Predicting memory formation over multiple study episodes

Repeated study typically improves episodic memory performance. Two different types of explanations of this phenomenon have been put forward: 1) reactivating the same representations strengthens and stabilizes memories, or, in contrast, 2) greater encoding variability - through changes in context - benefits memory by promoting richer traces and a larger variety of retrieval cues. The present experiment was designed to directly compare these predictions in a design with multiple repeated study episodes, allowing to dissociate memory for studied items and their context of study. Participants repeatedly encoded names of famous people four times, either in the same task (optimal encoding for a reactivation view), or in different tasks (optimal encoding for an encoding variability view). During the test phase, an old/new judgement task was used to assess item memory, followed by a source memory judgement about the encoding task. Consistent with predictions from the encoding variability view, encoding stimulus in different contexts resulted in higher item memory and lower rates of forgetting. In contrast, consistent with the reactivation view, source memory performance was higher when participants encoded stimuli in the same task repeatedly. Taken together, our findings indicate that encoding variability benefits episodic memory, by increasing the number of items that are recalled and by decreasing forgetting. These benefits are however at the expenses of source recollection and memory for details, which are decreased, likely due to interference and generalisation across contexts.