Unexpected Events Resist Directed Forgetting

This study examined whether expectation violations modulate the effectiveness of directed forgetting (DF) and whether this interaction varies with emotional valence. We hypothesised that unexpectedness may confer mnemonic resilience, protecting from later forgetting. Participants first learned symbol-stimulus contingencies (rule learning), followed by an encoding phase with new emotional and neutral stimuli that were either expected or violated the learned rule. Each stimulus was accompanied by a "remember" or "forget" cue, and a subsequent recognition test assessed memory performance for expected and unexpected items under both DF conditions. Unexpected stimuli were remembered better than expected ones, particularly through recollection, and this advantage persisted even under forget instructions, indicating resistance to DF. Forget cues reduced recollection overall, but this reduction was markedly stronger for expected than for unexpected items. Emotional valence partly moderated these effects with the expectation advantage for recollection being evident for negative and neutral stimuli but not for positive ones. Nevertheless, the weakening of the DF effect for unexpected stimuli occurred irrespective of emotional valence. These findings demonstrate that prediction error enhances memory formation and diminishes the efficacy of intentional forgetting, particularly for associatively richer, recollection-based memories. The results support a view of DF as a dynamic process constrained by encoding factors such as surprise and emotional salience, with implications for theories of memory control and applications in education and memory training.