Temporal Context Modulates Encoding and Retrieval of Overlapping Events.

Overlap between events can lead to interference because of a trade-off between encoding the present event and retrieving the past event. Temporal context information, "when" something occurred, a defining feature of episodic memory, can cue retrieval of a past event. However, the influence of temporal overlap, or proximity in time, on the mechanisms of interference is unclear. Here, by identifying brain states using scalp EEG from male and female human subjects, we show the extent to which temporal overlap promotes interference and induces retrieval. In this experiment, subjects were explicitly directed to either encode the present event or retrieve a past, overlapping event while perceptual input was held constant. We find that the degree of temporal overlap between events leads to selective interference. Specifically, greater temporal overlap between two events leads to impaired memory for the past event selectively when the top-down goal is to encode the present event. Using pattern classification analyses to measure neural evidence for a retrieval state, we find that greater temporal overlap leads to automatic retrieval of a past event, independent of top-down goals. Critically, the retrieval evidence we observe likely reflects a general retrieval mode, rather than retrieval success or effort. Collectively, our findings provide insight into the role of temporal overlap on interference and memory formation.SIGNIFICANCE STATEMENT When a present event overlaps with an event from the past, this leads to a trade-off between the tendency to encode the present event versus retrieve the past event. Here we show that, when two events are experienced nearby in time, the memory system is biased toward a retrieval state and that subsequent memory for the past event is impaired. These findings suggest an influence of bottom-up temporal factors on both interference and the trade-off between memory states.