Temporal compression in episodic memory for real-life events

The effects of emotion on retrospective duration memory using virtual reality

Our memories for temporal duration may be colored by the emotions we experience during an event. While emotion generally enhances some aspects of memory, temporal duration has been shown to be particularly susceptible to emotion-induced distortions. However, prior work has faced difficulty when studying this phenomenon, having to make some trade-offs on ecological validity or experimental control. Here, we sought to bridge this gap by studying the effects of emotion on temporal duration memory using virtual reality. In the present study, a final sample of 69 participants experienced a series of negative-emotional and neutral worlds within virtual reality. Following this, participants provided ratings of emotionality (arousal, valence, pleasantness) and retrospective duration estimates (i.e., remembered time). We hypothesized that negative events would be recalled as having a greater duration than neutral events (H1). We additionally hypothesized that negative, but not neutral, events would be recalled as being longer than the true duration (H2). The results supported H1 while failing to provide evidence in support of H2. Together, the results bolster the importance of emotion, especially negative emotion, in shaping how we remember the temporal unfolding of the past.

Experience and memory of time and emotions two years after the start of the COVID-19 pandemic

In this French longitudinal study, we assessed judgment of the passage of time in current life and the predictors of this judgment 2 years after the onset of the COVID-19 pandemic, i.e., at a time when there was no lockdown and no protective measures. We then compared these measures with the same participants' passage-of-time judgments assessed during each of the past three French lockdowns. We also assessed their memory representations of the passage of time in the past, i.e., for the various lockdowns. The results showed the persistence of the feeling of time slowing down outside of lockdown. However, this was no longer linked to external factors (lack of activity, disruption of everyday routines) as found in the previous studies conducted during the lockdowns, but to an individual internal factor, namely a high level of depression in the general population. Moreover, the results revealed that the experience of the passage of time for the past lockdowns was compressed in memory, being judged to be faster than it actually was. This time compression tended to be greater in depressed people. It was also associated with a positive bias for all the other examined factors (e.g., sleep quality, life routine, boredom, happiness). We assumed that this time compression would be related to processes involved in the recall of unfolding events, with certain moments being omitted or forgotten during recall, as well as to the process of reconstruction in autobiographical memory. Our study therefore shows the long-lasting effect of lockdowns on mental health of the general population, which was expressed by the persistent feeling of a slowing down of time. It is therefore necessary to take care of this psychologically fragile population and to avoid further lockdowns in response to a new health crisis, that they cannot cope with.

Neural signatures associated with temporal compression in the verbal retelling of past events

When we retell our past experiences, we aim to reproduce some version of the original events; this reproduced version is often temporally compressed relative to the original. However, it is currently unclear how this compression manifests in brain activity. One possibility is that a compressed retrieved memory manifests as a neural pattern which is more dissimilar to the original, relative to a more detailed or vivid memory. However, we argue that measuring raw dissimilarity alone is insufficient, as it confuses a variety of interesting and uninteresting changes. To address this problem, we examine brain pattern changes that are consistent across people. We show that temporal compression in individuals’ retelling of past events predicts systematic encoding-to-recall transformations in several higher associative regions. These findings elucidate how neural representations are not simply reactivated, but can also be transformed due to temporal compression during a universal form of human memory expression: verbal retelling.

Brain patterns measured while participants first watched a movie in the fMRI scanner, then recalled the movie’s key narrative features, demonstrate that temporal compression in individuals’ retelling of past events predicts encoding-to-recall transformations.

Temporal self-compression: Behavioral and neural evidence that past and future selves are compressed as they move away from the present

For centuries, great thinkers have struggled to understand how people represent a personal identity that changes over time. Insight may come from a basic principle of perception: as objects become distant, they also become less discriminable or “compressed.” In Studies 1–3, we demonstrate that people’s ratings of their own personality become increasingly less differentiated as they consider more distant past and future selves. In Study 4, we found neural evidence that the brain compresses self-representations with time as well. When we peer out a window, objects close to us are in clear view, whereas distant objects are hard to tell apart. We provide evidence that self-perception may operate similarly, with the nuance of distant selves increasingly harder to perceive.

