Time-of-Day Differences in Cognitive Performance

Objective: Previous research suggests that cognitive performance fluctuates with circadian changes in alertness and attention. This study aims to investigate the influence of time-of-day variations in cognitive performance on planning and problem-solving. Method: We administered the Zoo Map, a test of planning and problem solving, to 17 college students, 76% female, during one of three randomly assigned times: either morning (8:00-10:00 a.m.); mid-day (11:00 a.m.-1:00 p.m.); or late afternoon (2:00-4:00 p.m.). We hypothesize that performance will peak in conjunction with the circadian rhythm of alertness, which increases throughout the morning to a peak around noon, decreasing to a nadir in the late afternoon. Results: A one-way ANOVA revealed a significant effect of Zoo Map total score, based on time of day, F(2,17) = 4.46 p = .03, [eta] super(2) = 0.40. LSD post hoc analyses indicate that mid-day performance (M = 3.33) was better than morning performance (M = 1.80, p = .13, 95% CI: 0.38, 2.68) as well as better than late-afternoon performance (M = 2.17; p = .04, 95% CI [0.07, 2.26]). There was no significant difference between morning and late afternoon testing times (p = .51). Conclusion: Performance on Zoo Map, a challenging test of problem-solving and planning, was best at mid-day (11:00 a.m.-1:00 p.m.). This is consistent with previous studies investigating circadian fluctuations in working memory, attention, and set shifting, and follows the expected pattern of highs and lows in performance that mirror fluctuations in alertness. Clinicians should consider the potential influence of testing time when interpreting performance on cognitive tests of planning and problems-solving.