Second-Language Learning Facilitates Non-Adjacent Dependency Learning: Effects Moderated by Specific Language.

Statistical learning allows language learners to implicitly track regularities in input. Prior studies have suggested that second language (L2) learning affects statistical learning, but the nature of this relationship remains unclear. Does L2 learning broadly enhance sensitivity to statistical structure, selectively tune learners to patterns emphasized in the learned language, or both? We tested English-speaking adults enrolled in introductory Mandarin or Spanish courses, along with English monolingual controls, on two statistical learning tasks: a tonal word segmentation task and a non-adjacent dependency (NAD) learning task. Participants completed both tasks at the beginning of instruction and again after two academic terms. All groups performed above chance in the tonal task, but none showed significant improvement over time, including Mandarin learners. In contrast, only Spanish learners demonstrated increased sensitivity to NADs over time. These findings suggest that statistical learning is not uniformly boosted by L2 experience. Instead, L2 exposure may selectively tune learners' sensitivity to relational patterns that are emphasized in their linguistic experience. More broadly, the results highlight how the structure of linguistic experience can shape statistical learning mechanisms.