SUMMARY We 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 positively correlated 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.

Children with reading impairments have deficits in phonological awareness, phonemic categorization, speech-in-noise perception, and psychophysical tasks such as frequency and temporal discrimination. Many of these children also exhibit abnormal encoding of speech stimuli in the auditory brainstem, even though responses to click stimuli are normal. In typically developing children the auditory brainstem response reflects acoustic differences between contrastive stop consonants. The current study investigated whether this subcortical differentiation of stop consonants was related to reading ability and speech-in-noise performance. Across a group of children with a wide range of reading ability, the subcortical differentiation of 3 speech stimuli ([ba], [da], [ga]) was found to be correlated with phonological awareness, reading, and speech-in-noise perception, with better performers exhibiting greater differences among responses to the 3 syllables. When subjects were categorized into terciles based on phonological awareness and speech-in-noise performance, the top-performing third in each grouping had greater subcortical differentiation than the bottom third. These results are consistent with the view that the neural processes underlying phonological awareness and speech-in-noise perception depend on reciprocal interactions between cognitive and perceptual processes.brainstem ͉ dyslexia ͉ electrophysiology ͉ experience-dependent plasticity ͉ learning impairment L earning impairments, primarily reading disorders, are among the most prevalently diagnosed exceptionalities in school-aged children, affecting Ϸ 5% to 7% of the population (1). These impairments coincide with a number of perceptual deficits including inordinate difficulty perceiving speech in noise as well as neural encoding deficits in the auditory system. In typically developing children, differences in contrastive speech stimuli are encoded subcortically (2), but the possible relationship between subcortical encoding of stimulus differences and reading ability has not been previously explored.Behavioral Impairments. Children with reading impairments often show deficits in phonological processing, which may be caused by degraded phonological representations or an inability to access these representations effectively (3)(4)(5). This population also exhibits impairments in speech sound discrimination (i.e., contrastive syllables) relative to controls matched for age and reading level (6, 7), suggesting that impairments are not simply caused by a maturational delay. These effects are especially prevalent for place of articulation and voice onset time contrasts, which reflect dynamic spectral and temporal contrasts, respectively. Perceptual discrimination deficits seem to be limited to the rapid spectral transitions between consonants and vowels and are not found for steady-state vowels or when formant transitions are lengthened (8-10). Moreover, when presented with between-and within-phonemic category judgments, typically developing children successfully di...

Although it is largely agreed that phonological processing deficits are a major cause of poor reading, the neural origins of phonological processing are not well understood. We now show, for the first time, that phonological decoding, measured with a test of single-nonword reading, is significantly correlated with the timing of subcortical auditory processing and also, to a lesser extent, with the robustness of subcortical representation of the harmonic content of speech, but not with pitch encoding. The relationships we observe between reading and subcortical processing fall along a continuum, with poor readers at one end and good readers at the other. These data suggest that reading skill may depend on the integrity of subcortical auditory mechanisms and are consistent with the idea that subcortical representation of the acoustic features of speech may play a role in normal reading as well as in the development of reading disorders. These data establish a significant link between subcortical auditory function and reading, thereby contributing to the understanding of the biological bases of reading. At a more general level, these findings are among the first to establish a direct relationship between subcortical sensory function and a specific cognitive skill (reading). We argue that this relationship between cortical and subcortical function could be shaped during development by the corticofugal pathway and that this cortical-subcortical link could contribute to the phonological processing deficits experienced by poor readers.

Learning to read proceeds smoothly for most children, yet others struggle to translate verbal language into its written form. Poor readers often have a host of auditory, linguistic, and attention deficits, including abnormal neural representation of speech and inconsistent performance on psychoacoustic tasks. We hypothesize that this constellation of reading-related deficits arises from the human auditory system failing to respond to sound in a consistent manner, and that this inconsistency impinges upon the ability to relate phonology and orthography during reading. In support of this hypothesis, we show that poor readers have significantly more variable auditory brainstem responses to speech than do good readers, independent of resting neurophysiological noise levels. Thus, neural variability may be an underlying biological contributor to well-established behavioral and neural deficits found in poor readers.

Musicians are often reported to have enhanced neurophysiological functions, especially in the auditory system. Musical training is thought to improve nervous system function by focusing attention on meaningful acoustic cues, and these improvements in auditory processing cascade to language and cognitive skills. Correlational studies have reported musician enhancements in a variety of populations across the life span. In light of these reports, educators are considering the potential for co-curricular music programs to provide auditory-cognitive enrichment to children during critical developmental years. To date, however, no studies have evaluated biological changes following participation in existing, successful music education programs. We used a randomized control design to investigate whether community music participation induces a tangible change in auditory processing. The community music training was a longstanding and successful program that provides free music instruction to children from underserved backgrounds who stand at high risk for learning and social problems. Children who completed 2 years of music training had a stronger neurophysiological distinction of stop consonants, a neural mechanism linked to reading and language skills. One year of training was insufficient to elicit changes in nervous system function; beyond 1 year, however, greater amounts of instrumental music training were associated with larger gains in neural processing. We therefore provide the first direct evidence that community music programs enhance the neural processing of speech in at-risk children, suggesting that active and repeated engagement with sound changes neural function.

