Effects of breaks and goal switches on the vigilance decrement.

In this report, we examined the impact of rest breaks and goal switches on the vigilance decrement--the change in performance with time-on-task--and subjective stress and workload. In study 1, we examined the decrement in a visual line-length discrimination task employed in previous research. The task had a linear decrement in perceptual sensitivity with time-on-task based on the results of a trend analysis (orthogonal polynomial contrasts). In addition, the task had a profile of self-reported stress and workload similar to other moderately demanding vigilance tasks. In study 2, we examined the decrement in the same task with the factorial inclusion of rest breaks and goal switches late in the task. The inclusion of rest breaks resulted in a significant cubic trend in perceptual sensitivity. After the first rest break, there was a reversal of the linear downward decrement in perceptual sensitivity, but the second rest break did not elicit this change. The inclusion of goal switches did not cause any significant deviation from the linear trend and did not attenuate the decrement. In addition, the inclusion of rest breaks resulted in reduced self-reported effort and temporal demand. The results of the present study cohere with the expectations of a resource depletion account of the vigilance decrement.