it isn't that schizophrenic people don't see things sometimes...its that its far more common for them (and bipolar people) to hear things.

some of it may also be in how people are diagnosed. i read that, for a while at least, people with significant psychotic components to their problmes were called "Schizoaffective," not "Bipolar I." Now, from what I"ve seen...the Schizoaffective diagnosis is once again waning in popularity. anyway...maybe there are more visual hallucinations in the "Schizoaffective" category? I don't know.