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