Effects of time of day on age differences in working memory.

This study investigated the hypothesis that the influence of time of day on the efficiency of working memory is greater for older than younger adults. Groups of younger and older adults performed a working memory task on 4 consecutive days, twice in the morning and twice in the evening. Objective (body temperature) and subjective (alertness ratings) measures of arousal were taken during each session. Temperature increased across the day equally for younger and older adults, whereas alertness ratings were higher in the morning for older adults and in the evening for younger adults. The efficiency of the access and deletion functions paralleled the subjective alertness rating for younger and older adults, and age-related differences in these functions were greater when individuals were tested at nonoptimal times of day. The efficiency of the response inhibition function was similar for younger and older adults and paralleled changes in body temperature.