1. Magnitude and time course of illusory translation perception during off-vertical axis rotation Rens Vingerhoets Pieter Medendorp Jan Van Gisbergen

2. Contents Introduction - Sensors - Off-vertical axis rotation - Models Methods Results - Verbal estimates - Psychophysical data Model implications Conclusions Contents

3. Sensory signals involved in spatial orientation: Visual Cues Semicircular canals Otoliths Somatosensory cues Introduction - Sensors

4. The semi-circular canals Sensitive to angular acceleration High-pass filter

5. Introduction - Sensors The otoliths Sensitive to acceleration caused by: –Gravity –Inertial acceleration

6. Off-Vertical Axis RotationVertical Axis Rotation Introduction What is off-vertical axis rotation (OVAR)?

7. Rotation in yaw about an axis that is tilted relative to the direction of gravity.  Stimulation of both otoliths and canals Introduction Left Ear Down (LED)Right Ear Down (RED)Nose Up (NU) Nose Down (ND)

8. What causes this percept? Left Ear Down (LED) Right Ear Down (RED)Nose Up (NU) Nose Down (ND) Introduction What happens during OVAR? Otolith signal from tilt interpreted as translation? LED ND NU RED NDND LED RED NU R

9. Introduction – Otolith Disambiguation Neural strategy for otolith disambiguation: Filter hypothesis Acceleration

10. Introduction – Otolith Disambiguation Neural strategy for otolith disambiguation: Canal-Otolith interaction Acceleration Rotation

11. Introduction – research question Do these models apply to self-motion perception during OVAR? To check this quantitative data is required

12. Methods Experimental setup Picture of vestibular chair

13. Methods Experimental setup 6 subjects 2 series (only clockwise rotation) - Tilt series: 0, 15 and 30 deg tilt at 30 deg/s - Speed series: 20, 30, 40 and 50 deg/s at 15 deg tilt Each experimental condition consisted of 18-20 runs of 180 s each Subjects indicated verbally when cone illusion started Subjects reported the perceived radius Self-motion percept quantified with laser method

14. Experiment Laser method  v Screen and motorized laser on board of the chair Every NU and ND phase projection of moving laser dot Subject indicated with a toggle switch if the dot was moving too fast/slow in direction opposite to perceived selfmotion ‘Matching velocity’ obtained using two methods: - 0-110 s: Adaptive staircase over runs - 110-180 s: Method of constant stimuli

15. Results I Verbal Estimates

16. Results I – Verbal estimates Reported cone illusion latencies

17. Results I – Verbal Estimates Estimated Radii

18. Results II Time course

19. Results II – Staircase Data Staircase data from tilt series NU ND

20. Results II – Staircase Data Staircase data from tilt series NU ND

21. Results II – Staircase Data Staircase data from tilt series NU ND

22. Results II – Staircase Data Staircase data from speed series NU ND

23. Results II – Staircase Data Summary staircase data Stereotyped exponential decay to zero in 30-60 s in zero-tilt condition During OVAR short exponential decay followed by bifurcation into two opposite velocity levels Results in agreement with anecdotal reports Bifurcation depends on tilt angle Bifurcation depends on rotation speed

24. Results III Decomposition of response curves

25. Results III - Decomposition Decomposition of response curves Two processes (R & T) underlie self-motion perception. R follows the same time course in both phases (NU & ND) T has opposite sign in both phases Hence, matching velocity is: V NU = R +T V ND = R – T Consequently: R = (V ND + V NU )/2 T = (V NU - V ND )/2 LED RED NU ND T R + T R +

26. Results III - Decomposition Decomposition data from tilt series R T

27. Results III - Decomposition Decomposition data from tilt series R T

28. Results III - Decomposition Decomposition data from tilt series R T

29. Results III - Decomposition Decomposition data from speed series R T

30. Results III - Decomposition Summary decomposition data R component shows exponential decay to zero independent of tilt angle and rotation speed T component starts at zero and gradually climbs to an asymptotic level. T component increase not always starts right after rotation onset Asympotic value of T component depends on tilt angle and rotation speed.

31. Results III - Decomposition Fit to decomposition data Rotation component: R(t) = A * exp(-t/T R ) Translation component: T(t) = 0if t <  T T(t) = B * (1 – exp((-t-  T)/T T )if t >  T

32. Results III - Decomposition Examples of fit

33. Results III - Decomposition Fit parameters show us: R component R(t) = A * exp(-t/T R ) T R is constant across experimental conditions Initial amplitude (A) of R component increases with increasing rotation speed T component T(t) = 0if t <  T T(t) = B * (1 – exp((-t-  T)/T T ) Incorporating a delay (  T ) is essential Inter-subject differences for delay and T T Translation percept (B) increases both with tilt angle and rotation speed.

34. Results IV Constant stimuli data

35. Results IV – Constant Stimuli Constant stimuli data from tilt series NU ND

36. Results IV – Constant Stimuli Constant stimuli data from speed series NU ND

37. Results IV – Constant Stimuli Summary constant stimuli data Observations from staircase data confirmed: -Increase of matching velocity with tilt angle -Increase of matching velocity with rotation speed Width of psychometric curve increases with rotation speed

38. Models

39. Model predictions Canal-otolith interactionFiltering 30 o /s and 15 o tilt

40. Models Model predictions 30 o /s and 15 o tilt Canal-Otolith

41. Models Model predictions 30 o /s and 15 o tilt Canal-Otolith Filter

42. Models Model predictions 30 o /s and 15 o tilt Data Canal-Otolith Filter Models cannot account for observed time course

43. Models Model predictions 15 o tilt Data Canal-Otolith Filter Models predict too large translations

44. Conclusions

45. We have developed a method that is able to capture the motion percepts that occur during OVAR Contemporary model hypotheses such as canal-otolith interaction and frequency segregation cannot explain our results Conclusions

46. The End

47. Canal-otolith interaction model - + + - + + + - + Body DynamicsSensory Dynamics S scc (s) S oto (s) S scc (s) S oto (s) - + + x     ˆ   ˆ   ˆ  g  g  a  f  e   e f  e a  ˆ g  ˆ g  ˆ a  ˆ a  ˆ f ˆ  oto  ˆ  scc     oto k a k f k f  k   e f    ˆ  ˆ   ˆ f g = (-  x g)dt g = (-  x g)dt ˆˆˆ Model of Body Dynamics Model of Sensory Dynamics Merfeld