Perceptual boundaries cause mnemonic trade-offs between local boundary processing and across-trial associative binding

Abstract

Episodic memories are not veridical records of our lives, but rather are better described as organized summaries of experience. Theories and empirical research suggest that shifts in perceptual, temporal, and semantic information lead to a chunking of our continuous experiences into segments, or "events." However, the consequences of these contextual shifts on memory formation and organization remains unclear. In a series of 3 behavioral studies, we introduced context shifts (or "event boundaries") between trains of stimuli and then examined the influence of the boundaries on several measures of associative memory. In Experiment 1, we found that perceptual event boundaries strengthened associative binding of item-context pairings present at event boundaries. In Experiment 2, we observed reduced temporal order memory for items encoded in distinct events relative to items encoded within the same event, and a trade-off between the speed of processing at boundaries, and temporal order memory for items that flanked those boundaries. Finally, in Experiment 3 we found that event organization imprinted structure on the order in which items were freely recalled. These results provide insight into how boundary- and event-related organizational processes during encoding shape subsequent representations of events in episodic memory. (PsycINFO Database Record

Figure 1. Schematic of the Task

Participants made pleasant/unpleasant judgments on object-color pairs. Critically, the color switched every 6 trials. Object-color associative memory test. (Bottom, left) After encoding, participants performed a two alternative forced choice object-color memory test. The object-color test was in both Experiment 1 and 2. Temporal order memory test. (Bottom, right) After the color test, temporal order memory was tested using a two alternative forced choice task. Participants indicated which of two studied objects appeared first in the list. The temporal order test was only in Experiment 2.

Figure 2. Experiment 1 Results

Object-color associative memory accuracy (A) and response times are shown as a function of within-event position (B). Error bars represent 95% confidence intervals. *p < .05, **p < .005, ***p < .001.

Figure 3. Experiment 2 Results

(A) Memory accuracy is shown as a function of test and condition. (B) Temporal order memory accuracy split into terciles by encoding response time of intervening boundary (for across-event) or non-boundary (for within-event) trial. (C) Task response times during encoding as a function of event position. (D) Retrieval response times for correct trials as a function of condition and memory test. All error bars represent 95% confidence intervals. *p<.05, **p<.005, ***p<.001.

Figure 4. Experiment 3: Serial Position Curve and Lag-CRP

(A) Memory accuracy broken down by list position. (B) Given the recall of an item in position n, this graph plots the probability of recalling a neighboring items next in the recall sequence (+/− 5).

Figure 5. Experiment 3 Results

(A) Local forward (sum of n+1, n+2, n+3) transition likelihood as a function of within-event position. (B) Local backward (sum of n-1, n-2, n-3) transition likelihood as a function of within-event position. (C) Average transition distance as a function of within-event position. (D) Likelihood of transition from pre-boundary items as a function of within-event position. Error bars represent 95% confidence intervals. p<.10, *p<.05, **p<.005.