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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°. - PowerPoint PPT Presentation
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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
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Tilt angle [deg]
Resp
onse
err
or
[deg]
Spatial orientationSubjective 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
SBT
SVV
Dissociation: SBT ≠ SVV
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• 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)
Optokinetic (roll) stimulation (OKS)
This study
Combined measurements of these effects
Is there dissociation between optokinetic effects on SBT and SVV?
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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
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CCW-stimulusCW-stimulus Stationary
Optokinetic stimulation
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Results
• OKS causes shift in SBT
CW CCW
• OKS affects SBT differently than SVV
CW
CW CCW
CCW
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Effects differ for tilt-increasing and tilt-reducing OKSTilt-increasing OKS
Tilt-reducing OKS
ΔSVV
ΔSVV
ΔSBT
ΔSBT
CW CCW
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• No dissociation for tilt-reducing OKS• Dissociation for tilt-increasing OKS
Effects differ for tilt-increasing and tilt-reducing OKSTilt-increasing OKS
Tilt-reducing OKS
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Summary
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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
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Questions?
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Tilt dependence of optokinetic effect
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Ocular torsion
• Subjects performed another task:
- Align visual line with body axis (subjective line body, SLB)
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Future directions
See:De Vrijer, Medendorp & Van Gisbergen, JNP 2008
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