EFFECTS OF MOVEMENT DIRECTION UPON KINEMATIC CHARACTERISTICS OF VERTICAL ARM POINTING MOVEMENTS IN MAN

Vertical arm pointing movements in two directions (upwards and downwar ds), imposing two different loads (unload and 0.5 kg) and speeds (norm al and fast) have been studied in six subjects. Movements were recorde d using an optoelectronic system. Data analysis concentrated upon fing er-tip kinematics. Significant effects of movement direction were reco rded upon velocity profiles. The acceleration time, computed relative to total movement time, was greater for downward movements than for up ward movements. In contrast however, no effects of load or speed were observed. Movement time was not affected by movement direction or load , for both speeds tested. These results suggest different planning pro cesses, for movements with and against gravity and indicate that gravi tational force influences the processes controlling movement execution . (C) 1998 Published by Elsevier Science Ireland Ltd. All rights reser ved.