An Investigation Of Postural Sway As An Indicator Of Visually Induced Motion Sickness In Virtual Reality

Exposure to visual oscillations in virtual reality commonly generates visually induced motion sickness(VIMS).In the last three decades,many studies focused on investigating VIMS by using self-report methods(i.e.,questionnaires or oral self-report)to reflect the sickness level of participants.But these self-report methods have limitations,especially for people who have difficulty in understanding instructions or reporting orally(e.g.,autistic children).In 1991,Riccio and Stroffregen proposed Postural Instability theory that motion sickness is caused by instability in the control of the posture of the body and/or its segments.Therefore,postural sway has been used as an alternative method of measuring VIMS.Compared with self-report methods,postural sway is more objective as a physiological indexAlthough postural instability has been used to reflect VIMS,there is currently no gold standard in the field to define postural instability.Some studies used single frequency or mixed frequencies as visual stimuli,and tried to reflect VIMS by using indicators such as average distance of sway and area of sway.But these time domain indicators may lack information that are able to reflect VIMS.Therefore,this research aims to study the frequency response patterns of subjects by exploring the relative nausea-inducing characteristics of various frequencies of visual stimuli through Fourier transform.Experiment 1 used a head-mounted display to present forward and backward translational motions of a mixed frequency consisting of 6 harmonically independent frequencies from 0.021 Hz to 0.246 Hz.The second experiment used a Cave automatic virtual environment with a larger vision and a stronger sense of immersion than head-mounted display.Visual stimulus was same as experiment 1.In experiment 3,rotational motion was added on the basis of visual stimulus in experiment 2.The three experiments jointly found that the gain index and the time delay index had the same pattern across devices and visual stimuli,indicating that the pattern was relatively stable.At the same time,it is found that the gain index of 0.033 Hz can negatively predict visual motion sickness,which supports sensory conflict theory.