Predictive coding architecture for inference in hierarchical models. Each level in the hierarchy is located in a different brain region. Each region has a population of error units and a population of causal units. The error units are hypothesised to reside in superficial cortical laminae and causal units in deep laminae. Error units receive messages from the state units in the same level and the level above, whereas state units are driven by error units in the same level and the level below. The person near the centre of the image would be difficult to see without a top-down prediction that there was somebody walking along the path. This prediction may be derived from previous time steps, hence the need for dynamic models, or from higher level scene knowledge that people walk on paths.
