheral as the cochlea.

No Influence of Musicianship on the Effect of Contralateral Stimulation on Frequency Selectivity

The efferent system may control the gain of the cochlea and thereby influence frequency selectivity. This effect can be assessed using contralateral stimulation (CS) applied to the ear opposite to that used to assess frequency selectivity. The effect of CS may be stronger for musicians than for nonmusicians. To assess whether this was the case, psychophysical tuning curves (PTCs) were compared for 12 musicians and 12 nonmusicians. The PTCs were measured with and without a 60-dB sound pressure level (SPL) pink-noise CS, using signal frequencies of 2 and 4 kHz. The sharpness of the PTCs was quantified using the measure Q10, the signal frequency divided by the PTC bandwidth measured 10 dB above the level at the tip. Q10 values were lower in the presence of the CS, but this effect did not differ significantly for musicians and nonmusicians. The main effect of group (musicians vs. nonmusicians) on the Q10 values was not significant. Overall, these results do not support the idea that musicianship enhances contralateral efferent gain control as measured using the effect of CS on PTCs.

Narrow-band ripple glide direction discrimination and its relationship to frequency selectivity estimated using psychophysical tuning curves

The highest spectral ripple density at which the discrimination of ripple glide direction was possible (STRt_dir task) was assessed for one-octave wide (narrowband) stimuli with center frequencies of 500, 1000, 2000, and 4000 Hz and for a broadband stimulus. A pink noise lowpass filtered at the lower edge frequency of the rippled-noise stimuli was used to mask possible combination ripples. The relationship between thresholds measured using the STRt_dir task and estimates of the sharpness of tuning (Q10) derived from fast psychophysical tuning curves was assessed for subjects with normal hearing (NH) and cochlear hearing loss (CHL). The STRt_dir thresholds for the narrowband stimuli were highly correlated with Q10 values for the same center frequency, supporting the idea that STRt_dir thresholds for the narrowband stimuli provide a good measure of frequency resolution. Both the STRt_dir thresholds and the Q10 values were lower (worse) for the subjects with CHL than for the subjects with NH. For both the NH and CHL subjects, mean STRt_dir thresholds for the broadband stimulus were not significantly higher (better) than for the narrowband stimuli, suggesting little or no ability to combine information across center frequencies.

No Effect of Musical Training on Frequency Selectivity Estimated Using Three Methods

It is widely believed that the frequency selectivity of the auditory system is largely determined by processes occurring in the cochlea. If so, musical training would not be expected to influence frequency selectivity. Consistent with this, auditory filter shapes for low center frequencies do not differ for musicians and nonmusicians. However, it has been reported that psychophysical tuning curves (PTCs) at 4000 Hz were sharper for musicians than for nonmusicians. This study explored the origin of the discrepancy across studies. Frequency selectivity was estimated for musicians and nonmusicians using three methods: fast PTCs with a masker that swept in frequency, "traditional" PTCs obtained using several fixed masker center frequencies, and the notched-noise method. The signal frequency was 4000 Hz. The data were fitted assuming that each side of the auditory filter had the shape of a rounded-exponential function. The sharpness of the auditory filters, estimated as the Q₁₀ values, did not differ significantly between musicians and nonmusicians for any of the methods, but detection efficiency tended to be higher for the musicians. This is consistent with the idea that musicianship influences auditory proficiency but does not influence the peripheral processes that determine the frequency selectivity of the auditory system.

Same or different pitch? Effects of musical expertise, pitch difference, and auditory task on the pitch discrimination ability of musicians and non-musicians

Musical expertise promotes both the perception and the processing of music. The aim of the present study was to analyze if musicians compared to non-musicians already have auditory processing advantages at the neural level. 50 musicians and 50 non-musicians worked on a task to determine the individual auditory difference threshold (individual JND threshold). A passive oddball paradigm followed while the EEG activity was recorded. Frequent standard sounds (528 hertz [Hz]) and rare deviant sounds (individual JND threshold, 535 Hz, and 558 Hz) were presented in the oddball paradigm. The mismatch negativity (MMN) and the P3a were used as indicators of auditory discrimination skills for frequency differences. Musicians had significantly smaller individual JND thresholds than non-musicians, but musicians were not faster than non-musicians. Musicians and non-musicians showed both the MMN and the P3a at the 535 Hz and 558 Hz condition. In the individual JND threshold condition, non-musicians, whose individual JND threshold was at 539.8 Hz (and therefore even above the deviant sound of 535 Hz), predictably showed the MMN and the P3a. Musicians, whose individual JND threshold was at 531.1 Hz (and thus close to the standard sound of 528 Hz), showed no MMN and P3a-although they were behaviorally able to differentiate frequencies individually within their JND threshold range. This may indicate a key role of attention in triggering the MMN during the detection of frequency differences in the individual JND threshold range (see Tervaniemi et al. in Exp Brain 161:1-10, 2005).

