Motion sickness severity under interaction of vection and head movements.

Vection alone, or combined with head movements, has been shown to invoke motion sickness (MS). This study's purpose was to observe how different combinations of vection and head movements influenced the severity of MS. We tested 26 subjects in a rotating sphere at a speed of 45 degrees/s, resulting in vertical yaw, horizontal roll or pitch vection. Coincidently, subjects pitched, rolled, or yawed their heads (0.5 Hz, 20 degrees). We found that yaw vection combined with pitch or roll head movements significantly increased MS, while pitch vection with any type of head movement, or head and scene rotation about the same axis significantly reduced MS. When the head was kept stationary, pitch vection was most stressful for MS, followed by roll vection, then yaw vection, although yaw vection was the strongest sensation of self-rotation.