Beyond Inattention & Change blindness, I once heard a story about Christopher Columbus arriving in the new world.
When he walked onto the beach and talked with the Natives, it was said the Natives were UNABLE TO SEE the large sailing ships anchored in the bay.
The ships were so far removed from anything the Natives had experienced before, they were UNABLE TO SEE THEM.
The reining Shaman was able to see the ships, and after a few days of discussion and explanation, the other natives began to see the ships as well.
Related in a couple of interesting shows: "Brain Games" (from NatGeo) and "
What the @#$#% Do We Know".
No idea if the story is true, or simply a parable. But an interesting concept that could also explain why spectators sometimes ignore an unusual item.