The delusions and distortions of reality reported by people who suffer from psychosis are one of the most difficult aspects of the illness from the standpoint of the patient. No one wants to be told that what they perceive in the world around them is either not real or is in some fundamental way inaccurate or distorted.

As researchers have long known from observation of patients, their "delusions are tenaciously maintained, even in the face of clear evidence" that refutes their reality. This is the starting point for new research by 2020 BBRF Young Investigator Sonia Bansal, Ph.D., of the University of Maryland School of Medicine, and colleagues. She was first author of the team's paper in JAMA Psychiatry; James M. Gold, Ph.D., a 1997 BBRF Young Investigator, was the team's senior member.

Drs. Bansal, Gold and colleagues wanted to know more about the relationship between psychosis symptoms like delusions and hallucinations and mechanisms in the brain that process perceptions on a real-time basis. They note recent research suggesting that delusions and hallucinations may result from alterations in the way prior knowledge is integrated with new information.

At issue, they explained, is whether this is the result of problems with perceptual mechanisms or higher-order reasoning processes.

By comparing individuals diagnosed with schizophrenia or schizoaffective disorder who suffer delusions and/or hallucinations and comparing them with healthy controls, the researchers sought to discern any difference in the two groups' ability to update beliefs based on new evidence.

To make this determination, the team chose a relatively simple perceptual task, which they asked a total of 160 individuals in two independent samples to perform. Ninety of the participants were patients and the remainder were demographically matched controls; the average age was about 35, and a majority were male.

It was important to the team that the task they assigned participants posed minimal demands on conscious reasoning ability. In this way they could hope to capture potential problems in the processing of perceptions. The task called upon subjects to repeatedly respond to brief half-second or one-second trials, all of which involved dots in motion across a computer monitor. For each trial, participants were instructed simply to report the direction of the dots' motion at the end of the trial.

This was potentially revealing because in half of the trials, the direction of the dots did not change ("no-change trials"). But in the other half of the randomly assigned trials ("change trials"), the direction of 35% of dots shifted 90 degrees halfway through the trial. The question was: would those who suffered from delusions and hallucinations be able to update their initial impressions in trials in which dots suddenly changed direction?

The team found that those with psychosis tended to overweight initial information coming from sensory evidence in the "change trials," and thus tended to be unable to correctly report the change in the dots' direction.

The team interpreted this result as follows: "Even in a relatively simple perceptual paradigm patients with psychotic disorder fail to update their perceptual beliefs when faced with new information." They went on to note that the degree of updating failure was correlated with the severity of patients' symptoms and their degree of conviction about delusions they had previously experienced.

"This suggests that the severity of psychosis may reflect a fundamental alteration of basic perceptual and cognitive processes," the researchers suggested.

For a variety of reasons, the team rejected other possible explanations for the observed result. One was that patients with psychosis might be more likely to report the dots' initial direction of motion because of another symptom of the illness, slower neural processing speed. In this scenario, the patients might not have had enough time to process the second direction of the dots. But if this were the case, the team said, it would be more likely they would report the second direction, not the first.

In the end, the team said its results "suggest that failure to integrate new sensory evidence with prior knowledge may be associated with psychotic symptoms in schizophrenia."

The team also included Phillip Corlett. Ph.D., 2008 BBRF Young Investigator; Molly Erickson, Ph.D., 2017 BBRF Young Investigator; and Britta Hahn, Ph.D., 2010 BBRF Young Investigator.