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.

Context effects in subjective mental workload ratings.

The impact of performance context on subjective mental workload ratings was assessed with the Subjective Workload Assessment Technique (SWAT) and the NASA Task Load Index (TLX). In Experiment 1, a strong context effect was demonstrated. A low range of task difficulty produced considerably higher ratings on a common set of difficulty levels than did a high range of task difficulty. In Experiment 2, increasing the participants' range of experiences during practice eliminated the context effect. We recommend that methods for standardizing context, such as providing experience with the complete difficulty range, be developed for subjective mental workload evaluations. Actual or potential applications of this research include providing methodologies for controlling context effects in practical assessments of mental workload to increase the validity of subjective measures.

Status of spatial location in auditory sensory memory: evidence from rapidly presented lists.

Letters presented rapidly to separate spatial locations were used to test the precategorical acoustic storage (PAS) model's assumptions that memory information can be stored and masked selectively at separate spatial locations in auditory space and that spatial location can act as a retrieval cue in PAS. The suffix effect was present at the end of the list, even at a presentation rate of six per second. The data from three other experiments suggested that spatial locations do not act as memory repositories and that spatial location cannot be used as a retrieval cue at fast rates of presentation.