Table 1.

Predictive Coding and Positive Symptoms: Theory and Controversy

Symptom	Feature	Theory	Literature	Controversy
Hallucinations	Percepts without external stimulus	Strong perceptual priors	Powers et al.(120)	Entails weak and strong prior beliefs—for perception and action—in the same brain at the same time
	Speech from external agents	Weak corollary discharge	Thakkar et al.(86)
Delusions	Delusional mood/aberrant salience	Weak perceptual priors	Corlett et al.(121)	Necessitates a transition from weak to strong priors as delusions form, foment, and become ingrained
	Fixed in the face of contradictory evidence	Strong memory reconsolidation/strong conceptual priors	Corlett et al.(103); Schmack et al.(72)

Here we highlight the facets of hallucinations and delusions that have been addressed by predictive coding–based theories. Each has garnered empirical support; however, overarching theories—grounded in a broader multisensory and enactive framework that can accommodate the evolution and trajectories of positive symptoms—are required. We focus here on hallucinations and delusions. For consideration of other psychotic symptoms such as thought disorder and passivity phenomena from the viewpoint of predictive coding, please see Griffin and Fletcher (109) and Sterzer et al.(13).