The Validity of Factor Analytically Derived Cardiac Autonomic Components for Mental Workload Assessment
John K. Lenneman Richard W. Backs Central Michigan University
Heart rate has probably been used to assess mental workload in the field more often than any other psychophysiological measure. Heart rate has often been found to be a sensitive measure of mental workload. O'Donnell and Eggemeier ( 1986) define sensitivity as the "capability of a technique to detect changes in the amount of workload imposed on task performance" (p. 42-2). Heart rate typically increases as mental workload increases and decreases as mental workload decreases. However, heart rate does not always differ between conditions that impose different amounts of mental workload according to other measures such as task performance or subjective reports. For example, heart rate has not been found to differ between day and night conditions of flight ( Lewis, Jones, Austin, & Roman, 1967; Roscoe, 1978) or as the angle of approach during landing increases ( Roscoe, 1975).
Further, heart rate does not provide diagnostic information about the source of mental workload. O'Donnell and Eggemeier ( 1986) define diagnosticity as the "capability of a technique to discriminate the amount of workload imposed on different operator capacities or resources" (p. 42-3). Backs ( 1995) offers two reasons for heart rate's limited diagnostic utility. First, heart rate is affected by physical demands that may be independent of mental workload. Second, heart rate does not provide information about the separation of the sympathetic and parasympathetic nervous system activity.