Figure 3.

Initial response. Contact force profile against the unexpected softer environment. (A–F) Black lines: Parallel control model results. Gray lines: the effect of initial exposure to the compliant environment that would result from the force term alone, i.e., without the position control term. It is an ideal force controller that reduces to zero the limb's impedance at the point of contact. (G–L) Experimental results (mean ± s.d. over all subjects) with (darker intervals) and without visual feedback. Subjects undershot the target force in the required forward (G) direction and an erroneous component on the lateral (H) direction as predicted by the model. The results are confirmed by the motion trajectory (D–F,J–L). The panels on the right (C,F,I,L) display the vector plots of the applied forces and endpoint motions.