Memory editing: The role of temporal discontinuities in the compression of events in episodic memory editing.

Why does it take less time to remember an event than to experience it? Recent evidence suggests that the dynamic unfolding of events is temporally compressed in memory representations, but the exact nature of this compression mechanism remains unclear. The present study tested two possible mechanisms. First, it could be that memories compress the course of events into a sequence of moments or slices of prior experience, while omitting other segments, akin to edited films that give condensed accounts of events using sequences of separate shots (referred to as the discontinuity hypothesis). Alternatively, it may be that the entire stream of information is represented but is mentally replayed at a faster speed than the original experience (referred to as the acceleration hypothesis). In two experiments, these hypotheses were tested by comparing mental replay times for continuous movies depicting naturalistic events and edited versions of the same movies in which less informative parts were removed to mimic the presumed structure of memory representations according to the discontinuity hypothesis. We found that memories for videos in which less informative segments were replaced by temporal ellipses (Experiment 1) or by black screens of the same duration as removed segments (Experiment 2) were less compressed and contained a higher density of recalled units than did memories for complete videos. These results support the discontinuity hypothesis and suggest that segments of time that are redundant and predictable are omitted in episodic memory, while more informative segments are selectively retained to represent the unfolding of events. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Representational dynamics of memories for real-life events.

The continuous flow of experience that characterizes real-life events is not recorded as such in episodic memory but is condensed as a succession of event segments separated by temporal discontinuities. To unravel the neural basis of this representational structure, we recorded real-life events using wearable camera technology and used fMRI to investigate brain activity during their temporal unfolding in memory. We found that, compared to the representation of static scenes in memory, dynamically unfolding memory representations were associated with greater activation of the posterior medial episodic network. Strikingly, by analyzing the autocorrelation of brain activity patterns at successive time points throughout the retrieval period, we found that this network showed higher temporal dynamics when recalling events that included a higher density of event segments. These results reveal the key role of the posterior medial network in representing the dynamic unfolding of the event segments that constitute real-world memories.

Slices of the past: how events are temporally compressed in episodic memory.

Remembering everyday events typically takes less time than the actual duration of the retrieved episodes, a phenomenon that has been referred to as the temporal compression of events in episodic memory. Here, we review recent studies that have shed light on how this compression mechanism operates. The evidence suggests that the continuous flow of experience is not represented as such in episodic memory. Instead, the unfolding of events is recalled as a succession of moments or slices of past experience that includes temporal discontinuities-portions of past experience are omitted when remembering. Consequently, the rate of event compression is not constant but depends on the density of recalled segments of past experience.

The role of self-reference and personal goals in the formation of memories of the future.

Recent evidence suggests that some simulations of future events are encoded in memory and later recalled as "memories of the future," but the factors that determine the memorability of future simulations remain poorly understood. The current research aimed to test the hypothesis that imagined future events are better memorized when they are integrated in autobiographical knowledge structures. Across two experiments, we found that future events that involved the self were better recalled than future events that involved an acquaintance (Experiment 1), and that future events that were related to personal goals were better recalled than future events that were unrelated to goals (Experiment 2). Although self-reference and personal goals influenced the phenomenological characteristics of future simulations (e.g., their vividness and the clarity of event components), the enhanced recall of self-relevant and goal-relevant simulations was not simply due to these differences in the characteristics of simulations. Taken together, these findings suggest that the integration of simulated events with preexisting autobiographical knowledge is an important determinant of memories of the future.

The temporal compression of events during episodic future thinking.

While the cognitive and neural mechanisms that underlie episodic future thinking are increasingly well understood, little is known about how the temporal unfolding of events is represented in future simulations. In this study, we leveraged wearable camera technology to examine whether real-world events are structured and compressed in the same way when imagining the future as when remembering the past. We found that future events were simulated at proportionally higher speed than past events and that the density of experience units representing the unfolding of events was lower for future than for past episodes. Despite these differences, the nature of events influenced compression rates in the same way for past and future events. Furthermore, the perceived duration of both types of events depended on the density of represented experience units. These results provide novel insight into the mechanisms that structure the unfolding of events during future simulations.

