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Poster C72, Thursday, November 9, 10:00 – 11:15 am, Harborview and Loch Raven Ballrooms

Brain-behavior relationships in implicit learning of non-native phonetic categories

Sahil Luthra1, Pamela Fuhrmeister1, Peter J. Molfese2, Sara Guediche3, Sheila E. Blumstein4, Emily B. Myers1,5;1University of Connecticut, 2National Institutes of Health, 3Basque Center on Cognition, Brain and Language, 4Brown University, 5Haskins Laboratories

Learning non-native speech sounds in adulthood is notoriously difficult, and perceptual studies probing non-native phonetic learning in the laboratory have typically employed explicit training paradigms. Functional neuroimaging data from explicit training studies have suggested that learning involves a shift in processing from frontal regions to temporo-parietal ones (Golestani & Zatorre, 2004; Myers & Swan, 2012). However, it is unclear whether these same brain regions are also recruited for non-native phonetic learning in the absence of overt category labels. Of particular interest is whether activation observed in frontal areas in previous phonetic learning studies is a result of using an explicit categorization task. In this study, we examined participants’ behavioral sensitivity to a difficult non-native phonetic contrast (the Hindi dental-retroflex contrast) following several training sessions with an implicit learning paradigm (Vlahou, Protopapas & Seitz, 2012). To investigate potential relationships between brain and behavior, neuroimaging data were collected before and after training. Functional scans employed a short-interval habituation paradigm to test for differences in BOLD signal when phonetic category information was held constant (within-category trials) compared to when phonetic category information varied (between-category trials). As is common in non-native phonetic training studies, some participants appeared to be able to capitalize on the implicit training paradigm, whereas others showed no evidence of learning. In fact, implicitly-trained participants were not significantly better than a group of naïve participants, despite a numerical trend in the expected direction. To examine changes in brain activity as a function of individual differences in learning, we included factors of Session (before and after training) and Token Type (between- vs. within-category trials) and included behavioral post-training discrimination scores as a continuous covariate. Functional neuroimaging data revealed that bilateral middle and inferior frontal gyri were less active after training than before training (effect of Session), and LMFG and LIFG were sensitive to the phonetic category distinction (effect of Token Type). The left supramarginal gyrus was sensitive to the interaction between Session and Token Type, while the right SMG was sensitive to an interaction between Session, Token Type, and participants’ behavioral scores on the post-training discrimination assessment. A generalized psychophysiological (gPPI) interaction analysis indicated that the left frontal regions that were sensitive to the phonetic category distinction (LIFG/LMFG) showed increased functional connectivity with temporo-parietal regions (bilateral SMG and angular gyri) as a function of session and of post-training discrimination scores. Taken together, the data suggest that the same frontal areas recruited in explicit learning of non-native phonetic categories are recruited even in the absence of overt category labels. These findings are broadly consistent with non-native phonetic learning frameworks (e.g., Golestani & Zatorre, 2004; Myers & Swan, 2012) in which processing of non-native speech sounds extends beyond frontal areas and engages temporoparietal regions as a result of learning.

Topic Area: Perception: Speech Perception and Audiovisual Integration

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