Sensorimotor performance and haptic support in simulated weightlessness.

The success of many space missions critically depends on human capabilities and performance. Yet, it is known that sensorimotor performance is degraded under conditions of weightlessness. Therefore, astronauts prepare for their missions in simulated weightlessness under water. In the present study, we investigated sensorimotor performance in simulated weightlessness (induced by shallow water immersion) and whether performance can be improved by choosing appropriate haptic settings of the human-machine interface (e.g., motion damping). Twenty-two participants performed basic aiming and tracking tasks with a force feedback joystick under water and on land and with different haptic settings of the joystick (no haptics, three spring stiffnesses, and two motion dampings). While higher resistive forces should be avoided for rapid aiming tasks in simulated weightlessness, tracking performance is best with higher motions damping in both land and water setups, although the performance losses due to water immersion cannot be compensated. The overall result pattern also provides insights into the causal mechanism behind the slowing effect during aiming motions and decreased accuracy of tracking motions in simulated weightlessness. Findings provide evidence that distorted proprioception due to altered muscle spindle activity seemingly is the main trigger of impaired sensorimotor performance in simulated weightlessness.