Implicit memory reduced selectively for negative words with aging

Abstract

Background: Disproportionally better memory for positive versus negative information (mnemonic positivity effect, MPE) in older versus younger adults has been reported on tests of explicit memory (direct, intentional) as measured by recall and recognition. The purpose of this investigation was to examine whether the MPE would be observed for implicit memory (indirect, unintentional) under conditions where, based on previous research using single words, it was expected that the MPE for explicit memory would be absent.

Methods: This study investigated the influence of age on explicit and implicit memory for positive, negative, and neutral single words as measured by yes/no recognition and word identification on 24 older adults (aged 66-85) and 24 younger adults (aged 18-37) recruited from community centers in South Boston, Massachusetts.

Results: Older adults had lower recognition memory accuracy for positive, negative, and neutral words than younger adults, and, consistent with most prior studies, did not exhibit an explicit memory MPE for single words. For both groups, recognition accuracy was greatest for negative words, and was similar for positive and neutral words. In contrast, older adults exhibited implicit repetition priming, as measured by superior identification performance for repeated words, that was similar to younger adults for positive and neutral words. In younger adults, implicit memory was significantly greater for negative words than for positive and neutral words, whereas in older adults there were no significant differences in implicit memory for negative, positive, and neutral words. Therefore, selectively reduced priming for negative words in older adults was found in the context of enhanced priming for negative words in the younger adults.

Conclusion: These findings show that there was an implicit memory MPE in older adults for words even under conditions where there was no explicit memory MPE in the older adults. Dampening of negative valence implicit memory with aging expands the perimeter of the age-related positivity framework.

Keywords: aging; implicit memory; negative words; positivity effect; priming.

FIGURE 1

Mean priming (new-old, ms) as a function of age group and valence. Implicit memory was measured by priming. The formula was the exposure time (ms) to identify new words (unstudied) minus exposure time to identify old words (studied). Because it takes a longer exposure duration to identify new relative to old words, a greater difference score (new-old) indicates more priming. Error bars represent M ± SEM.

FIGURE 2

Mean recognition (old-new, %) as a function of age group and valence. Explicit memory was measured by yes/no recognition. The formula was the count for “yes” responses to old (studied, Hits) minus new (unstudied, False Alarms) words converted to percentages. A larger difference score (old-new) indicates greater yes/no recognition, more yes responses to old relative to new words. Error bars represent M ± SEM.