The role of the auditory brainstem in processing linguistically-relevant pitch patterns

Is source-resolved magnetoencephalographic mismatch negativity a viable biomarker for early psychosis?

Mismatch negativity (MMN) is an auditory event-related response reflecting the pre-attentive detection of novel stimuli and is a biomarker of cortical dysfunction in schizophrenia (SZ). MMN to pitch (pMMN) and to duration (dMMN) deviant stimuli are impaired in chronic SZ, but it is less clear if MMN is reduced in first-episode SZ, with inconsistent findings in scalp-level EEG studies. Here, we investigated the neural generators of pMMN and dMMN with MEG recordings in 26 first-episode schizophrenia spectrum (FEsz) and 26 matched healthy controls (C). We projected MEG inverse solutions into precise functionally meaningful auditory cortex areas. MEG-derived MMN sources were in bilateral primary auditory cortex (A1) and belt areas. In A1, pMMN FEsz reduction showed a trend towards statistical significance (F(1,50) = 3.31; p = .07), and dMMN was reduced in FEsz (F(1,50) = 4.11; p = .04). Hypothesis-driven comparisons at each hemisphere revealed dMMN reduction in FEsz occurred in the left (t(56) = 2.23; p = .03; d = .61) but not right (t(56) = 1.02; p = .31; d = .28) hemisphere, with a moderate effect size. The added precision of MEG source solution with high-resolution MRI and parcellation of A1 may be requisite to detect the emerging pathophysiology and indicates a critical role for left hemisphere pathology at psychosis onset. However, the moderate effect size in left A1, albeit larger than reported in scalp MMN meta-analyses, casts doubt on the clinical utility of MMN for differential diagnosis, as a majority of patients will overlap with the healthy individual's distribution.

[Application of speech induced ABR in rehabilitation intervention for hearing impaired children]

Objective:Exploring the electrophysiological changes of auditory rehabilitation in young children with hearing impairment, providing more methods for early assessment and intervention. Methods:Twenty children aged 2-4 were enrolled, with moderate hearing loss and no other abnormalities in the ears. Divide them into group 1 with normal hearing, group 2 with abnormal hearing, group 3 with abnormal hearing receiving hearing aid intervention for one year, and group 4 with abnormal hearing receiving hearing aid and language training rehabilitation for one year. The SmartEP auditory evoked potential instrument was used to detect speech induced ABR and conduct screening for 'Standards and Evaluating Hearing and Language Abilities of Children with Hearing Impairment in 80 enrolled children after rehabilitation training, and the latency、amplitude of speech induced ABR waveform and evaluation scale scores for each group after rehabilitation intervention were compared. Results:Compared with the normal group, the latency of each wave in the other three groups was prolonged. The differences in each wave between Group 2 and Group 3 were statistically significant, while the differences in D and F waves between Group 3 and Group 4 were statistically significant. Compared with the normal group, the maximum amplitude at F0 decreased in the other three groups, and the differences in maximum amplitude between Group 2 and Group 3, Group 2 and Group 4, and Group 3 and Group 4 were statistically significant. Compared with the normal group, the scores of the auditory language assessment scale in the hearing intervention group and the hearing aid plus language training group were significantly higher than those in the abnormal group in terms of recognition rate. The recognition rates of hearing impaired children with language training foundation are similar to those of the normal group of children. Conclusion:Auditory rehabilitation can alter the electrophysiological aspects of hearing and serve as a basis for early assessment and intervention in young children.

Exploring the role of singing, semantics, and amusia screening in speech-in-noise perception in musicians and non-musicians

Sentence repetition has been the focus of extensive psycholinguistic research. The notion that music training can bolster speech perception in adverse auditory conditions has been met with mixed results. In this work, we sought to gauge the effect of babble noise on immediate repetition of spoken and sung phrases of varying semantic content (expository, narrative, and anomalous), initially in 100 English-speaking monolinguals with and without music training. The two cohorts also completed some non-musical cognitive tests and the Montreal Battery of Evaluation of Amusia (MBEA). When disregarding MBEA results, musicians were found to significantly outperform non-musicians in terms of overall repetition accuracy. Sung targets were recalled significantly better than spoken ones across groups in the presence of babble noise. Sung expository targets were recalled better than spoken expository ones, and semantically anomalous content was recalled more poorly in noise. Rerunning the analysis after eliminating thirteen participants who were diagnosed with amusia showed no significant group differences. This suggests that the notion of enhanced speech perception-in noise or otherwise-in musicians needs to be evaluated with caution. Musicianship aside, this study showed for the first time that sung targets presented in babble noise seem to be recalled better than spoken ones. We discuss the present design and the methodological approach of screening for amusia as factors which may partially account for some of the mixed results in the field.

Systematic Review and Meta-analysis of Language Symptoms due to Cerebellar Injury

To date, cerebellar contribution to language is well established via clinical and neuroimaging studies. However, the particular functional role of the cerebellum in language remains to be clarified. In this study, we present the first systematic review of the diverse language symptoms in spoken language after cerebellar lesion that were reported in case studies for the last 30 years (18 clinical cases from 13 papers), and meta-analysis using cluster analysis with bootstrap and symptom co-occurrence analysis. Seven clusters of patients with similar language symptoms after cerebellar lesions were found. Co-occurrence analysis revealed pairs of symptoms that tend to be comorbid. Our results imply that the "linguistic cerebellum" has a multiform contribution to language function. The most possible mechanism of such contribution is the cerebellar reciprocal connectivity with supratentorial brain regions, where the cerebellar level of the language network has a general modulation function and the supratentorial level is more functionally specified. Based on cerebellar connectivity with supratentorial components of the language network, the "linguistic cerebellum" might be further functionally segregated.

Selecting auditory alerting stimuli for eagles on the basis of auditory evoked potentials

Development of wind energy facilities results in interactions between wildlife and wind turbines. Raptors, including bald and golden eagles, are among the species known to incur mortality from these interactions. Several alerting technologies have been proposed to mitigate this mortality by increasing eagle avoidance of wind energy facilities. However, there has been little attempt to match signals used as alerting stimuli with the sensory capabilities of target species like eagles. One potential approach to tuning signals is to use sensory physiology to determine what stimuli the target eagle species are sensitive to even in the presence of background noise, thereby allowing the development of a maximally stimulating signal. To this end, we measured auditory evoked potentials of bald and golden eagles to determine what types of sounds eagles can process well, especially in noisy conditions. We found that golden eagles are significantly worse than bald eagles at processing rapid frequency changes in sounds, but also that noise effects on hearing in both species are minimal in response to rapidly changing sounds. Our findings therefore suggest that sounds of intermediate complexity may be ideal both for targeting bald and golden eagle hearing and for ensuring high stimulation in noisy field conditions. These results suggest that the sensory physiology of target species is likely an important consideration when selecting auditory alerting sounds and may provide important insight into what sounds have a reasonable probability of success in field applications under variable conditions and background noise.

