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Last Updated: Tuesday, 25 October 2005, 07:24 GMT 08:24 UK
Schizophrenics 'spot illusions'
The work could help explain some schizophrenia symptoms
People with schizophrenia may be well attuned to spotting visual illusions, a study suggests.

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 University College London authors say.

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

Their vision can be more accurate than non-sufferers
Researcher Dr Steven Dakin

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 mis-attribute people's actions or feel persecuted.

It could also explain why they perform better on visual illusion tests, says Dr Steven Dakin, of UCL's 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."

The people with schizophrenia were better at spotting that the true match for the central target disc was the peripheral disc at 6 o'clock, while others often mistook the peripheral disc at 10 o'clock as the best match

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

He said this was critical because people can perform poorly for lots of reasons, but superior performance tends to be for a specific reason and is more revealing of the underlying cause.

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.

Better performance

Of the 15 volunteers with chronic schizophrenia, 12 were found to make more accurate judgements 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."

Paul Corry, of the charity Rethink, said: "We welcome any new research or progress into understanding the causes of schizophrenia, but it would need to be checked before it would make a difference to the thousands of people living with severe mental illness in the UK.

"In the meantime, reaching people early with the right care and treatment is the best way of recovering a meaningful and fulfilling life."

20 Dec 00 |  Medical notes

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