Abstract
Mental imagery represents a potential countermeasure for sensorimotor and cognitive dysfunctions due to spaceflight. It might help train people to deal with conditions unique to spaceflight. Thus, dynamic interactions with the inertial motion of weightless objects are only experienced in weightlessness but can be simulated on Earth using mental imagery. Such training might overcome the problem of calibrating fine-grained hand forces and estimating the spatiotemporal parameters of the resulting object motion. Here, a group of astronauts grasped an imaginary ball, threw it against the ceiling or the front wall, and caught it after the bounce, during pre-flight, in-flight, and post-flight experiments. They varied the throwing speed across trials and imagined that the ball moved under Earth’s gravity or weightlessness. We found that the astronauts were able to reproduce qualitative differences between inertial and gravitational motion already on ground, and further adapted their behavior during spaceflight. Thus, they adjusted the throwing speed and the catching time, equivalent to the duration of virtual ball motion, as a function of the imaginary 0 g condition versus the imaginary 1 g condition. Arm kinematics of the frontal throws further revealed a differential processing of imagined gravity level in terms of the spatial features of the arm and virtual ball trajectories. We suggest that protocols of this kind may facilitate sensorimotor adaptation and help tuning vestibular plasticity in-flight, since mental imagery of gravitational motion is known to engage the vestibular cortex.
Highlights
Space missions expose humans to the risk of multiple physiological alterations, due to weightlessness, ionizing radiations, confinement, and other stressors[1,2,3,4]
The results show that, on average, the instructions specified three discrete levels of these participants threw the virtual ball at considerably lower throwing force, all participants varied the speeds and waited for a longer time before catching back the ball throwing speed V widely across repetitions of the same reference when they imagined a 0 g condition than a 1 g condition
Inertial motion of weightless objects already on ground, and that they further adapted their behavior to the real weightless conditions of spaceflight
Summary
Space missions expose humans to the risk of multiple physiological alterations, due to weightlessness, ionizing radiations, confinement, and other stressors[1,2,3,4]. The participants are asked to grasp an imaginary ball in the hand, to throw it “up” so as to bounce on the ceiling, and to catch it on the fly when they think it has come back to be grasped (Fig. 1A) They must vary the throwing force and speed across trials and, in different blocks of trials, to imagine that the ball moves under Earth gravity (1 g) or weightlessness (0 g). On average they should throw the virtual ball at a lower speed (due to lower impulsive forces of the hand) and should wait for a longer time before catching the ball after the rebound for the imaginary 0 g condition carrying out the experiment on the ISS (Fig. 1A). In eight apparent in arm kinematics, in addition to the T versus V functions. astronauts (S5–S12), hand and arm movements were recorded at
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