How experience with tone in the native language affects the L2 acquisition of pitch accents

This paper tested the ability of Mandarin learners of German, whose native language has lexical tone, to imitate pitch accent contrasts in German, an intonation language. In intonation languages, pitch accents do not convey lexical information; also, pitch accents are sparser than lexical tones as they only associate with prominent words in the utterance. We compared two kinds of German pitch-accent contrasts: (1) a “non-merger” contrast, which Mandarin listeners perceive as different and (2) a “merger” contrast, which sounds more similar to Mandarin listeners. Speakers of a tone language are generally very sensitive to pitch. Hypothesis 1 (H1) therefore stated that Mandarin learners produce the two kinds of contrasts similarly to native German speakers. However, the documented sensitivity to tonal contrasts, at the expense of processing phrase-level intonational contrasts, may generally hinder target-like production of intonational pitch accents in the L2 (Hypothesis 2, H2). Finally, cross-linguistic influence (CLI) predicts a difference in the realization of these two contrasts as well as improvement with higher proficiency (Hypothesis 3, H3). We used a delayed imitation paradigm, which is well-suited for assessing L2-phonetics and -phonology because it does not necessitate access to intonational meaning. We investigated the imitation of three kinds of accents, which were associated with the sentence-final noun in short wh-questions (e.g., Wer malt denn Mandalas, lit: “Who draws PRT mandalas?” “Who likes drawing mandalas?”). In Experiment 1, 28 native speakers of Mandarin participated (14 low- and 14 high-proficient). The learners’ productions of the two kinds of contrasts were analyzed using General Additive Mixed Models to evaluate differences in pitch accent contrasts over time, in comparison to the productions of native German participants from an earlier study in our lab. Results showed a more pronounced realization of the non-merger contrast compared to German natives and a less distinct realization of the merger contrast, with beneficial effects of proficiency, lending support to H3. Experiment 2 tested low-proficient Italian learners of German (whose L1 is an intonation language) to contextualize the Mandarin data and further investigate CLI. Italian learners realized the non-merger contrast more target-like than Mandarin learners, lending additional support to CLI (H3).

Functional Hemispheric Activity and Asymmetry Markers of Effective Foreign Language Performance in 3rd-Grade, 10th-Grade, and University Students

The activity of the left hemisphere is often associated with linguistic functioning, including in a foreign language. At the same time, research results demonstrate that different structures in both hemispheres can be jointly activated in the performance of particular linguistic tasks. The current study aimed to identify functional hemispheric activity and asymmetry markers for effective foreign language performance. The study sample consisted of 27 3rd-grade, 26 10th-grade, and 21 university students, all native Russian. To measure functional hemispheric asymmetry and activity before and after an English class and before an English test, we used computer laterometry in the ‘two-source’ lead–lag dichotic paradigm. The study results reveal that left hemispheric functional dominance can be considered as a marker for effective activity during an English class and an English test in 3rd-grade and 10th-grade students. In university students, right hemispheric functional dominance predicted better efficacy during the English class. Therefore, the results obtained provide evidence about different hemispheric activity and asymmetry modes for different ages of foreign language mastering, and the results may support the hypothesis about the possibility of a ‘sensitive period’ for foreign language acquisition occurring at any age. These findings can be applied to the creation of biofeedback trainings for hemispheric profile optimization when learning a foreign language and may help in creating personalized learning schedules.

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.

Temporal Pitch Sensitivity in an Animal Model: Psychophysics and Scalp Recordings : Temporal Pitch Sensitivity in Cat

Cochlear implant (CI) users show limited sensitivity to the temporal pitch conveyed by electric stimulation, contributing to impaired perception of music and of speech in noise. Neurophysiological studies in cats suggest that this limitation is due, in part, to poor transmission of the temporal fine structure (TFS) by the brainstem pathways that are activated by electrical cochlear stimulation. It remains unknown, however, how that neural limit might influence perception in the same animal model. For that reason, we developed non-invasive psychophysical and electrophysiological measures of temporal (i.e., non-spectral) pitch processing in the cat. Normal-hearing (NH) cats were presented with acoustic pulse trains consisting of band-limited harmonic complexes that simulated CI stimulation of the basal cochlea while removing cochlear place-of-excitation cues. In the psychophysical procedure, trained cats detected changes from a base pulse rate to a higher pulse rate. In the scalp-recording procedure, the cortical-evoked acoustic change complex (ACC) and brainstem-generated frequency following response (FFR) were recorded simultaneously in sedated cats for pulse trains that alternated between the base and higher rates. The range of perceptual sensitivity to temporal pitch broadly resembled that of humans but was shifted to somewhat higher rates. The ACC largely paralleled these perceptual patterns, validating its use as an objective measure of temporal pitch sensitivity. The phase-locked FFR, in contrast, showed strong brainstem encoding for all tested pulse rates. These measures demonstrate the cat's perceptual sensitivity to pitch in the absence of cochlear-place cues and may be valuable for evaluating neural mechanisms of temporal pitch perception in the feline animal model of stimulation by a CI or novel auditory prostheses.

The effects of alphabetic literacy, linguistic-processing demand and tone type on the dichotic listening of lexical tones

Brain lateralization of lexical tone processing remains a matter of debate. In this study we used a dichotic listening paradigm to examine the influences of the knowledge of Jyutping (a romanization writing system which provides explicit Cantonese tone markers), linguistic-processing demand and tone type on the ear preference pattern of native tone processing in Hong Kong Cantonese speakers. While participants with little knowledge of Jyutping showed a previously reported left-ear advantage (LEA), those with a good level of Jyutping expertise exhibited either a right-ear advantage or bilateral processing during lexical tone identification and contour tone discrimination, respectively. As for the effect of linguistic-processing demand, while an LEA was found in acoustic/phonetic perception situations, this advantage disappeared and was replaced by a bilateral pattern in conditions that involved a greater extent of linguistic processing, suggesting an increased involvement of the left hemisphere. Regarding the effect of tone type, both groups showed an LEA in level tone discrimination, but only the Jyutping group demonstrated a bilateral pattern in contour tone discrimination. Overall, knowledge of written codes of tones, greater degree of linguistic processing and contour tone processing seem to influence the brain lateralization of lexical tone processing in native listeners of Cantonese by increasing the recruitment of the left-hemisphere language network.

The effect of lexical tone experience on English intonation perception in Mandarin-speaking cochlear-implanted children

To examine the effect of lexical tone experience on English intonation perception in Mandarin-speaking cochlear-implanted children during second language acquisition in Taiwan. A retrospective cohort study. A tertiary referred center. Fourteen children with cochlear implant (CI) in the experimental group, and 9 normal hearing children in the control group were enrolled in this study. Cochlear implantation and hearing rehabilitation. Two speech recognition accuracies were examined: (1) Lexical tone recognition (4-alternative forced choice, AFC), (2) English Sentence Intonation (2AFC). The overall accuracies for tone perception are 61.13% (standard deviation, SD = 10.84%) for CI group and 93.82% (SD = 1.80%) for normal hearing group. Tone 4 and Tone 1 were more easily to be recognized than tone 2 and tone 3 in the pediatric CI recipients (cCI) group. In English intonation perception, the overall accuracies are 61.82% (SD = 16.85%) for CI group, and 97.59% (SD = 4.73%) for normal hearing group. Significant high correlation (R = .919, P ≦ .000) between lexical tone perception and English intonation perception is noted. There is no significant difference for English intonation perception accuracies between Mandarin-speaking cCI (61.82%) and English-speaking cCI (70.13%, P = .11). Mandarin-speaking cochlear-implanted children showed significant deficits in perception of lexical tone and English intonation relative to normal hearing children. There was no tonal language benefit in Mandarin-speaking cochlear-implanted children's English intonation perception, compared to the English-speaking cochlear-implanted peers. For cochlear-implanted children, better lexical tone perception comes with better English intonation perception. Enhancing Mandarin prosodic perception for cochlear-implanted children may benefit their command of intonation in English.

