Discrimination of semantically similar verbal memory traces is affected in healthy aging

Abstract

Fluid cognitive abilities are affected in healthy aging via various changes in neural operations, while crystallized knowledge representations remain relatively intact. Yet, a few recent studies have suggested that age-related changes in fluid abilities may influence the access, manipulation, and processing of crystallized knowledge. For instance, mnemonic discrimination of highly similar memory traces, a key fluid ability supporting memory specificity, shows a clear age-related decline. However, the scope of this decline is not yet fully understood, as previous studies have often confounded operations and representations by almost exclusively testing mnemonic discrimination of visuospatial stimuli (e.g., objects or scenes). To address this gap, we designed a task to assess mnemonic discrimination of verbal stimuli as a function of semantic similarity. We manipulated similarity based on a Hungarian word-embedding which models semantic relationships between words. Forty young (Mage = 21.7 years) and 40 old adults (Mage = 69.8 years) first incidentally encoded adjective-noun phrases, then performed a surprise recognition test involving the same phrases as well as highly similar lures. We found that increasing semantic similarity negatively affected mnemonic discrimination in both age groups, and that compared to young adults, older adults showed worse discrimination and differential sensitivity to similarity independent of crystallized knowledge. These results indicate that specificity of semantic memory traces is affected in aging via less efficient mnemonic operations, and strengthen the notion that changes in fluid abilities in healthy aging influence the use of crystallized knowledge.