fMRI reveals the dynamic interface between explicit and implicit knowledge recruited during elicited imitation task

Abstract

Development of valid tasks that tap into implicit knowledge is a prerequisite for understanding the interface between explicit and implicit grammatical knowledge in second language (L2) acquisition. However, the extent to which elicited imitation tasks (EITs) draw on implicit or/and explicit knowledge has been a subject of controversy, due in part to the limitations of behavioral methods. To overcome this drawback, in this study, we used functional magnetic resonance imaging (fMRI) to examine the neural circuits underlying explicit and implicit knowledge (i.e., declarative and procedural memory) during the listening and speaking phases of an EIT performed by advanced L2 speakers of Japanese living in Japan. While the behavioral data suggest that the EIT primarily draws on automatized (speeded-up) explicit knowledge, the neuroimaging data revealed learners’ dynamic use of explicit and implicit knowledge during its comprehension and production phases. Higher explicit knowledge scores (derived from a metalinguistic knowledge task) were associated with greater declarative memory (left hippocampus) activation during the speaking EIT phase, indicating a prominent role of explicit knowledge in production. During the listening phase, however, higher explicit knowledge scores predicted lower activation in declarative memory (left hippocampus) and higher activation in procedural memory (left inferior frontal gyrus), suggesting that explicit knowledge plays both inhibitory and facilitative role in the use of implicit knowledge for comprehension. Taken together, these findings suggest that advanced L2 speakers utilize their explicit and implicit knowledge efficiently and dynamically—characterized as a hallmark of automaticity—for comprehension and production during the EIT.