Circadian effect on physiology and driving performance in semi-automated vehicles.

Human performance and physiology undergo circadian changes. The safety of driving tends to decrease at night and during the afternoon, and these changes cannot be solely addressed to the decreased visibility. Previous literature reported that circadian rhythmicity plays a role in these changes. A similar phenomenon might occur in semi-automated driving. Also, as physiology undergoes circadian changes, it was suggested that systems of driver state monitoring might have different accuracy during the day and at night. This paper investigated the circadian effect on driving performance and physiology of the driver in simulated semi-automated driving. 53 participants participated in the experiment twice, once during the day and once at night. They drove a driving simulator in the semi-automated driving scenario. Following psychophysiological functions were measured during the experiment: electromyography, electrooculography, electrocardiography, respiration, pulse, blood oxygenation, electrodermal activity, voice, sleepiness, fatigue, readiness to take-over manual control of the vehicles, mental workload, cortisol, and alpha-amylase. There was a significant correlation between circadian phase and sleepiness, fatigue, readiness to take-over manual driving, physical demand, mean autocorrelation of voice, mean noise to harmonics ratio in voice, horizontal eye movements, frequency of frontalis, mean power in frontalis, peak power in frontalis, cortisol level, and driving performance. [ABSTRACT FROM AUTHOR]