Episodic memory enhancement versus impairment is determined by contextual similarity across events

Abstract

For over a century, stability of spatial context across related episodes has been considered a source of memory interference, impairing memory retrieval. However, contemporary memory integration theory generates a diametrically opposite prediction. Here, we aimed to resolve this discrepancy by manipulating local context similarity across temporally disparate but related episodes and testing the direction and underlying mechanisms of memory change. A series of experiments show that contextual stability produces memory integration and marked reciprocal strengthening. Variable context, conversely, seemed to result in competition such that new memories become enhanced at the expense of original memories. Interestingly, these patterns were virtually inverted in an additional experiment where context was reinstated during recall. These observations 1) identify contextual similarity across original and new memories as an important determinant in the volatility of memory, 2) present a challenge to classic and modern theories on episodic memory change, and 3) indicate that the sensitivity of context-induced memory changes to retrieval conditions may reconcile paradoxical predictions of interference and integration theory.

Keywords: episodic memory; integration; interference; reconsolidation; spatial context.

Fig. 1.

Experimental design of Exp. 1. Participants imagined word pairs (AB) in unique context images. One day later, they encoded the same cue word (A) together with a new associate (C). Crucially, a third of the word pairs was presented on the same context image as the day before (same contexts), whereas another third was presented on a new context image (different contexts). For the remaining third of the original episodes, no new related episode was encoded (original memory control). On the final day, participants completed original (AB), new (AC), and inferential (BC) cued recall tests on white backgrounds.

Fig. 2.

Example trials of testing procedures (Left), and column charts of proportion correct recall per condition (Right). (A) Exp. 1 (n = 39). Participants completed separate original (AB), new (AC), and inferential memory (BC) tests. (B) Exp. 2 (n = 43). Participants could type in two words in single test trials (42). (C) Exp. 3 (n = 41). Participants performed original (AB) and new memory (AC) tests in the respective encoding contexts. Error bars represent SEM. ***P < 0.001, **P < 0.01, *P < 0.05, ^###P < 0.001 one-sided, ^#P < 0.05 one-sided, ns = not significant.

Fig. 3.

Example trial of testing procedure (Left), and column chart of proportion of new memory recall during original memory testing (C in AB) and original memory recall during new memory testing (B in AC) per condition (Right). (A) Exp. 1 (n = 39). (B) Exp. 3 (n = 41). Error bars represent SEM. ***P < 0.001, **P < 0.01, *P < 0.05, ns = not significant.

Fig. 4.

Results of a multilevel logistic regression. Original memory accuracy was regressed on correctness of the corresponding new memory trial (correct versus incorrect), and context condition (same context versus different context). Error bars represent SEM. EMMs = estimated marginal means.

Fig. 5.

Theoretical model of context-induced changes in episodic memory. Contextual similarity across episodes elicits integration during new learning, leading to bolstered recall of associated memories. However, with contextual reinstatement during recall, retrieval interference (or possibly source confusion) develops instead. Conversely, contextual dissimilarity across episodes induces memory competition, promoting new learning at the cost of original memories. These effects are again overturned by contextual reinstatement, such that accurate memory retrieval occurs instead.