The intention to forget reduces the accessibility of information in memory, which is commonly explained with temporary retrieval difficulties. Long-term effects have rarely been studied, and results are inconsistent. The present study re-assessed the long-term effects of directed forgetting (DF). Participants encoded a first list of items (L1), and were then instructed to forget or to remember this list. Immediately afterwards, all participants were presented with a second list to remember. In Experiment 1, memory for L1 and L2 was assessed after a 24-h delay. The forget cue reduced the number of items that were recalled from L1. Experiment 2 implemented a 12-h delay between encoding and test that was either filled with day-time wakefulness or night-time sleep. Replicating the findings of Exp. 1, recall of L1 was reduced in the forget in comparison to the remember condition. Sleep in comparison to wakefulness significantly strengthened L1 memory in the remember group only. Taken together, the present study shows that the intention to forget can have long-lasting consequences. This suggests that different mechanisms underlie the short- and long-term effects of DF, with long-term effects potentially reflecting the preferential consolidation of information that has been identified as important during encoding.
Keywords: Memory; consolidation; intentional forgetting; long-term effects; retrieval inhibition; sleep.