Stimulation of Right Temporal Cortex Enhances Talker Typicality Judgments

Listeners are exquisitely sensitive to the ways that different talkers produce speech sounds, and such sensitivity may allow listeners to condition speech perception on talker information. A growing body of neuroimaging data suggests that although phonetic processing is largely supported by the brain's left hemisphere, the integration of talker information during speech perception recruits the right hemisphere, especially right temporal cortex. However, an open question is whether recruitment of the right hemisphere is strictly necessary for integrating talker information and phonetic detail or simply incidental. Here, we leverage TMS to test for a causal role of the right middle temporal gyrus (RMTG) in accessing a listener's beliefs about a talker's phonetic signature. During an initial exposure phase, participants heard pairs of talkers, one of whom produced voiceless stop consonants (e.g., /k/) with a relatively short voice onset time (VOT) and one who employed relatively long VOTs; listeners learned what variation was typical of each talker without disruption from TMS. During a subsequent test, TMS was administered to the RMTG, left middle temporal gyrus (LMTG), or a control site (scalp vertex) before listeners judged whether VOT variants were typical of a learned talker. We found that listeners were best able to determine what phonetic variation was typical of a talker following RMTG stimulation; stimulation of the LMTG did not influence performance relative to vertex stimulation. Overall, results indicate that the balance of activation across the two hemispheres is critical for accessing talker-specific phonetic detail.