Cardiff University study on the science of hallucinations
Scientists at Cardiff University believe they can help explain why some people are prone to hallucinations.
Researchers worked with colleagues at the University of Cambridge to study the predictive nature of the brain.
They looked at the idea that hallucinations happen due to the brain's tendency to interpret the world using prior knowledge and predictions.
The study examined whether the brain creating this image of the world contributes to people's psychosis.
Research published on Monday in the journal Proceedings of the National Academy of Sciences studied 18 people who suffered from very early signs of psychosis who had been referred to a mental health service run by the Cambridgeshire and Peterborough NHS Foundation Trust.
They compared them to 16 healthy volunteers and asked them if they could make sense of vague black and white images.
All of them were then shown the full colour original picture to improve the brain's ability to understand the ambiguous image.
There was a larger performance improvement in people with early signs of psychosis compared to the healthy control group.
The University of Cambridge's Naresh Subramaniam said: "These findings are important because, not only do they tell us that the emergence of key symptoms of mental illness can be understood in terms of an altered balance in normal brain functions.
"Importantly, they also suggest that these symptoms and experiences do not reflect a 'broken' brain but rather one that is striving - in a very natural way - to make sense of incoming data that are ambiguous."
Look at the picture. Can you see anything?
Now look at the photograph below before taking another look. Scientists say it is likely that you can now make sense of it.
It is the brain's ability to fill in the blanks that could help explain why some people suffer from hallucinations.
One of the study's authors, Dr Christoph Teufel, from Cardiff University, said: "Vision is a constructive process - in other words, our brain makes up the world that we 'see'.
"It fills in the blanks, ignoring the things that don't quite fit, and presents to us an image of the world that has been edited and made to fit with what we expect."
An example of this would be a person walking into their living room and identifying a fast-moving black shape as their cat, despite the fact the visual information was no more than a blur.
The sensory input was minimal and prior knowledge did the creative work.
Prof Paul Fletcher of the University of Cambridge said: "Having a predictive brain is very useful - it makes us efficient and adept at creating a coherent picture of an ambiguous and complex world.
"But it also means that we are not very far away from perceiving things that aren't actually there, which is the definition of a hallucination."
He added that "altered perceptual experiences" are not limited to people with mental illnesses, but have been seen in a milder form across the whole population.