Acoustic Cry Characteristics of Infants as a Marker of Neurological Dysfunction: A Systematic Review and Meta-Analysis

BACKGROUND

Atypical cries have been identified in infants with neurological dysfunction. The aim of this study was to conduct a systematic review and meta-analysis to appraise existing evidence for associations between acoustic cry characteristics and neurological dysfunction in infants aged 18 months or less.

METHODS

PubMed/MEDLINE, PsycINFO, CINAHL, and Embase were searched for original, peer-reviewed studies published in English reporting cry variables in infants aged 18 months or less with or at risk of neurological dysfunction. Studies without a nonneurologically impaired control sample were excluded. Pooled effect sizes were estimated using standardized mean difference (SMD) and odds ratio (OR). I² indicated study heterogeneity, and the risk of bias was assessed using the Newcastle-Ottawa Scale.

RESULTS

From March 2018 to February 2019, 28,294 studies were retrieved. Eight were meta-analyzed. Infants with or at risk of neurological dysfunction exhibited higher mean (SMD = 0.11 [95% confidence interval, 0.00 to 0.23]) and minimum (SMD = 0.93 [0.64 to 1.23]) fundamental frequency; higher odds of hyperphonation (OR = 13.17 [1.05 to 165.87]), biphonation (OR = 10.62 [1.53 to 73.59]), rise-fall-rise melodies (OR = 4.66 [1.16 to 18.66]), and flat melodies (OR = 4.47 [1.27 to 15.68]); and lower odds of fall-rise-fall melodies (OR = 0.21 [0.05 to 0.83]).

CONCLUSIONS

Infants with underlying neuropathology have unique cries characterized by higher fundamental frequency, dysphonation, and atypical melodies, although study heterogeneity and imprecision of effect size estimates limited our interpretation. Assessment of acoustic cry characteristics offers the potential for noninvasive, rapid, point-of-care screening for neurologically high-risk infants.

Early auditory responses to speech sounds in Parkinson's disease: preliminary data

Parkinson’s disease (PD), as a manifestation of basal ganglia dysfunction, is associated with a number of speech deficits, including reduced voice modulation and vocal output. Interestingly, previous work has shown that participants with PD show an increased feedback-driven motor response to unexpected fundamental frequency perturbations during speech production, and a heightened ability to detect differences in vocal pitch relative to control participants. Here, we explored one possible contributor to these enhanced responses. We recorded the frequency-following auditory brainstem response (FFR) to repetitions of the speech syllable [da] in PD and control participants. Participants with PD displayed a larger amplitude FFR related to the fundamental frequency of speech stimuli relative to the control group. The current preliminary results suggest the dysfunction of the basal ganglia in PD contributes to the early stage of auditory processing and may reflect one component of a broader sensorimotor processing impairment associated with the disease.

Altered processing of communication signals in the subcortical auditory sensory pathway in autism

Autism spectrum disorder (ASD) is characterised by social communication difficulties. These difficulties have been mainly explained by cognitive, motivational, and emotional alterations in ASD. The communication difficulties could, however, also be associated with altered sensory processing of communication signals. Here, we assessed the functional integrity of auditory sensory pathway nuclei in ASD in three independent functional magnetic resonance imaging experiments. We focused on two aspects of auditory communication that are impaired in ASD: voice identity perception, and recognising speech‐in‐noise. We found reduced processing in adults with ASD as compared to typically developed control groups (pairwise matched on sex, age, and full‐scale IQ) in the central midbrain structure of the auditory pathway (inferior colliculus [IC]). The right IC responded less in the ASD as compared to the control group for voice identity, in contrast to speech recognition. The right IC also responded less in the ASD as compared to the control group when passively listening to vocal in contrast to non‐vocal sounds. Within the control group, the left and right IC responded more when recognising speech‐in‐noise as compared to when recognising speech without additional noise. In the ASD group, this was only the case in the left, but not the right IC. The results show that communication signal processing in ASD is associated with reduced subcortical sensory functioning in the midbrain. The results highlight the importance of considering sensory processing alterations in explaining communication difficulties, which are at the core of ASD.

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.

Cortical hemisphere preference and brainstem ear asymmetry reflect experience-dependent functional modulation of pitch

Temporal attributes of pitch processing at cortical and subcortical levels are differentially weighted and well-coordinated. The question is whether language experience induces functional modulation of hemispheric preference complemented by brainstem ear symmetry for pitch processing. Brainstem frequency-following and cortical pitch responses were recorded concurrently from Mandarin and English participants. A Mandarin syllable with a rising pitch contour was presented to both ears with monaural stimulation. At the cortical level, left ear stimulation in the Chinese group revealed an experience-dependent response for pitch processing in the right hemisphere, consistent with a functionalaccount. The English group revealed a contralateral hemisphere preference consistent with a structuralaccount. At the brainstem level, Chinese participants showed a functional leftward ear asymmetry, whereas English were consistent with a structural account. Overall, language experience modulates both cortical hemispheric preference and brainstem ear asymmetry in a complementary manner to optimize processing of temporal attributes of pitch.

Context-dependent Plasticity and Strength of Subcortical Encoding of Musical Sounds Independently Underlie Pitch Discrimination for Music Melodies

Subcortical auditory nuclei contribute to pitch perception, but how subcortical sound encoding is related to pitch processing for music perception remains unclear. Conventionally, enhanced subcortical sound encoding is considered underlying superior pitch discrimination. However, associations between superior auditory perception and the context-dependent plasticity of subcortical sound encoding are also documented. Here, we explored the subcortical neural correlates to music pitch perception by analyzing frequency-following responses (FFRs) to musical sounds presented in a predictable context and a random context. We found that the FFR inter-trial phase-locking (ITPL) was negatively correlated with behavioral performances of discrimination of pitches in music melodies. It was also negatively correlated with the plasticity indices measuring the variability of FFRs to physically identical sounds between the two contexts. The plasticity indices were consistently positively correlated with pitch discrimination performances, suggesting the subcortical context-dependent plasticity underlying music pitch perception. Moreover, the raw FFR spectral strength was not significantly correlated with pitch discrimination performances. However, it was positively correlated with behavioral performances when the FFR ITPL was controlled by partial correlations, suggesting that the strength of subcortical sound encoding underlies music pitch perception. When the spectral strength was controlled by partial correlations, the negative ITPL-behavioral correlations were maintained. Furthermore, the FFR ITPL, the plasticity indices, and the FFR spectral strength were more correlated with pitch than with rhythm discrimination performances. These findings suggest that the context-dependent plasticity and the strength of subcortical encoding of musical sounds are independently and perhaps specifically associated with pitch perception for music melodies.

