Age-related dedifferentiation and hyperdifferentiation of perceptual and mnemonic representations
Preliminary evidence indicates that occipito-temporal activation patterns for different visual stimuli are less distinct in older (OAs) than younger (YAs) adults, suggesting a dedifferentiation of visual representations with aging. Yet, it is unclear if this deficit (1) affects only sensory or also categorical aspects of representations during visual perception (perceptual representations), and (2) affects only perceptual or also mnemonic representations. To investigate these issues, we fMRI-scanned YAs and OAs viewing and then remembering visual scenes. First, using representational similarity analyses, we distinguished sensory vs. categorical features of perceptual representations. We found that, compared to YAs, sensory features in early visual cortex were less differentiated in OAs (i.e., age-related dedifferentiation), replicating previous research, whereas categorical features in anterior temporal lobe (ATL) were more differentiated in OAs. This is, to our knowledge, the first report of an age-related hyperdifferentiation. Second, we assessed the quality of mnemonic representations by measuring encoding-retrieval similarity (ERS) in activation patterns. We found that aging impaired mnemonic representations in early visual cortex and hippocampus but enhanced mnemonic representations in ATL. Thus, both perceptual and mnemonic representations in ATL were enhanced by aging. In sum, our findings suggest that aging impairs visual and mnemonic representations in posterior brain regions but enhances them in anterior regions.