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Effects of Signal Probability on Individual Differences in Vigilance

Decrements in the proportion of signals detected over time on task and large individual differences in performance are typical findings in studies of vigilance. This study investigates the effects of signal probability on individual differences in vigilance performance. Participants monitored stimulus events on computer displays over 2-h periods at three signal probability levels (.01, .04, & .12). Results were analyzed between groups, within groups, and within subjects. Detection decrements were found to be inversely related to signal probability levels across groups. High signal probabilities generated consistent within-group and within-subject performance, whereas low probabilities generated both lower performance and larger within-subject variance. This relationship between signal probability and within-group and within-subject variance has not been previously demonstrated. Future investigations should focus on the sources of both between-subjects and within-subject variation in vigilance performance in order to identify optimal interventions. Actual or potential applications include designing work to minimize vigilance decrement and maximize human performance under conditions that require sustained attention.