Perturbed reaching in real robot.

<p>(A) and (D) Joint angular error (RMS within each trial) during the 650 repetitions: 50 trials without force field, then 400 with a viscous force field (force field c₁ and force field c₂) and the last 200 again with null force field. The last phase clearly shows the after-effect phenomenon, occurring when the perturbation was suddenly canceled after a complete acquisition. For each force field, the curve is the average on the 12 tests, and the area is the standard deviation. (B) and (E) For each force field, Cartesian trajectories on the xz plane in some representative trials: ideal trajectory in dashed green, 1^st perturbed trial (51^st) in thick red, last perturbed trial (450^th) in thin red, 1^st re-unperturbed trial (451^st) in thick blue, last trial (650^th) in thin blue. (C) and (F) Raster plot of the recorded network activity (excluding the 1500 GRs), in one repetition (430^th repetition), where the acquisition had been completed, characterized by a stable compensation of the constant external perturbation. There was still an error (negative and positive), but the IOs fired at a very low rate. The DCN activity was evident almost only on the negative DCNs, which produced a negative corrective torque on the third joint, able to counterbalance the viscous force fields.