A massive study has debunked the leading theory that hallucinations are caused by the brain trusting its own expectations too much.
April 1, 2026
Original Paper
Reliance on Prior Expectations in Psychosis: A Systematic Review and Meta-Analysis of Perceptual Tasks
medRxiv · 10.64898/2026.03.31.26349835
The Takeaway
The 'predictive processing' theory is a cornerstone of modern psychiatry, suggesting the brain ignores reality in favor of internal expectations to create hallucinations. This meta-analysis of nearly 2,000 people found no evidence for this imbalance, essentially dismantling one of the most influential models of how the psychotic brain works.
From the abstract
Background: The highly influential predictive processing theory of psychosis posits that symptoms arise from imbalances in the weighting of predictions (priors) and sensory evidence. Despite this theory's increasing prominence, studies often present conflicting results. This is particularly problematic as findings from single tasks with modest sample sizes are frequently used to advance a theory for a generalised altered reliance on priors in psychosis. Methods: This study presents a random-effe