It is important in establishing and improving work management and work planning to estimate the arousal level of workers during operation and monitoring tasks. This paper proposes a technique based on experimental results to estimate the arousal level during job execution. In this experiment, both a monotonous low workload task which degrades the arousal level and a high workload task which has an awakening action were alternately applied to five subjects for three hours. Skin resistance level (SRL) as an index of arousal level of the autonous nervous system was measured with subjective drowsiness and task performance, that is, signal omission probability for low workload task and both reaction time and error probability for high workload task, as indexes of arousal level of the central nervous system. The following results were obtaind. (1) The results suggested that SRL as an index of arousal level of the autonous nervous system is significantly related and correlated with subjective drowsiness and signal omission probability as indexes of arousal level of the central nervous sytem. (2) The average reaction time and the error probability tended to increase by the application of high workload when the arousal level was degraded. The influence of degraded arousal continued for a short time and showed an unfavorable effect on task execution. The degree of this influence, however, differed between subjects. (3) SRL can be used as an index of arousal level of the autonous nervous system because the measurement is comparatively easy and is little influenced by artifacts due to body movements. (4) Using SRL at initial high workload period as the standard value, it is possible to quantify the SRL value at arbitrary time by estimating how many times the standard value goes into the SRL value. Based on this quantified value as an index of arousal level, comparison with task performance can be made. The proposed index of arousal level of the autonous nervous system showed a significant correlation with indexes of the central nervous system. This technique can be applied to various kinds of estimation on human characteristics accompanied with changes in arousal level.
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