Schematic model of hierarchical predictive processing in both a healthy context (left) and in the presence of a persecutory delusion (right). Arrows depict feedback signaling of priors and feedforward signaling of prediction errors (PEs), with arrow thickness indicating their relative precision. In the healthy model, prediction errors at both perceptual and cognitive levels guide continuous updating of beliefs in a balanced manner. By contrast, in the persecutory delusion example, auditory input, such as the sound of footsteps, leads to a low-level belief of being followed, which informs the high-level belief of being tracked by the government. Here, high-level priors gain excessive precision, compensating for the decreased precision priors of low-level beliefs and thus dominating interpretation of uncertain inputs.