BackgroundNeural sensitivity to acoustic regularities supports fundamental human behaviors such as hearing in noise and reading. Although the failure to encode acoustic regularities in ongoing speech has been associated with language and literacy deficits, how auditory expertise, such as the expertise that is associated with musical skill, relates to the brainstem processing of speech regularities is unknown. An association between musical skill and neural sensitivity to acoustic regularities would not be surprising given the importance of repetition and regularity in music. Here, we aimed to define relationships between the subcortical processing of speech regularities, music aptitude, and reading abilities in children with and without reading impairment. We hypothesized that, in combination with auditory cognitive abilities, neural sensitivity to regularities in ongoing speech provides a common biological mechanism underlying the development of music and reading abilities.MethodsWe assessed auditory working memory and attention, music aptitude, reading ability, and neural sensitivity to acoustic regularities in 42 school-aged children with a wide range of reading ability. Neural sensitivity to acoustic regularities was assessed by recording brainstem responses to the same speech sound presented in predictable and variable speech streams.ResultsThrough correlation analyses and structural equation modeling, we reveal that music aptitude and literacy both relate to the extent of subcortical adaptation to regularities in ongoing speech as well as with auditory working memory and attention. Relationships between music and speech processing are specifically driven by performance on a musical rhythm task, underscoring the importance of rhythmic regularity for both language and music.ConclusionsThese data indicate common brain mechanisms underlying reading and music abilities that relate to how the nervous system responds to regularities in auditory input. Definition of common biological underpinnings for music and reading supports the usefulness of music for promoting child literacy, with the potential to improve reading remediation.

It is well established that in the majority of the population language processing is lateralized to the left hemisphere. Evidence suggests that lateralization is also present in the brainstem. In the current study, the syllable /da/ was presented monaurally to the right and left ears and electrophysiological responses from the brainstem were recorded in adults with symmetrical interaural click-evoked responses. Responses to the right-ear presentation occurred earlier than those to left-ear presentation in two peaks of the frequency following response (FFR) and approached significance for the third peak of the FFR and the offset peak. Interestingly, there were no differences in interpeak latencies indicating the response to right-ear presentation simply occurred earlier over this region. Analyses also showed more robust frequency encoding when stimuli were presented to the right ear than the left ear. The effect was found for the harmonics of the fundamental that correspond to the first formant of the stimulus, but was not seen in the fundamental frequency range. The results suggest that left lateralization of processing acoustic elements important for discriminating speech extends to the auditory brainstem and that these effects are speech specific.

Children with dyslexia often exhibit increased variability in sensory and cognitive aspects of hearing relative to typically developing peers. Assistive listening devices (classroom FM systems) may reduce auditory processing variability by enhancing acoustic clarity and attention. We assessed the impact of classroom FM system use for 1 year on auditory neurophysiology and reading skills in children with dyslexia. FM system use reduced the variability of subcortical responses to sound, and this improvement was linked to concomitant increases in reading and phonological awareness. Moreover, response consistency before FM system use predicted gains in phonological awareness. A matched control group of children with dyslexia attending the same schools who did not use the FM system did not show these effects. Assistive listening devices can improve the neural representation of speech and impact reading-related skills by enhancing acoustic clarity and attention, reducing variability in auditory processing.C hildren with dyslexia, reading impairment not caused by deficits in ability or opportunity (1), often have difficulties with orienting and maintaining attention (2, 3). Although the ability to direct attention is still developing during the elementary school years (4), dyslexics have poorer task-dependent attentional shifting in both auditory and visual modalities than their typically developing peers even into adulthood (2, 3). These deficits may impact and be impacted by heightened variability in sensory processes, such as inconsistent representations of speech by the auditory nervous system, and could contribute to documented impairments in auditory processing (5-7) and difficulty with meaningfully disambiguating speech sounds (8). Children with dyslexia can exhibit abnormal subcortical processing of speech, particularly in response to acoustic elements crucial for differentiating speech sounds (9-11). Deficient auditory sensory representation and unsuccessful disambiguation of speech likely contribute to the well-documented impairments in phonological awareness and phonological memory seen in children with dyslexia (12-14), with auditory processing skills in prereaders predicting later language skill (15,16). Because the auditory system integrates both sensory and cognitive facets of hearing, we suggest that through repeated, impaired interaction with sound, children with dyslexia can develop abnormal sensory representations of speech as well as abnormal cognitive skills for the interpretation of speech. For example, a child who repeatedly misperceives the sounds "cat" as "bat" or "pat" fails to make a robust sound-to-meaning connection between those sounds and their referent. However, because of this same integrative nature of the auditory system, deficient function can be improved with auditory training.Auditory perception and neurophysiology can be altered with auditory training (17-23). These changes can be traced directly to cross-cortical and descending cortical influence on neural receptivity in animal m...