Object, spatial, and temporal memory: A behavioral analysis of visual scenes using a what, where, and when paradigm

Early cognitive neuroscientific research revealed that the hippocampus is crucial for spatial navigation in rodents, and for autobiographical episodic memory in humans. Researchers quickly linked these streams to propose that the human hippocampus supports memory through its role in representing space, and research on the link between spatial cognition and episodic memory in humans has proliferated over the past several decades. Different researchers apply the term "spatial" in a variety of contexts, however, and it remains unclear what aspect of space may be critical to memory. Similarly, "episodic" has been defined and tested in different ways. Naturalistic assessment of spatial memory and episodic memory (i.e., episodic autobiographical memory) is required to unify the scale and biological relevance in comparisons of spatial and mnemonic processing. Limitations regarding the translation of rodent to human research, human ontogeny, and inter-individual variability require greater consideration in the interpretation of this literature. In this review, we outline the aspects of space that are (and are not) commonly linked to episodic memory, and then we discuss these dimensions through the lens of individual differences in naturalistic autobiographical memory. Future studies should carefully consider which aspect(s) of space are being linked to memory within the context of naturalistic human cognition. This article is categorized under: Psychology > Memory.

What-Where-When (WWW) memory tasks have been used to study episodic(-like) memory in non-human animals. In this study, we investigate whether humans use episodic memory to solve such a WWW memory task. Participants are assigned to one of two treatments, in which they hide different coin types (what) in different locations (where) on two separate occasions (when). In the Active treatment, which mimics the animal situation as closely as possible, participants are instructed to memorize the WWW information; in the Passive treatment, participants are unaware of the fact that memory will be tested. In both groups, the majority of participants report using a mental time travel strategy to solve the task, and performance on a different episodic memory test significantly predicts performance on the WWW memory task. This suggests that the WWW memory task is a good test of episodic memory in humans. Participants remember locations and coins from the first hiding session better than they do those of the second hiding session, suggesting their memories may be reinforced during the second hiding session. We also investigated how well episodic memory performance predicted performance on the three aspects of the WWW memory task separately. In the Passive treatment, episodic memory performance predicts performance on all three aspects of the WWW memory task equally. However, in the Active treatment it only predicts performance on the what component. This could imply that during active encoding a different memory system is used for where and when information than during passive encoding. Encoding of what information seems to rely on episodic memory processing in both conditions.

Episodic memory is a critical capacity that involves remembering past events along with their spatial and temporal contexts. Relatively little is known about the relations between spatial and temporal information in long-term memory in children or adults. The present research examined the influence of the mental timeline (linear horizontal display extending from the left to right direction for English speakers) on memory for events and their spatial and temporal features in 7-year-olds, 9-year-olds, 11-year-olds and young adults (N = 146). During encoding, participants studied triplets of objects, varying on two dimensions of the mental timeline: linearity (whether objects were presented in linear succession or not) and direction (whether objects were presented from left-to-right or right-to-left). After a delay, during retrieval, participants were tested on their memory for individual objects, and either the spatial location or temporal order of the objects. We found that overall accuracy for spatial location was higher than accuracy for temporal order, and there was a parallel developmental trajectory for both these aspects of memory. Across age groups we found that memory for temporal order, but not spatial location, was influenced by linearity and direction (i.e., match to mental timeline). Thus, in both children and adults the spatiotemporal mental timeline supported memory for temporal order, converging with predictions generated within domains of language and thought and enhancing our understanding of how space and time are represented in the mind.

People retain more new verbal episodic information for at least 7 days if they rest for a few minutes after learning than if they attend to new information. It is hypothesized that rest allows for superior consolidation of new memories. In rodents, rest periods promote hippocampal replay of a recently travelled route, and this replay is thought to be critical for memory consolidation and subsequent spatial navigation. If rest boosts human memory by promoting hippocampal replay/consolidation, then the beneficial effect of rest should extend to complex (hippocampal) memory tasks, for example, tasks probing associations and sequences. We investigated this question via a virtual reality route memory task. Healthy young participants learned two routes to a 100% criterion. One route was followed by a 10-min rest and the other by a 10-min spot the difference game. For each learned route, participants performed four delayed spatial memory tests probing: (i) associative (landmark-direction) memory, (ii) cognitive map formation, (iii) temporal (landmark) order memory, and (iv) route memory. Tests were repeated after 7 days to determine any long-term effects. No effect of rest was detected in the route memory or cognitive map tests, most likely due to ceiling and floor effects, respectively. Rest did, however, boost retention in the associative memory and temporal order memory tests, and this boost remained for at least 7 days. We therefore demonstrate that the benefit of rest extends to (spatial) associative and temporal order memory in humans. We hypothesise that rest allows superior consolidation/hippocampal replay of novel information pertaining to a recently learned route, thus boosting new memories over the long term.

