Estimation of mental workload from information about peripheral vessels by non-contact measurement using microwave radar

Abstract

In this research, we aimed to estimate changes in mental workload from information on organic changes in peripheral vessels as measured by a non-contact sensing method using microwave radar. Experiments were conducted in a laboratory using two simple tasks, namely, a mental arithmetic task and an auditory task, in reference to the literature. Some previous studies have reported differences in the autonomic reflexes induced by voluntary and involuntary tasks. Moreover, these studies also found two types of physiological reflexes in response to the tasks. Heart rate variability (HRV) was induced by voluntary behavior, while stress was induced by a passive stimulus and showed an association with fluctuation of blood flow due to a change in the resistance of peripheral vessels. In our results, we detected changes in mental stress, undetectable by HRV, by using information about peripheral vessels measured by microwave radar without directly touching the body. We discuss possible application in driver state estimation via a driver–vehicle interface.