Schizophrenia - Delusion without illusion

Main Category: Schizophrenia
Article Date: 26 Oct 2005 - 0:00 PDT

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Scientists have discovered that schizophrenia sufferers are not fooled by a visual illusion and are able to judge it more accurately than non-schizophrenic observers. The study by UCL (University College London) and King's College London suggests that 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 might misattribute people's actions or feel persecuted.

The study, published in the journal Current Biology, used an illusion where 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 the 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 trick here was to use an illusion where a failure to use context worked to the advantage of people with schizophrenia. 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.

"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."

1 For more information or to set up an interview, please contact Jenny Gimpel at the UCL Media Relations Office on +44 (0)20 7679 9739, Mobile +44 (0)7990 675 947, Out of Hours: +44 (0)7917 271364 or e-mail j.gimpel@ucl.ac.uk.
2. 'Weak suppression of visual context in chronic schizophrenia', by Steve Dakin, Patricia Carlin and David Hemsley, is published in Current Biology on the 25th October 2005. To obtain copies of the paper please contact Heidi Hardman on hhardman@cell.com or tel: +1 617 397 2879.
3. Images of a visual illusion are available from the UCL Media Relations Office.

About UCL

Founded in 1826, UCL was the first English university established after Oxford and Cambridge, the first to admit students regardless of race, class, religion or gender, and the first to provide systematic teaching of law, architecture and medicine. In the government's most recent Research Assessment Exercise, 59 UCL departments achieved top ratings of 5* and 5, indicating research quality of international excellence.

UCL is the fourth-ranked UK university in the league table of the top 500 world universities produced by the Shanghai Jiao Tong University. UCL alumni include Mahatma Gandhi (Laws 1889, Indian political and spiritual leader); Jonathan Dimbleby (Philosophy 1969, writer and television presenter); Junichiro Koizumi(Economics 1969, Prime Minister of Japan); Lord Woolf (Laws 1954 - Lord Chief Justice of England & Wales), Alexander Graham Bell (Phonetics 1860s - inventor of the telephone), and members of the band Coldplay.

About King's College London

King's College London is one of the two oldest and largest colleges of the University of London with over 13,800 undergraduate students and nearly 5,700 postgraduates in nine schools of study. It is a member of the Russell Group: a coalition of the UK's major research-based universities.

The College has had 24 of its subject-areas awarded the highest rating of 5* and 5 for research quality, demonstrating excellence at an international level, and it has recently received an excellent result in its audit by the Quality Assurance Agency. King's is in the top group of UK universities for research earnings, with income from grants and contracts of £100 million, and has an annual turnover of more than £348 million. In 2004 the College was once again awarded an AA- financial credit rating from Standard & Poor's.

ucl.ac.uk

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