“Extrinsic Dexterity” is a way to get dexterous manipulation with a very simple hand, by coordinating finger motion with arm motion. The more common approach is to depend entirely on the fingers of the hand, which requires at least three fingers and at least nine motors. We have demonstrated Extrinsic Dexterity using the single motor of the MLab Hand, coordinated with the motions of the arm.
Extrinsic Dexterity can take many forms: using contact with obstacles to shift the object, using gravity to pivot the object in the grasp, or roll along the fingers from one grasp to another, or even using aggressive arm motions to execute controlled throws from one grasp to another. For demonstrations of these see the video at http://youtu.be/WAPgjZCI1gI
So far we have demonstrated the mechanical feasibility of Extrinsic Dexterity, and have just begun to explore the issues in perception, control, planning and learning.