Environmental overlap and individual encoding strategy modulate memory interference in spatial navigation.

There has been great interest in how previously acquired knowledge interacts with newly learned knowledge and how prior knowledge facilitates semantic and "schema" learning. In studies of episodic memory, it is broadly associated with interference. Very few studies have examined the balance between interference and facilitation over the course of temporally-extended events and its individual differences. In the present study, we recruited 120 participants for a two-day spatial navigation experiment, wherein participants on Day 2 navigated virtual routes that were learned from Day 1 while also learning new routes. Critically, half of the new mazes overlapped with the old mazes, while the other half did not, enabling us to examine interference and facilitation in the context of spatial episodic learning. Overall, we found that navigation performance in new mazes that overlapped with previously-learned routes was significantly worse than the new non-overlapping mazes, suggesting proactive interference. Interestingly, we found memory facilitation for new routes in familiar environments in locations where there was no direct overlap with the previously-learned routes. Cognitive map accuracy positively correlated with proactive interference. Moreover, participants with high self-report spatial ability and/or a preference for place-based learning experienced more proactive interference. Taken together, our results show that 1) both memory interference and facilitation can co-occur as a function of prior learning, 2) proactive interference within a route varied as a function of the degree of overlap with old knowledge, and 3) individual differences in spatial ability and strategy can modulate proactive interference.