Behavioral and Subjective Measures of Mental Fatigue and Workload: Examining Allocation of Effort During Extended Multiple Task Performance

The goal of the present study was to gain a better understanding of behavioral and subjective indicators of mental fatigue. Moreover, the effect of workload and mental fatigue on allocation of effort during prolonged multiple task performance was examined. Workload was manipulated between subjects and time was a within-subjects variable assessed over three consecutive 30-min periods. A behavioral measure was provided by the Multi - Attribute Task Battery {MAT; Comstock & Arnegard, 1992) that was revised to include a new task. This new task was modeled after Holding's (1983) choice of probability/ effort {COPE) paradigm and was developed to investigate allocation of effort over time. Holding suggested that fatigued participants attempt to conserve effort during extended task performance. Further, behaviors demonstrating a choice in effort should be moderated by fatigue. As such, fatigued people experiencing a multitasking situation were expected to alter their behavior such t hat performance on one task remained stable while performance of peripheral tasks deteriorated. Subjective assessments of fatigue, workload , mood, motivation, thinking style, and thinking content were taken before and after the task. In addition to expected pre - post differences , post subjective measures were expected to be correlated with third period performance measures. Group performance results suggest that a shift in effort did occur over time. During the second period, participants demonstrated their worst tracking performance but their best monitoring performance and COPE task accuracy. Resource management and the number of digits present during the COPE task were both observed to be best during the first and second periods. In the third period, tracking performance stabilized while resource management, monitoring, and COPE task performance deteriorated. The most dramatic shifts in allocation of effort we re observed for the high workload participants. Several significant correlations also demonstrated a high degree of consistency at the individual level of performance . These results suggest that varying workload in a multi-tasking situation can affect not only performance on concurrent tasks but also allocation of effort over time.