Retrieval context determines whether event boundaries impair or enhance temporal order memory

Meaningful changes in context create "event boundaries", segmenting continuous experience into distinct episodes in memory. A foundational finding in this literature is that event boundaries impair memory for the temporal order of stimuli spanning a boundary compared to equally spaced stimuli within an event. This seems surprising in light of intuitions about memory in everyday life, where the order of within-event experiences (did I have coffee before the first bite of bagel?) often seems more difficult to recall than the order of events per se (did I have breakfast or do the dishes first?). Here, we aimed to resolve this discrepancy by manipulating whether stimuli carried information about their encoding context during retrieval, as they often do in everyday life (e.g., bagel-breakfast). In Experiments 1 and 2, we show that stimuli inherently associated with a unique encoding context produce a "flipped" order memory effect, whereby temporal memory was superior for cross-boundary than within-event item pairs. In Experiments 3 and 4, we added context information at retrieval to a standard laboratory event memory protocol where stimuli were encoded in the presence of arbitrary context cues (colored frames). We found that whether temporal order memory for cross-boundary stimuli was enhanced or impaired relative to within-event items depended on whether the context was present or absent during the memory test. Taken together, we demonstrate that the effect of event boundaries on temporal memory is malleable, and determined by the availability of context information at retrieval.

Multisensory integration of contextual boundaries affects temporal order memory, but not encoding or recognition

We memorize our daily life experiences, which are often multisensory in nature, by segmenting them into distinct event models, in accordance with perceived contextual or situational changes. However, very little is known about how multisensory integration affects segmentation, as most studies have focused on unisensory (visual or audio) segmentation. In three experiments, we investigated the effect of multisensory integration on segmentation in memory and perception. In Experiment 1, participants encoded lists of visual objects while audio and visual contexts changed synchronously or asynchronously. After each list, we tested recognition and temporal associative memory for pictures that were encoded in the same audio-visual context or that crossed a synchronous or an asynchronous multisensory change. We found no effect of multisensory integration for recognition memory: Synchronous and asynchronous changes similarly impaired recognition for pictures encoded at those changes, compared to pictures encoded further away from those changes. Multisensory integration did affect temporal associative memory, which was worse for pictures encoded at synchronous than at asynchronous changes. Follow up experiments showed that this effect was not due to the higher complexity of multisensory over unisensory contexts (Experiment 2), nor that it was due to the temporal unpredictability of contextual changes inherent to Experiment 1 (Experiment 3). We argue that participants formed situational expectations through multisensory integration, such that synchronous multisensory changes deviated more strongly from those expectations than asynchronous changes. We discuss our findings in light of supportive and conflicting findings of uni- and multisensory segmentation.

Emotional arousal ripples across time to bind subsequent episodes in memory

Time unfolds continuously, yet our memories are stored as discrete episodes. Prior work shows that fluctuations between stability and change in an ongoing neutral context facilitates this formation of distinct and memorable events. However, less is known about how shifting emotional states influence these memory processes, despite ample evidence that emotion has a robust influence on non-temporal aspects of episodic memory. Here, we examined if emotional stimuli influence temporal memory for recent event sequences. Participants encoded lists of neutral object images while listening to pure auditory tones. At regular intervals within each list, participants heard emotional positive, negative, or neutral sounds, which served as ‘emotional event boundaries’ that divided each sequence into discrete auditory events. Temporal order memory was tested for neutral item pairs that either spanned an emotional sound (‘boundary-spanning’) or encountered within the same auditory event (‘same-context’). We found that highly arousing boundaries had opposite effects on binding ongoing versus subsequent sequential representations in memory. Specifically, highly arousing emotional sounds tended to lead to worse temporal order memory for boundary-spanning item pairs. By contrast, they led to better temporal order memory for same-context item pairs in the next event. Both of these arousal effects were specific to negative sounds. The carryover effect of negative arousal was also strongest for item pairs encountered closest to the boundary and diminished as the event unfolded. These findings suggest that temporally dynamic emotional states support the temporal integration of mnemonic events, which may contribute to the hyper-episodic nature of negative emotional memories.

Emotion Enhances Memory for the Sequential Unfolding of a Naturalistic Experience

The events of our lives unfold across time. When remembering these events, we often reference information about when they occurred and their sequential unfolding. How does emotion affect our ability to reconstruct in memory the elements of an event in the correct temporal order? The present study explored this question using naturalistic stimuli. Human participants (N = 276) saw movie clips that varied in emotion (high versus low). Later, participants were asked to reconstruct the events in the order they encoded them. Participants’ temporal-order memory was better in the high- versus low-emotion condition. Analysis of free-recall data showed that participants remembered the high-emotion clip with greater vividness, yet the consistency of details did not differ between conditions. Our findings shed novel light on the multifaceted effects of emotion on memory, suggesting that highly emotional events can be reconstructed with greater temporal fidelity. These findings have both theoretical and practical implications.

Implicitly Learned Higher Order Associations Differentiates Recent and Remote Retrieval of Temporal Order Memory

Memory of an ordered sequence of distinct events requires encoding the temporal order as well as the intervals that separates these events. In this study, using order place association task where the animal learns to associate the location of the food pellet to the order of entry into the event arena, we probe the nature of temporal order memory in mice. In our task, individual trials, become distinct events, as the animal is trained to form unique association between entry order and a correct location. The inter-trial intervals (> 30 mins) are chosen deliberately to minimise the working memory contributions. We develop this paradigm initially using 4 order place associates and later extend it to 5 paired associates. Our results show that animals not only acquire these explicit (entry order to place) associations but also higher order associations that can only be inferred implicitly from the temporal order of these events. As an indicator of such higher order learning during the probe trail the mice exhibit predominantly prospective errors that declines proportionally with temporal distance. On the other hand, prior to acquiring the sequence the retrospective errors are dominant. Additionally, we also tested the nature of such acquisitions when temporal order CS is presented along with flavour as a compound stimulus comprising of order and flavour both simultaneously being paired with location. Results from these experiments indicate that the animal learns both order-place and flavour-place associations. Comparing with pure order place training, we find that the additional flavour in compound training did not interfere with the ability of the animals to acquire the order place associations. When tested remotely, pure order place associations could be retrieved only after a reminder training. Further higher order associations representing the temporal relationship between the events is markedly absent in the remote time.

Hippocampal spatial and sequential representations of event structure scaffold precise episodic temporal order memory

The hippocampus plays an important role in representing spatial locations and sequences and for transforming representations via pattern separation and completion. How these representational structures and operations support memory for the temporal order of random items is still poorly understood. We addressed this question by leveraging the method of loci (MOL), a powerful mnemonic strategy for temporal order memory that particularly recruits hippocampus-dependent computations of spatial locations and associations. Applying representational similarity analysis to fMRI activation patterns revealed that hippocampal subfields contained representations of both temporal context and multiple features of sequence structure, including location identity, distance, and sequence boundaries. Critically, the hippocampal CA1 and CA23DG exhibited spatial and sequential pattern separation, respectively, enabling the encoding of multiple items in the same location and reducing swap errors across adjacent locations. Our results suggest that the hippocampus can flexibly reconfigure multiplexed event structure representations to support accurate temporal order memory.