Evaluating the Sensitivity of Various Measures of Operator Workload Using Random Digits as a Secondary Task

Abstract

Problems have been encountered in previous research in developing a secondary task measure of mental workload that is both sensitive and stable. Ordinarily a single measure of secondary task is analyzed as an indicator of difference in workload. The purpose of the experiment reported here was to determine whether alternate measures taken from a single secondary task might prove more sensitive. Twelve subjects participated in the experiment involving a primary task (meter pointer nulling) and a secondary task (reading random digits aloud). The independent variable (primary task difficulty level) was adjusted by changing the number of meters that had to be monitored (two, three, or four meters). Dependent measures were taken on the (1) number of random digits spoken (usual workload formula), (2) longest interval between spoken responses, (3) longest consecutive string of spoken digits, and (4) the number of “triplets” spoken. Results show that the dependent measures (1), (3), and (4) were significant with (1) being the most sensitive.

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