The investigators previously shown that a rotating optokinetic stimulus results in shifts of the subjective visual vertical in healthy human subjects. However, the origin of these shifts is still poorly understood. Both torsional displacement of the eyes and a shift in the internal estimate of direction of gravity have been proposed as potential explanations. Here the investigators use a vision-independent setup to differentiate between these two hypotheses, predicting no impact of a rotating stimulus on the subjective haptic vertical if torsion triggers the shift.

Inclusion Criteria:

• ages 18-65 years
• informed consent
• absence of exclusion criteria

Exclusion Criteria:

• peripheral-vestibular deficit
• disturbed consciousness
• history of sensory deficits
• visual field deficits
• other neurological or systemic disorder which can cause dementia or cognitive dysfunction
• intake of antidepressants, sedatives, or neuroleptics
• pregnancy, unless excluded by a negative pregnancy test
• known neck pain or status post neck trauma