Mental effort causes vigilance decrease due to resource depletion.

The resource view on vigilance performance was tested. First, a low demanding task was compared with a similar low demanding task in which stimulus presentation was less monotonous due to added, irrelevant, stimuli. The resource view, maintaining that vigilance is lowered by hard mental work, predicts that addition of irrelevant stimuli will not affect performance. The classic arousal theory, however, states that arousal drops due to monotonous stimulus presentation and predicts that decreasing monotony will enhance performance. Results showed that performance was unaffected by added stimuli. Second, we tested whether a high-demanding task (with identical stimulus presentation as the low demanding task, but different instruction) would cause a greater decline in performance than the low demanding task. Indeed, in the high-demanding task performance was affected most. In sum, it appears that vigilance decreases due to hard mental work, which requires many resources. Both overall performance and decrement in performance can be explained in terms of resources, and this suggests that vigilance tasks should be resource-demanding tasks, which do not have to be of long duration.