Inducers of motion sickness in vehicles: A systematic review of experimental evidence and meta-analysis

With the development of intelligent cabins and the popularity of smart devices, motion sickness has become an increasing concern. A number of theories have been proposed to explain the cause of motion sickness in vehicles. However, because of the diversity of the dynamical characteristics, road conditions, and in-vehicle human–machine interaction designs, the influence of the inducers on motion sickness in vehicles has not yet been fully quantified. Thus, in this paper, we aim to review and summarize the influential factors of motion sickness in road vehicles through a systematic review. In total, we identified 57 studies related to influential factors of motion sickness in vehicles, of which, 27 were further included for meta-analysis. In total, we identified eight categories of motion sickness inducers in vehicles, including the type of eye view, non-driving-related task availability, existence of artificial motion cues, head dynamic movement, vehicle dynamics, internal layout of vehicle, individual differences, and others. Most inducers had consistent effects on inducing motion sickness; however, inconsistent results have also been observed in vehicle dynamics, head dynamic movement, eye view, individual difference, and artificial motion cues (i.e., cues regarding the motion states of the ego-vehicle provided through in-vehicle auditory, tactile, or visual interfaces). Additional meta-analysis was conducted for motion cues. It was found that only natural present motion cues (i.e., cues regarding relative movement between the ego-vehicle and the environment through the windshield or side windows) and non-visual artificial anticipatory motion cues (i.e., auditory or tactile artificial motion cues regarding the future motion of ego-vehicle) were effective in alleviating motion sickness. Future research directions have been pointed out. Our study can provide insights into the optimization of vehicle design to mitigate motion sickness among occupants.