The sensitivity of physiological measures to evaluate workload was inv
estigated in a simulated flight task. Heart rate, blood pressure (from
beat to beat), respiration and eye blinks were recorded in 14 subject
s while they performed a complex task in a flight simulator. Workload
was manipulated by introducing an additional task and by varying the t
ask difficulty of segments of the flight scenarios. Heart rate and blo
od pressure were both affected by the different levels of task difficu
lty. Heart-rate variability was found to be confounded by respiration.
Slow respiratory activity contributed considerably to heart rate vari
ability, 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 res
piration. Eye blinks, in particular the duration, were specifically af
fected by the visual demands of the task and not by the workload in ge
neral. When subjects had to process visual information, the number and
duration of blinks decreased.