Schizophrenic Brains Not Fooled by Optical Illusion

Patients suffering from schizophrenia are less susceptible to various visual illusions. For example, healthy participants perceive a hollow, concave, mask as a normal, convex, face, presumably due to the strength of constraining top-down influences, while patients with schizophrenia do not. 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 brain retains memories of what faces look like, so whenever we see a face, of course it has to come out, overriding visual cues such as shadows.

But schizophrenics see the hollow face for what it is. About 7 out of 1000 Americans suffer from the disease, which is characterized by abnormalities in perception or expression of reality. It most commonly manifests as auditory hallucinations, paranoid or bizarre delusions, and poor planning, with significant social dysfunction. Some psychologists believe this dissociation from reality may result from an imbalance between bottom-up and top-down processing — a convenient hypothesis to test out with the hollow mask illusion.

However the neural mechanisms underpinning this effect remain poorly understood. Dima and Jonathan Roiser of University College London used functional magnetic resonance imaging (fMRI) to investigate the hollow mask illusion in schizophrenic patients and healthy controls. The goal of this study was to use measures of effective connectivity arising from dynamic causal modelling (DCM) to explain differences in both the perception of the hollow mask illusion and associated differences in neural responses between patients with schizophrenia and controls.

When healthy subjects looked at the hollow, concave faces, connections strengthened between the frontoparietal network, which is involved in top-down processing, whereas people with schizophrenia did not show such strengthening. These findings suggest that schizophrenic patients rely on stimulus-driven processing and are less able to employ conceptually-driven top-down strategies during perception.

Schizophrenics aren't the only ones who see the concave face. People who are drunk or high can also 'beat' the illusion. During these drug-induced states, a similar disconnection between what the brain sees and what is really there may be occurring!

Posted by Sarah Bello (10)