Speech perception is the process by which listeners hear and interpret the sounds of language. It is defined by the unique mapping of a highly variable and complex acoustic signal to a phonetic representation. A convergence of studies has implicated the human posterior superior temporal cortex for the specialized processing of speech sounds. Although localized, the basic neural mechanisms by which linguistic information is extracted are entirely unclear. We propose an innovative methodological approach using customized intracranial high-density electrode arrays to record detailed neural activity directly from the posterior temporal cortex in awake, behaving subjects undergoing clinical evaluation for epilepsy surgery. This method offers the highest possible spatial and temporal resolution, thereby overcoming many limitations of non-invasive imaging approaches. This research is positioned at a critical interface between the fields of auditory neuroscience and linguistics. Our previous results demonstrate that cortical representation of speech sounds manifest important non-linearities that correspond to perceptual boundaries over acoustic parameters (Chang et al, Nature Neuroscience 2010). Building on these findings, we propose experiments to determine: 1) the functional organization of the posterior temporal gyrus for acoustic and phonetic features, 2) the distributed, population-level encoding of emergent phonetic representation, and 3) the correlates of "robust" speech representation in the context of a multi-speaker listening environment. The results of these proposed experiments will have significant impact on the field of neurolinguistics and broader research on sensory perception and cognition.
Alterations in the cortical mechanisms supporting speech perception underlie the pathogenesis of an increasing number of acquired and developmental language disabilities, including aphasia, language learning delay, autism, and dyslexia. Revealing mechanisms by which the brain encodes speech sounds bears tremendous implications for our understanding of these disorders, and more importantly, will guide strategies for their remediation.
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