Proprioceptive roll and pitch interact in contributing to visual tilt-induced effects.

1. Proprioceptive roll and pitch interact in contributing to visual tilt-induced effects. Jennifer E. Corbett & James T. Enns The University of British Columbia

2. Visual and proprioceptive information calibrate our sense of upright.

3. Visual and proprioceptive information calibrate our sense of upright. • We rely on: • The tilt of the surrounding visual environment(visual • orientation cues)

4. Visual and proprioceptive information calibrate our sense of upright. • We rely on: • The tilt of the surrounding visual environment(visual • orientation cues)

5. Visual and proprioceptive information calibrate our sense of upright. • We rely on: • The tilt of the surrounding visual environment(visual • orientation cues) • & • Our sense of the body’s position in space (proprioception)

6. Visual and proprioceptive information calibrate our sense of upright. • We rely on: • The tilt of the surrounding visual environment(visual • orientation cues) • & • Our sense of the body’s position in space (proprioception)

7. Visual and proprioceptive information calibrate our sense of upright. • We rely on: • The tilt of the surrounding visual environment(visual • orientation cues) • & • Our sense of the body’s position in space (proprioception) To determine our perceptions of upright.

8. Mystery Spots and funhouses are everyday illustrations of how our perception of orientation may arise from an interaction between visual information and our proprioceptive sense.

9. Mystery Spots and funhouses are everyday illustrations of how our perception of orientation may arise from an interaction between visual information and our proprioceptive sense. The visual tilt of the cabin

10. Mystery Spots and funhouses are everyday illustrations of how our perception of orientation may arise from an interaction between visual information and our proprioceptive sense. The visual tilt of the cabin and the observer’s tilt inside the cabin

11. Mystery Spots and funhouses are everyday illustrations of how our perception of orientation may arise from an interaction between visual information and our proprioceptive sense. The visual tilt of the cabin and the observer’s tilt inside the cabin affect perceptions of upright.

12. In the present study…

13. In the present study… We examined how the roll (clockwise or counterclockwise rotation along the image plane) Roll

14. In the present study… We examined how the roll (clockwise or counterclockwise rotation along the image plane) Roll

15. In the present study… We examined how the roll (clockwise or counterclockwise rotation along the image plane) Roll

16. In the present study… We examined how the roll (clockwise or counterclockwise rotation along the image plane) and pitch (rotation up or down in the frontal plane) of the observer Pitch

17. In the present study… We examined how the roll (clockwise or counterclockwise rotation along the image plane) and pitch (rotation up or down in the frontal plane) of the observer Pitch

18. In the present study… We examined how the roll (clockwise or counterclockwise rotation along the image plane) and pitch (rotation up or down in the frontal plane) of the observer Pitch

19. Pitch Roll In the present study… We examined how the roll (clockwise or counterclockwise rotation along the image plane) and pitch (rotation up or down in the frontal plane) of the observer interact with tilted visual cues

20. In the present study… We examined how the roll (clockwise or counterclockwise rotation along the image plane) and pitch (rotation up or down in the frontal plane) of the observer interact with tilted visual cues to produce observers’ perceptions of orientation. Pitch Roll

21. Introduction

22. Introduction • (Asch & Witkin, 1948)

23. Introduction • (Asch & Witkin, 1948) - If true vertical (with respect to gravity) True vertical

24. Introduction • (Asch & Witkin, 1948) - If true vertical (with respect to gravity) and the • visual tilt of the environment are different, Visual tilt True vertical

25. Introduction • (Asch & Witkin, 1948) - If true vertical (with respect to gravity) and the • visual tilt of the environment are different, visual tilt will influence observers’ • perceived vertical = The tilt induced effect. Perceived vertical Visual tilt True vertical

26. Introduction • (Asch & Witkin, 1948) - If true vertical (with respect to gravity) and the • visual tilt of the environment are different, visual tilt will influence observers’ • perceived vertical = The tilt induced effect. • (Nelson & Prinzmetal, 2003) - Pitch and roll of the visual environment • contribute independently to visual tilt-induced effects.

27. Introduction • (Asch & Witkin, 1948) - If true vertical (with respect to gravity) and the • visual tilt of the environment are different, visual tilt will influence observers’ • perceived vertical = The tilt induced effect. • (Nelson & Prinzmetal, 2003) - Pitch and roll of the visual environment • contribute independently to visual tilt-induced effects. Manipulating one dimension does not affect the influence of the other dimension:

28. Introduction • (Asch & Witkin, 1948) - If true vertical (with respect to gravity) and the • visual tilt of the environment are different, visual tilt will influence observers’ • perceived vertical = The tilt induced effect. • (Nelson & Prinzmetal, 2003) - Pitch and roll of the visual environment • contribute independently to visual tilt-induced effects. Manipulating one dimension does not affect the influence of the other dimension: Q1. Do pitch and roll of the observer independently/interactively influence visual-tilt induced effects?

29. Introduction • (Asch & Witkin, 1948) - If true vertical (with respect to gravity) and the • visual tilt of the environment are different, visual tilt will influence observers’ • perceived vertical = The tilt induced effect. • (Nelson & Prinzmetal, 2003) - Pitch and roll of the visual environment • contribute independently to visual tilt-induced effects. • (Witkin & Asch, 1948) - Tilt-induced effects are increased when observers are • also tilted.

