Constraints on human arm movement trajectories.

AUSTKA< T The underlying pirn-esses in movement organization and control were studied by varying the conditions under which arm movements were made. The three-dimensional movement trajectories of the following conditions were contrasted: pointing to a target with the index linger versus grasping a disk the same size as the target, grasping a fragile object versus a soil resilient object, and grasping a disk either to throw into a large box or place into a light litting well. Results showed that the arm trajectories, as represented by the resultant velocity profile of the wrist, varied considerably in their shape with the main factor being when peak velocity was reached as a function of the total duration of the movement. It appeared that when task demands required greater precision, the main deceleration phase of the trajectory was increased in duration. These results do not support a movement production mechanism that has access to an abstract representation of a base velocity profile and that creates trajectories by a simple scaling procedure in the temporal domain. Rather, the results support a view of movement production as relatively specific to the past experience of the performer and the constraints of the task. Ix's processus a la base du controlc el de ('organisation du mouvement out etc etudies en variant les conditions sous lesquelles les mouvements du bras etaient executes. Les trajectoires de mouvemenl tridimcnsionncl des conditions suivantes etaient niises en contraste: pointer une cible avee l'index versus saisir un disque de la meme taille que la cible; saisir un objet fragile versus un object elastique. mou; ct, saisir un disque suit pour le lancer dans une grnnde boitc soit le placer dans un puits bien ajustc. Les resultats indiquent que les trajectoires du bras, lelles que represenlees par le prolil de velocite resultant du poignel, varicnt considerablement dans leur forme avec le facteur principal apparaissant au moment ou 1c pic de velocite etait atteinl en tant que function de la duiee tolale du mouvement. Lorsque la tache requiert line plus grande precision la phase de deceleration principale dc la trajecloire augmente en duree. Cos resultats n'appuient pas un mccanisme dc production du mouvemenl ayant acccs a line representation abslraitc d'un prolil dc velocite dc base et creant des trajectoires par un procedc d'echelonncment simple dans le domaine temporcl. Cos resultats supported! plulol I "idee d'unc production de mouvement coiiunc relativement specilique ii lexperience passcc du …