BOREDOM EFFECTS ON SLEEPINESS ALERTNESS IN THE EARLY AFTERNOON VS EARLY EVENING AND INTERACTIONS WITH WARM AMBIENT-TEMPERATURE

During the usual waking day there is a circadian propensity for sleepi ness in the early afternoon. This contrasts with the circadian peak of alertness in the early evening. The former is apt to be masked by var ious exogenous factors. Alertness was compared at these times of day ( 'afternoon': 1200-1600 hours and 'evening': 1800-2200 hours) under con trasting environmental conditions: boring vs. stimulating ('interest') x warm vs. cool ambient environment ('temperature'); making four comb inations, with two times of day-i.e. eight independent conditions, eac h containing six subjects (N = 48). The emphasis of the study was to m ake the conditions 'natural' and not unpleasant-e.g. the environmental temperatures were not extreme and kept within a comfortable range. Al l conditions were run in a climatic chamber. Alertness was measured by reaction times and subjective sleepiness scales. Heart rate and body temperature were monitored continuously. Apart from time of day, 'inte rest' exerted a powerful effect that was significant for all variables , and was particularly potent in the afternoon. By comparison, the 'te mperature' effects were minor. For our subjects the afternoon 'dip' ce ntered between 1500 and 1530 hours, and displayed bicircadian characte ristics.