Switching between the modes of control: Implications for the closed loop control of prostheses

From the point of view of a theory of human operator, closed loop control of an upper limb prosthesis is an interesting and challenging control task. Namely, the user has to switch between the two different controlled systems, i.e., the opening and closing of the hand is controlled via an integrator (first order system), while the force control is proportional (zero order system). Our goal was to investigate how the switching between different control modes affects the overall control performance. To test this experimentally, we have used a visuomanual tracking task. The preliminary results (collected from 3 subjects) show that both control modes can be learned quite easily. However, during switching, there is a significant performance drop, especially when changing from the first order to zero order system. This research can provide insights into the mechanisms relevant for the closed loop control of prosthesis and user training.