Affiliations: [a] Department of Neurology, University Hospital Zurich, Zurich, Switzerland
| [b] Department of Otorhinolaryngology, University Hospital Zurich, Zurich, Switzerland
| [c] Department of Ophthalmology, University Hospital Zurich, Zurich, Switzerland
| [d] Faculty of Medicine, University of Zurich, Switzerland
| [e] Center of Clinical Neurosciences, University Hospital Zurich, Switzerland
| [f]
Cantonal Hospital of Baden, Baden, Switzerland
Correspondence:
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Corresponding author: A.A. Tarnutzer, Department of Neurology, University Hospital Zurich, Frauenklinikstrasse 26, CH-8091 Zurich, Switzerland. Tel.: +41 44 255 1111; Fax: +41 44 255 4380; E-mail: alexander.tarnutzer@access.uzh.ch.
Abstract: BACKGROUND:While verticality perception is normally accurate when upright, a systematic bias (“post-tilt bias”) is seen after prolonged roll-tilt. The source of the bias could either be central (shifting “null” position) or related to changes in torsional eye-position. OBJECTIVE:To study the mechanisms of the post-tilt bias in vision-dependent and vision-independent paradigms and to characterize the impact of optokinetic stimulation. METHODS:The subjective visual-vertical (SVV) and subjective haptic-vertical (SHV) were measured after static roll-tilt (±90deg ear-down (“adaptation”) position; duration = 5 min; n = 9 subjects). To assess the effect of visual stimuli, a control condition (darkness) was compared with an optokinetic stimulus (clockwise/counter-clockwise rotation, 60deg/sec) during adaptation. RESULTS:A significant post-tilt bias was more frequent for the SVV than the SHV (72% vs. 54%, p = 0.007) with shifts pointing towards or away from the adaptation position with similar frequency. Exponential-decay time-constants were comparable for both paradigms and directions of shifts. The optokinetic stimulus had no effect on the bias for either paradigm. CONCLUSIONS:Emerging in both vision-dependent and vision-independent paradigms, the results support the hypothesis that the post-tilt bias results from a shift in the internal estimate of direction of gravity, while optokinetic nystagmus seems not to be a major contributor.
