SIGNAL PROBABILITY EFFECTS ON HIGH-WORKLOAD VIGILANCE TASKS

Signal probability is an important influence on vigilance. Typically, higher signal probability is associated with higher hit rate, lower re sponse criterion, and lower response:signal ratio. However, signal pro bability effects on demanding, high-workload vigilance tasks have not been investigated. It is believed that attentional resources become de pleted during performance of such tasks, leading to perceptual sensiti vity decrements. Forty subjects performed high- (.35) and low- (.10) p robability versions of a demanding vigilance task. Results differed in two important respects from those previously obtained with less deman ding tasks. First, the decrement in perceptual sensitivity over time w as greater for the high-probability task. Second, there were no effect s of signal probability on response criterion. Subjective workload was higher for the high-probability task. Implications of the data for re source-depletion and expectancy theories of vigilance are discussed.