 On the other version of the theory, we are told that even though we seem to locate something in public space, appearances are misleading; rather, we are locating private mental objects in a private phenomenal space, which is conceived to be a kind of space, not merely a representation of real space.  So, on this version, pains are not, after all, located in body parts, ordinarily understood. But it is not clear how these two spaces are supposed to relate to or interact with each other. Phenomenal space is not physical space, nor is it a subregion of that space. Thus the question of how they can causally interact becomes an issue for two reasons. First, there is the standard worry about how a physical event can influence or be influenced by a non-physical event in a non-physical space. Second, these two spaces need to be systematically correlated with each other, but it is not clear whether a principled mapping function can be defined for the correlation especially in the absence of causation. At any rate, these constitute significant challenges for the defenders of this view.