Parabolic flight as a tool to measure ocular counterrotation in a reduced force environment

Five unmedicated subjects were flown in parabolic flight. The aircraft, a Caravelle, performed single parabolae every 2 to four minutes. This resulted in alternating phases of normal, hyper-, hypo- and again hyper-gravity. Subjects sat yoga fashion upright facing towards the aircraft cockpit. Head and/or trunk were deflected 30 degrees from the upright, stimulating otolith and/or neck receptors. During each pullup, low-g phase and pullout of the parabolae a picture of the left eye was recorded on video tape. On the ground ocular roll (OCR) was determined from these video recordings. OCR ranged from 0.9 to 6.9 degrees in l-g and from 1 to 7.2 degrees under high-g, depending on head and trunk position. Neck receptor contribution was found to induce OCR of 0.2 degree to 2.1 degrees in two subjects.