The impact of age on the temporal compression of daily life events in episodic memory.

While age differences in episodic memory are well documented, the impact of age on the structure of memories for real-world events has not been investigated in detail. Recent research has shown that the continuous flow of information that constitutes daily life events is compressed in episodic memory, such that the time needed to mentally replay an event is shorter than the actual event duration. To examine whether this process of temporal compression of prior experience in episodic memory is affected by aging, we asked young and older adults to engage in a series of events that simulated daily life activities while their experience was automatically recorded using a wearable camera. Subsequently, participants were asked to mentally replay these events in as much detail as possible and then to verbally report recalled contents and to rate the subjective qualities of their memories. Results revealed that the rates of temporal compression of events during mental replay were similar in young and older adults. In both age groups, rates of temporal compression were predicted by the density of recalled moments of prior experience per unit of time of the actual event duration. Interestingly, however, the number of recalled moments predicted the subjective vividness of memories in young but not in older adults. Taken together, these results suggest that the process of temporal compression of events in episodic memory is unaffected by age but that the subjective experience of memory vividness becomes less tied to recalled moments that represent the unfolding of events. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Event segmentation and the temporal compression of experience in episodic memory.

Recent studies suggest that episodic memory represents the continuous flow of information that constitutes daily life events in a temporally compressed form, but the nature and determinants of this compression mechanism remain unclear. In the present study, we used wearable camera technology to investigate whether the temporal compression of experience in episodic memory depends on event segmentation. Participants experienced a series of events during a walk on a university campus and were later asked to mentally replay these events. The temporal compression of events in memory and grain size of event segmentation were estimated based on records of participants' experience taken by the camera. The results showed that the temporal compression of events in memory (i.e., the density of recalled moments of experience per unit of time of the actual event duration) closely corresponded to the grain size of event segmentation. Specifically, grain sizes of event segmentation and temporal compression rates were four to five times lower when remembering events that involved goal-directed actions compared to other kinds of events (e.g., spatial displacements). Furthermore, temporal compression rates in memory were significantly predicted by the grain size of event segmentation and event boundaries were more than five times more likely to be remembered than other parts of events. Together, these results provide new insights into the mechanism of temporal compression of events in episodic memory.

The time to remember: Temporal compression and duration judgements in memory for real-life events.

Recent studies suggest that the continuous flow of information that constitutes daily life events is temporally compressed in episodic memory, yet the characteristics and determinants of this compression mechanism remain unclear. This study examined this question using an experimental paradigm incorporating wearable camera technology. Participants experienced a series of real-life events and were later asked to mentally replay various event sequences that were cued by pictures taken during the original events. Estimates of temporal compression (the ratio of the time needed to mentally re-experience an event to the actual event duration) showed that events were replayed, on average, about eight times faster than the original experiences. This compression mechanism seemed to operate by representing events as a succession of moments or slices of prior experience separated by temporal discontinuities. Importantly, however, rates of temporal compression were not constant and were lower for events involving goal-directed actions. The results also showed that the perceived duration of events increased with the density of recalled moments of prior experience. Taken together, these data extend our understanding of the mechanisms underlying the temporal compression and perceived duration of real-life events in episodic memory.

Differential Contributions of Default and Dorsal Attention Networks to Remembering Thoughts and External Stimuli From Real-Life Events.

Episodic memories are typically composed of perceptual information derived from the external environment and representations of internal states (e.g., one's thoughts during prior episodes). To date, however, research has mostly focused on the remembrance of external stimuli, such that little is known about how internal mentation is represented within episodic memory. In the present fMRI study, we examined the neural correlates of these 2 components of episodic memories using a novel method of cuing memories from photographs taken during real-life events. We found that, compared with corresponding semantic memory tasks, memories for internal thoughts and external elements were associated with activity in brain areas supporting episodic recollection. Most importantly, however, the 2 kinds of memories also showed differential activation in large-scale brain networks: the remembrance of external elements was associated with greater activity in the dorsal attention network, whereas memories of internal thoughts mainly recruited default network areas. These findings shed new light on the representation of internal and external aspects of prior experience within episodic memory. The default network may contribute to the reinstatement of thoughts experienced during past events, whereas the dorsal attention network may support the allocation of attention to visuospatial features within episodic memory representations.

