Multiple measures of operator workload may dissociate, or fail to agree, for a given task. The goal of this study was to determine how workload as indexed by processing resource demand could explain the attendant variance in a second measure of workload—subjective ratings. A multiple structure model of processing resources (Wickens, 1984) guided construction of tasks that were both performed by subjects and rated on workload similarity. Multidimensional scaling analyses of the similarity ratings produced three dimensions of workload that were explained by parameters of the resource model. Performance data, effort ratings, and heart period variability scores used to support the scaling analyses revealed expected dissociations. These dissociations were examined within the structure of the resource model.
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