Musical training sharpens behavioral tuning more saliently than peripheral tuning

Musical training appears to enhance performance at both peripheral and central auditory sites. We compared behavioral and peripheral frequency tuning in normal-hearing musicians and nonmusicians, whose native language is Mandarin. The results indicate that, at higher probe frequencies, musical training sharpens behavioral tuning more saliently than peripheral tuning. The improved peripheral tuning for musician appears to result principally from efferent top-down control rather than local cochlear changes.

A lateral inhibition mechanism explains the dissociation between mismatch negativity and behavioral pitch discrimination

Although mismatch negativity (MMN), a change-specific component of auditory event-related potential, is considered to be an index of sound discrimination accuracy, the amplitude of the MMN responses elicited by pitch height deviations in musicians and tone language speakers with superior pitch discrimination is usually not enhanced compared to that elicited in individuals with inferior pitch discrimination. We hypothesized that superior pitch discrimination is accompanied by enhanced lateral inhibition, a critical neural mechanism that sharpens the tuning curves of the auditory neurons in the tonotopy. Forty Mandarin-speaking healthy adults completed an auditory EEG experiment in which MMN was elicited by pitch height deviations in both pure and harmonic tones. Their behavioral pitch discrimination was indexed by the difference limens measured using pure and harmonic tones. Behavioral pitch discrimination correlated significantly with the MMN elicited by pure tones, but not by harmonic tones; this could be due to lateral inhibition strongly influencing the MMN elicited by harmonic tones but having less effect on the MMN elicited by pure tones. As lateral inhibition is a neural mechanism for attenuating the amplitude of MMN, our results support the notion that an enhanced lateral inhibition mechanism underlies superior pitch discrimination.

Characteristic of Stimulus Frequency Otoacoustic Emissions: Detection Rate, Musical Training Influence, and Gain Function

Stimulus frequency otoacoustic emission (SFOAE) is an active acoustic signal emitted by the inner ear providing salient information about cochlear function and dysfunction. To provide a basis for laboratory investigation and clinical use, we investigated the characteristics of SFOAEs, including detection rate, musical training influence, and gain function. Sixty-five normal hearing subjects (15 musicians and 50 non-musicians, aged 16-45 years) were tested and analyzed at the probe level of 30 and 50 dB sound pressure levels (SPL) in the center frequency of 1 and 4 kHz in the study. The results indicate that (1) the detection rates of SFOAE are sensitive to the gender, (2) musicians reveal enhanced hearing capacity and SFOAE amplitudes compared with non-musicians, and (3) probe frequency has a significant effect on the compression threshold of SFOAE. Our findings highlight the importance of SFOAE in the clinical hearing screening and diagnosis and emphasize the use of musical training for the rehabilitation enhancement of the auditory periphery and hearing threshold.

Auditory T-Complex Reveals Reduced Neural Activities in the Right Auditory Cortex in Musicians With Absolute Pitch

Absolute pitch (AP) is the ability to identify the pitch names of arbitrary musical tones without being given a reference pitch. The acquisition of AP typically requires early musical training, the critical time window for which is similar to that for the acquisition of a first language. This study investigated the left-right asymmetry of the auditory cortical functions responsible for AP by focusing on the T-complex of auditory evoked potentials (AEPs), which shows morphological changes during the critical period for language acquisition. AEPs evoked by a pure-tone stimulus were recorded in high-AP musicians, low-AP musicians, and non-musicians (n = 19 each). A balanced non-cephalic electrode (BNE) reference was used to examine the left-right asymmetry of the N1a and N1c components of the T-complex. As a result, a left-dominant N1c was observed only in the high-AP musician group, indicating "AP negativity," which has previously been described as an electrophysiological marker of AP. Notably, this hemispheric asymmetry was due to a diminution of the right N1c rather than enhancement of the left N1c. A left-dominant N1a was found in both musician groups, irrespective of AP. N1c and N1a exhibited no left-right asymmetry in non-musicians. Hence, music training and the acquisition of AP are both accompanied by a left-dominant hemispheric specialization of auditory cortical functions, as indexed by N1a and N1c, respectively, but the N1c asymmetry in AP possessors was due to reduced neural activities in the right hemisphere. The use of a BNE is recommended for evaluating these radially oriented components of the T-complex.

