Illusory gravitational forces affect aimed limb movements

The authors report on 2 experiments in which participants produced rapid wrist-rotation movements in a clockwise direction to move a cursor from a home position into a target region. The display was constructed such that the target could be depicted above, below, or beside the home position, so that the clockwise wrist rotation could produce upward, downward, or rightward movements of the cursor. By parsing the movements into component submovements, the authors found that upward movements were consistently less forceful, as evidenced by shorter primary submovements, compared with downward and horizontal movements. Those results suggested a new virtual gravity illusion: Participants apparently overcompensated for the absence of the anticipated effects of gravity by adjusting the initial force they used to propel the cursor toward the target.