COMMON ORGANIZATION FOR UNIMANUAL AND BIMANUAL REACH-TO-GRASP TASKS

In two experiments comparisons between characteristics of performance of a unimanual and a bimanual reach-to-grasp (prehension) task were ma de on an individual subject basis. The unimanual prehension task used required that the object be grasped by finger and thumb pad opposition , the bimanual task required that the grasp be made by opposing the pa ds on the two index fingers. Experiment 1 examined adaptation of prehe nsion movements to objects of different size (width) but equal grasp s urface area placed at different distances. Experiment 2 examined adapt ation of movements to objects of different grasp surface areas. It was found that the aperture and transport components of the two prehensio n tasks developed over time in very similar fashion in all subjects. M ovements were adapted to different task constraints in the same way as has previously been reported in the literature and were very similar in both tasks: maximum aperture increases with increasing object size and occurs later in the movement for larger objects; movement time inc reases with target distance; time of maximum aperture occurs earlier i n the movement for targets with smaller grasp surface areas; movement times are longer for such objects, largely due to increases in the dec eleration phase of the movement. These results support the notion that there is an effector independent level of organization that governs t he coordination of movements during performance of reaching and graspi ng tasks.