A comparison of subjective and physiological workload assessment techniques during a 3-dimensional audio vigilance task

The shift from platform-centric to network-centric warfare will require the use of sophisticated collaborative and communication technologies that can enhance shared situation awareness, thus improving military capabilities. However, the communication-intensive environment related with the use of these technologies may impose a high degree of mental workload as it is typical for operators to monitor and transmit on eight or more simultaneous channels. A net-centric communication management suite called Multi-Modal Communication (MMC) has been developed that offers a 3-dimensional spatial audio feature that can enhance the intelligibility of critical messages, but the workload associated with its use has not been thoroughly investigated. Twenty-two operators were assigned to monitor for the presence of critical phrases during a 40-min vigilance session with 6 different communicators in either a 3d spatial audio condition or a monaural radio condition. Cerebral blood flow velocity, a new index of mental workload, was measured during task performance and compared with a subjective measure of workload, the NASA-TLX. Results showed that there was a significant vigilance decrement over time, but that overall detection probability was higher in the 3d spatial audio than in the monaural radio condition. CBFV declined significantly over time, and a three way hemisphere x periods x presentation mode interaction revealed that CBFV was elevated during performance with monaural radio, but the decrement was most pronounced in the left hemisphere for the spatial audio task. Workload ratings from the NASA-TLX were insensitive to the differences in workload for the two task types. Results are interpreted in terms of a resource model of vigilance, and cerebral lateralization of vigilance and the potential limitations of subjective rating scales are discussed.

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