Hierarchical Control of the Human Hand
Mark L. Latash, Ph.D.
Department of Kinesiology
Penn State University
Host: Boris Prilutsky
Time: noon-1pm Wednesday, November 11
Location: Student Center, room 320
Abstract:
Studies of human prehension have used the notion of a prehension synergy as a co-varied (across trials) adjustment of elemental variables that stabilizes their combined mechanical output. Prehension synergies were studied at two levels of a hypothetical control hierarchy. At the upper level, the thumb and the virtual finger (VF, an imagined digit with the mechanical action equal to the sum of the actions of the four fingers) generate elemental variables (forces and moments of force) that co-vary to stabilize the total force and moment of force exerted on the hand-held object. At the lower level, the forces and moments of force produced by the fingers co-vary to stabilize the action of the VF. Recent studies have demonstrated a trade-off between synergies at the two hierarchical levels. In particular, the resultant normal force acting on the hand-held object is stabilized by synergic adjustments of the thumb and VF forces, while VF normal force is not stabilized by such adjustments of individual finger forces. We explored these effects using unexpected unloading of quick lifting actions. Prehension synergies may be viewed as consequences of control with excitation thresholds for neuronal pools that lead to changes in referent values for salient variables. Such control can naturally lead to co-varied adjustments in elemental variables stabilizing their combined output.