Unexpected vection predicts cybersickness in passive virtual reality

Vection, the visually induced illusion of self-motion commonly experienced in virtual reality, has been widely proposed as a cause of cybersickness. However, prior research has largely treated vection as a single phenomenon. Here, we distinguish between expected vection (feelings of self-motion that align with the user’s perceptual expectations derived from the scene) and unexpected vection (feelings of self-motion that violate those expectations). This study experimentally manipulated experiences of expected and unexpected vection and examined how these different types of vection were related to cybersickness under passive HMD-VR conditions. Forty participants viewed 3-D first-person 360º videos of racing gameplay under both “predictable” and “erratic” driving conditions (over 2 playback trials lasting up to 10 min each). As expected, “erratic” driving conditions were found to generate more unexpected vection events (and more cybersickness) than “predictable” driving conditions. We found that participant reports of unexpected vection predicted the minute-by-minute occurrence and severity of cybersickness. These experiences of unexpected vection were also associated with an increased likelihood of participants dropping out of the trial early due to sickness. Crucially, consistent with our unexpected vection hypothesis , we found strong statistical support for unexpected vection events preceding (and thus likely causing) cybersickness.