1. M. De Vrijer, W.P. Medendorp, J.A.M. Van Gisbergen
Optokinetic effect on the subjective visual vertical and body tilt perception
Thank you. This presentation is about the influence of moving visual patterns on human spatial orientation.

2. Dissociation: SBT ≠ SVV
Spatial orientation
Subjective body tilt (SBT)
Accurate in whole tilt range
Subjective visual vertical (SVV)
Undercompensation
at tilt angles > 60°
Van Beuzekom, Medendorp, Van Gisbergen, Vision Res., 2001
Tilt angle [deg]
Response error [deg]
SVV
Dissociation:
SBT ≠ SVV
SBT

3. Optokinetic (roll) stimulation (OKS)
Affects body tilt percept (SBT)
Young et al. (1975)
Affects subjective visual vertical (SVV)
Dichgans et al. (1972, 1974)
Both effects increase at larger tilts
Example of roll-optokinetic stimulus (OKS)
This study
Combined measurements of these effects
Is there dissociation between optokinetic effects on SBT and SVV?

4. Experiments SBT task SVV task
Subjects (n=8) were roll-tilted in darkness to various tilt angles (-135 to 135°)
Upon arrival, an optokinetic drum was turned on (Ø 76°, rotation velocity: -35, 0 or +35 °/s)
SBT task
SVV task

5. Optokinetic stimulation CW-stimulus CCW-stimulus Stationary

6. Results OKS causes shift in SBT OKS affects SBT differently than SVV
CCW
OKS causes shift in SBT CW
 CCW
CW 
OKS affects SBT differently than SVV
 CCW
CW 

7. Effects differ for tilt-increasing and tilt-reducing OKS
Tilt-increasing OKS
ΔSBT
Tilt-reducing OKS
ΔSVV
 CCW
CW 

8. Effects differ for tilt-increasing and tilt-reducing OKS
Tilt-increasing OKS
Tilt-reducing OKS
No dissociation for tilt-reducing OKS
Dissociation for tilt-increasing OKS

9. Summary

10. Conclusions
In absence of optokinetic stimulation, subjects have veridical SBT, whereas SVV is biased at tilts > 60°
Presence of optokinetic stimulus affects both SBT and SVV:
Tilt-reducing optokinetic stimulus affects SBT and SVV equally
Tilt-increasing optokinetic stimulus affects SVV more severely than SBT
The dissociation between SBT and SVV in the tilt-increasing condition is further evidence for the notion that these percepts are based on different computational principles

11. Questions?

12. Tilt dependence of optokinetic effect

13. Ocular torsion Subjects performed another task:
- Align visual line with body axis (subjective line body, SLB)

14. Future directions
See:
De Vrijer, Medendorp & Van Gisbergen, JNP 2008