Hi Erin!
The vestibulo-ocular reflex is the reflex that allows us to maintain gaze stability while turning our heads (our eyes move equal and opposite to our head). VOR cancellation is a central vestibular function that allows us to override that reflex in instances when we want our eyes and head to move together.
VOR is tested with the head impulse test and/or by measuring dynamic visual acuity.
VOR cancellation is screened by sitting in front of a patient, turning their head side-to-side, and asking them to keep their eyes focused on your nose. You will move side-to-side with the patient, forcing them to suppress their VOR. It might be easier to see someone performing the screen: https://www.youtube.com/watch?v=7Nw3TgieAjI