Familiarity deficits in aMCI under conditions that minimize the influence of recollection.

Objective: Familiarity, the sense of knowing without recalling specific details, plays a critical role in memory processing and is mediated by the perirhinal cortex (PRC), a brain region that is critical for differentiating objects with high feature overlap, and is affected first by amnestic mild cognitive impairment (aMCI). Investigating familiarity in aMCI is crucial for insights into early diagnostic markers of cognitive impairment.

Method: We conducted two studies probing familiarity in aMCI. The first study employed a response deadline procedure (RDP) where participants were presented with pictures of objects and then completed an item recognition test under two deadlines: a long deadline of 5000 ms, indexing recollection, and a short deadline of 1200ms, indexing familiarity. The second study utilized a frequency judgment (FJ) task in which participants saw pictures of highly similar objects a variable number of times, and then were asked how many times each object was presented. Their frequency judgments were correlated with the actual presentation frequencies as a measure of familiarity.

Results: In the RDP, individuals with aMCI had significantly lower recognition accuracy than healthy counterparts, in the long and short deadline, indicating impaired recollection and familiarity. In the FJ task, individuals with aMCI had significantly lower frequency judgment correlations, indicating impaired familiarity.

Discussion: These results highlight the importance of minimizing the role of recollection when aiming to understand familiarity deficits and underscore the potential of familiarity as an early diagnostic marker of cognitive decline.