Abrupt deceleration (AD) of the VOR slow phase during initial fixation of a target 20° upward by representative subject with left chronic UVD who was rotated contralesionally. Positive values indicate upward, rightward, and clockwise rotations. a The AD rapidly reversed horizontal velocity. b AD corresponded to a discontinuity in horizontal eye position from the VOR slow phase. c VOR slow phase eye torsion did not match head torsion. Torsion during the AD deviated from ideal Listing's torsion. d Failing to match the head, slow phase eye torsion remained close to LP. During the AD, eye torsion trajectory was approximately perpendicular to LP, and caused eye torsion to exceed the negative of head torsion (gray dots)