Evaluation of adaptation to visually induced motion sickness by using physiological index associated with baroreflex function

Visual images including intensive motions and the experience of virtual reality sometimes induce visually-indeuced motion sickness (VIMS). There are few studies that have objectively evaluated the effects of repetitive exposures to these stimuli on humans. In this study, an experiment was carried out in which the same video image was presented to human subjects three times. We evaluated changes of the intensity of VIMS they suffered from with a subjective score and a physiological index, ρ_max, which is defined as the maximum cross-correlation coefficient between heart rate and pulse wave transmission time and is considered to reflect baroreflex function. The results showed that the adaptation to VIMS could be represented by a decrease in the objective index ρ_max as well as the subjective score. On the contrary, however, some subjects' ρ_max increased in a few similar time regions at every trial. This fact suggests that we can specify the part of the video image which is closely related to VIMS by analyzing the change ρ_max with time.