May, C. P., Hasher, L., Foong, N. (2005). Implicit memory, age, and time of day: Paradoxical priming effects. Psychological Science, 16, 96-100.
Memory retrieval can occur by at least two routes, a deliberate one, as when we attempt to retrieve an event or fact, and an unintentional one, as when our behavior is triggered by the past without our knowledge or awareness. We assessed the efficacy of these retrieval systems as a function of circadian arousal and time of day. Evening-type younger adults and morning-type older adults were tested at either peak (morning for old; evening for young) or off-peak times on implicit and explicit stem completion (Experiment 1) or on implicit category generation (Experiment 2). Results for the explicit stem cued recall replicate better performance for each age group at their different peak times. In stark contrast, implicit performance was better at off peak than at peak times of day, raising the possibility that the processes that serve these tasks are on different circadian schedules, and highlighting the need to consider individual differences in circadian arousal when assessing either memory system.
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