Time is of the essence: Exploring temporal and spatial organisation in episodic memory

Recall initiation instructions influence how space and time interact in memory

Recent work has examined the interaction between space and time in memory search, but there is still limited understanding of this relationship. Here, we test the hypothesis that individuals can exert control over how time and space interact in response to subtle differences in task instructions. To test this hypothesis, we analyzed two experiments where participants completed two immediate free recall tasks, a verbal task involving words presented at a central location and a spatial task involving squares presented at different locations. Some participants were free to recall the words or locations spontaneously in any order they preferred. In contrast, another group was subtly biased toward temporal information by instructions to begin recall from the last presented item before recalling the remaining items in any order they wished. Replicating recent work, all conditions showed clear evidence that recall was organized along both the temporal and the spatial dimensions. Extending this work, we found that the subtle change in recall instructions increased the reliance on temporal information in the spatial recall task. Correlational analyses suggest that spatial and temporal information do not compete when participants search memory spontaneously. However, they do compete when instructions favor temporal information. These findings highlight that individuals can exert some cognitive control over how associative dimensions interact during memory search and emphasize the importance of incorporating such processes into theoretical models.

Attentional fluctuations and the temporal organization of memory

Event boundaries and temporal context shape the organization of episodic memories. We hypothesized that attentional fluctuations during encoding serve as "events" that affect temporal context representations and recall organization. Individuals encoded trial-unique objects during a modified sustained attention task. Memory was tested with free recall. Response time variability during the encoding tasks was used to characterize "in the zone" and "out of the zone" attentional states. We predicted that: 1) "in the zone", vs. "out of the zone", attentional states should be more conducive to maintaining temporal context representations that can cue temporally organized recall; and 2) temporally distant "in the zone" states may enable more recall "leaps" across intervening items. We replicated several important findings in the sustained attention and memory fields, including more online errors during "out of the zone" vs. "in the zone" attentional states and recall that was temporally structured. Yet, across four studies, we found no evidence for either of our main hypotheses. Recall was robustly temporally organized, and there was no difference in recall organization for items encoded "in the zone" vs. "out of the zone". We conclude that temporal context serves as a strong scaffold for episodic memory, one that can support organized recall even for items encoded during relatively poor attentional states. We also highlight the numerous challenges in striking a balance between sustained attention tasks (long blocks of a repetitive task) and memory recall tasks (short lists of unique items) and describe strategies for researchers interested in uniting these two fields.

Space and time in the similarity structure of memory

Space and time are both essential aspects of human episodic memory. Yet, behavioral studies into the dynamics of recall have focused more on time than space. For instance, it is now well known that temporally contiguous events are more likely to be subsequently recalled than temporally remote events, as measured by the lag-conditional response probability (lag-CRP), which represents the probability of recalling item i + lag after recalling item i. The present study administered both verbal and spatial delayed free recall (DFR) tasks to a sample of 168 participants in order to measure lag-CRPs along both spatial and temporal associative dimensions. Whereas only the temporal lag-CRP could be measured in the verbal DFR task, both temporal and spatial lag-CRPs could be measured in the spatial DFR task. As expected, the results obtained in the verbal DFR task indicated the typical temporal contiguity effect. More importantly, the results obtained in the spatial DFR task indicated significant contiguity effects along both associative dimensions, and the spatial contiguity effect was found to be significantly larger than the temporal contiguity effect. In addition, the relatively small temporal contiguity effect observed in the spatial DFR task was also found to be significantly smaller than the temporal contiguity effect observed in the verbal DFR task. Altogether, the present findings provided novel evidence that spatial and temporal proximity can both cue sequential dependencies between successive recalls. As such, retrieved context models of episodic memory should be expanded to include spatial context as well as temporal context.