Cumulative vs. local models of operator utilization describing an air traffic control task

Using classical methods the time course of workload over a work session is rarely observed. Subjective measures of necessity are for the entire session rather than instantaneous. While this distinction makes little difference to researchers wanting to compare task difficulty, it is important to designers of systems that wish to schedule operator attention because they must predict workload. The present study provides an experimental setting in which intervals of continuous work and uninterrupted rest can be precisely controlled. No differences in probability of error or latency of response were found for the length of break/rest intervals or their location in a sequence of intervals. The local utilization within a break/work interval (ratio of work/(work + rest)), however, was significant, suggesting that utilization effects are strictly local and that simple algorithms could be used to optimize human-system performance for such tasks.