The Effects of Prior Knowledge on Mnemonic Discrimination in Young and Older Adults, and in Hippocampal Amnesia

The hippocampus is critical to discriminating between newly learned, highly similar stimuli; less clear is its role in discriminating representations based on prior knowledge. In this study, young adults, older adults divided by performance on a cognitive screening measure, and people with hippocampal amnesia were asked to discriminate between pairs of real-world familiar landmarks and well-known animals using the metrics of geographical distance and size. Results showed all participants had lower accuracy for judgments with more similar item pairs. Low-performing older adults showed selectively worse performance on judgments with more similar item pairs. Amnesic individuals performance appeared to depend on lesion location. Only patient BL, who has selective bilateral dentate gyrus lesions, had difficulty on the landmark task when judging between highly similar distances. These results reinforce the importance of investigating representation similarity, even for well-established representations, and offer insight into mnemonic discrimination across the lifespan and within amnesia.