The relationship between vection, cybersickness and head movements elicited by illusory motion in virtual reality

Cybersickness is an unpleasant side effect of Virtual Reality and is often detrimental to a user's experience. It shows a complex relationship to vection (illusory self-motion) as well as postural instability. Three experiments were conducted presenting both expanding and rotating colourful optimised Fraser Wilcox illusions as well as grey-scaled controlled versions of the illusions. Cybersickness and vection were reported and head movements in medio-lateral and anterior-posterior direction were recorded. The experiments found that perceived visual motion (illusory motion) is sufficient to elicit vection in the absence of any stimulated visual motion. The strength of motion perceived in the illusions was related to the experience of cybersickness and vection, with illusions that were perceived as moving more eliciting stronger experiences of both. Surprisingly, rotating illusions were continuously perceived as moving more compared to expanding motion illusions, which could be related to missing stereoscopic motion-in-depth cues. Head movements were unrelated to any stimuli properties, suggesting that the motion signal elicited by the illusions might not have been strong enough to cause postural instability. Finally, dizziness has been identified as the possible link between cybersickness, vection and head movements supporting sensory conflict as well postural instability theories of cybersickness.