Effect of spaceflight on ability to sense and control roll tilt: human neurovestibular studies on SLS-2.

To measure adaptive changes in the ability to sense tilt after spaceflight, we measured the ability of four astronauts to control roll tilt in the presence of a pseudorandom motion disturbance before and after a 14-day Spacelab mission. The subjects were tested 1) in the dark, 2) with an independent sum-of-sines visual display, and 3) by using a control condition in which the visual cues confirmed the motion cues (counterrotating). The two subjects tested on the landing day exhibited significant decrements (P < 0.05) in their ability to control roll tilt in the dark, whereas no significant performance decrements were observed in the control condition. The absence of changes in the control condition suggests that changes in the neuromuscular component of the task and postflight fatigue were not major factors contributing to the observed performance decrement in the dark. These findings indicate an adaptive change in the way the nervous system interprets tilt cues. Readaptation of all responses appeared to be rapid, with a return to preflight values within 1-2 days after landing.