Adaptive Repulsion of Long-Term Memory Representations Is Triggered by Event Similarity.

We tested whether similarity between events triggers adaptive biases in how those events are remembered. We generated pairs of competing objects that were identical except in color and varied the degree of color similarity for the competing objects. Subjects (N = 123 across four experiments) repeatedly studied and were tested on associations between each of these objects and corresponding faces. As expected, high color similarity between competing objects created memory interference for object-face associations. Strikingly, high color similarity also resulted in a systematic bias in how the objects themselves were remembered: Competing objects with highly similar colors were remembered as being further apart (in color space) than they actually were. This repulsion of color memories increased with learning and served a clear adaptive purpose: Greater repulsion was associated with lower associative-memory interference. These findings reveal that similarity between events triggers adaptive-memory distortions that minimize interference.

Long-term memory interference is resolved via repulsion and precision along diagnostic memory dimensions.

When memories share similar features, this can lead to interference, and ultimately forgetting. With experience, however, interference can be resolved. This raises the important question of how memories change, with experience, to minimize interference. Intuitively, interference might be minimized by increasing the precision and accuracy of memories. However, recent evidence suggests a potentially adaptive role for memory distortions. Namely, similarity can trigger exaggerations of subtle differences between memories (repulsion). Here, we tested whether repulsion specifically occurs on feature dimensions along which memories compete and whether repulsion is predictive of reduced memory interference. To test these ideas, we developed synthetic faces in a two-dimensional face space (affect and gender). This allowed us to precisely manipulate similarity between faces and the feature dimension along which faces differed. In three experiments, participants learned to associate faces with unique cue words. Associative memory tests confirmed that when faces were similar (face pairmates), this produced interference. Using a continuous face reconstruction task, we found two changes in face memory that preferentially occurred along the feature dimension that was "diagnostic" of the difference between face pairmates: (1) there was a bias to remember pairmates with exaggerated differences (repulsion) and (2) there was an increase in the precision of feature memory. Critically, repulsion and precision were each associated with reduced associative memory interference, but these were statistically dissociable contributions. Collectively, our findings reveal that similarity between memories triggers dissociable, experience-dependent changes that serve an adaptive role in reducing interference.