Fig. 1. Illustration of vestibulo-ocular reflex (VOR) and ocular tilt reflex (OTR). A. Bird-watcher standing in a rocking boat traveling downstream. B. As the boat pitches up and down, the angular VOR moves the eyes in the opposite direction, synchronous with the angular motion of the head. C. As the boat moves down the river toward the bird, the linear VOR moves the eyes horizontally in the opposite direction, synchronous with the linear motion of the boat. D. As the boat tilts to the left and right, the OTR tilts the eyes and head in the opposite direction to maintain an earth-horizontal plane. The figure shows what happens with tilt to the right. The right eye is elevated in the orbit and the left eye is depressed (skew deviation); both eyes undergo torsion to the left within the orbit (counter-roll deviation) and the head is tilted to the left on the body.