Posted by jeremy on February 6, 2011 8:35 pm.

… and yes, I failed it.

…recent advances in neuroimaging have made it possible to measure this difference between a schizophrenic’s brain and a healthy person’s brain.

The hollow-mask optical illusion is a simple test for the neurological dysfunction associated with schizophrenia. The visual senses of a person with a healthy brain will be overwhelmed by the illusion; a schizophrenic person reliably sees right through it.

What is the hollow-mask illusion? When a hollow mask is turned away from you, it will appear to be facing you; the nose, for example, will appear to be protruding from the mask. The illusion is so powerful that even if a test subject is told in advance what to look for, and even if he watches the illusion unfolding, his senses will still deceive him.

Try it yourself:

The brain activity responsible for the illusion

Mental health professionals have known about schizophrenics’ immunity to optical illusions like this one for some time. And now, recent advances in neuroimaging have made it possible to measure this difference between a schizophrenic’s brain and a healthy person’s brain.

A 2009 study of 29 volunteers used a functional MRI (fMRI) and a new analysis technique called dynamic causal modeling to identify how the volunteers process visual illusions. The results were conclusive, showing that schizophrenics’ failure to get taken in by the hollow mask illusion could be reliably detected.

A Science Daily article has a writeup for laymen:

[This] 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… … 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.

Caveats

Seeing through the illusion isn’t a completely reliable indicator of schizophrenia. Some alcoholic test subjects may not be fooled by the hollow mask illusion. Being under the influence of cannabis (marijuana) may also yield a false positive.