Fig. 2.

This figure shows the results of simulated action (writing), under active inference, in terms of conditional expectations about hidden states of the world (b), consequent predictions about sensory input (a) and the ensuing behavior (c) that is caused by action (d). The autonomous dynamics that underlie this behavior rest upon the expected hidden states that follow Lotka–Volterra dynamics: these are the six (arbitrarily) colored lines in b. The hidden physical states have smaller amplitudes and map directly on to the predicted proprioceptive and visual signals (a). The visual locations of the two joints are shown as blue and green lines, above the predicted joint positions and angular velocities that fluctuate around zero. The dotted lines correspond to prediction error, which shows small fluctuations about the prediction. Action tries to suppress this error by ‘matching’ expected changes in angular velocity through exerting forces on the joints. These forces are shown in blue and green in d. The dotted line corresponds to exogenous forces, which were omitted in this example. The subsequent movement of the arm is traced out in c; this trajectory has been plotted in a moving frame of reference so that it looks like synthetic handwriting (e.g. a succession of ‘j’ and ‘a’ letters). The straight lines in c denote the final position of the two jointed arm and the hand icon shows the final position of its extremity. (Color figure online)