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List-method directed forgetting usually involves asking people to study a list, followed by a cue to forget it, and then studying a second list. Prior work suggests that List 2 encoding is necessary for directed forgetting to occur, but recent studies have found that moving the forget cue from List 1 to List 2 allows people to selectively forget List 2. These results were attributed to an inhibitory mechanism. In four experiments, we aimed to replicate these findings and provide an alternative explanation based on the list-before-the-last paradigm. We propose that in the forget condition, participants may strategically retrieve List 1 in response to the forget cue, contributing to selective forgetting. Previous research suggests that explicit retrieval of earlier-leaned information causes a contextual shift, resulting in forgetting of target information. Verbal reports from Experiments 1 and 2 indicated that participants often covertly select a retrieval strategy to forget the most recent list. In Experiment 3, explicit instructions to retrieve resulted in significant forgetting. Directly manipulating forgetting strategy between participants in Experiment 4 suggested that retrieval may be one of several effective mechanisms to forget recently-encountered information. In the retrieval conditions, the data support our claim that in the absence of explicit postcue encoding, people can strategically retrieve earlier-learned information to forget. This novel forgetting mechanism is probably also used outside of the laboratory to "roll back" memory for incorrect information.

Some previous studies have shown that increased stress hormone levels have beneficial effects on memory encoding; however, there is no clear consensus on which encoding-related processes are affected by stress hormones. In the present study, we investigated the relationship between interindividual differences in neuroendocrine response to acute stress and interference resolution (i.e., mnemonic discrimination). Participants were healthy young adults who were exposed to physical and psychological stressors (Socially Evaluated Cold Pressor Test). Then participants completed the modified version of the Mnemonic Similarity Task. Specifically, they were presented with photographs of emotionally arousing (negative and positive) and nonarousing (neutral) scenes followed by a recognition memory test where they saw a mixture of old and new stimuli. Crucially, participants were also presented with critical lure items, that is, visually similar stimuli to ones presented at encoding. We found that participants who had higher cortisol response to the stressors were better in discriminating between the studied items and their visually similar lures. This effect was present for the arousing and nonarousing materials as well. These findings suggest that increased hormonal response to acute stress has a beneficial impact on the formation of distinct, nonoverlapping, unique memory representations, and consequently, on episodic memory encoding processes.

The "testing effect" refers to the striking phenomenon that repeated retrieval practice is one of the most effective learning strategies, and certainly more advantageous for long-term learning, than additional restudying of the same information. How retrieval can boost the retention of memories is still without unanimous explanation. In 3 experiments, focusing on the reaction time (RT) of retrieval, we showed that RT of retrieval during retrieval practice followed a power function speed up that typically characterizes automaticity and skill learning. More important, it was found that the measure of goodness of fit to this power function was associated with long-term recall success. Here we suggest that the automatization of retrieval is an explanatory component of the testing effect. As a consequence, retrieval-based learning has the properties characteristic of skill learning: diminishing involvement of attentional processes, faster processing, resistance to interference effects, and lower forgetting rate.

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