The relationship between morningness–eveningness, time-of-day, speed of information processing, and intelligence

Morningness–Eveningness refers to individual differences in circadian phase position of spontaneous sleep–wake rhythms and to subject alertness. There is some evidence indicating that performance on cognitive tasks may be influenced by Morningness–Eveningness and time-of-day. Given the potential importance of such a finding for the assessment of cognitive ability we conducted a study assessing the relationship between Morningness–Eveningness, time-of-day, and performance on the Multidimensional Aptitude Battery IQ (MAB-IQ) and Inspection Time (IT) task. Twenty male and 50 female participants classified according to their scores on the Morningness–Eveningness dimension (Horne & Östberg, 1976) were administered the MAB and IT tasks in the morning (0900 h) and in the late afternoon (1500 h). No significant effect of time of testing, and Morningness–Eveningness was observed except for the Spatial subtest of the MAB. Morning Type-participants performed significantly worse in the morning session in Spatial subtest and better in the late afternoon session and Evening Type-participants performed significantly better in the morning than in the late afternoon session. These results do not support the hypothesis that there is a reliable relationship between Morningness–Eveningness, time-of-day and cognitive ability.