PERCEPTUAL RESPONSES TO LINEAR ACCELERATION AFTER SPACEFLIGHT - HUMANNEUROVESTIBULAR STUDIES ON SLS-2

Perceptual responses of four astronauts were measured before and after a 14-day Spacelab Life Sciences-2 mission during interaural (y-axis) and rostrocaudal (z-axis) linear acceleration to measure adaptive chan ges in perceptual responses to inertial cues. In one test, subjects us ed a joystick to null a pseudorandom velocity disturbance. Postflight, two of three subjects showed a significantly enhanced ability to null linear self-motion in the v-axis and z-axis orientations. In another test, the subjects used a joystick to indicate their direction of moti on during a series of low-acceleration steps. The postflight responses of three of the four subjects showed a significant increase in the re sponse latency for both y-axis and z-axis orientations. In a third tes t, subjects were asked to track a stationary but unseen target with th eir eyes while they translated linearly in the dark. No significant ch anges were observed in tile postflight responses. The observed changes , when present, may be due to a reinterpretation of Inertial cues that are functionally adaptive for the microgravity environment but are no t optimal for responses on Earth.