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The optical illusion that can ‘test for schizophrenia’

Important: This illusion should not be used as a diagnosis tool for Schizophenia or any other mental health issue and Lenstore accepts no liability for its use. Always consult a medical professional in matters relating to mental health.

There’s a good chance you’ve seen a version of the “hollow mask” illusion before. In the most common variant, you’re presented with what appears to be a slowly rotating, concave face. However, as the face turns, it quickly becomes clear you’ve been looking at the back side of a hollow mask.

It’s an impressive illusion for most, but not everyone is fooled. Studies show that the effect is weakened for schizophrenia sufferers, as many are able to consistently perceive the concave object instead of the convex illusion.

Concave convex optical illusion masksThe hollow mask illusion takes advantage of our brain’s tendency to find patterns in what we see. We recognise the visual cues in front of us from past experience. Our brains assume that, because the vast majority of faces we’ve seen are convex, this face is probably convex too.

This effect is so strong that it overrides obvious cues that reveal the mask’s concave shape. Things like mismatched shadows are ignored in favour of seeing what our brains expect to see. This process is referred to as top-down processing.

Schizophrenia sufferers have a lessened ability to automatically interpret images based on visual experience. Because of this, they instead see the concave mask for exactly what it is.

“Under normal conditions, cognitive factors apparently override the binocular disparity cues,” concludes a research study led by U. Schneider of the Medical School of Hannover. “This internal mechanism… appears to be disturbed in psychotic states.”

The same research study also found that schizophrenic patients under successful treatment were more likely to see the illusion. “The inversed faces were seen as more illusionary, driven by an increase in top–down processing.” By the end of treatment, researchers found no significant difference between the schizophrenic patients and healthy control group’s perception of the illusion.

Although the perception of this illusion has been linked with the symptoms of schizophrenia, it should not be used as a conclusive tool for diagnosis. If you’re ever worried about your own mental health, you should always contact a medical professional.

1 Schneider, U. Understanding Why Patients with Schizophrenia Do Not Perceive the Hollow-mask Illusion Using Dynamic Causal Modelling. (2009)