Measuring workload during a dynamic supervisory control task using cerebral blood flow velocity and the NASA-TLX

Abstract

While automated systems have been shown to improve safety and efficiency in operational environments, automation failures can lead to abrupt shifts in workload. Subjective workload scales have been shown to be sensitive to differences in workload, but they are limited in their ability to assess dynamic, moment-to-moment workload variations. Physiological measures may be better suited to assess dynamic workload in complex environments. This study explored the feasibility of a relatively new physiological measure, Transcranial Doppler Sonography (TCD), as a candidate for adaptive automation studies. Participants performed long duration, supervisory control tasks under varying levels of taskload. In one group, enemy threats increased once late in the simulation, and in another group enemy threats increased at two points; once early and once late within the simulation. All participants completed a comparison condition in which there was no variation in the number of incoming enemy threats. Cerebral blood flow velocity (CBFV), as measured by TCD, was measured during task performance. Performance was assessed by the ability of the operator to protect a no-fly zone from enemy incursion. Subjective mental workload was assessed using the NASA-TLX. As performance decreased during periods of high load, CBFV increased, and there was a close parallel between the CBFV and performance measures. The NASA-TLX was sensitive in detecting differences in workload between the two conditions, but the patterns of results of this subjective measure were insensitive to specific task elements. The results are interpreted in terms of a resource theory of task performance and show that the CBFV measure is sensitive to dynamic changes in taskload in complex environments.