Mental fatigue and the efficiency of information processing in relation to work times

Mental fatigue was studied by analysing performance and mental effort in a memory search task in relation to the temporal structuring of preceding work periods. Performance was measured by reaction time and error rate. Mental effort was measured via spectral analysis of the 0.10 Hz component in the heart rhythm signal. It was shown that subjects protected their performance by spending more effort in the unfavorable conditions: after several hours of work and after continuous work without short rest breaks. In the most unfavorable condition, after 8 h of work combined with sleep loss, the efficiency of information processing broke down. Performance could no longer be protected by invested effort. This breakdown phenomenon is interpreted as a serious sign of mental fatigue. Relevance to industry The present study describes a method of analysing mental fatigue, based on the analysis of the performance related to the mental effort invested in a standard memory-search task. This method could be applied in the practical evaluations of work systems.