Dissociations among measures of mental workload: Effects of experimenter-induced inadequacy

Patricia Ann Casper, Purdue University


In order to test the hypothesis that false feedback manipulations indicating performance either at the performance goal, 7% short of the goal, or 14% short of the goal would differentially affect subjective ratings, heart rate, and performance indices of mental workload, 18 subjects performed easy and difficult versions of a dual line length judgment task. It was predicted that performance measures of workload would be sensitive to the perceived distance from the goal for a difficult (resource-limited) task but not for an easy (data-limited) task. Subjective ratings, d$\sp\prime$, and reaction time were sensitive to the task difficulty manipulation, while mean cardiac inter-beat interval was not. Subjective ratings increased monotonically with the distance from the goal as indicated by feedback, while the other measures did not. There was an interaction between task difficulty, level of feedback, and type of workload measure, although the predicted dissociations between subjective and performance measures of workload were not found. Subscales of the subjective rating tool associated with aspects of the experimental task mirrored the performance measure results, while subscales linked to operator-related factors were sensitive to the feedback manipulation. The benefits of trying to consolidate results from different classes of measures are discussed, as well as the utility of the workload concept as more than a general descriptive term.




McDaniel, Purdue University.

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