Perceiving one's own movements when using a tool.

The present study examined what participants perceive of their hand movements when using a tool. In the experiments different gains for either the x-axis or the y-axis perturbed the relation between hand movements on a digitizer tablet and cursor movements on a display. As a consequence of the perturbation participants drew circles on the display while their covered hand movements followed either vertical or horizontal ellipses on the digitizer tablet. When asked to evaluate their hand movements, participants were extremely uncertain about their trajectories. By varying the amount of visual feedback, findings indicated that the low awareness of one's own movements originated mainly from an insufficient quality of the humans' tactile and proprioceptive system or from an insufficient spatial reconstruction of this information in memory.