Their brain is no connection between expectations and realnostyu
Optical illusions - a very curious phenomenon. One of them - the illusion of "hollow mask" when the concave side of the mask appears convex. But there are people, which are not optical illusions - schizophrenics.
Most people give in illusion, because the mind has a "fund of images", which he uses to understand what he sees. When the picture looks familiar, the mind associates with what is, with what we expect, and combines these two components to form and identify the image that you see. In some cases, the wait can be stronger than reality, and you will see not what it actually is, and what we expected.
In people with schizophrenia, expectation and reality in the brain are not connected - they see what is really there. Shadows and other signs give them to understand that the mask concave and convex not. People are in a state of alcohol or drugs is also not "caught" on optical illusions, which means that alcohol and drugs destroy the connections in the brain between expectations and reality.