Schizophrenics 'spot illusions'

Despite experiencing hallucinations as part of their condition, schizophrenic volunteers to a study were better able to spot "real" visions than others.

The 'Current Biology' work could help shed light on the brain mechanisms involved in schizophrenia, the UCL authors say.

It might be down to a difficulty dealing with context, they believe.

For example, people with schizophrenia tend to take less account of the circumstances and conditions that surround a situation or event that often help us to interpret it.

This could explain why some people with schizophrenia might misattribute people's actions or feel persecuted.

It could also explain why they perform better on visual illusion tests, says Dr Steven Dakin, of the UCL Institute of Ophthalmology.

"We often think of people with schizophrenia as not seeing the world the way it really is. But we have shown that sometimes their vision can be more accurate than non-sufferers." …

His team used an illusion where a failure to use context worked to the advantage of people with schizophrenia. …

The participants were asked to select which of one of eight peripheral patterned discs was the best match for a central patterned disc that was located within the middle of a larger "distracting" patterned circle.

The illusion works because normal visual perception leads the individual to believe that the central disc is of lower contrast than it actually is because it is set against a higher-contrast background - the distracting circle.

Of the 15 volunteers with chronic schizophrenia, 12 were found to make more accurate judgments than the most accurate person in the control group of 33 non-schizophrenic volunteers.

Dr Dakin said: "Our findings may shed some light on the brain mechanisms involved in schizophrenia.

"Normally, contextual processes in the brain help us to focus on what's relevant and stop our brains being overwhelmed with information.

"This process seems to be less effective in the schizophrenic brain, possibly due to insufficient inhibition - that is, the process by which cells in the brain switch each other off." …

BBC Online