Context-Dependent Encoding in the Human Auditory Brainstem Relates to Hearing Speech in Noise: Implications for Developmental Dyslexia

SummaryWe examined context-dependent encoding of speech in children with and without developmental dyslexia by measuring auditory brainstem responses to a speech syllable presented in a repetitive or variable context. Typically developing children showed enhanced brainstem representation of features related to voice pitch in the repetitive context, relative to the variable context. In contrast, children with developmental dyslexia exhibited impairment in their ability to modify representation in predictable contexts. From a functional perspective, we found that the extent of context-dependent encoding in the auditory brainstem correlated positively with behavioral indices of speech perception in noise. The ability to sharpen representation of repeating elements is crucial to speech perception in noise, since it allows superior “tagging” of voice pitch, an important cue for segregating sound streams in background noise. The disruption of this mechanism contributes to a critical deficit in noise-exclusion, a hallmark symptom in developmental dyslexia

Why would Musical Training Benefit the Neural Encoding of Speech? The OPERA Hypothesis

Mounting evidence suggests that musical training benefits the neural encoding of speech. This paper offers a hypothesis specifying why such benefits occur. The “OPERA” hypothesis proposes that such benefits are driven by adaptive plasticity in speech-processing networks, and that this plasticity occurs when five conditions are met. These are: (1) Overlap: there is anatomical overlap in the brain networks that process an acoustic feature used in both music and speech (e.g., waveform periodicity, amplitude envelope), (2) Precision: music places higher demands on these shared networks than does speech, in terms of the precision of processing, (3) Emotion: the musical activities that engage this network elicit strong positive emotion, (4) Repetition: the musical activities that engage this network are frequently repeated, and (5) Attention: the musical activities that engage this network are associated with focused attention. According to the OPERA hypothesis, when these conditions are met neural plasticity drives the networks in question to function with higher precision than needed for ordinary speech communication. Yet since speech shares these networks with music, speech processing benefits. The OPERA hypothesis is used to account for the observed superior subcortical encoding of speech in musically trained individuals, and to suggest mechanisms by which musical training might improve linguistic reading abilities

Music drives brain plasticity

Music is becoming more and more of an issue in the cognitive neurosciences. A major finding in this research area is that musical practice is associated with structural and functional plasticity of the brain. In this brief review, I will give an overview of the most recent findings of this research area

Behavioral and subcortical signatures of musical expertise in Mandarin Chinese speakers

Both musical training and native language have been shown to have experience-based plastic effects on auditory processing. However, the combined effects within individuals are unclear. Recent research suggests that musical training and tone language speaking are not clearly additive in their effects on processing of auditory features and that there may be a disconnect between perceptual and neural signatures of auditory feature processing. The literature has only recently begun to investigate the effects of musical expertise on basic auditory processing for different linguistic groups. This work provides a profile of primary auditory feature discrimination for Mandarin speaking musicians and nonmusicians. The musicians showed enhanced perceptual discrimination for both frequency and duration as well as enhanced duration discrimination in a multifeature discrimination task, compared to nonmusicians. However, there were no differences between the groups in duration processing of nonspeech sounds at a subcortical level or in subcortical frequency representation of a nonnative tone contour, for f(o) or for the first or second formant region. The results indicate that musical expertise provides a cognitive, but not subcortical, advantage in a population of Mandarin speakers.Peer reviewe

The Influence of Tone Inventory on ERP without Focal Attention: A Cross-Language Study

This study investigates the effect of tone inventories on brain activities underlying pitch without focal attention. We find that the electrophysiological responses to across-category stimuli are larger than those to within-category stimuli when the pitch contours are superimposed on nonspeech stimuli; however, there is no electrophysiological response difference associated with category status in speech stimuli. Moreover, this category effect in nonspeech stimuli is stronger for Cantonese speakers. Results of previous and present studies lead us to conclude that brain activities to the same native lexical tone contrasts are modulated by speakers’ language experiences not only in active phonological processing but also in automatic feature detection without focal attention. In contrast to the condition with focal attention, where phonological processing is stronger for speech stimuli, the feature detection (pitch contours in this study) without focal attention as shaped by language background is superior in relatively regular stimuli, that is, the nonspeech stimuli. The results suggest that Cantonese listeners outperform Mandarin listeners in automatic detection of pitch features because of the denser Cantonese tone system

Hearing It Again and Again: On-Line Subcortical Plasticity in Humans

Background: Human brainstem activity is sensitive to local sound statistics, as reflected in an enhanced response in repetitive compared to pseudo-random stimulus conditions [1]. Here we probed the short-term time course of this enhancement using a paradigm that assessed how the local sound statistics (i.e., repetition within a five-note melody) interact with more global statistics (i.e., repetition of the melody). Methodology/Principal Findings: To test the hypothesis that subcortical repetition enhancement builds over time, we recorded auditory brainstem responses in young adults to a five-note melody containing a repeated note, and monitored how the response changed over the course of 1.5 hrs. By comparing response amplitudes over time, we found a robust time-dependent enhancement to the locally repeating note that was superimposed on a weaker enhancement of the globally repeating pattern. Conclusions/Significance: We provide the first demonstration of on-line subcortical plasticity in humans. This complements previous findings that experience-dependent subcortical plasticity can occur on a number of time scales, including life-long experiences with music and language, and short-term auditory training. Our results suggest that the incoming stimulus stream is constantly being monitored, even when the stimulus is physically invariant and attention is directed elsewhere, to augment the neural response to the most statistically salient features of the ongoing stimulus stream. These real-tim

