Schizophrenia sufferers aren’t fooled by an optical illusion known as the “hollow mask” that the rest of us fall for because connections between the sensory and conceptual areas of their brains might be on the fritz.
In the hollow mask illusion, viewers perceive a concave face (like the back side of a hollow mask) as a normal convex face. The illusion exploits our brain’s strategy for making sense of the visual world: uniting what it actually sees — known as bottom-up processing — with what it expects to see based on prior experience — known as top-down processing.
"Our top-down processing holds memories, like stock models," explains Danai Dima of Hannover Medical University, in Germany, co-author of a study in NeuroImage. "All the models in our head have a face coming out, so whenever we see a face, of course if has to come out."
This powerful expectation overrides visual cues, like shadows and depth information, that indicate anything to the contrary.
But patients with schizophrenia are undeterred by implausibility: They see the hollow face for what it is. About seven out of 1000 Americans suffer from the disease, which is characterized by hallucinations, delusions, and poor planning. Some psychologists believe this dissociation from reality may result from an imbalance between bottom-up and top-down processing — a hypothesis ripe for testing using the hollow mask illusion.
In healthy viewers, the illusion is so powerful that even when aware of the illusion (see video below), they are unable to see the concave face — the mind just flips it back. Though the illusion is strong for faces, it doesn’t work well with other objects, or even with upside-down faces. This bias is likely due to the special relationship we humans have with faces. Many neuroscientists believe we have brain regions dedicated to processing faces, and some brain injuries can leave patients unable to recognize faces, even though their vision and other memories remain intact.
Dima and Jonathan Roiser of University College London wanted to understand why people with schizophrenia aren’t fooled. They put 13 schizophrenia patients and 16 healthy control subjects in an fMRI scanner that measures brain activity, and showed them 3D images of concave or convex faces. As expected, all of the schizophrenic patients reported seeing the concave faces, while none of the control subjects did.
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Originally Posted by Suzanimal
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