Categorical Encoding of Vowels in Primary Auditory Cortex

Speech perception involves mapping from a continuous and variable acoustic speech signal to discrete, linguistically meaningful units. However, it is unclear where in the auditory processing stream speech sound representations cease to be veridical (faithfully encoding precise acoustic properties) and become categorical (encoding sounds as linguistic categories). In this study, we used functional magnetic resonance imaging and multivariate pattern analysis to determine whether tonotopic primary auditory cortex (PAC), defined as tonotopic voxels falling within Heschl's gyrus, represents one class of speech sounds-vowels-veridically or categorically. For each of 15 participants, 4 individualized synthetic vowel stimuli were generated such that the vowels were equidistant in acoustic space, yet straddled a categorical boundary (with the first 2 vowels perceived as [i] and the last 2 perceived as [i]). Each participant's 4 vowels were then presented in a block design with an irrelevant but attention-demanding level change detection task. We found that in PAC bilaterally, neural discrimination between pairs of vowels that crossed the categorical boundary was more accurate than neural discrimination between equivalently spaced vowel pairs that fell within a category. These findings suggest that PAC does not represent vowel sounds veridically, but that encoding of vowels is shaped by linguistically relevant phonemic categories.

Auditory brainstem response asymmetries in older adults: An exploratory study using click and speech stimuli

Background

Some evidence suggests that young adults exhibit a selective laterality of auditory brainstem response (ABR) elicited with speech stimuli. Little is known about such an auditory laterality in older adults.

Objective

The aim of this study was to investigate possible asymmetric auditory brainstem processing between right and left ear presentation in older adults.

Methods

Sixty-two older adults presenting with normal hearing thresholds according to their age and who were native speakers of Quebec French participated in this study. ABR was recorded using click and a 40-ms /da/ syllable. ABR was elicited through monaural right and monaural left stimulation. Latency and amplitude for click-and speech-ABR components were compared between right and left ear presentations. In addition, for the /da/ syllable, a fast Fourier transform analysis of the sustained frequency-following response (FFR) of the vowel was performed along with stimulus-to-response and right-left ear correlation analyses.

Results

No significant differences between right and left ear presentation were found for amplitudes and latencies of the click-ABR components. Significantly shorter latencies for right ear presentation as compared to left ear presentation were observed for onset and offset transient components (V, A and O), sustained components (D and E), and voiced transition components (C) of the speech-ABR. In addition, the spectral amplitude of the fundamental frequency (F0) was significantly larger for the left ear presentation than the right ear presentation.

Conclusions

Results of this study show that older adults with normal hearing exhibit symmetric encoding for click stimuli at the brainstem level between the right and left ear presentation. However, they present with brainstem asymmetries for the encoding of selective stimulus components of the speech-ABR between the right and left ear presentation. The right ear presentation of a /da/ syllable elicited reduced neural timing for both transient and sustained components compared to the left ear. Conversely, a stronger left ear F0 encoding was observed. These findings suggest that at a preattentive, sensory stage of auditory processing, older adults lateralize speech stimuli similarly to young adults.

Lifelong Tone Language Experience does not Eliminate Deficits in Neural Encoding of Pitch in Autism Spectrum Disorder

Atypical pitch processing is a feature of Autism Spectrum Disorder (ASD), which affects non-tone language speakers' communication. Lifelong auditory experience has been demonstrated to modify genetically-predisposed risks for pitch processing. We examined individuals with ASD to test the hypothesis that lifelong auditory experience in tone language may eliminate impaired pitch processing in ASD. We examined children's and adults' Frequency-following Response (FFR), a neurophysiological component indexing early neural sensory encoding of pitch. Univariate and machine-learning-based analytics suggest less robust pitch encoding and diminished pitch distinctions in the FFR from individuals with ASD. Contrary to our hypothesis, results point to a linguistic pitch encoding impairment associated with ASD that may not be eliminated even by lifelong sensory experience.

Frequency selectivity of tonal language native speakers probed by suppression tuning curves of spontaneous otoacoustic emissions

Native acquisition of a tonal language (TL) is related to enhanced abilities of pitch perception and production, compared to non-tonal language (NTL) native speakers. Moreover, differences in brain responses to both linguistically relevant and non-relevant pitch changes have been described in TL native speakers. It is so far unclear to which extent differences are present at the peripheral processing level of the cochlea. To determine possible differences in cochlear frequency selectivity between Asian TL speakers and Caucasian NTL speakers, suppression tuning curves (STCs) of spontaneous otoacoustic emissions (SOAEs) were examined in both groups. By presenting pure tones, SOAE levels were suppressed and STCs were derived. SOAEs with center frequencies higher than 4.5 kHz were recorded only in female TL native speakers, which correlated with better high-frequency tone detection thresholds. The suppression thresholds at the tip of the STC and filter quality coefficient Q_10dB did not differ significantly between both language groups. Thus, the characteristics of the STCs of SOAEs do not support the presence of differences in peripheral auditory processing between TL and NTL native speakers.

Tinnitus Impacts on Speech and Non-speech Stimuli

OBJECTIVE

To investigate how tinnitus affects the processing of speech and non-speech stimuli at the subcortical level.

STUDY DESIGN

Cross-sectional analytical study.

SETTING

Academic, tertiary referral center.

PATIENTS

Eighteen individuals with tinnitus and 20 controls without tinnitus matched based on their age and sex. All subjects had normal hearing sensitivity.

INTERVENTION

Diagnostic.

MAIN OUTCOME MEASURES

The effect of tinnitus on the parameters of auditory brainstem responses (ABR) to non-speech (click-ABR), and speech (sABR) stimuli was investigated.

RESULTS

Latencies of click ABR in waves III, V, and Vn, as well as inter-peak latency (IPL) of I to V were significantly longer in individuals with tinnitus compared with the controls. Individuals with tinnitus demonstrated significantly longer latencies of all sABR waves than the control group. The tinnitus patients also exhibited a significant decrease in the slope of the V-A complex and reduced encoding of the first and higher formants. A significant difference was observed between the two groups in the spectral magnitudes, the first formant frequency range (F1) and a higher frequency region (HF).

CONCLUSIONS

Our findings suggest that maladaptive neural plasticity resulting from tinnitus can be subcortically measured and affects timing processing of both speech and non-speech stimuli. The findings have been discussed based on models of maladaptive plasticity and the interference of tinnitus as an internal noise in synthesizing speech auditory stimuli.

Simultaneous EEG and MEG recordings reveal vocal pitch elicited cortical gamma oscillations in young and older adults

The frequency-following response with origin in the auditory brainstem represents the pitch contour of voice and can be recorded with electrodes from the scalp. MEG studies also revealed a cortical contribution to the high gamma oscillations at the fundamental frequency (f₀) of a vowel stimulus. Therefore, studying the cortical component of the frequency-following response could provide insights into how pitch information is encoded at the cortical level. Comparing how aging affects the different responses may help to uncover the neural mechanisms underlying speech understanding deficits in older age. We simultaneously recorded EEG and MEG responses to the syllable /ba/. MEG beamformer analysis localized sources in bilateral auditory cortices and the midbrain. Time-frequency analysis showed a faithful representation of the pitch contour between 106 Hz and 138 Hz in the cortical activity. A cross-correlation revealed a latency of 20 ms. Furthermore, stimulus onsets elicited cortical 40-Hz responses. Both the 40-Hz and the f₀ response amplitudes increased in older age and were larger in the right hemisphere. The effects of aging and laterality of the f₀ response were evident in the MEG only, suggesting that both effects were characteristics of the cortical response. After comparing f₀ and N1 responses in EEG and MEG, we estimated that approximately one-third of the scalp-recorded f₀ response could be cortical in origin. We attributed the significance of the cortical f₀ response to the precise timing of cortical neurons that serve as a time-sensitive code for pitch.

