Same behavior, different brain: A triangulated neurocognitive re-evaluation of task engagement in TBLT

This study aims to scrutinize discourse-analytic measures of task engagement by triangulating those with neurophysiological and learning outcome measures. Eighty Japanese learners of English as a foreign language performed interactive information-gap tasks, with target multiword expressions practiced either before (pre-task) or after (post-task) the communicative tasks. One-week delayed posttests measured declarative knowledge and processing automaticity of target multiword expressions. Engagement during the tasks was operationalized via eight discourse-analytic measures and subjected to principal component analysis, revealing two distinct components: Lexis Engagement (target multiword expression use and related negotiation) and Co-Construction Engagement (peer completion and negotiation for clarification/elaboration). Functional near-infrared spectroscopy (fNIRS) hyperscanning was used to measure inter-brain synchronization (IBS) during task performance. The results showed that the engagement–IBS relationship was moderated by instructional timing. Higher levels of Lexis and Co-Construction Engagement were linked with greater neural synchronization in social-cognitive brain regions in the pre-task conditions. In the post-task conditions, however, Co-Construction Engagement was negatively linked with neural synchronization in language-processing regions. These findings suggest that co-constructive behaviors may serve as an indicator of socially and cognitively coordinated work in one instructional setting, whereas the same behaviors could indicate compensatory interactional effort arising from limited L2 resources in another. Additionally, Lexis Engagement predicted the automaticity of multiword expressions but not declarative knowledge, underscoring the importance of incorporating multifaceted linguistic outcomes into engagement research. Taken together, the findings of this study highlight the value of triangulating discourse-analytic indicators with neurophysiological and learning outcome measures.