Multivariate Decoding and Drift-diffusion Modeling Reveal Adaptive Control in Trilingual Comprehension

Background/Objectives: The Adaptive Control Hypothesis suggests different language contexts require varying control demands. While bilinguals navigate one dual-language context, trilinguals manage three distinct contexts (L1-L2, L2-L3, L1-L3). This study examined whether these contexts impose differential control demands in trilingual comprehension, investigating proactive and reactive control mechanisms. Methods:Thirty-six Uyghur-Chinese-English trilinguals completed an auditory word-picture matching task across three dual-language contexts during EEG recording. We employed behavioral analysis, drift-diffusion modeling, event-related potential (ERP) analysis, and multivariate pattern analysis (MVPA) to examine comprehension efficiency, evidence accumulation, and neural mechanisms. The design crossed context (L1-L2, L2-L3, L1-L3) with trial type (switch vs. repetition) and switching direction (to dominant vs. non-dominant language). Results: Despite comparable behavioral performance, drift-diffusion modeling revealed distinct processing profiles across contexts, with the L1-L2 context showing the lowest comprehension efficiency due to slower evidence accumulation compensated by response bias adjustments. ERP analysis demonstrated context-specific neural signatures: N400 amplitudes revealed the strongest semantic competition in the L1-L2 context. Proactive control varied significantly across contexts, with language dominance reversal occurring exclusively in the L1-L3 context. Notably, no reactive control (switch costs) was observed across any dual-language context. MVPA successfully classified contexts and switching directions, revealing distinct spatiotemporal neural patterns. Conclusions: Trilingual language comprehension efficiency varies systematically across dual-language contexts due to differential proactive control demands rather than reactive control mechanisms. L2-L3 and L1-L3 contexts demonstrated higher efficiency than L1-L2 context, supporting a nuanced, context-dependent model of multilingual language control with important implications for theories of cognitive control in multilingual populations.