VOR versus smooth pursuit

Recall from Sections 5.3, 5.4, and 6.2 that eye movements play an important role in visual perception. An evaluator should in mind the particular eye movement mode when evaluating whether an object in the virtual world is actually stationary when it is supposed to be. If a canonical yaw motion is made while eyes are fixated on the object, then the vestibulo-ocular reflex (VOR) is invoked. In this case, then the evaluator can determine whether the object appears to move or distort its shape while the image of the object is fixed on the retina. Similarly, if an object is slowly moving by and the head is fixed, the evaluator performs smooth pursuit to keep the object on the retina. As indicated in Section 5.4, the way in which an object appears to distort for a line-by-line scanout display depends on whether the motion is due to VOR or smooth pursuit. If the object moves by very quickly and the eyes do not keep it fixed on the retina, then it may be possible to perceive the zipper effect.