Recollection and Familiarity Exhibit Dissociable Similarity Gradients: A Test of the Complementary Learning Systems Model

Memory can often be triggered by retrieval cues that are quite different from the originally encoded events, but how different memory processes respond to variations in cue–target similarity is poorly understood. We begin by presenting simulations using a neurocomputational model of recognition memory (i.e., the complementary learning systems model), which proposes that the hippocampus supports recollection of associative information whereas the surrounding cortex supports assessments of item familiarity. The simulations showed that increases in the similarity between retrieval cues and learned items led to relatively linear increases in a cortex-based memory signal but led to steeper and more thresholded increases in the hippocampal signal. We then tested the predictions of the model by examining the effects of varying cue–target similarity in two recognition memory experiments in which participants studied a list of computer-generated faces and then, at test, gave confidence and remember/know responses to morphed faces. In both experiments, as cue–target similarity was increased, familiarity-based recognition increased in a gradual and relatively linear fashion, whereas recollection showed significantly steeper gradients. The results show that recollection and familiarity exhibit distinct similarity functions in recognition memory that correspond with predicted retrieval dynamics of the hippocampus and cortex, respectively.