30. Introduction • (Asch & Witkin, 1948) - If true vertical (with respect to gravity) and the • visual tilt of the environment are different, visual tilt will influence observers’ • perceived vertical = The tilt induced effect. • (Nelson & Prinzmetal, 2003) - Pitch and roll of the visual environment • contribute independently to visual tilt-induced effects. • (Witkin & Asch, 1948) - Tilt-induced effects are increased when observers are • also tilted. Observers tilted congruently

31. Introduction • (Asch & Witkin, 1948) - If true vertical (with respect to gravity) and the • visual tilt of the environment are different, visual tilt will influence observers’ • perceived vertical = The tilt induced effect. • (Nelson & Prinzmetal, 2003) - Pitch and roll of the visual environment • contribute independently to visual tilt-induced effects. • (Witkin & Asch, 1948) - Tilt-induced effects are increased when observers are • also tilted. Observers tilted congruently experience larger tilt-induced effects >

32. Introduction • (Asch & Witkin, 1948) - If true vertical (with respect to gravity) and the • visual tilt of the environment are different, visual tilt will influence observers’ • perceived vertical = The tilt induced effect. • (Nelson & Prinzmetal, 2003) - Pitch and roll of the visual environment • contribute independently to visual tilt-induced effects. • (Witkin & Asch, 1948) - Tilt-induced effects are increased when observers are • also tilted. Observers tilted congruently experience larger tilt-induced effects than incongruently tilted observers. >

33. Introduction • (Asch & Witkin, 1948) - If true vertical (with respect to gravity) and the • visual tilt of the environment are different, visual tilt will influence observers’ • perceived vertical = The tilt induced effect. • (Nelson & Prinzmetal, 2003) - Pitch and roll of the visual environment • contribute independently to visual tilt-induced effects. • (Witkin & Asch, 1948) - Tilt-induced effects are increased when observers are • also tilted. Observers tilted congruently experience larger tilt-induced effects than incongruently tilted observers. > (0.8o)

34. Introduction • (Asch & Witkin, 1948) - If true vertical (with respect to gravity) and the • visual tilt of the environment are different, visual tilt will influence observers’ • perceived vertical = The tilt induced effect. • (Nelson & Prinzmetal, 2003) - Pitch and roll of the visual environment • contribute independently to visual tilt-induced effects. • (Witkin & Asch, 1948) - Tilt-induced effects are increased when observers are • also tilted. Q2. Are visual tilt-induced effects really greater when the observer is tilted incongruently vs. congruently with the visual environment? (0.8o is pretty weak…)

35. Introduction • (Asch & Witkin, 1948) - If true vertical (with respect to gravity) and the • visual tilt of the environment are different, visual tilt will influence observers’ • perceived vertical = The tilt induced effect. • (Nelson & Prinzmetal, 2003) - Pitch and roll of the visual environment • contribute independently to visual tilt-induced effects. • (Witkin & Asch, 1948) - Tilt-induced effects are increased when observers are • also tilted. Q3. Do observers actively maintaining an upright posture on a tilted surface experience the same degree of visual tilt-induced effects as passively- tilted observers?

36. Summary of research questions

37. Summary of research questions Q1. Do pitch and roll of the observer independently/interactively influence visual-tilt induced effects?

38. Summary of research questions Q1. Do pitch and roll of the observer independently/interactively influence visual-tilt induced effects? Q2. Are visual tilt-induced effects really greater when the observer is tilted incongruently vs. congruently with the visual environment?

39. Summary of research questions Q1. Do pitch and roll of the observer independently/interactively influence visual-tilt induced effects? Q2. Are visual tilt-induced effects really greater when the observer is tilted incongruently vs. congruently with the visual environment? Q3. Do observers actively maintaining an upright posture on a tilted surface experience the same degree of visual tilt-induced effects as passively- tilted observers?

40. Apparatus for visual tilt-induced effects

41. Apparatus for visual tilt-induced effects A Rod-Frame box

42. Apparatus for visual tilt-induced effects A Rod-Frame box rolled 20o along the roll axis

43. Apparatus for visual tilt-induced effects A Rod-Frame box rolled 20o along the roll axis produced standard visual-tilt induced effects.

44. Perceptual measure The experimenter rolled the rod independently of the tilted box until the subject indicated that the rod was “vertical with respect to gravity.”

45. Perceptual measure The experimenter rolled the rod independently of the tilted box until the subject indicated that the rod was “vertical with respect to gravity.” The deviation from vertical of the observer’s rod adjustment (angle of illusion) was measured by a ruler on the backside of the rod with 0o corresponding to true vertical position of the rod.

46. Perceptual measure A 10o illusion in rod adjustment:

47. Perceptual measure A 10o illusion in rod adjustment:

48. Perceptual measure A 10o illusion in rod adjustment:

49. Active observers • Observers standing on a tilted platform actively maintained an upright • posture

50. Active observers • Observers standing on a tilted platform actively maintained an upright • posture while determining the vertical position of the rod.