Quantitative evaluation of effects of visually-induced motion sickness based on causal coherence functions between blood pressure and heart rate

Recent advances in video and computer graphics technologies have been accelerating creation of novel visual images including complex and intensive motion of the visual point. However, there are concerns about adverse effects of these images on humans such as visually-induced motion sickness (VIMS). To evaluate the effects of VIMS, the present study has analyzed the linearity of the baroreflex system and that of the mechanical hemodynamic system by using causal coherence functions. The causal coherence functions have a capability of calculating linear correlation between two systems independently even if the systems are connected with each other to compose a closed-loop system. In the experiment, healthy human subjects’ heart rate and continuous blood pressure were measured to obtain the causal coherence functions when the subjects were watching an unstable video image. The results showed that there were significant differences in the causal coherence functions as well as the traditional coherence function between the sick and the well groups and that the hemodynamic system was mainly disturbed by VIMS rather than the baroreflex system. These findings suggest that the causal coherence functions of the two systems and the traditional coherence function of the whole system gave different information from one another. This fact implies that the causal coherence functions will be useful and objective means to quantify VIMS as functions of time.