SUBJECTIVE SENSE OF HAND LOCATION IN A PERTURBED POINTING TASK - A TEST FOR FEEDBACK PROCESSING

The aim of the present study was to compare the spatial accuracy of a pointing movement subjected to inertial perturbation with the accuracy of subjective position sense of the hand at final position. Pointing movements were performed without visual control, on an armchair which was either stationary or rotating at a constant velocity (120 deg.s(-1 )). During the rotation, the combined presence of Coriolis and centrif ugal forces induced a perturbation of hand displacement in amplitude a nd direction. As shown in previous experiments (Coello & Orliaguet, 19 94; Coello, Orliaguet, & Prablanc, 1996), the first performance on the rotating armchair suggested 'on-line' adjustment of the movement ampl itude despite the absence of direct visual control of arm displacement . However, considerable inaccuracy was noted in the subjective sense o f hand position for this spatial parameter. The discrepancy between ac tual and subjective accuracy increased continuously throughout the exp erimental session. Conversely, a sharp angular error was noted at the end of the first perturbed trial, opposite to the armchair's direction of rotation, and correction of movement direction required the rehear sal of several trials. This lack of on-line control of the direction p arameter contrasted with the accuracy of the subjective sense of the a zimuth of the terminal hand position. Overall, results suggested that although proprioceptive information resulting from hand displacement c ontributed to on-line and off-line control of the movement, its partic ipation to the subjective sense of position seemed to be more related to direction than to amplitude parameter.