The effect of musicianship, contralateral noise, and ear of presentation on the detection of changes in temporal fine structure

Musicians are better than non-musicians at discriminating changes in the fundamental frequency (F0) of harmonic complex tones. Such discrimination may be based on place cues derived from low resolved harmonics, envelope cues derived from high harmonics, and temporal fine structure (TFS) cues derived from both low and high harmonics. The present study compared the ability of highly trained violinists and non-musicians to discriminate changes in complex sounds that differed primarily in their TFS. The task was to discriminate harmonic (H) and frequency-shifted inharmonic (I) tones that were bandpass filtered such that the components were largely or completely unresolved. The effect of contralateral noise and ear of presentation was also investigated. It was hypothesized that contralateral noise would activate the efferent system, helping to preserve the neural representation of envelope fluctuations in the H and I stimuli, thereby improving their discrimination. Violinists were significantly better than non-musicians at discriminating the H and I tones. However, contralateral noise and ear of presentation had no effect. It is concluded that, compared to non-musicians, violinists have a superior ability to discriminate complex sounds based on their TFS, and this ability is unaffected by contralateral stimulation or ear of presentation.

No otoacoustic evidence for a peripheral basis of absolute pitch

Absolute pitch (AP) is the ability to identify the perceived pitch of a sound without an external reference. Relatively rare, with an incidence of approximately 1/10,000, the mechanisms underlying AP are not well understood. This study examined otoacoustic emissions (OAEs) to determine if there is evidence of a peripheral (i.e., cochlear) basis for AP. Two OAE types were examined: spontaneous emissions (SOAEs) and stimulus-frequency emissions (SFOAEs). Our motivations to explore a peripheral foundation for AP were several-fold. First is the observation that pitch judgment accuracy has been reported to decrease with age due to age-dependent physiological changes cochlear biomechanics. Second is the notion that SOAEs, which are indirectly related to perception, could act as a fixed frequency reference. Third, SFOAE delays, which have been demonstrated to serve as a proxy measure for cochlear frequency selectivity, could indicate tuning differences between groups. These led us to the hypotheses that AP subjects would (relative to controls) exhibit a. greater SOAE activity and b. sharper cochlear tuning. To test these notions, measurements were made in normal-hearing control (N = 33) and AP-possessor (N = 20) populations. In short, no substantial difference in SOAE activity was found between groups, indicating no evidence for one or more strong SOAEs that could act as a fixed cue. SFOAE phase-gradient delays, measured at several different probe levels (20-50 dB SPL), also showed no significant differences between groups. This observation argues against sharper cochlear frequency selectivity in AP subjects. Taken together, these data support the prevailing view that AP mechanisms predominantly arise at a processing level in the central nervous system (CNS) at the brainstem or higher, not within the cochlea.

Musicianship enhances ipsilateral and contralateral efferent gain control to the cochlea

Human hearing sensitivity is easily compromised with overexposure to excessively loud sounds, leading to permanent hearing damage. Consequently, finding activities and/or experiential factors that distinguish "tender" from "tough" ears (i.e., acoustic vulnerability) would be important for identifying people at higher risk for hearing damage. To regulate sound transmission and protect the inner ear against acoustic trauma, the auditory system modulates gain control to the cochlea via biological feedback of the medial olivocochlear (MOC) efferents, a neuronal pathway linking the lower brainstem and cochlear outer hair cells. We hypothesized that a salient form of auditory experience shown to have pervasive neuroplastic benefits, namely musical training, might act to fortify hearing through tonic engagement of these reflexive pathways. By measuring MOC efferent feedback via otoacoustic emissions (cochlear emitted sounds), we show that dynamic ipsilateral and contralateral cochlear gain control is enhanced in musically-trained individuals. Across all participants, MOC strength was correlated with the years of listeners' training suggested that efferent gain control is experience dependent. Our data provide new evidence that intensive listening experience(s) (e.g., musicianship) can strengthen the ipsi/contralateral MOC efferent system and sound regulation to the inner ear. Implications for reducing acoustic vulnerability to damaging sounds are discussed.