Why Do We Hallucinate? | IFLScience

For those with certain mental illnesses, like schizophrenia, perceiving things – sights, smells and tastes – that aren’t there can be a common, and often terrifying, experience that comes with psychosis, a loss of contact with external reality. But what underlies these psychotic experiences? A new study is offering us some insight, suggesting that people prone to psychosis display visual perception that favors prior knowledge, rather than the available incoming sensory evidence.