[Changes in mental workload and fatigue during performance of a mental task. 1. An experiment in 8-h self-paced transcribing task].

The changes in mental workload and fatigue during a one-day transcribing task were examined by determining some subjective and physiological measures which reflect mental activity. With an interval of one week between the three test days, 12 male students rested and performed self-paced transcribing task with moderate and maximum effort for 8 h each. The subjects transcribed more characters in the task with maximum effort than with moderate effort. In both the morning and afternoon, adrenaline excretion increased and heart rate decreased with the lapse of time. In linear proportion to the total working hours, occipital midline beta-2 amplitude, subjective rating of tiredness and subjective symptoms of fatigue rose, but critical flicker values fell slightly in the task with maximum effort. It was inferred from these results that with lapse of working hours intellectual activity and feeling of fatigue increase and the level of arousal slightly declines. Hence, it was considered that mental workload becomes heavier and subjective feeling of fatigue increases as the working hours become longer.