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Spatial perception during optokinetic stimulation

Spatial perception during optokinetic stimulation. Rik Hendrix Supervision: Maaike de Vrijer Jan van Gisbergen Bachelor internship Biomedical sciences, main course: human movement sciences Department of biophysics, Radboud University Nijmegen, March 3 rd – July 4 th.

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Spatial perception during optokinetic stimulation

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  1. Spatial perception during optokinetic stimulation Rik Hendrix Supervision: Maaike de Vrijer Jan van Gisbergen Bachelor internship Biomedical sciences, main course: human movement sciences Department of biophysics, Radboud University Nijmegen, March 3rd – July 4th

  2. Two spatial perception tasks • Subjective Body Tilt (SBT): Verbal estimate of body tilt → negligible errors at all tilt angles • Subjective Visual Vertical (SVV): Aligning a line with gravity → systematic tilt undercompensation at large tilt angles

  3. Optokinetic roll stimulation Optokinetic stimulation: stimulation with moving images Dichgans (1974) showed that optokinetic stimulation affects: • Subjective body tilt (SBT) • Subjective visual vertical (SVV) However: Dichgans never directly compared these effects!

  4. Optokinetic roll stimulation Causes tilt illusion opposite to rotation direction

  5. Research question Can optokinetic effects on SVV be explained by changes in perceived body tilt (SBT)?

  6. Methods • 8 Subjects (6 male, 2 female; 5 naïve) • Vestibular chair • 3 optokinetic conditions: • Stationary (control) • Clockwise (CW) • Counterclockwise (CCW) • Adjustable visual line • Tasks: • Subjective Body Tilt (SBT) • Subjective Visual Vertical (SVV)

  7. SBT task • Tilt angles between -135° and 135° with 15° intervals • Rotation to randomly chosen tilt angle in the dark • Continuous optokinetic stimulation • Verbal estimate of body tilt angle after 30 seconds • Rotation back to upright. • 30 Seconds rest period (lights on)

  8. SVV task • Tilt angles between -120° and 120° with 30° intervals • Rotation to randomly chosen tilt angle in the dark • Continuous optokinetic stimulation • Align visual line with gravity (3 trials) • Rotation back to upright • 30 Seconds rest period (lights on)

  9. Results

  10. Pooled SBT Results • Stationary: negligible errors at all body tilt angles • CW: Rather constant effect, overestimation when tilted to the left, underestimation when tilted to the right • CCW: Rather constant effect, opposite to CW

  11. Pooled SVV Results • Stationary: negligible errors at small tilt angles (≤30°) and systematic errors at large tilt angles (≥60°) • CW: constant effect when tilted to the right, increasing effect when tilted to the left. Asymmetry! • CCW: constant effect when tilted to the left, increasing effect when tilted to the right. Asymmetry!

  12. Graphical illustration of SVV results Stationary: • Negligible errors ≤30° • Systematic errors ≥60° Clockwise: • Constant effect when tilted to the left • Increasing when tilted to the right Counterclockwise: • Constant effect when tilted to the right • Increasing effect when tilted to the left

  13. Regrouped data Effect constant Effect increasing with tilt angle

  14. Δ SBT Δ SBT Δ SVV Δ SVV Results of regrouped data SBT SVV

  15. SVV task: effect of tilt increasing stimulus larger than effect of tilt decreasing stimulus  Asymmetry • SBT task: effects of tilt increasing and decreasing stimuli are roughly equal  No asymmetry Is asymmetry task dependant?

  16. Δ SVV Δ SBT Δ SVV Δ SBT Tilt increasing/Tilt decreasing • Tilt increasing stimulus has a different effect on the SVV than a tilt decreasing stimulus • Analysis of the research question for both tilt increasing and tilt decreasing stimuli • Two comparisons: • Δ SVV vs Δ SBT • SVV compensation vs SBT

  17. DSVV vs DSBT Comparison of optokinetic effects in SBT and SVV: • Tilt decreasing stimulus: D SVV = D SBT • Tilt increasing stimulus: D SVV > D SBT

  18. SVV compensation vs SBT

  19. SVV compensation vs SBT Stationary stimulus: SBT > SVV compensation angle Tilt decreasing stimulus: SBT >> SVV compensation angle Tilt increasing stimulus: SBT = SVV compensation angle

  20. Conclusions • Even if different combinations of physical tilt and optokinetic stimulation produce the same tilt percept (SBT), the percept of verticality (SVV) varies.

  21. Can optokinetic effects on SVV be explained by changes in perceived body tilt (SBT)? Ambiguous answer: sometimes effects on SVV can be explained by changes in SBT, but not all the time.

  22. Can optokinetic effects on SVV be explained by changes in perceived body tilt (SBT)? • Yes, but the relation is different for tilt-increasing and tilt-decreasing stimulation • The question remains whether this can be explained by current models

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