Semantic influences on episodic memory distortions

Stimuli, data and analysis cod

Schematic memories develop quickly, but are not expressed unless necessary

Episodic memory retrieval is increasingly influenced by schematic information as memories mature, but it is unclear whether this is due to the slow formation of schemas over time, or the slow decay of the episodes. To address this, we separately probed memory for newly learned schemas as well as their influence on episodic memory decisions. In this experiment, participants encoded images from two categories, with the location of images in each category drawn from a different spatial distribution. They could thus learn schemas of category locations by encoding specific episodes. We found that images that were more consistent with these distributions were more precisely retrieved, and this schematic influence increased over time. However, memory for the schema distribution, measured using generalization to novel images, also became less precise over time. This incongruity suggests that schemas form rapidly, but their influence on episodic retrieval is dictated by the need to bolster fading memory representations

Semantic influences on episodic memory distortions

Semantic knowledge can facilitate or distort new memories,depending on their alignment. We aimed to quantifydistortions in memory by examining how categorymembership biases new encoding. Across two experiments,participants encoded and retrieved image-locationassociations on a 2D grid. The locations of images weremanipulated so that most members of a category (e.g. birds)were clustered near each other, but some were in randomlocations. Memory for an item’s location was more precisewhen it was near members of the same category.Furthermore, typical category members’ retrieved locationswere more biased towards their semantic neighbors, relativeto atypical members. This demonstrates that the organizationof semantic knowledge can explain bias in new memories

Semantic influences on episodic memory distortions

Prior knowledge can facilitate or distort new episodic memories, depending on their alignment. However, it remains unclear how the structure of semantic memory explains systematic variation in how new memories are formed and retrieved. We aimed to quantify distortions in memory by examining how category membership and typicality bias new memories. Across four experiments, participants encoded and retrieved image-location associations. Most members of a category (e.g. birds) were located near each other, such that participants could learn locations of categories as they encoded specific image locations. Critically, some typical and atypical category members were in random locations. We decomposed location memory into two measures: error, a measure of episodic specificity, and bias towards other category members, a measure of the influence of prior knowledge. First, we found that location memory was more accurate for images that were spatially consistent with their category membership. Second, when images were spatially inconsistent, retrieval of typical category members was more biased towards other category members relative to atypical ones. These effects replicated across three experiments, disappeared when images were not arranged by category, and were stronger than effects observed with images arranged by visual similarity rather than category membership. Our observations provide compelling evidence that memory is a reconstruction of multiple sources of information, integrating memory for specific events with relevant semantic knowledge. Furthermore, systematic differences in the magnitude of this integration suggest that the organization of semantic memory can govern the extent of distortion in new episodic memories

How the Organization of Autobiographical Memories Changes Over Time

Cognitive scientists have discovered much about the acquisition, consolidation, and retrieval of episodic memories; how-ever, much less is known about how memories of our daily experiences are organized, nor how this organization maychange as memories become consolidated. Here, we apply computational network science methodologies to quantify theorganization of recent (within the past year) and remote (5 10 years ago) autobiographical memories and quantitativelyexamine how these networks change over time. We found that remote memories exhibited higher global connectivityrelative to recent memories, and that this increased connectivity is coupled with lower subjective ratings of vividness. Ourresults demonstrate how such cognitive features of episodic memory can be quantitatively examined and shed novel lighton the organization and reconfiguration of episodic memories over time

The Relation between Gist and Item Memory Over a Month

Memory requires both individuation of specific episodes aswell as extraction of gist across related experiences. Thisstudy developed a spatial memory paradigm to track changesin item memory (memory for specific locations) and gistmemory (estimate of the center of the locations) across aperiod of a month, and to measure the relation between thesetwo forms of memory. We found that item memories decayedcompared to gist memory after a month, yet there was apositive relationship between the two forms of memory thatpersisted. Moreover, item memories were biased towards gistmemory only after a month. These findings together indicatethat gist memory, initially extracted from item memories,gradually develops into a stable representation that can guideitem memory retrieval over longer durations

Age-related increases in posterior hippocampal granularity are associated with remote detailed episodic memory in development

Episodic memory is critical to human functioning. In adults, episodic memory involves a distributed neural circuit in which the hippocampus plays a central role. As episodic memory abilities continue to develop across childhood and into adolescence, studying episodic memory maturation can provide insight into the development and construction of these hippocampal networks, and ultimately clues to their function in adulthood. While past developmental studies have shown that the hippocampus helps to support memory in middle childhood and adolescence, the extent to which ongoing maturation within the hippocampus contributes to developmental change in episodic memory abilities remains unclear. In contrast, slower maturing regions, such as the PFC, have been suggested to be the neurobiological locus of memory improvements into adolescence. However, it is also possible that the methods used to detect hippocampal development during middle childhood and adolescence are not sensitive enough. Here, we examine how temporal covariance (or differentiation) in voxel representations within anterior and posterior hippocampus change with age to support the development of detailed recollection in male and female developing humans. We find age-related increases in the distinctiveness of temporal activation profiles in the posterior, but not anterior, hippocampus. Second, we show that this measure of granularity, when present during postencoding rest periods, correlates with the recall of detailed memories of preceding stimuli several weeks postencoding, suggesting that granularity may promote memory stabilization.SIGNIFICANCE STATEMENT Studying hippocampal maturation can provide insight into episodic memory development, as well as clues to episodic functioning in adulthood. Past work has shown evidence both for and against hippocampal contributions to age-related improvements in memory performance, but has relied heavily on univariate approaches (averaging activity across hippocampal voxels), which may not be sensitive to nuanced developmental change. Here we use a novel approach, examining time signatures in individual hippocampal voxels to reveal regionally specific (anterior vs posterior hippocampus) differences in the distinctiveness (granularity) of temporal activation profiles across development. Importantly, posterior hippocampus granularity during windows of putative memory stabilization was associated with long-term memory specificity. This suggests that the posterior hippocampus gradually builds the capacity to support detailed episodic recall