The way I think about it: our brains create perception by combining raw observations with expectations derived from a mental model built on experience, in a process similar to a Kalman filter. Most of the time, the correction based on the mental model helps, such as when an object is partially obscured. Cases like the concave face are false positives for normal people, where experience overrides percpetion. Schizophrenics weight the observations more heavily than the predictions, so they are less likely to experience false positives, but I would expect them to be consequently more likely to experience false negatives (ie. perceiving things too literally, in spite of logic).

There are actually several diagnosable mental illnesses where the main feature or one of the main features is being able to see reality more accurately than other people. This is especially true with certain types of depression depression (e.g. depressive realism) and autism. My favorite though is delusional disorder, which basically just means that you're happier than other people think you should be given your circumstances.

This is really interesting. What more am I missing out from the "real" world?. If there wasn't an "authority" telling me that this face is concave I'll call anyone telling otherwise crazy.

this is exactly what I thought, too

I think we all labor under certain types of illusions on a daily basis - i.e. we ignore the dangers of driving because we have the illusion of control. If we thought about all of the permutations and repercussions of every action it might paralyze us. The mechanisms that we use to allow us to function day-to-day probably dull our senses.