New research suggests origin of hallucinations, delusions experienced by people with schizophrenia

Though persistent hallucinations and delusions are defining characteristics of schizophrenia and schizoaffective disorders, their origins are unknown. But something as simple as a bunch of moving dots might suggest how it is possible to see and hear things that are not there.

Imagine looking at a black screen with moving white dots on it. At first, many dots move to the right. Then, after a short amount of time, they switch to moving straight down.

“This task is simple, but not easy,” said Gi-Yeul Bae, assistant professor of psychology at Arizona State University. “Because not all the dots are moving toward the same direction, you need to keep paying attention and detect when the motion changes direction.”

Bae and collaborators recently published a study in JAMA Psychiatry using this task. The study shows that people diagnosed with schizophrenia or schizoaffective disorder had difficulties detecting motion changes that were easily reported by healthy control participants. This work suggests that hallucinations and delusions could result from the brain failing to update what is perceived based on new information, like a change in motion direction. 

“People with schizophrenia and schizoaffective disorder show different types of symptoms, including hallucinations and delusions, which are at a very basic level unusual perceptual phenomena,” Bae said. “This study tested the idea that hallucinations and delusions might happen because people fail to update perceptual information.”

The research team also measured the severity of psychotic symptoms experienced by the participants diagnosed with schizophrenia or schizoaffective disorder. Symptom severity was positively correlated with how frequently participants with schizophrenia or schizoaffective disorder did not report motion changes. 

“The proportion of times a participant with schizophrenia or schizoaffective disorder reported the initial motion direction, and not the change in motion, was significantly correlated with how severe their symptoms were,” Bae said.

The research team replicated the experiment with participants recruited from Baltimore and New Haven, Connecticut. The findings were the same in both experiments: People with schizophrenia or schizoaffective disorder were less likely to report changes in dot motion, unlike the healthy control participants.

“The replication of these findings provides strong evidence that sensory hallucinations and delusions might be rooted in a failure of updating perceptual evidence,” Bae said.

This study was a collaboration between the ASU Department of Psychology; University of Maryland School of Medicine; University of Chicago, Illinois; Yale University; and the University of California, Davis.