Researchers from Hannover Medical School (HMS) and University College London (UCL) have discovered that sufferers of schizophrenia can’t be fooled by a common optical illusion, known as the “hollow mask”.
In the hollow mask illusion, participants with a normally functioning brain perceive a concave face (such as the underside of a hollow mask) as a typical convex face. As WIRED reports, this happens because the illusion manipulates the brain’s usual method for piecing together the visual world: merging what it actually sees – known as bottom-up processing – with what it expects to see based on previous experience – known as top-down processing.
“Our top-down processing holds memories, like stock models,” states Danai Dima of HMS, and co-author of the study. “All the models in our head have a face coming out, so whenever we see a face, of course it has to come out.”
If this doesn’t seem like am illusion then, uhm, how do i say this. You are schizophrenic https://t.co/xmiQJk1FfR
— Riya Ashok (@riyaashokr) January 31, 2016
According to WIRED, our expectation is powerful enough to override visual cues, such as shadows and depth information, which mark anything out of the ordinary.
In order to observe the effects of this illusion, Dima, alongside Jonathan Rosier of UCL, put 16 healthy participants and 13 schizophrenic participants through an fMRI machine, measuring cerebral activity as each participant was shown the illusion.
When healthy participants saw the image, scientists found that networks between the top-down system and bottom-up parts of the brain became stronger. The connection is in fact so strong that even when the participant is aware of the illusion, they remain unable to see a concave face.
But when it comes to schizophrenic participants, people for whom delusions and hallucinogenic tendencies are the norm, the connection between top-down and bottom-up processing does not exist, and this allows them to perceive the illusion as it truly is.
Whether the image is moving, static, expanding or changing colour, scientists will continue to use the optical illusion as a means to unravel the complex workings of the human brain.
Image via WIRED.