Cross language studies of tonal perception have suggested that language experience influences pitch processing at the cortical level. Our current research has focused on delineating the dimensions, and the underlying neural mechanisms of language experience-dependent enhancement of pitch in the human brainstem. Our long-term objective is to advance our knowledge of how pitch mechanisms at the two stages of processing interact to enhance encoding of behaviorally relevant sounds and to determine their respective roles in the hierarchical processing of the temporal structure of sound. A cross language approach utilizing a tonal language (Chinese) and a non-tonal control language (English) will permit us to distinguish between language-universal and language-dependent effects. Using speech and no speech stimuli varying in lexical status, pitch contour, and pitch salience, and recordings in quiet and adverse listening conditions will enable us to directly address questions of tone, feature, and contour specificity as well as the resilience of experience- dependent pitch representations to degradation in adverse listening conditions. We propose a novel electrophysiological approach to evaluate pitch representations at the brainstem (frequency following response, FFR) and auditory cortex (cortical pitch response, CPR) concurrently. Comparing these brainstem and cortical pitch representations with behavioral measures of pitch will allow us to determine if pitch-relevant neural activity contributes to the pitch percept.
The specific aims are to assess (i) the sensitivity of the CPR to specific features of pitch; (ii) the characteristics of the language experience-dependent enhancement of pitch at the cortical level and its relationship with brainstem, and behavioral measures of pitch; and (iii) if experience- driven pitch mechanisms at the cortical and brainstem levels are more resilient to degradation in adverse listening conditions. Our hypothesis is that early, preattentive enhanced representation of pitch in the brainstem and auditory cortex of Chinese listeners reflects language-dependent influence of specific, linguistically-relevant parameters of the auditory signal, and that these robust and stable representations are less susceptible to degraded effects of noise and reverberation. Our findings promise to advance our knowledge about (i) how experience-driven pitch mechanisms in the brainstem and in the auditory cortex interact to enhance behaviorally relevant features of complex sounds important for pitch perception in quiet and degraded listening conditions. With this expanded knowledge base about the neurobiology of speech prosody in the human auditory system, we are in a better position to favorably influence the recovery from hearing-related impairments. Our scalp-recorded responses may be used as a new clinical tool to assess the integrity of pitch representation in a target population; monitor changes in pitch representation under a retraining protocol and/or in the development of optimal signal processing strategies for conventional hearing aids and/or cochlear implants.
Speech prosody itself is clinically relevant because it is known to carry a large proportion of the communication load in non-tone as well as tone languages. Our ability to favorably influence the recovery from hearing-related impairments will depend upon a better understanding of the neurobiological basis of speech prosody in the human auditory system. These responses carrying pitch-relevant information may be used as a new clinical tool to assess the integrity of pitch representation in a target population; monitor changes in pitch representation under a retraining protocol and/or in the development of optimal signal processing strategies for conventional hearing aids and/or cochlear implants
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