Optical illusions are fascinating because of their ability to suspend reality tricking people into seeing a false image.
And research indicates that one particular illusion fails to fool those who suffer from schizophrenia.
The hollow mask is an illusion in which healthy viewers (i.e. the majority) perceive a convex, rather than a concave face - while those with schizophrenia see it for what it really is.
The average brain perceives the world using a combination of bottom-up (what it sees) and top-down processing (the expectation based on experience), Wired reports.
Danai Dima, Hannover Medical University and Jonathan Roiser of UCL put 16 healthy subjects and 13 schizophrenia patients through an fMRI machine, and measured their brain activity when they were presented with the image.
Our top-down processing holds memories, like stock models, all the models in our head have a face coming out, so whenever we see a face, of course it has to come out.
When a healthy person looked at the image, links strengthened between the top-down process and the visual areas of the brain receiving the image.
Such is the strength of the connection, it makes the person perceive the illusion even when they know it to be one.
A schizophrenia patient however, prone to delusions and hallucinations, does not have this connection, and sees the image as it is.
Whether an image appears to be moving, growing or changing colour, scientists continue to use optical illusions as a way to understand how the brain works.