SURREALIST paintings may never be the same again. Scientists have deciphered the secret behind how the brain can be tricked by optical illusions.
Psychologists at Glasgow University used advanced brain-imaging technology to map the brainwaves of volunteers as they looked at surreal images.
They found that the participants' brains absorbed all the information from a painting by breaking it down into separate "brainwaves", tiny electrical impulses in the brain.
But the researchers claim that while all the brainwaves occur at once, the brain is only able to decode one at a time, meaning the volunteers could only concentrate on a single aspect of the painting.
Dr Phillipe Schynes, who led the project, claims this explains why the brain is so easily fooled by optical illusions featuring hidden images that seem difficult to miss once they are noticed.
Examples include the picture where viewers will either see two faces opposing each other or a vase.
Schynes believes the brain has to switch between these brainwaves in order to "see" another part of the image, explaining why people experience a sudden moment of clarity.
He now hopes to use the research to understand why people can recognise faces. He believes that familiar faces trigger brainwaves that are easier for the brain to decode than unfamiliar ones, giving a feeling of recognition.
"We are really examining how the brain processes information and interprets images," he said. "In ambiguous paintings, people will see two possible interpretations of a painting but they will not see both at once.
"The brainwaves associated with one part of a painting may be slow, while another part may be fast. Although both sets of waves are created at the same time, the brain is only sensitive to one at a time, so it has to switch between them in order to see each, but cannot see both at once."
The study used paintings by artist Salvador Dali, who regularly hid images in his paintings as optical illusions, to examine brain activity.
When volunteers stared at his Slave Market with the Disappearing Bust of Voltaire, they either saw a scene featuring two nuns at the centre or the face of the great 18th-century French philosopher Voltaire.
They never saw both at once.
By breaking the painting down into two components, the researchers were able to measure the frequency of brain activity associated with each part.
They found that while the nuns sparked fast brainwaves, the brain activity produced by the parts of the painting necessary to see Voltaire were far slower.
Brain mapping techniques showed that due to these differences, the brain was only able to cope with one kind of brainwave at a time. Those that saw the nuns had to "switch" to the other kind of brainwaves to see Voltaire.
Schynes, who has helped to set up a neuro-imaging unit at Glasgow University to study the human brain, added: "Each person will use different parts of the same image before they can perceive it. By masking all other parts of the painting we were able to isolate the information that each volunteer needed to see either the nuns or Voltaire.
"We were able to break down that information and work out how the brain responded to those pieces of information."
Professor Dawn Ades, an expert on optical illusions in art at Essex University, said: "This is a very interesting discovery. Dali produced many double images which were brilliant exercises in the mysteries of perception."