Circadian performance differences between morning and evening ‘types’

Two groups of subjects identified as either morning (M) or evening (E) types, determined by a self-assessment questionnaire, were measured for performance efficiency at a simulated production-line inspection task given for 15 sessions at different times of the waking day.

Abstract

Abstract Two groups of subjects identified as either morning (M) or evening (E) types, determined by a self-assessment questionnaire, were measured for performance efficiency at a simulated production-line inspection task given for 15 sessions at different times of the waking day. Systematic fatigue and practice effects were minimised by a random presentation of these sessions over a series of days. Although there were no significant within- or between-group changes with circadian trends for items erroneously rejected, significant differences were apparent with the number of items correctly rejected. M types' correct rejection levels were significantly better than E types' in the morning, whereas they were worse during the evening. Whilst E types showed a steady improvement throughout the day, M types showed a general decline. A post-lunch dip in performance was quite evident for M types, but not for E types. In addition, the circadian trends in correct rejection levels and body temperature were highly positively correlated for E types, but a significant negative relationship between these parameters was found for M types. These findings are discussed.