Predicting memory from the network structure of naturalistic events

ABSTRACTWhen we remember events, we often do not only recall individual events, but also the connections between them. However, extant research has focused on how humans segment and remember discrete events from continuous input, with far less attention given to how the structure of connections between events impacts memory. Here we conduct a functional magnetic resonance imaging study in which subjects watch and recall a series of realistic audiovisual narratives. By transforming narratives into networks of events, we demonstrate that more central events—those with stronger semantic or causal connections to other events—are better remembered. During encoding, central events evoke larger hippocampal event boundary responses associated with memory formation. During recall, high centrality is associated with stronger activation in cortical areas involved in episodic recollection, and more similar neural representations across individuals. Together, these results suggest that when humans encode and retrieve complex real-world experiences, the reliability and accessibility of memory representations is shaped by their location within a network of events.</jats:p

A generalized cortical activity pattern at internally-generated mental context boundaries during unguided narrative recall

AbstractCurrent theory and empirical studies suggest that humans segment continuous experiences into events based on the mismatch between predicted and actual sensory inputs; detection of these “event boundaries” evokes transient neural responses. However, boundaries can also occur at transitions between internal mental states, without relevant external input changes. To what extent do such “internal boundaries” share neural response properties with externally-driven boundaries? We conducted an fMRI experiment where subjects watched a series of short movies and then verbally recalled the movies, unprompted, in the order of their choosing. During recall, transitions between movies thus constituted major boundaries between internal mental contexts, generated purely by subjects’ unguided thoughts. Following the offset of each recalled movie, we observed stereotyped spatial activation patterns in the default mode network, especially the posterior medial cortex, consistent across different movie contents and even across the different tasks of movie watching and recall. Surprisingly, the between-movie boundary patterns did not resemble patterns at boundaries between events within a movie. Thus, major transitions between mental contexts elicit neural phenomena shared across internal and external modes and distinct from within-context event boundary detection, potentially reflecting a cognitive state related to the flushing and reconfiguration of situation models.</jats:p

P2-19: The Effect of item Repetition on Item-Context Association Depends on the Prior Exposure of Items

Previous studies have reported conflicting findings on whether item repetition has beneficial or detrimental effects on source memory. To reconcile such contradictions, we investigated whether the degree of pre-exposure of items can be a potential modulating factor. The experimental procedures spanned two consecutive days. On Day 1, participants were exposed to a set of unfamiliar faces. On Day 2, the same faces presented on the previous day were used again in half of the participants, whereas novel faces were used for the other half. Day 2 procedures consisted of three successive phases: item repetition, source association, and source memory test. In the item repetition phase, half of the face stimuli were repeatedly presented while participants were making male/female judgments. During the source association phase, both the repeated and the unrepeated faces appeared in one of the four locations on the screen. Finally, participants were tested on the location in which a given face was presented during the previous phase and reported the confidence of their memory. Source memory accuracy was measured as the percentage of correct non-guess trials. As results, we found a significant interaction between prior exposure and repetition. Repetition impaired source memory when the items had been pre-exposed on Day 1, while it led to greater accuracy in novel ones. These results show that pre-experimental exposure can modulate the effects of repetition on associative binding between an item and its contextual information, suggesting that pre-existing representation and novelty signal interact to form new episodic memory

What can narratives tell us about the neural bases of human memory?

Narratives are increasingly used to study naturalistic human memory and its brain mechanisms. Narratives—audiovisual movies, spoken stories, and written stories—consist of multiple inter-related and temporally unfolding events which are rich in semantic and emotional content. These characteristics drive intersubject neural synchrony in the default mode network, where abstract situation models are represented and reinstated. Medial temporal lobe structures interact with the cortical sub-regions of the default mode network to support the encoding and recall of narrative events. Narrative memories are frequently communicated across individuals, resulting in the transmission of experiences and neural activity patterns between people. Recent advances in neuroimaging and naturalistic stimulus analysis provide valuable insights into narrative memory and the human memory system in general

A functional neuroimaging dataset acquired during naturalistic movie watching and narrated recall of a series of short cinematic films

Whole-brain functional magnetic resonance imaging (fMRI) data from twenty healthy human participants were collected during naturalistic movie watching and free spoken recall tasks. Participants watched ten short (approximately 2 – 8 min) audiovisual movies and then verbally described what they remembered about the movies in their own words. Participants’ verbal responses were audio recorded using an MR-compatible microphone. The audio recordings were transcribed and timestamped by independent coders. The neural and behavioral data were organized in the Brain Imaging Data Structure (BIDS) format and made publicly available via OpenNeuro.org. The dataset can be used to explore the neural bases of naturalistic memory and other cognitive functions including but not limited to visual/auditory perception, language comprehension, and speech generation

What can narratives tell us about the neural bases of human memory?

