LIMITED CONSCIOUS MONITORING OF MOTOR-PERFORMANCE IN NORMAL SUBJECTS

Normal subjects traced sagittal lines on a graphic tablet using a styl us held in their right hand. The hand was hidden by a mirror in which they saw the lines projected from a computer screen. In normal trials, the line seen in the mirror exactly corresponded to the traced line. In perturbed trials, a bias was introduced by the computer, so that th e line appeared to deviate in one direction (right or left) by a varia ble angle (2, 5, 7 or 10 degrees). Subjects consistently displaced the ir hand in the opposite direction for producing a visually sagittal li ne. After each trial, they were asked in which direction they thought their hand had moved. In perturbed trials, they grossly underestimated the hand deviation. In addition, a post-hoc analysis revealed that on e group of subjects misperceived the direction of their hand movement in the direction opposite to the perturbation (Group 1, including 9 Ss ), whereas the other group gave responses in the correct direction (Gr oup 2, including 4 Ss). In a second session using the same experimenta l paradigm, a motor response was asked for: subjects had to indicate t he perceived direction of their hand during each trial by drawing a li ne with their eyes closed. Again, responses indicated a poor conscious monitoring of motor performance. These results suggest that normal su bjects are not aware of signals generated by their own movements. (C) 1998 Elsevier Science Ltd. All rights reserved.