Effects of Task Demands and Age on Vigilance and Subjective Workload

Abstract

Sensory and cognitive vigilance were directly compared in two experiments. The question of whether sensory and cognitive vigilance task demands can be differentiated on the basis of perceived workload was also addressed. A third focus of the study was to investigate changes in sensory and cognitive vigilance across the adult life span. In Experiment 1 60 subjects from three age categories—young, middle, and elderly were studied. Experiment 2 consisted of 20 subjects from only the young and old age categories. Subjects performed a visual sensory and a cognitive vigilance task at low and high event rates. Each task used identical stimulus sets (pairs of digits) and differed only in the definition of a critical target. Task demands were a major determinant of vigilance performance. Cognitive vigilance was more resistant to decrement over time than sensory vigilance. On the other hand, the cognitive task was more adversely affected by high event rate than the sensory task. Older subjects had lower hit rates than young and middle-aged subjects on the cognitive task, particularly at the high event rate. Subjective workload results suggested that the increased mental demands required of the cognitive task at the high event rate were associated with performance differences between sensory and cognitive tasks. However, the results also revealed an apparent dissociation between performance and subjective workload measures. Implications of the results for display design and assessment of individual differences in monitoring capability are discussed.