Figure 4.

Models of predictive coding. (A) A framework of predictive coding based on movement initiation. A motor command signal (bottom left) triggers motor execution (solid arrow) and sends a copy of the motor command to sensory cortices (efference copy or corollary discharge, dashed arrow). The forward model converts the motor command to a pattern of predicted sensory input. This predicted sensory input is subtracted from the feedforward sensory input, canceling out the reafferent (self-generated) component. Unexpected signals, not predicted by self-generated movement, are not subtracted and therefore propagate forward. Efference and prediction signals are carried by feedback pathways (dashes arrows) whereas sensory signals are carried by feedforward pathways (solid arrows). (B) A framework of predictive coding based on sensory expectation. Sensory expectation evokes signals reflecting the pattern of predicted sensory input, to subtract from afferent sensory input. Unexpected signals, not predicted by sensory expectation, are not subtracted and therefore propagate forward. Prediction signals are carried by feedback pathways (dashes arrows) whereas sensory signals are carried by feedforward pathways (solid arrows).