People have implicit knowledge of how the world works since infancy, which allows them to interact appropriately with the environment. In particular, gravity is detected accurately based on an internal model of its effects. We previously showed that during space flight the motor responses of the astronauts were still tuned to gravitational acceleration. Astronauts asked to catch a ball that was projected “downward” from the ceiling contracted their limb muscles too early, anticipating non-existent gravity effects. In the study just published in NPJ Microgravity, the astronauts were asked to throw an imaginary ball toward the ceiling and to catch it upon rebound.

They had to imagine that the ball moved under Earth gravity or in weightlessness. Surprisingly, we found that astronauts were able to implicitly reproduce the 0g conditions already on ground, prior to their mission, although their performance improved over the course of their time in space. There is a striking dissociation between the motor control system and the cognitive system. The former drives automatic responses tuned to Earth’s gravity, and the anticipation of gravity persists even in space. However, the cognitive system allows one to imagine 0g movements even on the ground and is endowed with a more general implicit knowledge of Newton's laws.

Thus, mental imagery can play an important role in training people to deal with conditions unique to spaceflight. It also represents a potential countermeasure for sensorimotor and cognitive dysfunctions due to spaceflight. Finally, protocols of mental imagery also offer benefits on Earth, because brain injured patients experience many of the same challenges as the astronauts. 

Gravano S, Lacquaniti F, Zago M. Mental imagery of object motion in weightlessness. NPJ Microgravity. 2021 Dec 3;7(1):50. doi: 10.1038/s41526-021-00179-z.