Our daily lives unfold continuously, yet our memories are organised into distinct events, situated in a specific context of space and time, and chunked when this context changes (at event boundaries). Previous research showed that this process, termed event segmentation, enhances object-context binding but impairs temporal order memory. Physiologically, peaks in pupil dilation index event segmentation, similar to emotion-induced bursts of autonomic arousal. Emotional arousal also modulates object-context binding and temporal order memory. Yet, these two critical factors have not been systematically studied together. To address this gap, we ran a behavioural experiment using a paradigm validated to study event segmentation and extended it with emotion manipulation. During encoding, we sequentially presented greyscale objects embedded in coloured frames (colour changes defining events), with a neutral or aversive sound. During retrieval, we tested participants’ memory of temporal order memory and object-colour binding. We found opposite effects of emotion and event segmentation on episodic memory. While event segmentation enhanced object-context binding, emotion impaired it. On the contrary, event segmentation impaired temporal order memory, but emotion enhanced it. These findings increase our understanding of episodic memory organisation in laboratory settings, and potentially in real life with perceptual changes and emotion fluctuations constantly interacting.

Memory for temporal order in patients with schizophrenia

Progress on the hippocampal circuits and functions based on sharp wave ripples

Induction and measurement of episodic memories in healthy adults

Mental time travel is defined as the human ability to remember unique personal past experiences (episodic memory) and to anticipate and plan future events. Considerable debate has arisen around the question of whether nonhuman animals are also capable of mental time travel, ranging from complete denial of the ability in nonhumans to the suggestion that they have episodic memory and readily plan for the future. We evaluate the current evidence available from comparative cognition experiments and human-developmental research. Studies of episodic-like memory in birds and nonhuman mammals have centered on their ability to remember what, where, and when a single event occurred. Although clear evidence for memory of what and where has been shown, memory of when does not always appear and may depend on both the species tested and the experimental design used. We argue for a clear distinction between remembering when in absolute time an event occurred and remembering how long ago it occurred. Studies of neural processes indicate that the hippocampus is necessary for episodic memory in humans and episodic-like memory in rats. It is argued that studies of nonhumans should not focus on presence versus absence of human traits but should examine alternative mental time travel abilities in animals that may have evolved independently as adaptations to a particular ecological niche.

Episodic memory: what can animals remember about their past?

In complex real life situations, memories for temporal and spatial information are naturally linked since sequential events coincide in time and space. Whether this connection is inseparable or instead whether these processes are functionally dissociable was investigated in this patient study. Spatial object-location and temporal order memory tasks were administered to 36 stroke patients and 44 healthy control participants. On group level, patients with a stroke in the left hemisphere performed worse on temporal order memory, compared to the control participants. On individual level, using a multiple case-study approach, a clear pattern of dissociations was found between memory for temporal and for spatial features. These findings indicate that location and temporal order memory contain functionally separable processes. This adds to our understanding of how context information is processed in human memory. (JINS, 2017, 23, 421-430).

Temporal stability and change in neutral contexts can transform continuous experiences into distinct and memorable events. However, less is known about how shifting emotional states influence these memory processes, despite ample evidence that emotion impacts non-temporal aspects of memory. Here, we examined if emotional stimuli influence temporal memory for recent event sequences. Participants encoded lists of neutral images while listening to 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 events. Temporal order memory was tested for neutral item pairs that either spanned an emotional sound or were encountered within the same auditory event. Encountering a highly arousing event boundary led to faster response times for items encoded within the next event. Critically, we found that highly arousing sounds had different effects on binding ongoing versus ensuing sequential representations in memory. Specifically, highly arousing sounds were significantly more likely to enhance temporal order memory for ensuing information compared to information that spanned those boundaries, especially for boundaries with negative valence. These findings suggest that within aversive emotional contexts, fluctuations in arousal help shape the temporal organisation of events in memory.

A novel experimental approach to episodic memory in humans based on the privileged access of odors to memories

Two strategies used to uncover neural systems for episodic-like memory in animals are discussed: (i) an attribute of episodic memory (what? when? where?) is examined in order to reveal the neuronal interactions supporting that component of memory; and (ii) the connections of a structure thought to be central to episodic memory in humans are studied at a level of detail not feasible in humans. By focusing on spatial memory (where?) and the hippocampus, it has proved possible to bring the strategies together. A review of lesion, disconnection and immediate early-gene studies in animals reveals the importance of interactions between the hippocampus and specific nuclei in the diencephalon (most notably the anterior thalamic nuclei) for spatial memory. Other parts of this extended hippocampal system include the mammillary bodies and the posterior cingulate (retrosplenial) cortex. Furthermore, by combining lesion and immediate early-gene studies it is possible to show how the loss of one component structure or tract can influence the remaining regions in this group of structures. The validity of this convergent approach is supported by new findings showing that the same set of regions is implicated in anterograde amnesia in humans.

Episodic Memory: A Rat Model of Source Memory