So my book takes place in a Fantasy world and focuses on a teenage girl (Ash) who has been blind from a young age. Using magical medicine another race replaces her eyes (the actual eyeball) from a dead person who donated them. After her surgery she begins to see things. Things from the past, the future, things going on in another place. She also can see things from the lives/deaths of those who has the eyes previously. (the eyes have a long history and a bit of a life of their own. They begin to control their host either for good or bad and shape how he/she sees the world). No idea what the actual plot line is yet but is this believable? I mean what part of the body allows an oracle to see the future? Would it be more brain that vision. I don't want to build a story around a poor premise.
Oftentimes eyes are usually what's tied to visions. I think you're overthinking it trying to go back to the 'brain'. And really, even if it wasn't something traditional, you could still entirely make it work! I love stories that put little twists on things like that. As for believable, well, it's fantasy so yeah. Anything goes when you slap that 'fantasy' label on it.
I've only seen this movie once and don't really recall how it goes other than it's something along the lines you describe (and you may have seen it, too). While I don't trust wikipedia, here's their spin on it: https://en.wikipedia.org/wiki/The_Eye_(2008_film)
1. No. It is not believable. It's fantacy. It does not need to be believable. 2. That is a tough question. Does oracle really see the future? Or does he make it happen? Or does he guess or reason or focus on indicators others miss or hallucinate or see the patters in the dynamics of how things happen or... (Traffic lights. Red. Two lines. One car standing in both lines. I'm gonna turn right after some time. On the right side is Audi A4 and male driver in his thirties alone. On the left side is Nissan Micra, female driver talking with another female person - both in their fifties. I'm gonna pick right side because that Audi will be 2o meters from lights before this Nissan starts to move. 95% of the cases. I can't see future. I have seen enough past to expect that to happen.)