Diagnosticity and multidimensional subjective workload ratings.

A new multidimensional subjective workload assessment instrument -- Workload Profile -- was introduced and evaluated against two unidimensional instruments -- Bedford and Psychophysical scaling. Subjects performed two laboratory tasks separately (single task) and simultaneously (dual task). The multidimensional procedure compared well with the unidimensional procedures in terms of sensitivity to task demands, concurrent validity with performance, and test-retest reliability. The results suggested that the subjective workload profiles would only have limited predictive value on performance. However, results of the canonical analysis demonstrated that the multidimensional ratings provided diagnostic information on the nature of task demands. Further, the diagnostic information was consistent with the a priori task characterization. This strongly supports the notion that mental workload is multidimensional and that subjects are capable of reporting the demands on separate workload dimensions. Theoretical implications on mental workload models and practical implications on the assessment approaches are discussed.