The Role of Frontal and Temporal Brain Areas in the Perception of Phonetic Category Structure

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ABSTRACT/PROJECT SUMMARY Successful language comprehension requires mapping a complex and variable acoustic signal onto meaningful units. Many studies show that perception of the speech signal recruits both left and right hemisphere temporal brain regions, yet only individuals with left hemisphere damage typically have deficits in processing sound structure that impact comprehension. A persistent mystery is the role of the right hemisphere in speech perception. In the current proposal, we test two key hypotheses about the role of the right hemisphere in speech sound processing. In Aim 1, a series of studies test the hypothesis that right and left temporal lobes differ in the precision with which they respond to speech, with left hemisphere showing sharp, categorical responses and the right having less precise and more gradient responses to speech. In Aim 2, motivated by work from the last grant cycle, we test the role of the right hemisphere in a process that is key to efficient language processing: learning the specific phonetic qualities of talkers. We approach these questions using converging methods, using neural decoding techniques on functional neuroimaging (fMRI) data to measure differences in neural tuning to phonetic stimuli, implementing a “virtual lesion” approach using transcranial magnetic stimulation (TMS) to examine the consequences of left and right hemisphere disruption, and testing individuals with right and left temporal lesions to understand the functional consequences of damage to the systems supporting speech perception in both hemispheres. In concert, this work will delineate the neural systems that support efficient and flexible processing of the speech signal. This grant’s innovation stems from its multi-method approach and the focus on right hemisphere function, a neglected component of the language architecture. Finally, this line of work will inform successful remediation of stroke, revealing the roles and functions of spared left and right hemisphere systems that can be leveraged for therapeutic purposes.