Though the question of how information gets into Ni is a curly one. Luckily hubris will come to our rescue, in the form of however much distress I can cause by pointing out that if Ni is essentially dependent on some crippled Ne, then booyah INTPs, eat Te dust.
The ability of an introverted function to reflect the real world is genuinely different from how that introverted function is to acquire representations. It seems to make sense to suggest that there is raw information and there is information as it appears to and in cognitive function space. Unless I'm mistaken, it's fairly well known that human nervous systems are bombarded with far more raw information than is actually ever attended to. From there it's a very short step to observe that however information is getting inside these introverted functions, once there it's as if it was always there. I suspect it is not appropriate to say, for example, INTJs get access to the real world via Se. It is appropriate to say that when INTJs are accessing the real world, they're attending to such aspects of it as fall under the purview of Se. But for actually collecting basic information.... is reading a book an example of Se? It can't possibly be other than incidentally, because the information being taken in is ideas and whatever else gets evoked by words. The information taken only incidentally includes the texture of the page, the font of the printing, the color of the ink, the weight of the book as it moves from hand to hand.... Probably it is better to say that, for example an INTJ reader, is dealing with the content of the book as if it were already Ni/Te(/Fi) subject matter. Instant translation. The eyes are open, and the brain is doing what it always does, stealing ideas away from the objective world. For an INTJ, Ne has no place in this story. The ideas don't arise from interaction with the world. They are first transported away from the world and only after that can they begin to be interacted with. We are after all talking of preferred kinds of cognition, which is a layer of structure over and above raw biological input (and output).
Since Ni is subjective, it matters not a wit how close or far what's inside is from the external world. But since Ni works in tandem with something else or not at all, then other priorities will also come into play. An objectivity requirement will be included as some kind of priority. Any and all of Te, Fe and Se will make this a priority (in different ways) for the person. Whatever goes on in the Ni realm will NOT work for the person unless it bears some relationship to those other functions. Se for example, even sitting way down in inferior position for an INTJ, will exert some influence on how Ni functions.
But all that is type dynamics and one big Pffft for the moment since we have yet to discover how or what goes on inside Ni.
Various commentators have suggested Ni is one kind of memory. I dislike this suggestion since I don't consciously use Ni as a source of reflection on the past. "Memory" does not seem to be the right word. It certainly doesn't capture the sense of moderately heedless forward movement one "feels". But that forward attention isn't heedless at all. It is attention built on preconceived notions, the "memory" aspect of Ni, where past events have been gone over, abstracted from, turned into supposedly timeless implicative "memories", useable at later times for determination of "what will come next". or "what should come next". Dear reader, don't turn up your nose at the obvious subjectivity. But, surely we must, mustn't we? How can some past event tell you what to do in the future? How can it be anything other than some plain, even severe, limitation on what's possible? This mystical function surely is as close minded as a stone--how can it possibly be called future focused if all it does is recycle the past? Where is possibility? Where is that essence of all notions of intuition in this story? Where?