The impact of making music on aural perception and language skills: A research synthesis

This paper provides a synthesis of research on the relationship between music and language, drawing on evidence from neuroscience, psychology, sociology and education. It sets out why it has become necessary to justify the role of music in the school curriculum and summarizes the different methodologies adopted by researchers in the field. It considers research exploring the way that music and language are processed, including differences and commonalities; addresses the relative importance of genetics versus length of time committed to, and spent, making music; discusses theories of modularity and sensitive periods; sets out the OPERA hypothesis; critically evaluates research comparing musicians with non-musicians; and presents detailed accounts of intervention studies with children and those from deprived backgrounds, taking account of the importance of the nature of the musical training. It concludes that making music has a major impact on the development of language skills

The effects of musical training on perception and neural representation of temporal fine structure

One of the most common complaints of persons with sensorineural hearing loss is difficulty hearing in background noise. Temporal fine structure (TFS) is one of the factors that contributes to understanding speech in the presence of background noise. TFS refers to the periodic information in speech which helps us to identify which speech sound we are listening to. TFS is also negatively affected by hearing loss, as well as age. In a quest to discover how TFS processing and thus speech-in-noise understanding can be improved, this study examined the effects of musical training on behavioral and physiological measures of temporal fine structure, as well as the brain-behavior relationship as it relates to frequency representation in the brainstem. This relationship was measured by two behavioral tests: frequency discrimination and a measure of speech understanding in background noise – the Hearing-in-Noise test (HINT), and one physiologic measure, the frequency following response (FFR). The stimuli for frequency discrimination and the FFR were tonebursts of 500 Hz in quiet, 1000 Hz in quiet, 500 Hz in noise, and 1000 Hz in noise. A total of 28 subjects were tested, 16 musicians and 12 non-musicians. The results showed that musicians had better frequency difference limens (FDLs) than non-musicians. For the physiologic measure, musical experience did not affect phase-locked representations of TFS. Musicians also did not have better signal-to-noise ratios on the HINT. There were no significant brain-behavior relationships between measures except that lower or better FDL thresholds at 1000 Hz in quiet implied lower or worse phase coherence at 1000 Hz in quiet. A greater number of years of musical experience related to lower or better FDLs for the conditions in quiet but not in noise. The years of training did not relate to performance on FFR phase coherence, amplitude, or HINT scores. It was concluded that musical training significantly enhanced behavioral TFS processing, however no significant effects were noted for neural representation of TFS or speech-in-noise understanding

Neural Mechanisms Underlying Hierarchical Speech-in-Noise Processing

One of the most commonly reported complaints related to hearing is difficulty understanding speech-in-noise (SIN). Numerous individuals struggle to effectively communicate in adverse listening conditions, even those with normal hearing. These difficulties are exacerbated due to age and hearing-related deficits such as hearing loss and auditory processing disorders. Despite the high prevalence of SIN deficits in individuals across the lifespan, the neural mechanisms underlying successful speech comprehension in noise are not well understood. Communication in noise is an incredibly complex process that requires efficient processing throughout the entire auditory pathway as well as contributions from higher-order cognitive processes including working memory, inhibition, and attention. In a series of studies using electrophysiologic (EEG) and behavioral measures, this dissertation evaluated the neural correlates of SIN perception across subcortical and cortical levels of the auditory system to identify how top-down and bottom-up influences aid SIN understanding. The first study examined the effects of hearing loss on SIN processing in older adults at the cortical level using frequency-specific neural oscillations (i.e., brain rhythms) and functional connectivity (i.e., directed neural transmission). We found that low-frequency alpha and beta oscillations within and between prefrontal and auditory cortices reflect the ability to flexibly allocate neural resources and recruit top-down predictions to compensate for hearing-related declines and facilitate efficient SIN perception. The second study, in younger adults, investigated the role of attention in SIN processing and how it interacts with early sensory encoding. Hierarchical processing in brainstem and cortex was assessed by simultaneously recording frequency-following responses (FFRs) and event-related potentials (ERPs) at the source level. We found that attention modulates SIN processing at both subcortical and cortical levels and strengthens bidirectional neural signaling within the central auditory pathway. A relative disengagement of corticofugal transmission was observed in noise but only for passive listening suggesting attention aids SIN perception by maintaining top-down reinforcement of acoustic feature encoding within the primary auditory pathways. Taken together, these results indicate that the neural networks engaged during SIN perception depend on a complex interplay between bottom-up and top-down factors including signal clarity, listeners hearing status, and attentional deployment

The frequency-following response (FFR) to speech stimuli: a normative dataset in healthy newborns

The Frequency-Following Response (FFR) is a neurophonic auditory evoked potential that reflects the efficient encoding of speech sounds and is disrupted in a range of speech and language disorders. This raises the possibility to use it as a potential biomarker for literacy impairment. However, reference values for comparison with the normal population are not yet established. The present study pursues the collection of a normative database depicting the standard variability of the newborn FFR. FFRs were recorded to /da/ and /ga/ syllables in 46 neonates born at term. Seven parameters were retrieved in the time and frequency domains, and analyzed for normality and differences between stimuli. A comprehensive normative database of the newborn FFR is offered, with most parameters showing normal distributions and similar robust responses for /da/ and /ga/ stimuli. This is the first normative database of the FFR to characterize normal speech sound processing during the immediate postnatal days, and corroborates the possibility to record the FFRs in neonates at the maternity hospital room. This normative database constitutes the first step towards the detection of early FFR abnormalities in newborns that would announce later language impairment, allowing early preventive measures from the first days of life