The purpose of this study is to evaluate the relative contribution of head- and trunk-based sensory systems to internal estimates of direction of gravity in healthy human subjects. To implement this assessment experimentally, the investigators will use a motor-driven 3D-turntable and a thermoplastic mask to keep the head in a stable, either roll-tilted (±30°) or aligned with the trunk. The investigators will then obtain measurements of the subjective visual vertical in seven different whole-body roll positions (max. 90° roll-tilt). Analysis will be driven by a state-of-the art Bayesian integration model. The investigators hypothesize that different sensory input signals are combined in a statistically optimal fashion.

Inclusion Criteria:

• ages 18-60 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