Different Object Features Shape Mnemonic Discrimination in Younger and Older Adults

The ability to discriminate experiences in memory is an important indicator of cognitive health in older age, and a sensitive marker of hippocampal integrity. Measures of mnemonic discrimination, such as the mnemonic similarity task (MST) have the potential to become early diagnostic tools of Alzheimer's dementia. It is thus important to understand how hippocampus-dependent memory functions interact with non-mnemonic processes to determine mnemonic discrimination performance. In this study we investigate which features contribute to mnemonic discrimination in younger and older age. First, we found in a sample of younger (n=93, 20-30 years) and older adults (n=103, 65-82 years) that age impacted performance on the MST above and beyond the effect of perceptual discrimination of 2D novel configurative objects. However, the association between mnemonic and perceptual discrimination slightly diverged across age groups. While we found a weak association in younger adults, there was no relationship in the older group. Next, we acquired similarity and feature difference ratings for the MST lures from younger (n=24, 20-25 years) and older adults (n=26, age>65). Using random forest regression and representational similarity analysis, we found that the two groups exhibited unique similarity rating patterns. Finally, enriching our memory data with the feature information, we showed on the trial-level that mnemonic decisions of older and younger adults are affected by distinct object features. Altogether, these results provide evidence that older adults perceive the differences of lure images distinctively, and they may rely on different levels of representations for mnemonic discrimination.