Temporal compression in episodic memory for real-life events.

Remembering an event typically takes less time than experiencing it, suggesting that episodic memory represents past experience in a temporally compressed way. Little is known, however, about how the continuous flow of real-life events is summarised in memory. Here we investigated the nature and determinants of temporal compression by directly comparing memory contents with the objective timing of events as measured by a wearable camera. We found that episodic memories consist of a succession of moments of prior experience that represent events with varying compression rates, such that the density of retrieved information is modulated by goal processing and perceptual changes. Furthermore, the results showed that temporal compression rates remain relatively stable over one week and increase after a one-month delay, particularly for goal-related events. These data shed new light on temporal compression in episodic memory and suggest that compression rates are adaptively modulated to maintain current goal-relevant information.

Accessibility and characteristics of memories of the future.

Recent research suggests that some imagined future events are encoded in memory, leading to the formation of "memories of the future". However, questions remain regarding the exact components of future event simulations that are encoded and the factors that determine their accessibility. To address these questions, the present study investigated memory for previously imagined future events using both free and cued recall tasks. The results showed that most future event simulations were successfully encoded and remained available in memory after a one week delay, but only some of them were readily accessible, whereas others could only be accessed when relevant cues were provided. Persons and locations were particularly well remembered, suggesting that these components are central to the simulation and memorisation of future events. We also found that memory for future event simulations was related to the clarity and familiarity of represented persons, the subjective feelings of pre-experience and mental time travel, the importance of imagined events to personal goals, and their emotional intensity during the initial simulation phase. Taken together, these findings expand our understanding of the formation, accessibility, and characteristics of memories of the future.

Prevalence and determinants of direct and generative modes of production of episodic future thoughts in the word cueing paradigm.

Recent research suggests that episodic future thoughts can be formed through the same dual mechanisms, direct and generative, as autobiographical memories. However, the prevalence and determinants of the direct production of future event representations remain unclear. Here, we addressed this issue by collecting self-reports of production modes, response times (RTs), and verbal protocols for the production past and future events in the word cueing paradigm. Across three experiments, we found that both past and future events were frequently reported to come directly to mind in response to the cue, and RTs confirmed that events were produced faster for direct than for generative responses. When looking at the determinants of direct responses, we found that most past and future events that were directly produced had already been thought of on a previous occasion, and the frequency of previous thoughts predicted the occurrence of direct access. The direct production of autobiographical thoughts was also more frequent for past and future events that were judged important and emotionally intense. Collectively, these findings provide novel evidence that the direct production of episodic future thoughts is frequent in the word cueing paradigm and often involves the activation of personally significant "memories of the future."

The neural basis of temporal order processing in past and future thought.

Although growing evidence has shown that remembering the past and imagining the future recruit a common core network of frontal-parietal-temporal regions, the extent to which these regions contribute to the temporal dimension of autobiographical thought remains unclear. In this fMRI study, we focused on the event-sequencing aspect of time and examined whether ordering past and future events involve common neural substrates. Participants had to determine which of two past (or future) events occurred (or would occur) before the other, and these order judgments were compared with a task requiring to think about the content of the same past or future events. For both past and future events, we found that the left posterior hippocampus was more activated when establishing the order of events, whereas the anterior hippocampus was more activated when representing their content. Aside from the hippocampus, most of the brain regions that were activated when thinking about temporal order (notably the intraparietal sulcus, dorsolateral pFC, dorsal anterior cingulate, and visual cortex) lied outside the core network and may reflect the involvement of controlled processes and visuospatial imagery to locate events in time. Collectively, these findings suggest (a) that the same processing operations are engaged for ordering past events and planned future events in time, (b) that anterior and posterior portions of the hippocampus are involved in processing different aspects of autobiographical thought, and (c) that temporal order is not necessarily an intrinsic property of memory or future thought but instead requires additional, controlled processes.