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Poster C66, Thursday, November 9, 10:00 – 11:15 am, Harborview and Loch Raven Ballrooms

Speech processing and plasticity in the right hemisphere predict real-world foreign language learning in adults

Zhenghan Qi1, Michelle Han1, Yunxin Wang1, Carlo de los Angeles1, Qi Liu1, Keri Garel1, Ee San Chen1, Susan Whitfield-Gabrieli1, John D. E. Gabrieli1, Tyler K. Perrachione2;1Massachusetts Institute of Technology, 2Boston University

Goals: Foreign language learning in adulthood often takes place in classrooms where learning outcomes vary widely among students, both for initial learning and for long-term retention. Despite the fundamental role of speech perception in first language acquisition, the role of speech perception in real-world foreign language learning outcomes remains unknown. Using both a speech discrimination functional magnetic resonance imaging (fMRI) task and resting-state fMRI before and after an intensive, classroom-based, Mandarin Chinese course, we examined how variations in pre-training organization, as well as pre-to-post reorganization, of brain functions predicted successful holistic language learning in native English-speaking learners. Methods: Twenty-four adult native speakers of English underwent a month-long, classroom-based Mandarin course. Students’ holistic Mandarin attainment was assessed immediately after the course and long-term retention of Mandarin skills was assessed 90 days later. Participants took part in two identical MRI scanning sessions in a Siemens Trio 3T scanner before and after the language learning. In the tone-discrimination fMRI task, participants indicated whether the pitch contours of consecutive pairs of sounds were the same or different for real Mandarin words or nonspeech sinusoidal tones. Participants completed two task runs (TR = 2.7 s; TA = 0.5 s; 145 volumes) and one resting-state scan (TR = 2.5 s; 147 volumes) in each session. fMRI Group-level statistics were based on non-parametric permutation and correction for multiple comparisons was accomplished by controlling cluster-level family-wise error at p < 0.05. Results: Prior to the course, greater activation in right inferior frontal gyrus (IFG) in response to discriminating Mandarin speech tones (versus nonspeech sinewave tones) was associated with greater future success in Mandarin attainment. After four weeks of class, more successful learners showed greater pre-to-post reduction of right IFG activation and greater pre-to-post enhancement of resting-state connectivity between left and right IFG. On average, learners showed increased post-training activation in left IFG to lexical tones, but variation in neither left IFG activation nor left IFG plasticity was related to learning outcomes. Predictive models using neural features (pre-training activation and pre-to-post activation change in right IFG) predicted long-term retention of holistic Mandarin skills more accurately than models using behavioral features (pre-training Mandarin speech-sound discrimination accuracy and pre-to-post accuracy change). Conclusion: This study provides critical new evidence about the importance of the right hemisphere in speech perception for successful acquisition of a whole language in adults. Although the left hemisphere was increasingly recruited in most learners after training, individual differences in speech perception, immediate language learning attainment, and long-term retention of high-level foreign language skills were all related to differences in initial right-IFG engagement and subsequent right-IFG disengagement. The right-to-left transition was accompanied by an increase in resting-state functional connectivity between bilateral IFG regions. Taken together, these findings significantly refine the neurobiological model of ecological adult language learning and retention.

Topic Area: Multilingualism

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