Long, N. M. | Search bioRxiv

bioRxiv2022

Semantic overlap protects from interference by restoring encoding mechanisms

Overlap between experiences can have both facilitative and detrimental effects for memory. Our aim was to establish whether overlap along one dimension (e.g. contextual, semantic, temporal) can counteract overlap-driven interference along another dimension. We hypothesized that semantic overlap facilitates episodic memory formation by modulating encoding mechanisms. We recorded scalp electroencephalography (EEG) while human participants performed a free recall task. Half of the items from late in each study list semantically overlapped with an item presented earlier in the list. We find that semantic overlap selectively improves memory and influences the neural signals engaged during the study of late list items. Relative to other recalled items, late list items that are later recalled consecutively with semantically overlapping items elicited increased high frequency activity and decreased low frequency activity, a hallmark of successful encoding. Our findings demonstrate that semantic overlap can protect from interference due to temporal overlap by modulating encoding mechanisms. Statement of RelevancExperiences can overlap along different dimensions, including contextual, semantic, and tempo-ral. We tested the hypothesis that semantic overlap - shared meaning between experiences - may protect from interference due to temporal overlap, when experiences occur close together in time. Although evidence suggests that attention and/or encoding resources diminish across a series of study items presented in close temporal proximity, we find that semantic overlap can enable recovery of these encoding resources. Specifically, items that would typically be forgotten due to interference are better remembered and recruit distinct neural mechanisms when they share meaning with an earlier study item. These findings indicate that encoding mechanisms can be modulated by the degree of semantic overlap between two experiences. More broadly, our results suggest that experiences do not exist in isolation, rather that a prior experience can directly influence the neural mechanisms recruited to process a current experience.

neuroscience↗

bioRxiv2021

Spatiotemporal context modulates encoding and retrieval of overlapping events

Overlap between events can lead to interference due to a tradeoff 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 are unclear. Here, by identifying brain states using scalp electroencephalography (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.

neuroscience↗