Rich autobiographical memory benefits from both novelty and similarity to other daily experiences.

Much existing laboratory research has shown that both novelty and prior knowledge benefit episodic memory, however they do so through differing mechanisms. Critically, autobiographical experiences are rarely completely novel or congruent with prior experience, existing within a spectrum from 'absolute' novelty to 'absolute' congruency. A prospective real-world autobiographical event sampling study was conducted to investigate memory outcomes for events that varied along this spectrum. We found that events that participants labeled as 'new' were later recalled with greater vividness compared to events labeled 'periodic' and 'routine'. Crucially, however, within the 'new' events, those that were more semantically similar (to all other events reported within participant during the 14-day diary period) were recalled with the greatest vividness and were associated with higher happiness and excitement ratings. We also found that relative emotional distinctiveness across all other events predicted greater vividness and recalled episodic detail. Our results suggest that a combination of novelty and relative semantic similarity, rather than 'maximal' novelty, may be more impactful for well-being and vivid recall, which we are calling the 'something old, something new' principle.