Schizophrenia: Delusion without illusion

October 25, 2005

British scientists say schizophrenics aren't fooled by a visual illusion and can judge it more accurately than can non-schizophrenic observers.

The study by University College London and King's College London researchers suggests in everyday life, schizophrenics take less account of visual context. If this is part of a more general failure to deal appropriately with context, it could explain why some sufferers misattribute people's actions or feel persecuted.

The researchers used an illusion in which an object's contrast appears reduced by its surroundings. A medium-contrast patterned disc was shown to volunteers, who had to judge its appearance in the presence of a high-contrast background. Of 15 participants with chronic schizophrenia, 12 were found to make more accurate judgments than the most accurate person in a control group of 33 non-schizophrenic volunteers.

Dr Steven Dakin of the UCL Institute of Ophthalmology says: "We often think of people with schizophrenia as not seeing the world the way it really is -- for example, during hallucinations -- but we have shown that sometimes their vision can be more accurate than non-sufferers."

The study appears in the journal Current Biology,

Copyright 2005 by United Press International

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