Anatta is not a philosophical notion. Anatta is reality, which, according to books, can be directly experienced in deep meditation, thereby putting an end to all doubt. A "philosophical notion" is not a directly verifiable fact. If it is then it won't be a mere "philosophical notion". No, I don't think impermanence is a "perceived reality". It is reality no matter how you perceive it through your sensory organs. There is a tree in your garden. You leave for work and the tree is no more there in your sensory scope. You don't see it or think of it. Yet when you come back home, the tree still there. What does that tell you?