1. Astrid J.A. Lubeck, MSc 1 Jelte E. Bos, PhD 1,2 John F. Stins, PhD 1 1 Research Institute MOVE, Faculty of Human Movement Sciences, VU University Amsterdam, the Netherlands 2 TNO Perceptual and Cognitive Systems, Soesterberg, the Netherlands Moving and still images can induce comparable amounts of postural sway, but different levels of sickness 1

2. Introduction at VIMS 2011… Lubeck et al. (2011): Postural sway and visually induced motion sickness (VIMS). Results 1.During exposure: Postural sway ↑ and VIMS ↑ 2.After exposure: Postural sway ↑ and VIMS ↓ Discussion 1.Increase in sway and VIMS due to motion in images? 2.Decoupling of sway and VIMS after exposure  Subjective vertical mismatch theory (Bos et al., 2008). 2

3. Introduction Research question and hypothesis Research question – Is motion (in FPS games) essential for causing an increase in postural sway and VIMS? Hypothesis – Motion does cause an increase in postural sway and VIMS. No changes in still images condition. Changes in moving images condition. 3

4. Method Subjects and design Subjects – 15 subjects – 6 males, 9 females – Mean (SD) age: 29.5 (5.9) years Design – Within subject design – Experimental condition: Moving images – Control condition: Still images – 2 measurements: Pre and post 4

5. Method Images 5

6. Method Measurements Postural sway – Force plate – Normal double stance Eyes closed – Duration: 60 seconds – Center of pressure (CoP) data Sway path length Visually induced motion sickness (VIMS) – Simulator sickness questionnaire (SSQ; Kennedy et al., 1993) – Only total score 6

7. Results Total simulator sickness scores 7

8. Results Sway path length 8

9. Discussion Postural sway – Increase in SPL after exposure to both moving and still images VIMS – Only an increase in VIMS after exposure to moving images Decoupling of postural sway and VIMS – Postural instability seems not to be necessary and sufficient for getting VIMS. No difference in postural sway after exposure – Puzzling? 9 Puzzling results?

10. Discussion 10 2 possible explanations

11. Wallpaper illusions – Can cause changes in postural sway (Kelly et al., 2005) – Can cause disorientation (Cohn & Lasley, 1990) Discussion Moved by still images

12. Discussion Moved by a first person shooter (FPS) game 12

13. Vection – Illusion of self-motion Do players experience vection or some other sensation? – Images may not contain adequate flow Sustained and unidirectional – Other possible mechanisms at work? Vection does not seem to be necessary to cause VIMS – In accordance with the subjective vertical mismatch theory (Bos et al., 2008) Discussion Vection in FPS games?

14. Still images can cause an increase in postural sway but only moving images cause motion sickness. Conclusion Take home message