Demands on perceptual and mnemonic fidelity are a key determinant of age-related cognitive decline throughout the lifespan

Ageing is associated with less detailed memory recall. We tested whether poorer representational fidelity across perception, short-term and long-term memory (STM/LTM) are among the earliest signs of cognitive ageing. Our paradigm probed target-lure object mnemonic discrimination and precision of object-location binding. In a lifespan sample, cognitive deficits were observed in midlife when complex, detailed stimulus representations were required for perceptual and short/long-term Forced Choice mnemonic discrimination. A continuous metric of object-location source memory combined with computational modelling demonstrated that errors in short- and long-term memory in middle-aged adults were largely driven by a loss of precision for retrieved memories, not necessarily by forgetting. On a trial-by-trial basis, the fidelity of item and spatial information was more tightly bound in long- as opposed to short-term memory with this association being unaffected by ageing. Standard neuropsychological tests without demands on memory quality were less sensitive to age effects than memory precision. Perceptual discrimination predicted mnemonic discrimination across tasks. Neuropsychological proxies for prefrontal executive functions correlated with short-term, but not long-term, memory fidelity. Conversely, neuropsychological indicators of hippocampal integrity correlated with mnemonic discrimination and precision of both STM and LTM, suggesting partially dissociable mechanisms of inter-individual variability in short- and long-term memory fidelity.