A basic principle of perception is that as objects increase in distance from an observer, they also become logarithmically compressed in perception (i.e., not differentiated from one another), making them hard to distinguish. Could this basic principle apply to perhaps our most meaningful mental representation: our own sense of self? Here, we report four studies that suggest selves are increasingly non-discriminable with temporal distance from the present as well. In Studies 1 through 3, participants made trait ratings across various time points in the past and future. We found that participants compressed their past and future selves, relative to their present self. This effect was preferential to the self and could not be explained by the alternative possibility that individuals simply perceive arbitrary self-change with time irrespective of temporal distance. In Study 4, we tested for neural evidence of temporal self-compression by having participants complete trait ratings across time points while undergoing functional MRI. Representational similarity analysis was used to determine whether neural self-representations are compressed with temporal distance as well. We found evidence of temporal self-compression in areas of the default network, including medial prefrontal cortex and posterior cingulate cortex. Specifically, neural pattern similarity between self-representations was logarithmically compressed with temporal distance. Taken together, these findings reveal a “temporal self-compression” effect, with temporal selves becoming increasingly non-discriminable with distance from the present.

Degree of learning and linear forgetting

The aim of this study was to assess whether the degree of learning influences the observation of memory retention and forgetting that follows a linear pattern. According to our retention accuracy from fragmented traces (RAFT) model, one factor that should increase the likelihood of this is when there is greater learning of the material. Higher levels of learning can increase the number of trace components, making it more likely that reconstruction or partial retrieval can lead to an accurate response on a memory test. Here, we report three new experiments, as well as re-analyses of existing data from the literature, to show that increasing the level of learning in some ways can lead to increases in the likelihood of observing linear forgetting. For Experiment 1, people learned materials to different levels. This learning involved cued recall testing during memorisation. Linear forgetting was observed with increased learning. For Experiment 2, learning did not involve cued recall testing. Linear forgetting was not observed. Although our aim was not to test theories of retrieval practice, for Experiment 3, we showed that when people engage in this process, the pattern of retention and forgetting becomes more linear. Overall, these data are consistent with the RAFT theory and support mechanisms that it suggests can lead to the observation of linear forgetting.

Time changes: Timing contexts support event segmentation in associative memory

We tend to mentally segment a series of events according to perceptual contextual changes, such that items from a shared context are more strongly associated in memory than items from different contexts. It is also known that timing context provides a scaffold to structure experiences in memory, but its role in event segmentation has not been investigated. We adapted a previous paradigm, which was used to investigate event segmentation using visual contexts, to study the effects of changes in timing contexts on event segmentation in associative memory. In two experiments, we presented lists of 36 items in which the interstimulus intervals (ISIs) changed after a series of six items ranging between 0.5 and 4 s in 0.5 s steps. After each list, participants judged which one of two test items were shown first (temporal order judgment) for items that were either drawn from the same context (within an ISI) or from consecutive contexts (across ISIs). Further, participants judged from memory whether the ISI associated to an item lasted longer than a standard interval (2.25 s) that was not previously shown (temporal source memory). Experiment 2 further included a time-item encoding task. Results revealed an effect of timing context changes in temporal order judgments, with faster responses (Experiment 1) or higher accuracy (Experiment 2) when items were drawn from the same context, as opposed to items drawn from across contexts. Further, in both experiments, we found that participants were well able to provide temporal source memory judgments based on recalled durations. Finally, replicated across experiments, we found subjective duration bias, as estimated by psychometric curve fitting parameters of the recalled durations, correlated negatively with within-context temporal order judgments. These findings show that changes in timing context support event segmentation in associative memory.

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 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.

Sequence Memory in the Hippocampal-Entorhinal Region

Episodic memories are constructed from sequences of events. When recalling such a memory, we not only recall individual events, but we also retrieve information about how the sequence of events unfolded. Here, we focus on the role of the hippocampal-entorhinal region in processing and remembering sequences of events, which are thought to be stored in relational networks. We summarize evidence that temporal relations are a central organizational principle for memories in the hippocampus. Importantly, we incorporate novel insights from recent studies about the role of the adjacent entorhinal cortex in sequence memory. In rodents, the lateral entorhinal subregion carries temporal information during ongoing behavior. The human homologue is recruited during memory recall where its representations reflect the temporal relationships between events encountered in a sequence. We further introduce the idea that the hippocampal-entorhinal region might enable temporal scaling of sequence representations. Flexible changes of sequence progression speed could underlie the traversal of episodic memories and mental simulations at different paces. In conclusion, we describe how the entorhinal cortex and hippocampus contribute to remembering event sequences-a core component of episodic memory.

