In addition to determining the link between cause and effect in terms of offending stimuli, we should also try to understand why the body is reacting adversely to VR. What physiological and psychological mechanisms are involved in the process? Why might one person be unable to quickly adapt to certain stimuli, while other people are fine? What is particularly bad about the stimulus that might be easily fixed without significantly degrading the experience? The determination of these mechanisms and their reasons for existing falls under etiology. Although, there is no widely encompassing and accepted theory that explains motion sickness or VR sickness, some useful and accepted theories exist.
One of must relevant and powerful theories for understanding VR sickness is sensory conflict theory [132,145]. Recall the high-level depiction of VR systems from Figure 2.1 of Section 2.1. For VR, two kinds of mismatch exist:
Unsurprisingly, the most important conflict for VR involves accelerations. In the case of vection, the human vision system provides optical flow readings consistent with motion, but the signals from the vestibular organ do not match. Note that this is the reverse of a common form of motion sickness, which is traveling in a moving vehicle without looking outside of it. For example, imagine reading a book while a passenger in a car. In this case, the vestibular system reports the accelerations of the car, but there is no corresponding optical flow.
Steven M LaValle 2016-12-31