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With the recent, rapid developments of computers, adaptation between the human being and computer is being improved. On the other hand, mental fatigue is increased by continuous, long-time use. The problem of mental fatigue is now a new focus of research. This study proposes a method of evaluating mental fatigue. In this study, we used a method to extract signals related to fatigue using Independent Component Analysis (ICA). The subjects were 10 male students. After assuming a workload of simulated visual display terminal (VDT) operation for 30 min, the subjects sat in a relaxed position for 30 min. In this process, we measured work performance, subjective symptoms of feelings of fatigue and physiological measures. As a result, there was a high value of the correlation coefficient between these signals and the subjective symptoms of feeling of fatigue. We suggest that by using ICA we can determine the relationship between Independent Components and subjective feelings of fatigue for those under work stress, work strain and in a state of fatigue and stress. However, further experiments are needed to obtain conclusive findings of our research.

The methods for assessing VDT workload based on individual capabilities are necessary to evaluate general fatigue by VDT work. We have developed a new computer program for assessing data entry performance of each individual. Four healthy male volunteers conducted a data entry task at their own pace using this program under a controlled environment. They performed the task for 30 minutes twice with 10 minutes rest between them. As a result, the average number of inputs was 133.2 characters/min in the first task and 129.1 characters/min after taking the rest. The error rate was 8.6% and 10.6% in each task. This program was useful to evaluate their data entry performance. We also reported our concern with a drop in nasal skin temperature that was observed during these VDT tasks.