Manual asymmetries in response to rapid target movement

Two studies are reported that examine reaching responses of the two hands to unexpectedly displaced targets, located along the midline and to the left and right. In the first study, subjects used the index finger to point to the targets. The left hand movement time and time to peak velocity were longer than for the right hand. For both hands, performance was superior when reaching into ipsilateral space. No evidence was found for early (before peak velocity) trajectory corrections in response to perturbations. In the second study, subjects reached and grasped dowels which appeared to move unexpectedly. Again, movement times were smaller when reaching with the right hand when compared to the left, but only on trials when the dowel was located on the subject's right. When subjects reached to the left, the left hand had shorter movement times. Early trajectory corrections were observed in the velocity profiles; the pattern was similar for both hands. These data are discussed in terms of visual processing abilities of the left and right cerebral hemispheres, and visual processing abilities when pointing and grasping.