Pointing to a target from an upright position in human: tuning of posturalresponses when there is target uncertainty

Human subjects performed, from a standing position, rapid hand pointings to visual targets located within or beyond the prehension space. To examine t he interaction between posture and the goal-directed movement we introduced a visual double-step perturbation requiring a reprogramming of the hand mo vement. Trials directed towards the same spatial goal but differentiated on ly by the likeliness of a visual double-step were compared. The hand kinema tics was not affected by the uncertainty of the visual perturbation; an inc reased trunk bending, however, was observed. This suggests that uncertainty constraints are integrated in a predictive manner for the optimal coordina tion of the hand and postural control systems. (C) 2000 Elsevier Science Ir eland Ltd. All rights reserved.