The neurocognitive basis of metamemory: Using the N400 to study the contribution of fluency to judgments of learning.

Metamemory is crucial for monitoring, evaluating, and optimizing memory performance. The basis of metamemory, however, is a matter of considerable debate. In the present study, we examined the contribution of processing fluency-the ease of processing information during learning-to metamemory judgments. We recorded event-related potentials (ERPs) while participants studied related and unrelated word pairs across two study-test cycles in a judgment of learning (JOL) task. In the first study-test cycle, related pairs were associated with better cued recall, higher JOLs, and a reduced N400 amplitude than unrelated pairs. Crucially, between- and within subject correlational analyses indicated that reduced N400 amplitudes, indexing more fluent processing, were associated with higher JOLs. Furthermore, single-trial N400 mediated a small but significant portion of the relatedness effect on JOLs. In the second study-test cycle, relatedness still increased recall and JOLs. However, related and unrelated pairs did not differ in N400 amplitude. Rather, unrelated pairs elicited a parietal positivity in a later time window that partially mediated the relatedness effect on JOLs. Together, these results suggest that processing fluency, indexed by the N400, contributes to the relatedness effect on JOLs when novel word pairs are learned, but not when previously studied pairs are relearned. Our results also imply that aspects of fluency not captured by the N400 and/or explicit beliefs about memory contribute to JOLs. This study demonstrates the utility of ERPs in gaining new insights into the neurocognitive mechanisms of metamemory.