ABSTRACT
In this study, a distinction was drawn between dynamic and static typc vigilance tasks. The former are tasks in which signal/noise discriminations are difficult or moderately difficult and the focus of performance evaluation is upon the accuracy of signal detection. In the latter, signal/noise discriminations are rel atively easy or are not required; the mere appearance of a predetellnined stimulus event is a critical signal for detection. In this case, the focus of performance evaluation is upon response time to signal detection since detection accuracy is at a ceiling . At the heart of the dynamic/static issue, is a long-standing belief that accuracy and speed
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are interchangeable indices o f the same underlying process in vigilance (Buck, 1 966) . The present study shows that there are maj or differences between these two types of tasks in terms of cerebral hemodynamics and perceived mental workload. Clearly, the view that per cent correct and response time are equivalent measures of a common underlying process in vigilance is incorrect and vigilance researchers need to consider the dynamic/static task distinction in their models of vigilance performance .
