Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)




Research suggests that some cognitive processes follow a circadian rhythm, and the peak performance periods correlate with individual patterns of physiological arousal. Recent findings in the literature suggest that the optimal time synchrony may modulate the magnitude of age differences in cognitive performance across time of day. The first goal of the present study was to further investigate the so-called “synchrony effects” in younger and older adults. The second purpose was to offer and examine an alternative explanation for the “synchrony effect” phenomenon related to deficits in attentional resources rather than inefficient inhibition. And the third purpose of this study was to examine the relationship between age and time of day in cognitive functioning in a different context; namely, in conditions of divided attention. Participants were 48 UND students and 45 elderly adults from the Greater Grand Forks community. They were tested individually on a prose recall task and a “garden-path” task that is a procedure to assess inhibitory control over no-longer-relevant material. The latter task was administered in a dual-task condition. A series of mixed analyses of variance with two between-subject factors (Age, Time of Day) and two within-subjects factors (Passage Type and Levels of Importance for prose recall; Priming Effects and Tone for the “garden-path”) was performed. Additionally, analyses of covariance were conducted. The present results confirm the well-documented age differences in prose recall, prose reading time, and reaction time to the secondary task in a dual-task procedure. However, in none of the four different mental operations investigated in the present study were the expected “synchrony effects” found. Moreover, in one of the tasks a statistically significant interaction was found, indicating a relationship in the opposite direction. The analysis of the attentional cost of the underlying mental processes in the “garden-path” procedure suggests that the modulating effects of time of day on age-differences may indeed be related to deficits in attentional resources. Discrepancies of the present results with other research findings in this area are discussed. In addition, conclusions, limitations, and recommendations for future research are provided.

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