Figure 6. Controlling a biophysical model of the human arm.
(A) (top left): A model of the human upper skeleton with 4 degrees of freedom (shoulder and elbow joints), actuated by 16 muscles at the shoulder, chest and arm (colored strings represent muscles; blue indicates low activation, red indicates high activation). The task is to reach either of two target balls (blue or red), depending on a context input. (B) (top right): During training, the error (measured by the distance between tip of hand and target ball at the end of each trial) improves immediately and reaches a low residual plateau after about 3000 trials. (C) (bottom): frame-by-frame illustrations of a right-target trial (top row) and a left-target trial (bottom row), after training.