Elaborately rehearsed information can be forgotten: A new paradigm to investigate directed forgetting

In previous item-method directed forgetting (DF) studies, forgetting may have occurred when the maintenance rehearsal of memory items was performed. In this study, a modified item-method DF paradigm was adopted to investigate whether forgetting instruction could produce a positive effect on forgetting the items that were elaborately rehearsed. During the study phase, a to-be-forgotten (TBF) word was followed by a forgetting cue. If no cue followed, the word was a to-be-remembered (TBR) item. Participants were required to intentionally memorize the word when it appeared. During the test phase, a yes/no recognition (Experiment 1) or a remember/know procedure (Experiment 2) was adopted. The behavioural results revealed that both the hit rate (Experiment 1) and remembering rate (Experiment 2) were higher for TBR relative to TBF words. For correctly identified old words, reaction times were consistently shorter for TBR compared to TBF words. These results revealed superior memory retention for TBR than for TBF words. The event-related potential (ERP) results revealed that, during both FN400 and late-positive complex (LPC) time windows, the remembered TBR words evoked more positive ERPs than the remembered TBF words and correctly rejected (CR) words (i.e., FN400 and LPC old/new effects). However, more negative ERPs were evoked for both remembered and forgotten TBF words than for CR words during the LPC time window (i.e., reversed LPC old/new effect). These results demonstrated that TBF words were associated with lower level of familiarity and recollection process than TBR words. The memory representation of TBF information might be inhibited.