Double Trade-off Curves with Different Cognitive Processing Combinations: Testing the Cancellation Axiom of Mental Workload Measurement Theory

The accomplishment model of average mental workload--a formal axiomatic measurement theory--was used as a basis for developing and testing secondary task indices of mental workload (H. A. Colle & G. B. Reid, 1997). Its cancellation axiom implies global sensitivity, which is an important theoretical and practical criterion for mental workload indices. Performance levels of different secondary tasks were empirically equated in mental workload and then used to test the cancellation axiom. Cognitive processing similarity--including orthographic, phonemic, and semantic processing of pairs of operator and secondary tasks--was manipulated in three experiments. Equivalencies between secondary tasks were independent of secondary-operator task similarity, consistent with the cancellation axiom and the global sensitivity of these secondary tasks. The results suggest that standardized secondary task techniques can be developed for the practical measurement of mental workload. Actual or potential applications of this research include the development of functionally useful and realistic secondary task measures of mental workload.