[Logicseeker]

Cognitive psychologists have studied these pheomena for decades.
As for the native americans, it is possible that they didn't have much open fields, plains. etc. and therefore their eyes hadn't been developed for "seeing" depth. It's also possible that the story is BS.

There are some documented cases where perception differs between different geographical groups etc. In one, the europeans could see a pedistal on a drawing - looking at the same drawing an african from a tribe saw a tree.
So perception of what we see can differ depending on knowledge, but our eyes "take in" the same information.

The information is taken in by "saccades". This means that our eyes are sweeping from one point to another and only registering what is in those points. A bottom-up process in the brain is then responsible for analyzing simple figures, letters etc. and special neurons corresponds to different lines in those figues. Neurons for verical lines, neurons for horizental lines etc. There is also top-down processing for perception of more complex figues, i.e. determining "what is this?".

Our social conditition do not affect the saccades and the input process from our eyes. After the bottom-up process we already have those angels and things in our brain and without brain damage it is impossible to miss them. So the theory that social conditioning makes us blind to paranormal physical objects seems to be false. Growing up could make us see angels as "girls" or some other thing that might make better sence but they would not just disappear. And it is quite seldom for people to notice unfamiliar girls in unusal places, like in their livingroom etc.