Exploring neural mechanisms of Mandarin tone sandhi perception via fNIRS: the role of gesture in multimodal integration.

Introduction: The use of pitch gestures in teaching Mandarin tone (i.e., gesture-augmented instruction) has been reported to facilitate lexical tone acquisition. However, the neural mechanisms underlying how gestures aid the learning of complex phonological rules, such as tone sandhi, remain unclear. This study investigated whether gesture-based learning enhances tone sandhi perception primarily through multimodal integration or by promoting cognitive control. Methods: Forty-four Vietnamese-speaking learners were randomly assigned to either a gesture training group or a no-gesture control group. Post-training, participants performed a disyllabic tone discrimination task while functional near-infrared spectroscopy (fNIRS) data and behavioral responses were recorded. Results: Results revealed significantly greater neural responses in the left dorsolateral prefrontal cortex (L-DLPFC) in the gesture group compared to the control group. Moreover, enhanced L-DLPFC activation was positively correlated with improved behavioral discrimination accuracy. The gesture group also exhibited strengthened functional connectivity between the L-DLPFC and bilateral prefrontal cortices, accompanied by accelerated hemodynamic responses. Discussion: Collectively, these findings suggest that gesture-assisted learning facilitates tone sandhi mastery primarily by augmenting prefrontal executive control and fostering multisensory integration. This pattern aligns with a weak embodied cognition framework, in which gestures serve as distributed scaffolds that support, rather than replace, abstract tonal representations.