Analyzing the FFR: A tutorial for decoding the richness of auditory function

The frequency-following response, or FFR, is a neurophysiological response to sound that precisely reflects the ongoing dynamics of sound. It can be used to study the integrity and malleability of neural encoding of sound across the lifespan. Sound processing in the brain can be impaired with pathology and enhanced through expertise. The FFR can index linguistic deprivation, autism, concussion, and reading impairment, and can reflect the impact of enrichment with short-term training, bilingualism, and musicianship. Because of this vast potential, interest in the FFR has grown considerably in the decade since our first tutorial. Despite its widespread adoption, there remains a gap in the current knowledge of its analytical potential. This tutorial aims to bridge this gap. Using recording methods we have employed for the last 20 + years, we have explored many analysis strategies. In this tutorial, we review what we have learned and what we think constitutes the most effective ways of capturing what the FFR can tell us. The tutorial covers FFR components (timing, fundamental frequency, harmonics) and factors that influence FFR (stimulus polarity, response averaging, and stimulus presentation/recording jitter). The spotlight is on FFR analyses, including ways to analyze FFR timing (peaks, autocorrelation, phase consistency, cross-phaseogram), magnitude (RMS, SNR, FFT), and fidelity (stimulus-response correlations, response-to-response correlations and response consistency). The wealth of information contained within an FFR recording brings us closer to understanding how the brain reconstructs our sonic world.

Afferent-efferent connectivity between auditory brainstem and cortex accounts for poorer speech-in-noise comprehension in older adults

Speech-in-noise (SIN) comprehension deficits in older adults have been linked to changes in both subcortical and cortical auditory evoked responses. However, older adults' difficulty understanding SIN may also be related to an imbalance in signal transmission (i.e., functional connectivity) between brainstem and auditory cortices. By modeling high-density scalp recordings of speech-evoked responses with sources in brainstem (BS) and bilateral primary auditory cortices (PAC), we show that beyond attenuating neural activity, hearing loss in older adults compromises the transmission of speech information between subcortical and early cortical hubs of the speech network. We found that the strength of afferent BS→PAC neural signaling (but not the reverse efferent flow; PAC→BS) varied with mild declines in hearing acuity and this "bottom-up" functional connectivity robustly predicted older adults' performance in a SIN identification task. Connectivity was also a better predictor of SIN processing than unitary subcortical or cortical responses alone. Our neuroimaging findings suggest that in older adults (i) mild hearing loss differentially reduces neural output at several stages of auditory processing (PAC > BS), (ii) subcortical-cortical connectivity is more sensitive to peripheral hearing loss than top-down (cortical-subcortical) control, and (iii) reduced functional connectivity in afferent auditory pathways plays a significant role in SIN comprehension problems.

Frequency following responses to tone glides: Effects of frequency extent, direction, and electrode montage

The spectral (frequency) and amplitude cues in speech change rapidly over time. Study of the neural encoding of these dynamic features may help to improve diagnosis and treatment of speech-perception difficulties. This study uses tone glides as a simple approximation of dynamic speech sounds to better our understanding of the underlying neural representation of speech. The frequency following response (FFR) was recorded from 10 young normal-hearing adults using six signals varying in glide direction (rising and falling) and extent of frequency change (13, 23, and 1 octave). In addition, the FFR was simultaneously recorded using two different electrode montages (vertical and horizontal). These factors were analyzed across three time windows using a measure of response strength (signal-to-noise ratio) and a measure of temporal coherence (stimulus-to-response correlation coefficient). Results demonstrated effects of extent, montage, and a montage-by-window interaction. SNR and stimulus-to-response correlation measures differed in their sensitivity to these factors. These results suggest that the FFR reflects dynamic acoustic characteristics of simple tonal stimuli very well. Additional research is needed to determine how neural encoding may differ for more natural dynamic speech signals and populations with impaired auditory processing.

A tonal-language benefit for pitch in normally-hearing and cochlear-implanted children

In tonal languages, voice pitch inflections change the meaning of words, such that the brain processes pitch not merely as an acoustic characterization of sound but as semantic information. In normally-hearing (NH) adults, this linguistic pressure on pitch appears to sharpen its neural encoding and can lead to perceptual benefits, depending on the task relevance, potentially generalizing outside of the speech domain. In children, however, linguistic systems are still malleable, meaning that their encoding of voice pitch information might not receive as much neural specialization but might generalize more easily to ecologically irrelevant pitch contours. This would seem particularly true for early-deafened children wearing a cochlear implant (CI), who must exhibit great adaptability to unfamiliar sounds as their sense of pitch is severely degraded. Here, we provide the first demonstration of a tonal language benefit in dynamic pitch sensitivity among NH children (using both a sweep discrimination and labelling task) which extends partially to children with CI (i.e., in the labelling task only). Strong age effects suggest that sensitivity to pitch contours reaches adult-like levels early in tonal language speakers (possibly before 6 years of age) but continues to develop in non-tonal language speakers well into the teenage years. Overall, we conclude that language-dependent neuroplasticity can enhance behavioral sensitivity to dynamic pitch, even in extreme cases of auditory degradation, but it is most easily observable early in life.

Interactive effects of linguistic abstraction and stimulus statistics in the online modulation of neural speech encoding

Speech processing is highly modulated by context. Prior studies examining frequency-following responses (FFRs), an electrophysiological 'neurophonic' potential that faithfully reflects phase-locked activity from neural ensembles within the auditory network, have demonstrated that stimulus context modulates the integrity of speech encoding. The extent to which context-dependent encoding reflects general auditory properties or interactivities between statistical and higher-level linguistic processes remains unexplored. Our study examined whether speech encoding, as reflected by FFRs, is modulated by abstract phonological relationships between a stimulus and surrounding contexts. FFRs were elicited to a Mandarin rising-tone syllable (/ji-TR/, 'second') randomly presented with other syllables in three contexts from 17 native listeners. In a contrastive context, /ji-TR/ occurred with meaning-contrastive high-level-tone syllables (/ji-H/, 'one'). In an allotone context, TR occurred with dipping-tone syllables /ji-D/, a non-meaning-contrastive variant of /ji-TR/. In a repetitive context, the same /ji-TR/ occurred with other speech tokens of /ji-TR/. Consistent with prior work, neural tracking of /ji-TR/ pitch contour was more faithful in the repetitive condition wherein /ji-TR/ occurred more predictably (p = 1) than in the contrastive condition (p = 0.34). Crucially, in the allotone context, neural tracking of /ji-TR/ was more accurate relative to the contrastive context, despite both having an identical transitional probability (p = 0.34). Mechanistically, the non-meaning-contrastive relationship may have augmented the probability to /ji-TR/ occurrence in the allotone context. Results indicate online interactions between bottom-up and top-down mechanisms, which facilitate speech perception. Such interactivities may predictively fine-tune incoming speech encoding using linguistic and statistical information from prior context.

Effects of Phase-Locking Deficits on Speech Recognition in Older Adults With Presbycusis

Objective: People with presbycusis (PC) often report difficulties in speech recognition, especially under noisy listening conditions. Investigating the PC-related changes in central representations of envelope signals and temporal fine structure (TFS) signals of speech sounds is critical for understanding the mechanism underlying the PC-related deficit in speech recognition. Frequency-following responses (FFRs) to speech stimulation can be used to examine the subcortical encoding of both envelope and TFS speech signals. This study compared FFRs to speech signals between listeners with PC and those with clinically normal hearing (NH) under either quiet or noise-masking conditions.

