Time of day effects on the use of distraction to minimise forgetting

Recent research found that implicit rehearsal of distraction can reduce forgetting for older adults, in part due to their inefficient regulation of irrelevant information. Here, we investigated whether young adults’ memory can also benefit from critical information presented as distraction. Participants recalled a list of words initially and then again after a 15-min delay, with some of the critical studied words exposed as distraction during the delay. We tested young adults at an optimal versus non-optimal time of day, the latter a condition intended to mirror patterns of those with reduced attention regulation. We also varied task instruction to assess whether awareness of an upcoming memory task would influence implicit rehearsal of distraction. The task instruction manipulation was ineffective, but desynchronising time of testing and period of optimal cognitive arousal resulted in a memory benefit. Young adults tested at a non-optimal time showed minimal forgetting of words repeated as distraction, while those tested at an optimal time showed no memory benefit for these items, consistent with research suggesting that attention regulation is greatly affected by circadian arousal.

Synchrony Affects Performance for Older but not Younger Neutral-Type Adults

Circadian rhythms influence performance on a broad range of cognitive tasks, including attention shifting, implicit learning, memory retrieval, suppression of distracting information, creativity, and problem solving. Much of the research on circadian arousal and cognition has examined the consequence of testing individuals at times that are synchronous or asynchronous with their personal circadian peaks. To date, the studies examining these synchrony effects in cognitive function have focused primarily on the performance of individuals who show strong morningness or strong eveningness tendencies; little is known about individuals with neutral chronotypes and whether their performance varies over the day. The lack of data on neutral types is a serious gap in our knowledge, as up to 60% of young adults and 25% of older adults do not show strong morning or evening preferences. The present study assessed the performance of neutral-type younger and older adults at three times of day (early morning, midday, and evening) on a battery of cognitive tasks, including inhibitory processing, executive function, memory, perceptual speed, and access to well-learned knowledge. Older neutral-types showed synchrony effects for inhibitory processing, executive function, long-term memory, and forgetting, and generally had best performance on these tasks at midday. Consistent with other findings, older neutral-types showed no synchrony effects for measures of general knowledge and perceptual speed. Younger neutral-types, by contrast, showed no effects of time of testing on performance over the day for any measure, suggesting greater cognitive flexibility over the day relative to younger evening-types, older morning-types, or older neutral-types.

Implicit Memory, Age, and Time of Day

Memory retrieval can occur by at least two routes: a deliberate one, as when one attempts to retrieve an event or fact, and an unintentional one, as when one's behavior is triggered by the past without one's 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 explicit stem-cued recall replicated better performance for each age group at its peak time. In stark contrast, implicit performance was better at off-peak than at peak times of day, raising the possibility that the processes that serve explicit and implicit retrieval are on different circadian schedules, and highlighting the need to consider individual differences in circadian arousal when assessing either memory system.