Mnemonic prediction errors promote detailed memories

Abstract

When our experience violates our predictions, it is adaptive to update our knowledge to promote a more accurate representation of the world and facilitate future predictions. Theoretical models propose that these mnemonic prediction errors should be encoded into a distinct memory trace to prevent interference with previous, conflicting memories. We investigated this proposal by repeatedly exposing participants to pairs of sequentially presented objects (A → B), thus evoking expectations. Then, we violated participants' expectations by replacing the second object in the pairs with a novel object (A → C). The following item memory test required participants to discriminate between identical old items and similar lures, thus testing detailed and distinctive item memory representations. In two experiments, mnemonic prediction errors enhanced item memory: Participants correctly identified more old items as old when those items violated expectations during learning, compared with items that did not violate expectations. This memory enhancement for C items was only observed when participants later showed intact memory for the related A → B pairs, suggesting that strong predictions are required to facilitate memory for violations. Following up on this, a third experiment reduced prediction strength prior to violation and subsequently eliminated the memory advantage of violations. Interestingly, mnemonic prediction errors did not increase gist-based mistakes of identifying old items as similar lures or identifying similar lures as old. Enhanced item memory in the absence of gist-based mistakes suggests that violations enhanced memory for items' details, which could be mediated via distinct memory traces. Together, these results advance our knowledge of how mnemonic prediction errors promote memory formation.

Figure 1.

Experimental design, all experiments. (A) During prediction learning (day 1), participants repeatedly viewed pairs of sequentially presented objects embedded within a stream of objects. Participants indicated whether each object was bigger or smaller than the previous object (experiments 1 and 2) or than a shoe box (experiment 3). (B) In the violation phase (day 2, preceded by a reminder of the predictions, not shown) (see the text for details), novel items were inserted to the sequence of objects, either instead of the second object in the pair, thus violating learned predictions (violation, in orange), or after the second object in a pair (no-violation, purple). The colors appear here for illustration; no color frames appeared on the screen. The task was identical to the prediction learning phase. (C) During the item memory test (day 2, immediately following the violation phase), the participants were presented with either identical copies of the violation and no violation items presented during the violation phase (identical old), or with another exemplar of the same item (similar lure) or novel items that did not appear in the experiment before (novel foil). Participants indicated whether an item was “old,” “similar,” or “new.” (D) We tested memory for the original predictive pair (day 2), by presenting participants with the first object in a pair and asking which of three bottom objects followed the top object during the study. Distractors were intralist within condition.

Figure 2.

Memory for violation (orange) and no-violation (purple) identical old items in experiments 1 (left) and 2 (right). “Old” responses are presented in darker colors, “similar” responses are presented in lighter colors. Results are for items for which participants remembered the corresponding original pair. (*) P < 0.05, (***) P < 0.005, (∼) marginally significant interaction (P < 0.1), (⊗) significant interaction (P < 0.05). Error bars reflect ±SEM.