ABSTRACT
Human sensory-motor control is dynamically adapted and calibrated to the terrestrial force background provided by the gravitational acceleration of Earth. The existence of this calibration becomes perceptually apparent when movements are carried out during exposure to greater than 1G levels of acceleration. Under this circumstance, the surface of support no longer feels stable as one moves in relation to it, and one misperceives the extent of one's body movements.
If repeated whole-body movements are made during exposure to a high level of acceleration, the apparent stability of self and environment during voluntary movement is gradually regained, but at the cost of a loss of adaptation to the force background of Earth. Consequently, on re-exposure to 1G acceleration levels, voluntary locomotion again elicits illusory motion of self and environment, but it is now of opposite sign. Such observations provide a basis for understanding many of the postural and sensory-motor aftereffects that astronauts and cosmonauts experience on return to Earth after space flight.