Methods: FFRs to a 170-ms speech syllable /da/ were recorded under either a quiet or noise-masking (with a signal-to-noise ratio (SNR) of 8 dB) condition in 14 older adults with PC and 13 age-matched adults with NH. The envelope (FFR_ENV) and TFS (FFR_TFS) components of FFRs were analyzed separately by adding and subtracting the alternative polarity responses, respectively. Speech recognition in noise was evaluated in each participant.

Results: In the quiet condition, compared with the NH group, the PC group exhibited smaller F0 and H3 amplitudes and decreased stimulus-response (S-R) correlation for FFR_ENV but not for FFR_TFS. Both the H2 and H3 amplitudes and the S-R correlation of FFR_ENV significantly decreased in the noise condition compared with the quiet condition in the NH group but not in the PC group. Moreover, the degree of hearing loss was correlated with noise-induced changes in FFR_TFS morphology. Furthermore, the speech-in-noise (SIN) threshold was negatively correlated with the noise-induced change in H2 (for FFR_ENV) and the S-R correlation for FFR_ENV in the quiet condition.

Conclusion: Audibility affects the subcortical encoding of both envelope and TFS in PC patients. The impaired ability to adjust the balance between the envelope and TFS in the noise condition may be part of the mechanism underlying PC-related deficits in speech recognition in noise. FFRs can predict SIN perception performance.

Neural representation of interaural correlation in human auditory brainstem: Comparisons between temporal-fine structure and envelope

Central processing of interaural correlation (IAC), which depends on the precise representation of acoustic signals from the two ears, is essential for both localization and recognition of auditory objects. A complex soundwave is initially filtered by the peripheral auditory system into multiple narrowband waves, which are further decomposed into two functionally distinctive components: the quickly-varying temporal-fine structure (TFS) and the slowly-varying envelope. In rats, a narrowband noise can evoke auditory-midbrain frequency-following responses (FFRs) that contain both the TFS component (FFR_TFS) and the envelope component (FFR_Env), which represent the TFS and envelope of the narrowband noise, respectively. These two components are different in sensitivity to the interaural time disparity. In human listeners, the present study investigated whether the FFR_TFS and FFR_Env components of brainstem FFRs to a narrowband noise are different in sensitivity to IAC and whether there are potential brainstem mechanisms underlying the integration of the two components. The results showed that although both the amplitude of FFR_TFS and that of FFR_Env were significantly affected by shifts of IAC between 1 and 0, the stimulus-to-response correlation for FFR_TFS, but not that for FFR_Env, was sensitive to the IAC shifts. Moreover, in addition to the correlation between the binaurally evoked FFR_TFS and FFR_Env, the correlation between the IAC-shift-induced change of FFR_TFS and that of FFR_Env was significant. Thus, the TFS information is more precisely represented in the human auditory brainstem than the envelope information, and the correlation between FFR_TFS and FFR_Env for the same narrowband noise suggest a brainstem binding mechanism underlying the perceptual integration of the TFS and envelope signals.

Subcortical sources dominate the neuroelectric auditory frequency-following response to speech

Frequency-following responses (FFRs) are neurophonic potentials that provide a window into the encoding of complex sounds (e.g., speech/music), auditory disorders, and neuroplasticity. While the neural origins of the FFR remain debated, renewed controversy has reemerged after demonstration that FFRs recorded via magnetoencephalography (MEG) are dominated by cortical rather than brainstem structures as previously assumed. Here, we recorded high-density (64 ch) FFRs via EEG and applied state-of-the art source imaging techniques to multichannel data (discrete dipole modeling, distributed imaging, independent component analysis, computational simulations). Our data confirm a mixture of generators localized to bilateral auditory nerve (AN), brainstem inferior colliculus (BS), and bilateral primary auditory cortex (PAC). However, frequency-specific scrutiny of source waveforms showed the relative contribution of these nuclei to the aggregate FFR varied across stimulus frequencies. Whereas AN and BS sources produced robust FFRs up to ∼700 Hz, PAC showed weak phase-locking with little FFR energy above the speech fundamental (100 Hz). Notably, CLARA imaging further showed PAC activation was eradicated for FFRs >150 Hz, above which only subcortical sources remained active. Our results show (i) the site of FFR generation varies critically with stimulus frequency; and (ii) opposite the pattern observed in MEG, subcortical structures make the largest contribution to electrically recorded FFRs (AN ≥ BS > PAC). We infer that cortical dominance observed in previous neuromagnetic data is likely due to the bias of MEG to superficial brain tissue, underestimating subcortical structures that drive most of the speech-FFR. Cleanly separating subcortical from cortical FFRs can be achieved by ensuring stimulus frequencies are >150-200 Hz, above the phase-locking limit of cortical neurons.

Subcortical encoding of speech cues in children with congenital blindness

BACKGROUND

Congenital visual deprivation underlies neural plasticity in different brain areas, and provides an outstanding opportunity to study the neuroplastic capabilities of the brain.

OBJECTIVES

The present study aimed to investigate the effect of congenital blindness on subcortical auditory processing using electrophysiological and behavioral assessments in children.

METHODS

A total of 47 children aged 8-12 years, including 22 congenitally blind (CB) children and 25 normal-sighted (NS) control, were studied. All children were tested using an auditory brainstem response (ABR) test with both click and speech stimuli. Speech recognition and musical abilities were tested using standard tools.

RESULTS

Significant differences were observed between the two groups in speech ABR wave latencies A, F and O (p≤0.043), wave amplitude F (p = 0.039), V-A slope (p = 0.026), and three spectral magnitudes F0, F1 and HF (p≤0.002). CB children showed a superior performance compared to NS peers in all the subtests and the total score of musical abilities (p≤0.003). Moreover, they had significantly higher scores during the nonsense syllable test in noise than the NS children (p = 0.034). Significant negative correlations were found only in CB children between the total music score and both wave A (p = 0.039) and wave F (p = 0.029) latencies, as well as nonsense-syllable test in noise and the wave A latency (p = 0.041).

CONCLUSION

Our results suggest that neuroplasticity resulting from congenital blindness can be measured subcortically and has a heightened effect on temporal, musical and speech processing abilities. The findings have been discussed based on models of plasticity and the influence of corticofugal modulation in synthesizing complex auditory stimuli.

Involvement of the Serotonin Transporter Gene in Accurate Subcortical Speech Encoding

A flourishing line of evidence has highlighted the encoding of speech sounds in the subcortical auditory system as being shaped by acoustic, linguistic, and musical experience and training. And while the heritability of auditory speech as well as nonspeech processing has been suggested, the genetic determinants of subcortical speech processing have not yet been uncovered. Here, we postulated that the serotonin transporter-linked polymorphic region (5-HTTLPR), a common functional polymorphism located in the promoter region of the serotonin transporter gene (SLC6A4), is implicated in speech encoding in the human subcortical auditory pathway. Serotonin has been shown as essential for modulating the brain response to sound both cortically and subcortically, yet the genetic factors regulating this modulation regarding speech sounds have not been disclosed. We recorded the frequency following response, a biomarker of the neural tracking of speech sounds in the subcortical auditory pathway, and cortical evoked potentials in 58 participants elicited to the syllable /ba/, which was presented >2000 times. Participants with low serotonin transporter expression had higher signal-to-noise ratios as well as a higher pitch strength representation of the periodic part of the syllable than participants with medium to high expression, possibly by tuning synaptic activity to the stimulus features and hence a more efficient suppression of noise. These results imply the 5-HTTLPR in subcortical auditory speech encoding and add an important, genetically determined layer to the factors shaping the human subcortical response to speech sounds.

