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.