Individual differences on diurnal variations of the task performance

In order to understand psychophysiological background of the individual differences on the diurnal variation of task performance, the task performance (i.e. the number of a simple adding calculation performed in one minute) was measured from 09:30 in the morning to 21:30 in the late evening for 9 healthy university male students. Heart rate (HR) and body temperature were also continuously recorded for 35 hours. There were two different types in the diurnal variation of the task performance; the morning type who shows the best performance in the morning, and the evening type who shows it in the evening. The body temperature curve during daytime in the evening type goes gradually up to the evening, on the contrary, that in the morning type rapidly rises to the maximum point in the morning or the afternoon. HR during daytime were higher in the morning type than the evening type. These results indicate that the morning type has a tendency of the higher mental tension compared with the evening type. And they also suggest that the individual differences on the task performance with a large mental concentration are caused by some kinds of subject's psychosomatic state.