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Boosting statistical language learning by modulating interhemispheric interaction with tACS
Poster Session A, Wednesday, September 30, 11:00 am - 1:00 pm, Wangari Maathai
Alex Shapero1, Riikka Möttönen1; 1University of Helsinki
Language networks typically lateralize to the left hemisphere in adults. Still, the right hemisphere’s analogous regions are active during speech processing, and interhemispheric interaction has been suggested to support early stages of second language learning in adults. Here, we investigated the causal role of interhemispheric interaction in statistical language learning (SLL), i.e., learning of statistical regularities from speech streams. Using transcranial alternating current stimulation (tACS), we aimed to modulate interhemispheric interaction between the left and right-hemisphere language networks. 28 Finnish-speaking adults were exposed to speech streams with hidden regularities under bihemispheric in-phase and sham tACS (40 Hz, 1000 μA). SLL was tested offline using a behavioural memory task with confidence judgements. Participants also performed dichotic listening tasks under in-phase and sham tACS conditions, which allowed us to calculate Laterality Indexes (LI). Higher behavioural LI under tACS has been shown to reflect increased functional connectivity between the left and right hemispheres, providing a metric for the degree to which tACS modulated interhemispheric interaction in each participant. Across all participants, we found a non-significant trend of increased learning under bihemispheric tACS. As the effects of tACS on interhemispheric interactions are known to differ across individuals, we further divided our participants into two groups based on the effect of stimulation on LIs. Participants with higher LIs (i.e., more left-lateralized) under stimulation (relative to sham) demonstrated significantly enhanced SLL performance under tACS. Analysis of confidence ratings revealed that acquisition of both implicit and explicit knowledge was enhanced under tACS in these participants. In contrast, SLL was unchanged in participants whose LIs decreased while stimulated. These results point to a facilitatory effect of bihemispheric interaction on extracting statistical regularities from speech streams. Ongoing studies aim to replicate and extend these findings using bihemispheric in-phase and anti-phase tACS protocols.
Topic Areas: Speech Perception, Language Development/Acquisition