Laurence R. Young, Sc.D., Kathleen Sienko, M.S., Lisette Lyne, M.S., Heiko Hecht, Ph.D., Alan Natapoff, Ph.D., Man-Vehicle Lab, Massachusetts Institute of Technology, Cambridge, MA

Our research has found evidence of context-specific adaptation of the vestibulo-ocular reflex (VOR). Such adaptation is indispensable when an observer's sensory environment is systematically changed, such as in weightlessness. Head movements made in the unusual environment of a short- radius centrifuge produce strong conflicts between vestibular and visual or proprioceptive information, which result in inappropriate eye movements, sensory illusions, disorientation and often times motion sickness. We investigated the sensory adaptation of humans to this conflict by repeatedly exposing eight subjects to horizontal short-radius centrifugation (radius = 2 m) at 23 rpm over an eight-day period. The dependent measures were inappropriate vertical VOR, subjective tilt, and motion sickness in response to out-of-plane head movements. Inappropriate vertical VOR and subjective tilt were measured in response to 9???yaw out- of-plane head movements during rotation in the dark. Post-experiment motion-sickness scores were collected following exposure to rotation. Significant adaptation effects were found for normalized slow phase velocity of vertical nystagmus, the reported magnitude of the subjective tilt experienced during head turns, and motion-sickness scores. Retention of adaptation over a six-day rest period without centrifugation occurred, but was not complete for all measures. Adaptation for VOR was completely maintained while subjective tilt was partially maintained and motion sickness scores continued to decrease. Practical and theoretical implications of these findings are discussed.

Laurence R. Young, Sc.D. is the Apollo Program Professor of Astronautics at the Massachusetts Institute of Technology (MIT), and the Director of the National Space Biomedical Research Institute. In 1962, he joined the MIT faculty and co-founded the Man-Vehicle laboratory, which does research on the visual and vestibular systems, visual-vestibular interactions, space motion sickness, flight simulation, and manual control and displays. In 1991 Prof. Young was selected as a Payload Specialist for Spacelab Life Sciences 2. He spent two years training at Johnson Space Center and served as Alternate Payload Specialist during the October 1993 mission. He has been Principal Investigator on five Spacelab experiments. Prof. Young's contributions to the field of human factors research have been recognized by the Paul Hansen Award of the Aerospace Human Factors Association, the Dryden Lectureship in Research, the Jeffries Medical Research Award of the AIAA, and the Franklin Taylor Award of the IEEE. Most recently he was awarded the prestigious Koetser Foundation Prize for his contributions to neuroscience. A member of the National Academy of Engineering, the Institute of Medicine and the International Academy of Astronautics, Prof. Young is the author of more than 250 journal articles, largely in the areas of space physiology and human factors, including review chapters in Fundamentals of Aerospace Medicine and the Handbook of Physiology. His translation of Ernst Mach's Fundamentals of the Theory of Movement Perception will appear in late 2001.