Time structure of a goal-directed bimanual skill and its dependence on task constraints

The aim of the study was to elucidate the underlying principles of bimanual coordination and to establish quantitative coordination criteria. Healthy human subjects were instructed to open a loaded drawer with the left hand a nd to grasp, lift and reinsert with the right hand a small peg in the drawe r recess. This bimanual goal-oriented task was executed promptly and consis tently after a few trials. The temporal structure of the individual limb ac tions was assessed for computing interlimb synchronization and temporal cor relation. In all subjects, both hands were well synchronized at the goal wi th high intermanual correlation in reaching the goal (event times of drawer opening and grasping the peg). This temporal goal-invariance was independe nt of movement speed and of the highly variable timing of the individual ha nds and persisted when subjects were blindfolded. Unilateral loading of the pulling hand and cutaneous anesthesia of the left index finger and thumb u sed for grasping the drawer handle significantly increased the pull-phase. This slowing of the left hand was matched by an adaptive delay of the right non-disturbed hand, thus preserving goal invariance. As a working hypothes is, we propose that multimodal sensory signals generated in the leading arm be transmitted centrally to re-parameterize the non-disturbed arm. (C) 199 9 Elsevier Science B.V. All rights reserved.