Adaptive repulsion of long-term memory representations is triggered by event similarity

ABSTRACTWe tested whether similarity between events triggers an adaptive repulsion of long-term memories. Subjects completed an associative learning task in which objects were paired with faces. Critically, the objects consisted of pairs that were identical except for their color values, which were parametrically varied in order to manipulate interference. Performance on associative memory tests confirmed that color similarity robustly influenced interference. Separate tests of color memory showed that high similarity triggered a repulsion of long-term memories, wherein remembered colors were biased away from colors of competing objects. This repulsion effect was replicated across three experiments. In a fourth experiment, the repulsion effect was fully eliminated when task demands promoted integration, instead of discrimination, of similar memories. Finally, we show that repulsion of color memory was highly adaptive: greater repulsion was associated with less memory interference. These findings reveal that similarity between events triggers adaptive distortions in how events are remembered.SUPPLEMENTARY INFORMATIONThree supplementary figures are included.

Visual interference can help and hinder memory: Capturing representational detail using the Validated Circular Shape Space

Although we can all agree that interference induces forgetting, there is surprisingly little consensus regarding what type of interference most likely disrupts memory. We previously proposed that the similarity of interference differentially impacts the representational detail of color memory. Here, we extend this work by applying the Validated Circular Shape Space (Li et al., 2020) for the first time to a continuous retrieval task, in which we quantified both the visual similarity of distracting information as well as the representational detail of shape memory. We found that the representational detail of memory was systematically and differentially altered by the similarity of distracting information. Dissimilar distractors disrupted both fine- and coarse-grained information about the target, akin to memory erasure. In contrast, similar distractors disrupted fine-grained target information but increased reliance on coarse-grained information about the target, akin to memory blurring. Notably, these effects were consistent across two mixture models that each implemented a different scaling metric (either angular distance or perceived target similarity), as well as a parameter-free analysis that did not fit the mixture model. These findings suggest that similar distractors will help memory in cases where coarse-grained information is sufficient to identify the target. In other cases where precise fine-grained information is needed to identify the target, similar distractors will impair memory. As these effects have now been observed across both stimulus domains of shape and color, and were robust across multiple scaling metrics and methods of analyses, we suggest that these results provide a general set of principles governing how the nature of interference impacts forgetting.

The adaptive nature of false memories is revealed by gist-based distortion of true memories

Human memory systems are subject to many imperfections, including memory distortions and the creation of false memories. Here, we demonstrate a case where memory distortion is adaptive, increasing the overall accuracy of memories. Participants viewed multiple real-world objects from a given category (10 airplanes, 10 backpacks…), and later recalled the color of each object. Participants were generally accurate, but even when they remembered having seen an item and remembered its color, they nevertheless reported the color as closer to the average color of its category than it really was. Although participants’ memories were systematically distorted, they were distorted in a way that is consistent with minimizing their average error according to a simple Bayesian analysis. In addition, and consistent with the Bayesian analysis, the bias toward the category center was larger when participant’s had greater uncertainty about the color of an item, but was present in all circumstances -- even when participants remembered an item, remembered its color, and reported high confidence in their color memory. Thus, memory distortion may not always be maladaptive: in some cases, distortion can result from a memory system that optimally combines information in the service of the broader goals of the person. Furthermore, this framework for thinking about memory distortion suggests that false memory can be thought of on a continuum with true memory: the greater uncertainty participants have about an individual item memory, the more they weight their gist memory; with no item information, they weight only their gist memory.