Pointing movement in an artificial perturbing inertial field: a prospective paradigm for motor control study.

The present experiment focused on spatial accuracy and kinematics of fast pointing movements submitted to a multi-directional inertial perturbation. Pointing movements were performed without direct visual control, on a rotating armchair adding centrifugal and Coriolis forces to the natural displacement of the arm. The simultaneous action of these two forces induced a perturbation of the arm displacement both in amplitude and direction. Results showed that these two parameters were adjusted differently according to their own temporal constraint. Movement amplitude was adjusted on-line from the very first trial through the amendment of the whole acceleration pattern. Conversely, adjustment to directional perturbation was progressively achieved through several movement rehearsals. This correction appeared to be primarily due to a modification of the initial orientation of the arm trajectory, based seemingly on kinaesthetic knowledge from previous performances. The amendment of spatial parameters during motor response in the perturbing environment was discussed with an emphasis on the involvement of the cerebellum in reaching movement and the learning process.