Narratives are increasingly used to study naturalistic human memory and its brain mechanisms. Narratives—audiovisual movies, spoken stories, and written stories—consist of multiple inter-related and temporally unfolding events which are rich in semantic and emotional content. These characteristics drive intersubject neural synchrony in the default mode network, where abstract situation models are represented and reinstated. Medial temporal lobe structures interact with the cortical sub-regions of the default mode network to support the encoding and recall of narrative events. Narrative memories are frequently communicated across individuals, resulting in the transmission of experiences and neural activity patterns between people. Recent advances in neuroimaging and naturalistic stimulus analysis provide valuable insights into narrative memory and the human memory system in general.</p

Pre-experimental stimulus familiarity modulates the effects of item repetition on source memory

[Citation: Lee, H., Kim, K., &amp; Yi, D.-J. (2020). Preexperimental stimulus familiarity modulates the effects of item repetition on source memory. Journal of Experimental Psychology: Learning, Memory, and Cognition, 46(3), 539–548. https://doi.org/10.1037/xlm0000743] Previous studies have reported contradictory findings regarding the effects of item repetition on the subsequent encoding of contextual details associated with items (i.e., source memory). Whereas some studies reported repetition-induced enhancement in source memory, other studies observed repetition-induced impairment. To resolve these conflicting results, we examined the modulatory role of pre-experimental stimulus familiarity in the relationship between item repetition and new source memory formation by orthogonally manipulating pre-experimental stimulus familiarity and intra-experimental item repetition. In a series of experiments consisting of three phases (item repetition, item-source association, and source memory test), we found that item repetition impaired source memory for pre-experimentally familiar items (famous faces or words), whereas the same manipulation improved source memory for pre-experimentally novel items (non-famous faces or pseudowords). Crucially, item repetition impaired, rather than improved, source memory for pre-experimentally novel items when these items had been pre-exposed to participants prior to the three-phase procedure. Collectively, these findings provide strong evidence that pre-experimental stimulus familiarity determines the relative costs and benefits of experimental item repetition on the encoding of new item-source associations. By demonstrating the interaction between different types of stimulus familiarity, the present findings advance our understanding of how prior experience affects the formation of new episodic memories

Pre-experimental stimulus familiarity modulates the effects of item repetition on source memory

Previous studies have reported contradictory findings regarding the effects of item repetition on the subsequent encoding of contextual details associated with items (i.e., source memory). Whereas some studies reported repetition-induced enhancement in source memory, other studies observed repetition-induced impairment. To resolve these conflicting results, we examined the modulatory role of pre-experimental stimulus familiarity in the relationship between item repetition and new source memory formation by orthogonally manipulating pre-experimental stimulus familiarity and intra-experimental item repetition. In a series of experiments consisting of three phases (item repetition, item-source association, and source memory test), we found that item repetition impaired source memory for pre-experimentally familiar items (famous faces or words), whereas the same manipulation improved source memory for pre-experimentally novel items (non-famous faces or pseudowords). Crucially, item repetition impaired, rather than improved, source memory for pre-experimentally novel items when these items had been pre-exposed to participants prior to the three-phase procedure. Collectively, these findings provide strong evidence that pre-experimental stimulus familiarity determines the relative costs and benefits of experimental item repetition on the encoding of new item-source associations. By demonstrating the interaction between different types of stimulus familiarity, the present findings advance our understanding of how prior experience affects the formation of new episodic memories. [Citation: Lee, H., Kim, K., &amp; Yi, D.-J. (2020). Preexperimental stimulus familiarity modulates the effects of item repetition on source memory. Journal of Experimental Psychology: Learning, Memory, and Cognition, 46(3), 539–548.