The impact of abnormal hours of work on various modes of information processing: a process model on human costs of performance

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Abstract
Most laboratory experiments on task performance show a performance deterioration due to a disturbed sleep/wake pattern. Field studies on performance, errors and accidents during night and shiftwork conditions, however, do not provide sufficient converging evidence in this respect. The conflicting results of field studies are probably caused by the measurement methods being based on the material aspects of performance, in which many confounding factors play an important role. Though workers seem to make more errors at night and react less efficiently, the time-of-day effect will often be overshadowed by the influence of situational, task-related and person-related factors. In particular the nature of the involved mental processes, the psychophysiological state of the person, and the invested effort are important for the outcome of performance. With respect to the nature of the involved mental processes, a taxonomy of mental tasks is presented, in which two types of mental tasks are distinguished with respect to their attention-demanding nature. With respect to the psychophysiological state of the person and the invested effort, it is concluded that (a) the state and with that the performance capacity can be considered as sub-optimal when working during abnormal hours, and (b) effort is required to compensate this sub-optimal state in order to meet the task-demands. Hence, in order to determine the effect of a disturbed sleep/wake pattern on performance, a more appropriate method may be to focus research also on the effects on the person who is performing the task rather than to concentrate research on the effects on the material outcome of performance alone. Therefore a process model of human costs of performance at abnormal hours of work is presented.