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Hallucinations may emerge by attempts to make sense of an ambiguous world.

Psychosis is sometimes accompanied by changes in perception, to the extent that people may see, feel, smell and taste things that are not actually there - hallucinations. To make sense of ambiguous stimuli we use our sensory information and information about prior knowledge of the environment to represent the world more clearly. For example, we discern a fast-moving black shape as the cat, even though the visual input was blurry, our prior knowledge did the extra creative work.

"Having a predictive brain is very useful to build a coherent picture of an ambiguous and complex world. But it means we are not far away from perceiving things that aren't actually there - hallucinations” Professor Paul Fletcher from University of Cambridge.

Look at the black and white image. It probably looks like a meaningless pattern of black and white blotches. But now take a look at the image on the left and return to the picture: now you can make sense of it. Researchers at Cardiff University and University of Cambridge believe this could help explain why some people are prone to hallucinations. Participants were shown various ambiguous black and white pictures and then shown the full colour versions but were not told the connected between the pictures. Participants with early signs of psychosis were more likely to use the colour picture to make sense of the ambiguous black and white picture.  This may be because hallucinations come from a greater tendency to superimpose predictions on the world, so people who were prone to hallucinations would be better at using this information. Within the healthy population, tasks scores were on a continuum and may be used to detect early onset of psychotic symptoms. This may suggest that the emergency of symptoms in psychosis may be a result of altered balance of brain functions. Also, most importantly, this does not suggest a ‘broken’ brain but one that is working extra hard to make sense of the incoming stimuli that is ambiguous.

Click here for the journal article.

Click here for the news article.


By: Abigail Christine Wright
Last updated: Friday, 30 October 2015

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