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Optokinetic effect on the subjective visual vertical and body tilt perception

M. De Vrijer, W.P. Medendorp, J.A.M. Van Gisbergen. Optokinetic effect on the subjective visual vertical and body tilt perception. Spatial orientation. Subjective body tilt (SBT) Accurate in whole tilt range. Subjective visual vertical (SVV) Undercompensation at tilt angles > 60°.

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Optokinetic effect on the subjective visual vertical and body tilt perception

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  1. M. De Vrijer, W.P. Medendorp, J.A.M. Van Gisbergen Optokinetic effect on the subjective visual vertical and body tilt perception

  2. 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 SVV Dissociation: SBT ≠ SVV Tilt angle [deg] Response error [deg] 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 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. CCW-stimulus CW-stimulus Stationary Optokinetic stimulation

  6. Results 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 ΔSVV ΔSVV ΔSBT ΔSBT Tilt-reducing OKS  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. Subjects performed another task: • - Align visual line with body axis (subjective line body, SLB) Ocular torsion

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

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