Semantic relatedness and distinctive processing may inflate older adults' positive memory bias

Emotional stimuli are often more semantically interrelated and relatively distinct than neutral stimuli. These factors can enhance memory for emotional stimuli in young adults, but their effects in older adults-and on the age-related positive memory bias-remain unknown. In the present article, we tested whether item relatedness and distinctiveness affect emotional memory in young adults (Exps. 1 and 2) and the positive memory bias in older adults (Exp. 2). In both experiments, participants studied positive, negative, and neutral pictures and performed free recall after 1 min and 45 min. To manipulate relatedness, the neutral pictures were either as highly interrelated as the emotional pictures ("related neutral") or lower in semantic relatedness ("unrelated neutral"). To manipulate distinctiveness, we had participants process the emotional pictures in either a relatively distinct manner (mixed condition), by studying emotional and neutral pictures at the same time, or in a nondistinctive manner (unmixed condition), by studying and recalling each picture category separately. Overall, higher semantic relatedness (i.e., related-neutral vs. unrelated-neutral pictures) increased memory in both age groups. Distinctiveness did not affect memory in young adults, but it did alter the positive memory bias in older adults. Older adults recalled more positive than negative pictures when the pictures were processed in mixed sets, but not when they were processed in unmixed sets. These findings were consistent across both test delays. This suggests that previous reports, which were often based on mixed designs in which item interrelatedness was not controlled, may have overestimated the size and/or robustness of the positivity bias in older adults.