  A mathematical model of motion sickness incidence (MSI) is derived by
integrating neurophysiological knowledge of the vestibular system to predict
the severity of motion sickness of humans. Bos et al. proposed the successful
mathematical model of motion sickness based on the neurophysiological mechanism
based on the subject vertical conflict (SVC) theory. We expand this model to
6-DOF motion, including head rotation, by introducing the otolith-canal
interaction. Then the model is applied to an analysis of passengers' comfort.
It is known that the driver is less susceptible to motion sickness than are the
passengers. In addition, it is known that the driver tilts his/her head toward
the curve direction when curve driving, whereas the passengers' head movement
is likely to occur in the opposite direction. Thus, the effect of the head tilt
strategy on motion sickness was investigated by the proposed mathematical
model. The head movements of drivers and passengers were measured in slalom
driving. Then, the MSI of the drivers and that of the passengers predicted by
the proposed model were compared. The results revealed that the head movement
toward the centripetal direction has a significant effect in reducing the MSI
in the sense of SVC theory.
