Feedforward adaptation to stable and unstable dynamics in arm movements

In daily life, humans must compensate for the resultant forces arising from interaction with the physical environment. Recent studies have shown that humans can acquire a neural representation of the relation between motor command and movement, i.e. learn an internal model of the environment dynamics. The present paper discusses the feedforward adaptation under a varying dynamical environment during reaching movements. Subjects first learned reaching movements in a position-dependent divergent force field (DF) and velocity-dependent force field (VF), and then in a switched force field SF1 (DF→VF) and SF2 (VF→DF). The experimental results show that the adaptation to the switched force fields has been achieved by combining the internal model-based control and the impedance control in a feedforward manner.