  Objective: We investigated the effect of the passenger head-tilt strategy on
the severity of carsickness in lateral acceleration situations in automobiles.
Background: It is well known that the driver is generally less susceptible to
carsickness than are the passengers. However, it is also known that the driver
tilts his or her head toward the curve center when negotiating a curve, whereas
the passenger's head moves in the opposite direction. Therefore, we
hypothesized that the head-tilt strategy has the effect of reducing the
severity of carsickness. Method: A passenger car was driven on a quasi-oval
track with a pylon slalom while the participant sat in the navigator seat. The
experiment was terminated when either the participant felt the initial symptoms
of motion sickness or the car finished 20 laps. In the natural head-tilt
condition, the participants were instructed to sit naturally, to relax, and not
to oppose the lateral acceleration intentionally. In the active head-tilt
condition, the participants were asked to tilt their heads against the
centrifugal acceleration, thus imitating the driver's head tilt. Results: The
number of laps achieved in the active condition was significantly greater than
that in the natural condition. In addition, the subjective ratings of motion
sickness and symptoms in the active condition were significantly lower than
those in the natural condition. Conclusion: We suggest that an active head tilt
against centrifugal acceleration reduces the severity of motion sickness.
Application: Potential applications of this study include development of a
methodology to reduce carsickness.
