Cognitive Test Performance Is Better at One’s Chosen Optimal Time of Day

Much research assessing time of day (ToD) effects on cognitive performance typically assign participants to a morning or evening condition. However, this may not accurately reflect variations in peak arousal as the best ToD of taking part in cognitive tasks may fluctuate throughout the day. Sleep and caffeine consumption may also interact with the ToD of testing and could potentially affect cognitive test scores. The aim of this study was to understand differences in cognitive performance when participants are allowed to choose their preferred optimal and non-optimal ToD of taking part and explore interaction effects of the ToD of testing with sleep and caffeine on a range of memory tasks. Twenty-seven cognitively-healthy young adults completed a sleep, ToD, and caffeine questionnaire followed by a series of memory tasks online, at two separate time points (once at their chosen optimal ToD and once at their chosen non-optimal ToD) within a 24-hour period. Findings revealed that participants performed significantly better at their chosen optimal ToD compared to their chosen non-optimal ToD on all the memory tasks. The findings have important implications for the need to consider ones subjective ToD preferences when taking part in a range of memory tasks in various contexts.