Diurnal differences between morning-type and evening-type subjects in self-rated alertness, body temperature and the visual and auditory evoked potential.

On the basis of their score on a morningness/eveningness questionnaire 9 extreme morning-type (M-type) and 9 extreme evening-type (E-type) subjects were selected. During a morning and an evening session both groups performed a reaction-time task with a visual and an auditory warning signal. The results showed that (i) M-types have a higher self-rated activation level in the morning than in the evening, while E-types show the reverse; (ii) M-types do not differ in oral temperature between the two sessions, while E-types show an increased temperature in the evening; (iii) M-types have a larger N1-P2 amplitude of the visual and auditory AEP in the morning than in the evening, while E-types show the reverse.