Motion Sickness Side Effects and Aftereffects of Immersive Virtual Environments Created with Helmet- Mounted Visual Displays

We have investigated side effects and aftereffects evoked by moving the head to interact with a virtual environment (VE) shown in a helmet mounted visual display (HMD). The graphics computer of such a VE must monitor the HMD’s spatial orientation and position in order to present images from the proper perspective. Delays between head movements and image updating cause aberrant visual motion of a virtual world. We found that above delays of 40 ms motion sickness and postural instability are evoked minutes after head movements begin. The severity of side effects is a function of the latency between head movement and visual update delay. Fifteen minutes of making head movements in a VE with a 254 ms delay causes motion sickness severe enough to make 28% of subjects withdraw from the situation. Users appear recovered 15 minutes after VE exposure ends if they remain immobile, but normal activities quickly revive their motion sickness symptoms, indicating that they were sensitized by exposure to visual update delays. We conclude that visual update delays are a unique cause of side effects and aftereffects in VEs utilizing HMDs.