Fig. 1

Schematics of dynamic SVV testing using the hemispheric dome method [1, 3]. A: a beamer (1) projects a dot pattern and a central line onto a spherical half-dome (2) which covers the entire visual field of the subject who is seated in front of the half-dome with head movement restricted by a chin rest (3). The central line is tilted in the roll plane at random intervals. The dots rotate in the roll plane for a minimum of 20 s in clockwise or counterclockwise direction (orange arrow); after 20 s, the subject is asked to orientate the central line from its offset position to the true verticality using a hand knob (4) while the dots continue to move. This measurement is repeated for multiple times in cw and ccw stimulus direction. B: The angular difference between the subject-submitted verticality and the true verticality is measured in 0.25° increments. An ipsidirectional stimulus-dependent angular tilt is physiological, whereas asymmetrical stimulus-dependent deviations are pathological. While dynamic SVV itself measures this difference between true verticality and the subject provided subjective verticality (defined as the mean of cw and ccw stimulus-dependent deviations), in this analysis we looked at the total angular deviation in clockwise and counterclockwise measurements by calculating the sum of mean absolute deviations