SIGNIFICANCE STATEMENT

The accurate encoding of speech sounds in the subcortical auditory nervous system is of paramount relevance for human communication, and it has been shown to be altered in different disorders of speech and auditory processing. Importantly, this encoding is plastic and can therefore be enhanced by language and music experience. Whether genetic factors play a role in speech encoding at the subcortical level remains unresolved. Here we show that a common polymorphism in the serotonin transporter gene relates to an accurate and robust neural tracking of speech stimuli in the subcortical auditory pathway. This indicates that serotonin transporter expression, eventually in combination with other polymorphisms, delimits the extent to which lifetime experience shapes the subcortical encoding of speech.

Differential sensitivity to changes in pitch acceleration in the auditory brainstem and cortex

The cortical pitch-specific response (CPR) is differentially sensitive to pitch contours varying in rate of acceleration-time-variant Mandarin Tone2 (T2) versus constant, linear rising ramp (Linear)-as a function of language experience (Krishnan, Gandour, & Suresh, 2014). CPR and brainstem frequency following response (FFR) data were recorded concurrently from native Mandarin listeners using the same stimuli. Results showed that T2 elicited larger responses than Linear at both cortical and brainstem levels (CPR: Na-Pb, Pb-Nb; FFR). However, Pb-Nb exhibited a larger difference in magnitude between T2 and Linear than either Na-Pb or FFR. This finding highlights differential weighting of brain responses elicited by a specific temporal attribute of pitch. Consistent with the notion of a distributed, integrated hierarchical pitch processing network, temporal attributes of pitch are differentially weighted by subcortical and cortical level processing.

Functional Interplay Between the Putative Measures of Rostral and Caudal Efferent Regulation of Speech Perception in Noise

Efferent modulation has been demonstrated to be very important for speech perception, especially in the presence of noise. We examined the functional relationship between two efferent systems: the rostral and caudal efferent pathways and their individual influences on speech perception in noise. Earlier studies have shown that these two efferent mechanisms were correlated with speech perception in noise. However, previously, these mechanisms were studied in isolation, and their functional relationship with each other was not investigated. We used a correlational design to study the relationship if any, between these two mechanisms in young and old normal hearing individuals. We recorded context-dependent brainstem encoding as an index of rostral efferent function and contralateral suppression of otoacoustic emissions as an index of caudal efferent function in groups with good and poor speech perception in noise. These efferent mechanisms were analysed for their relationship with each other and with speech perception in noise. We found that the two efferent mechanisms did not show any functional relationship. Interestingly, both the efferent mechanisms correlated with speech perception in noise and they even emerged as significant predictors. Based on the data, we posit that the two efferent mechanisms function relatively independently but with a common goal of fine-tuning the afferent input and refining auditory perception in degraded listening conditions.

Language-dependent changes in pitch-relevant neural activity in the auditory cortex reflect differential weighting of temporal attributes of pitch contours

There remains a gap in our knowledge base about neural representation of pitch attributes that occur between onset and offset of dynamic, curvilinear pitch contours. The aim is to evaluate how language experience shapes processing of pitch contours as reflected in the amplitude of cortical pitch-specific response components. Responses were elicited from three nonspeech, bidirectional (falling-rising) pitch contours representative of Mandarin Tone 2 varying in location of the turning point with fixed onset and offset. At the frontocentral Fz electrode site, Na-Pb and Pb-Nb amplitude of the Chinese group was larger than the English group for pitch contours exhibiting later location of the turning point relative to the one with the earliest location. Chinese listeners' amplitude was also greater than that of English in response to those same pitch contours with later turning points. At lateral temporal sites (T7/T8), Na-Pb amplitude was larger in Chinese listeners relative to English over the right temporal site. In addition, Pb-Nb amplitude of the Chinese group showed a rightward asymmetry. The pitch contour with its turning point located about halfway of total duration evoked a rightward asymmetry regardless of group. These findings suggest that neural mechanisms processing pitch in the right auditory cortex reflect experience-dependent modulation of sensitivity to weighted integration of changes in acceleration rates of rising and falling sections and the location of the turning point.

Sustained Cortical and Subcortical Measures of Auditory and Visual Plasticity following Short-Term Perceptual Learning

Short-term training can lead to improvements in behavioral discrimination of auditory and visual stimuli, as well as enhanced EEG responses to those stimuli. In the auditory domain, fluency with tonal languages and musical training has been associated with long-term cortical and subcortical plasticity, but less is known about the effects of shorter-term training. This study combined electroencephalography (EEG) and behavioral measures to investigate short-term learning and neural plasticity in both auditory and visual domains. Forty adult participants were divided into four groups. Three groups trained on one of three tasks, involving discrimination of auditory fundamental frequency (F0), auditory amplitude modulation rate (AM), or visual orientation (VIS). The fourth (control) group received no training. Pre- and post-training tests, as well as retention tests 30 days after training, involved behavioral discrimination thresholds, steady-state visually evoked potentials (SSVEP) to the flicker frequencies of visual stimuli, and auditory envelope-following responses simultaneously evoked and measured in response to rapid stimulus F0 (EFR), thought to reflect subcortical generators, and slow amplitude modulation (ASSR), thought to reflect cortical generators. Enhancement of the ASSR was observed in both auditory-trained groups, not specific to the AM-trained group, whereas enhancement of the SSVEP was found only in the visually-trained group. No evidence was found for changes in the EFR. The results suggest that some aspects of neural plasticity can develop rapidly and may generalize across tasks but not across modalities. Behaviorally, the pattern of learning was complex, with significant cross-task and cross-modal learning effects.

Stability and plasticity in neural encoding of linguistically relevant pitch patterns

While lifelong language experience modulates subcortical encoding of pitch patterns, there is emerging evidence that short-term training introduced in adulthood also shapes subcortical pitch encoding. Here we use a cross-language design to examine the stability of language experience-dependent subcortical plasticity over multiple days. We then examine the extent to which behavioral relevance induced by sound-to-category training leads to plastic changes in subcortical pitch encoding in adulthood relative to adolescence, a period of ongoing maturation of subcortical and cortical auditory processing. Frequency-following responses (FFRs), which reflect phase-locked activity from subcortical neural ensembles, were elicited while participants passively listened to pitch patterns reflective of Mandarin tones. In experiment 1, FFRs were recorded across three consecutive days from native Chinese-speaking (n = 10) and English-speaking (n = 10) adults. In experiment 2, FFRs were recorded from native English-speaking adolescents (n = 20) and adults (n = 15) before, during, and immediately after a session of sound-to-category training, as well as a day after training ceased. Experiment 1 demonstrated the stability of language experience-dependent subcortical plasticity in pitch encoding across multiple days of passive exposure to linguistic pitch patterns. In contrast, experiment 2 revealed an enhancement in subcortical pitch encoding that emerged a day after the sound-to-category training, with some developmental differences observed. Taken together, these findings suggest that behavioral relevance is a critical component for the observation of plasticity in the subcortical encoding of pitch.NEW & NOTEWORTHY We examine the timescale of experience-dependent auditory plasticity to linguistically relevant pitch patterns. We find extreme stability in lifelong experience-dependent plasticity. We further demonstrate that subcortical function in adolescents and adults is modulated by a single session of sound-to-category training. Our results suggest that behavioral relevance is a necessary ingredient for neural changes in pitch encoding to be observed throughout human development. These findings contribute to the neurophysiological understanding of long- and short-term experience-dependent modulation of pitch.