In Medio Stat Virtus: intermediate levels of mind wandering improve episodic memory encoding in a virtual environment

Episodic memory encoding is highly influenced by the availability of attentional resources. Mind wandering corresponds to a shift of attention toward task-unrelated thoughts. Few studies, however, have tested this link between memory encoding and mind wandering. The goal of the present work was to systematically investigate the influence of mind wandering during encoding on episodic memory performances in an ecological setting. Fifty-two participants were asked to navigate in a virtual urban environment. During the walk, they encountered different scenes that, unbeknownst to the participants, were target items presented in a subsequent recognition task associated with a Remember-Know-Guess paradigm. Each item triggered, after a random interval, a thought probe assessing current mind wandering. We found a significant linear positive relationship between the ratio of correctly recognized items and the overall mind wandering reported after the task. Moreover, we found a quadratic reversed U-shaped relationship between the probability of giving a 'Remember' response and both on-line and mind wandering reported a posteriori. The nearer to the medium value the level of mind wandering was, the higher was the probability to have a recollection-based recognition. Our results indicate that in a complex environment, the highest probability of actually remembering a scene would be when participants present a medium attentional level: neither distracted by inner thoughts nor too focused on the environment. This open attentional state would allow a better global processing of the environment by preventing one's attention from being captured by internal thoughts or narrowed by an over-focusing on the environment.

Zooming In and Out on One's Life: Autobiographical Representations at Multiple Time Scales

The ability to decouple from the present environment and explore other times is a central feature of the human mind. Research in cognitive psychology and neuroscience has shown that the personal past and future is represented at multiple timescales and levels of resolution, from broad lifetime periods that span years to short-time slices of experience that span seconds. Here, I review this evidence and propose a theoretical framework for understanding mental time travel as the capacity to flexibly navigate hierarchical layers of autobiographical representations. On this view, past and future thoughts rely on two main systems-event simulation and autobiographical knowledge-that allow us to represent experiential contents that are decoupled from sensory input and to place these on a personal timeline scaffolded from conceptual knowledge of the content and structure of our life. The neural basis of this cognitive architecture is discussed, emphasizing the possible role of the medial pFC in integrating layers of autobiographical representations in the service of mental time travel.

The dynamics of memory retrieval for internal mentation

Daily life situations often require people to remember internal mentation, such as their future plans or interpretations of events. Little is known, however, about the principles that govern memory for thoughts experienced during real-world events. In particular, it remains unknown whether factors that structure the retrieval of external stimuli also apply to thought recall, and whether some thought features affect their accessibility in memory. To examine these questions, we asked participants to undertake a walk on a university campus while wearing a lifelogging camera. They then received unexpected recall tasks about the thoughts they experienced during the walk, rated the phenomenological features of retrieved thoughts, and indicated the moment when they were experienced. Results showed that thought retrieval demonstrates primacy, recency, and temporal contiguity effects, and is also influenced by event boundaries. In addition, thoughts that involved planning and that were recurrent during the walk were more accessible in memory. Together, these results shed new light on the principles that govern memory for internal mentation and suggest that at least partially similar processes structure the retrieval of thoughts and stimuli from the external environment.

From a Lived Event to Its Autobiographical Memory: An Ecological Study Using Wearable Camera in Schizophrenia

Cognitive disorders are considered as a core symptom of schizophrenia. Importantly, episodic autobiographical memory deficits are strongly related to patients' social dysfunction. Although the cognitive mechanisms underlying autobiographical memory deficit are highly important to open the door for specific cognitive remediation, they are yet to be understood. The present study focused on event segmentation to check to which extent possible impairments in temporal ordering and segmenting in patients hinder memories construction. Twenty-seven patients with schizophrenia and 27 matched controls took part in an outdoor circuit while wearing a wearable camera. A week later, their memory and the temporal organization of this event have been assessed. Results showed that patients, compared with control participants, reported a reduced amount of details, especially less actions with interaction related to the event. Contrary to our initial hypotheses, event segmentation abilities in patients were not affected. The relationship between event segmentation and memory is discussed.

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.