This tutorial provides a comprehensive overview of the methodological approach to collecting and analyzing auditory brainstem responses to complex sounds (cABRs). cABRs provide a window into how behaviorally relevant sounds such as speech and music are processed in the brain. Because temporal and spectral characteristics of sounds are preserved in this subcortical response, cABRs can be used to assess specific impairments and enhancements in auditory processing. Notably, subcortical function is neither passive nor hardwired but dynamically interacts with higher-level cognitive processes to refine how sounds are transcribed into neural code. This experience-dependent plasticity, which can occur on a number of time scales (e.g., life-long experience with speech or music, short-term auditory training, online auditory processing), helps shape sensory perception. Thus, by being an objective and non-invasive means for examining cognitive function and experience-dependent processes in sensory activity, cABRs have considerable utility in the study of populations where auditory function is of interest (e.g., auditory experts such as musicians, persons with hearing loss, auditory processing and language disorders). This tutorial is intended for clinicians and researchers seeking to integrate cABRs into their clinical and/or research programs.

Music and speech are very cognitively demanding auditory phenomena generally attributed to cortical rather than subcortical circuitry. We examined brainstem encoding of linguistic pitch and found that musicians show more robust and faithful encoding compared with nonmusicians. These results not only implicate a common subcortical manifestation for two presumed cortical functions, but also a possible reciprocity of corticofugal speech and music tuning, providing neurophysiological explanations for musicians' higher language-learning ability.Both music and spoken language involve the use of functionally and acoustically complex sound and are generally attributed to the neocortex [1][2][3][4] . Less is known about how long-term experience using these complex sounds shapes subcortical circuitry and the context specificity and reciprocity of this tuning 5 . By measuring the frequency following response (FFR), which presumably originates from the auditory brainstem (inferior colliculus) and encodes the energy of the stimulus fundamental frequency (f 0 ) with high fidelity 6 , previous work 7 has found increased linguistic pitch pattern encoding in Mandarin-speaking subjects relative to English-speaking subjects. These results reflect Mandarin-speaking subjects' long-term exposure to linguistic pitch patterns, as Mandarin Chinese, a tone language, uses pitch to signal word meaning (for example, /ma/ spoken with high or rising pitch patterns means 'mother' or 'numb', respectively). Moreover, similar to research on short-term perceptual learning 8 , these results can be viewed as context specific (that is, linguistic experiences, subserved by the cortex, enhance the encoding of linguistic information at the Correspondence should be addressed to P.C.M.W. (pwong@northwestern.edu). 5 These authors contributed equally to this work.Note: Supplementary information is available on the Nature Neuroscience website. COMPETING INTERESTS STATEMENTThe authors declare no competing financial interests. Author Manuscript brainstem). The nonspecificity of this long-term usage effect, though largely unknown, is both theoretically interesting and clinically and educationally relevant. Nonspecificity would suggest that either speech-or music-related experience can tune sensory encoding in the auditory brainstem via the corticofugal pathway. Notably, this tuning, whether speech-or music-induced, would enhance all relevant auditory functions (both speech and music) subserved by the rostral brainstem. HHS Public AccessWe measured FFR responses to linguistic pitch patterns at the rostral brainstem in ten amateur musicians and ten nonmusicians who had no previous exposure to a tone language (see Supplementary Table 1 online). Musicians (instrumentalists) had at least 6 years of continuous musical training (mean = 10.7 years) starting at or before the age of 12.Nonmusicians had nomore than3 years (mean = 1.2 years) at any time in their life. Informed written consent was obtained from all subjects. While watching a video, subjects listened...

Musical training is known to modify cortical organization. Here, we show that such modifications extend to subcortical sensory structures and generalize to processing of speech. Musicians had earlier and larger brainstem responses than nonmusician controls to both speech and music stimuli presented in auditory and audiovisual conditions, evident as early as 10 ms after acoustic onset. Phaselocking to stimulus periodicity, which likely underlies perception of pitch, was enhanced in musicians and strongly correlated with length of musical practice. In addition, viewing videos of speech (lip-reading) and music (instrument being played) enhanced temporal and frequency encoding in the auditory brainstem, particularly in musicians. These findings demonstrate practice-related changes in the early sensory encoding of auditory and audiovisual information.brainstem ͉ plasticity ͉ visual ͉ multisensory language

Musical experience appears to enhance the ability to hear speech in challenging listening environments. Large group differences were found for QuickSIN, and the results also suggest that this enhancement is derived in part from musicians' enhanced working memory and frequency discrimination. For HINT, in which performance was not linked to frequency discrimination ability and was only moderately linked to working memory, musicians still performed significantly better than the nonmusicians. The group differences for HINT were evident in the most difficult condition in which the speech and noise were presented from the same location and not spatially segregated. Understanding which cognitive and psychoacoustic factors as well as which lifelong experiences contribute to SIN may lead to more effective remediation programs for clinical populations for whom SIN poses a particular perceptual challenge. These results provide further evidence for musical training transferring to nonmusical domains and highlight the importance of taking musical training into consideration when evaluating a person's SIN ability in a clinical setting.

Musicians have lifelong experience parsing melodies from background harmonies, which can be considered a process analogous to speech perception in noise. To investigate the effect of musical experience on the neural representation of speech-in-noise, we compared subcortical neurophysiological responses to speech in quiet and noise in a group of highly trained musicians and nonmusician controls. Musicians were found to have a more robust subcortical representation of the acoustic stimulus in the presence of noise. Specifically, musicians demonstrated faster neural timing, enhanced representation of speech harmonics, and less degraded response morphology in noise. Neural measures were associated with better behavioral performance on the Hearing in Noise Test (HINT) for which musicians outperformed the nonmusician controls. These findings suggest that musical experience limits the negative effects of competing background noise, thereby providing the first biological evidence for musicians' perceptual advantage for speech-in-noise.

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.