Movements are the fundamental source of interaction between the human body and the external world. The achievement of common actions, such as goal directed arm movement or object manipulation, requires the computation and execution of a motor plan which involves forward control based on prediction as well as feedback control based on sensory inflow.

DEXTEROUS investigates the adaptation of internal models when gravity no longer drives the arm. Object manipulation is an ideal framework for the study of internal models. This forward control relies on a prediction of arm motor command’s consequences and estimation of object’s mass in order to predict the increase in load. In weightlessness the necessity to modulate Grip Force with Load Force applies as well when accelerating downward since gravity no longer acts in this direction. Two human subjects will be asked to sit in front of a metallic vertical structure on which LED’s are fixed (one vertical bar for one subject). Both subjects will be fastened to their seat and will hold a specialised joystick (medically called a manipulandum) between the thumb and the index finger of the right hand. The experiment will be performed several times in order to increase the number of subjects and to refine the conclusions.

Subjects will be asked to perform free oscillations between the two LED’s that are turned on. The movement that the subject will realize must be performed with a straight-arm shoulder rotation.