Figure 1.

A hypothetical model of hierarchical action–perception loops. Forward models receive the current state (dash-dot arrows) and an efference copy (dotted arrows) from lower loops and send their predicted state to higher loops; inverse models receive a copy of the current state (dashed arrows) and the goal state (solid arrows) from higher loops and send the motor command to lower loops. The same model can also be interpreted in a different manner: higher motor regions (inverse models) send motor commands (solid arrows) to lower motor regions and collateral efference copies (dotted arrows) to sensory regions (forward models). Lower sensory regions send predictions (dash-dot arrows) to higher areas and collateral motor commands (dashed arrows) to motor regions. Hence the ascending predictions (dash-dot arrows) can be viewed as efference copies of their collaterals (dashed arrows). The two views emphasize the inability to separate sensory/perception from motor/action in such hierarchical loops.