Air traffic controllers' long-term speech-in-noise training effects: A control group study

Introduction:

Speech perception in noise relies on the capacity of the auditory system to process complex sounds using sensory and cognitive skills. The possibility that these can be trained during adulthood is of special interest in auditory disorders, where speech in noise perception becomes compromised. Air traffic controllers (ATC) are constantly exposed to radio communication, a situation that seems to produce auditory learning. The objective of this study has been to quantify this effect.

Subjects and Methods:

19 ATC and 19 normal hearing individuals underwent a speech in noise test with three signal to noise ratios: 5, 0 and −5 dB. Noise and speech were presented through two different loudspeakers in azimuth position. Speech tokes were presented at 65 dB SPL, while white noise files were at 60, 65 and 70 dB respectively.

Results:

Air traffic controllers outperform the control group in all conditions [P<0.05 in ANOVA and Mann-Whitney U tests]. Group differences were largest in the most difficult condition, SNR=−5 dB. However, no correlation between experience and performance were found for any of the conditions tested. The reason might be that ceiling performance is achieved much faster than the minimum experience time recorded, 5 years, although intrinsic cognitive abilities cannot be disregarded.

Discussion:

ATC demonstrated enhanced ability to hear speech in challenging listening environments. This study provides evidence that long-term auditory training is indeed useful in achieving better speech-in-noise understanding even in adverse conditions, although good cognitive qualities are likely to be a basic requirement for this training to be effective.

Conclusion:

Our results show that ATC outperform the control group in all conditions. Thus, this study provides evidence that long-term auditory training is indeed useful in achieving better speech-in-noise understanding even in adverse conditions.

Correlation between the frequency difference limen and an index based on principal component analysis of the frequency-following response of normal hearing listeners

Subcortical phase locking tends to reflect performance differences in tasks related to pitch perception across different types of populations. Enhancement or attenuation in its strength may correspond to population excellence or deficiency in pitch perception. However, it is still unclear whether differences in perceptual capability among individuals with normal hearing can be predicted by subcortical phase locking. In this study, we examined the brain-behavior relationship between frequency-following responses (FFRs) evoked by pure/sweeping tones and frequency difference limens (FDLs). FFRs are considered to reflect subcortical phase locking, and FDLs are a psychophysical measure of behavioral performance in pitch discrimination. Traditional measures of FFR strength were found to be poorly correlated with FDL. Here, we introduced principal component analysis into FFR analysis and extracted an FFR component that was correlated with individual pitch discrimination. The absolute value of the score of this FFR principal component (but not the original score) was negatively correlated with FDL, regardless of stimulus type. The topographic distribution of this component was relatively constant across individuals and across stimulus types, and the inferior colliculus was identified as its origin. The findings suggest that subcortical phase locking at certain but not all FFR generators carries the neural information required for the prediction of individual pitch perception among humans with normal hearing.

Context-dependent plasticity in the subcortical encoding of linguistic pitch patterns

We examined the mechanics of online experience-dependent auditory plasticity by assessing the influence of prior context on the frequency-following responses (FFRs), which reflect phase-locked responses from neural ensembles within the subcortical auditory system. FFRs were elicited to a Cantonese falling lexical pitch pattern from 24 native speakers of Cantonese in a variable context, wherein the falling pitch pattern randomly occurred in the context of two other linguistic pitch patterns; in a patterned context, wherein, the falling pitch pattern was presented in a predictable sequence along with two other pitch patterns, and in a repetitive context, wherein the falling pitch pattern was presented with 100% probability. We found that neural tracking of the stimulus pitch contour was most faithful and accurate when listening context was patterned and least faithful when the listening context was variable. The patterned context elicited more robust pitch tracking relative to the repetitive context, suggesting that context-dependent plasticity is most robust when the context is predictable but not repetitive. Our study demonstrates a robust influence of prior listening context that works to enhance online neural encoding of linguistic pitch patterns. We interpret these results as indicative of an interplay between contextual processes that are responsive to predictability as well as novelty in the presentation context.

NEW & NOTEWORTHY

Human auditory perception in dynamic listening environments requires fine-tuning of sensory signal based on behaviorally relevant regularities in listening context, i.e., online experience-dependent plasticity. Our finding suggests what partly underlie online experience-dependent plasticity are interplaying contextual processes in the subcortical auditory system that are responsive to predictability as well as novelty in listening context. These findings add to the literature that looks to establish the neurophysiological bases of auditory system plasticity, a central issue in auditory neuroscience.

Cortical auditory evoked potentials (CAEPs) represent neural cues relevant to pitch perception

Components of auditory event-related potentials (ERPs) may represent various aspects of the cortical processing of pitch. However, evidence hints an earlier representation of pitch perception in auditory ERPs of cortical origin. In this study, we examined whether earlier waves in cortical auditory evoked potentials (CAEPs) might reflect pitch-relevant features of both listeners and stimuli. CAEPs were elicited by pure tones and sweeping tones, and individual behavioral performance in pitch discrimination reflected by frequency difference limen (FDL) was also measured. Results show that CAEPs evoked by sweeping tones significantly correlate to FDL around ~50 ms, but CAEPs evoked by pure tones do not. Also, CAEPs are significantly affected by pitch-shift direction around ~130 ms. CAEPs evoked by ascending sweeping tones are larger in magnitude than those evoked by descending ones. Therefore, listeners' personal attributes relevant to pitch perception have already been reflected at a very early stage of cortical auditory processing, whilst certain pitch-related features of stimuli are recognized and represented at a later stage.

Sex differences and endocrine regulation of auditory-evoked, neural responses in African clawed frogs (Xenopus)

Mating depends on the accurate detection of signals that convey species identity and reproductive state. In African clawed frogs, Xenopus, this information is conveyed by vocal signals that differ in temporal patterns and spectral features between sexes and across species. We characterized spectral sensitivity using auditory-evoked potentials (AEPs), commonly known as the auditory brainstem response, in males and females of four Xenopus species. In female X. amieti, X. petersii, and X. laevis, peripheral auditory sensitivity to their species own dyad-two, species-specific dominant frequencies in the male advertisement call-is enhanced relative to males. Males were most sensitive to lower frequencies including those in the male-directed release calls. Frequency sensitivity was influenced by endocrine state; ovariectomized females had male-like auditory tuning while dihydrotestosterone-treated, ovariectomized females maintained female-like tuning. Thus, adult, female Xenopus demonstrate an endocrine-dependent sensitivity to the spectral features of conspecific male advertisement calls that could facilitate mating. Xenopus AEPs resemble those of other species in stimulus and level dependence, and in sensitivity to anesthetic (MS222). AEPs were correlated with body size and sex within some species. A frequency following response, probably encoded by the amphibian papilla, might facilitate dyad source localization via interaural time differences.