Comparing Different Measures of Overall Workload in a Multimodal Postural/Auditory Dual-Task Environment

OCCUPATIONAL APPLICATIONS This study investigated the effects of a multimodal dual-task paradigm (balance and cognitive tasks) on overall mental workload. The balance task did not affect the performance of the cognitive task, and the presence of the cognitive task led to better balance performance with unstable seating. Simultaneously, measures of overall mental workload showed a general increase when the cognitive task was added and, in some cases, when the balancing task became harder (more unstable). These results generate two important implications. First, the performance levels of two multimodal tasks being done concurrently are insufficient to explain the overall workload in the system. Even if performance is not negatively (or even positively) affected initially, workload increases and may approach or reach overload. Second, any single measure of performance or workload taken in situ might very well be insufficient to explain effectively the way an individual is interacting with their multitasking environment. TECHNICAL ABSTRACT Background: Audition and balance are important aspects of many multitasking environments; auditory signals are used for myriad different alerts and alarms, and balance is pivotal in the realms of factory and construction to avoid falling and risking injury or death. Furthermore, the demands of multiple tasks at once can interact, creating complex environments for which measures of overall workload would be beneficial. Purpose: The goal of this research was to quantify the effects of a cognitive/postural dual-task environment on overall workload. Methods: We utilized a dual-task protocol pairing an auditory discrimination task with a seated balancing task. We then measured performance on both tasks and overall workload using subjective (NASA Task Load Index) and physiological (heart rate variability) measures. Results: Cognitive task performance did not change across different balance conditions, while the presence of the cognitive task decreased postural sway when the participants were unstable. The results regarding workload measures were varied; however, most indicated an increase in workload with the cognitive task. Conclusions: These two results might seem contradictory, with performance in the postural task increasing as the overall workload increases. Taken together, though, they suggest two important conclusions: the need to use more than one method of workload measurement and the importance of understanding the arousal level created by the environment and task difficulty. Designs of auditory alerts in situations involving physical demands should consider arousal levels and possible overload and avoid overvaluing single metrics.