Physiological indices of workload in a simulated flight task.

The sensitivity of physiological measures to evaluate workload was investigated in a simulated flight task. Heart rate, blood pressure (from beat to beat), respiration and eye blinks were recorded in 14 subjects while they performed a complex task in a flight simulator. Workload was manipulated by introducing an additional task and by varying the task difficulty of segments of the flight scenarios. Heart rate and blood pressure were both affected by the different levels of task difficulty. Heart-rate variability was found to be confounded by respiration. Slow respiratory activity contributed considerably to heart rate variability, especially after periods of high workload (for example, after landing). The gain between blood-pressure and heart-rate variability (modulus) was sensitive to mental effort and was not influences by respiration. Eye blinks, in particular the duration, were specifically affected by the visual demands of the task and not by the workload in general. When subjects had to process visual information, the number and duration of blinks decreased.