Artificial gravity : adaptation of the vestibulo-ocular reflex to head movements during short-radius centrifugation

Abstract

Short-radius centrifugation is currently being pursued as a potential countermeasure to long duration space flight. Short-radius centrifugation requires relatively high angular velocities (on the order of 30 rpm) to create centripetal accelerations on the order of 1 g. Unfortunately, out-of-plane head movements during centrifugation induce inappropriate vestibulo-ocular reflexes, debilitating motion sickness symptoms, and illusory tilt sensations due to conflicting visual and vestibular signals. Practical use of an intermittent short-radius centrifuge as a countermeasure requires that crew members be capable of rapidly adapting to the unexpected semicircular canal inputs with minimal side- or post-effects. Furthermore, adaptation not only has to be achieved, it also has to be appropriate for the environment (stationary, rotating, 1 g, or 0 g). The purpose of this research was to investigate humans' ability to attain and maintain adaptation to rotating environments. Subjects participated in a series of pre-/per-/and post-rotation data collection sessions consisting of both eye reflex recordings during head movements, a subjective battery of tests, and autonomic measurements. Eight subjects were tested on three days (D=1, 2, 8). Eye movements were measured in response to out-of-plane head movements during rotation at 23 rpm on-board the MIT short-radius centrifuge (r=2 m). Slow phase eye velocity (SPV) was reconstructed from filtered and de-saccaded eye movement data. The significant main effect of day and pre-/post-adaptation phase demonstrated that normalized SPV decreased following adaptation in the light.