Hollow mask illusion fails to fool schizophrenia patients

Hollow mask illusion fails to fool schizophrenia patients

April 6th, 2009 in Medicine & Health / Neuroscience

Patients with schizophrenia are able to correctly see through an illusion known as the 'hollow mask' illusion, probably because their brain disconnects 'what the eyes see' from what 'the brain thinks it is seeing', according to a joint UK and German study published in the journal NeuroImage. The findings shed light on why cannabis users may also be less deceived by the illusion whilst on the drug.

People with schizophrenia, a mental illness affecting about one per cent of the population, are known to be immune to certain vision illusions. The latest study confirms that patients with schizophrenia are not fooled by the 'hollow mask' illusion, and that this may relate to a difference in the way two parts of their brains communicate with each other - the 'bottom-up' process of collecting incoming visual information from the eyes, and the 'top-down' process of interpreting this information.

Illusions occur when the brain interprets incoming sensory information on the basis of its context and a person's previous experience, so called top-down processing. Sometimes this process can mean that people's perception of an object is quite different to reality - a phenomenon often exploited by magicians. The new study, by scientists at the Hannover Medical School in Germany and UCL Institute of Cognitive Neuroscience in the UK, suggests that patients with schizophrenia rely considerably less on top-down processing during perception.

The study used a variation on the three-dimensional 'hollow mask' illusion. In this illusion, a hollow mask of a face (pointing inwards, or concave) appears as a normal face (pointing outwards, or convex). During the experiment, 3D normal faces and hollow faces were shown to patients with schizophrenia and control volunteers while they lay inside an fMRI brain scanner, which monitored their brain responses.

As expected, all 16 control volunteers perceived the hollow mask as a normal face - mis-categorising the illusion faces 99 percent of the time. By contrast, all 13 patients with schizophrenia could routinely distinguish between hollow and normal faces, with an average of only six percent mis-categorisation errors for illusion faces.

The results of the brain imaging analysis suggested that in the healthy volunteers, connectivity between two parts of the brain, the parietal cortex involved in top-down control, particularly spatial attention, and the lateral occipital cortex involved in bottom-up processing of visual information, increased when the hollow faces were presented. In the patients with schizophrenia, this connectivity change did not occur. These results suggest that patients with schizophrenia have difficulty coordinating responses between different brain areas, also known as 'dysconnectivity', and that this may contribute to their immunity to visual illusions. The research group is now investigating dysconnectivity in schizophrenia further, which will hopefully advance our understanding of this disorder.

Danai Dima, Hannover Medical School, says: "The term 'schizophrenia' was coined almost a century ago to mean the splitting of different mental domains, but the idea has now shifted more towards connectivity between brain areas. The prevailing theory is that perception principally comprises three components: firstly, sensory input (bottom-up); secondly, the internal production of concepts (top-down); and thirdly, a control (a 'censor' component), which covers interaction between the two first components. Our study provides further evidence of 'dysconnectivity' between these components in the brains of people with schizophrenia."

Dr Jonathan Roiser, UCL Institute of Cognitive Neuroscience, says: "Our findings also shed light on studies of visual illusions which have used psychomimetics - drugs that mimic the symptoms of psychosis. Studies using natural or synthetic tetrahydrocannabinol (THC), the ingredient of cannabis resin responsible for its psychotic-like effects, have found that people under the influence of cannabis are also less deceived by the hollow mask illusion. It may be that THC causes a temporary "disconnection" between brain areas, similar to that seen in patients with schizophrenia, though this hypothesis needs to be tested in further research."

Often, schizophrenia and multiple personality disorder (MPD) are confused, and some people believe they are the same. In reality, they are two distinctly different disorders. Schizophrenia is a brain disorder that some people are born with -- it may be inherited, but symptoms don't usually develop for many years. In men, symptoms often develop in late adolescence or the early 20s; for women, symptoms often appear in the 20s or 30s. Sometimes, symptoms do develop during childhood, but this is rare.

When a person has schizophrenia, he experiences hallucinations and delusions, seeing things that aren't there and believing things that are clearly not true. For example, he may see demons sitting next to him at dinner or believe he is the son of God. A person with this condition also suffers from disordered thinking, decreased attention span, and problems with focusing. Typically, those with this disorder withdraw socially. It's also common for those with this condition to appear expressionless and lose their ability to initiate and carry out plans.

Often, a person with schizophrenia will believe the voices that he hears are working to control or harm him. He is likely to be very fearful. He may sit for hours without moving or talking, and he may not make sense when he does speak. However, some people with this disorder exhibit what seems like normal behavior until they start talking and others learn what they are thinking. This disorder is also marked by clumsy, uncoordinated movement and an inability to care for oneself or work a job.

A major difference between multiple personality disorder and schizophrenia is that those with multiple personality disorder aren't born with it. This mental condition is induced by something that happens in life, and it is usually related to a trauma that occurs during childhood, such as physical or sexual abuse. A patient with this disorder develops additional personalities as a way of coping with the traumatic event. To be diagnosed with MPD, a person must have at least one alter personality that controls the person's behavior at times.

A person with MPD may develop as many as 100 personalities, but the average is 10. She may take on alter personalities of the same sex, a different sex, or both sexes at the same time. Sometimes a MPD patient even takes on the physical characteristics of her different personalities, such as a certain way of walking or moving. Additionally, depression and self-mutilation are common.

There are some ways that schizophrenia and multiple personality disorder are alike. A person with schizophrenia is likely to have hallucinations, and while hallucinations are not present in all cases of MPD, about one third of patients do experience them. People with MPD may also develop behavioral problem in childhood as well as difficulty concentration on schoolwork. This may cause some to confuse the disorder with schizophrenia, as these issues often develop in child or teenage schizophrenics as well.

The age of onset of the two disorders is a major difference. While schizophrenia is more likely to develop in those who are approaching adulthood or are already in their 20s or 30s, the average age of onset of multiple personality disorder is 5.9. However, people with both conditions are alike in that they are more likely to attempt suicide.