IMO, the idea is pure SF. I'd use this analogy:
You've got a teaspoon of water in one hand, and in the other you hold the Mississippi river. What we "know" about the brain and its functioning is analogous to the teaspoon; what we don't know, including all of the unproven theories we have, is analogous to the Mississippi.
It's important to separate the mechanical processes we're pretty sure about from the ones we have no clue about. For instance, the concept of tapping into the optic nerve to provide camera input into the nerve to reverse the plight of the blind, is a pretty straightforward concept. Knowing exactly how to do that, though, in such a way as to duplicate human vision, and knowing how to do it reliably in most all cases of blindness, is quite the trick indeed, because of the fact that there are still many pieces of the puzzle completely unkown to us at this time. At a deeper level, the mechanism by which the brain makes sense of the images it receives from the eyes, and integrates them into what we perceive as "conscious thought," is simply not understood clearly if at all. Theories abound, but so far none of them are workable in any practical sense.
In terms of complexity, the structure and functioning of the human brain contrasted with the structure and function of the most powerful computer on earth is analogous to the cellular complexity of the human body, including the brain, compared to that of a one-celled amoeba.
Because of this, neuro-science is still in a very primitive stage, such that often the way we find out about brain function is by lopping off people's skull caps and physically inserting probes and electrodes into various areas of their brains just to "see what happens" and record the results...
This is where our "brain maps" come from which neatly divide the brain into segments from which control of various bodily and/or mental functions are thought to "reside." Understanding it any more clearly than that, however, in terms of what the structures are in each of those areas and how and why they do what they do, is quite beyond us at this time, apart from a rudimentary understanding that electro-chemical processes are involved. Take the phrase "synapses firing," for instance. We know that they "fire" but as to how and why they fire in the ways that they do we have no clue...
The pattern of firing in the brain is so incredibly complex that often the firing appears as simply "random" as we can't see any patterns to it that we can explain or understand. It's not at all "random," of course--it's just that we have no clue as to it's organization or purpose or function..
It's like looking at the brain through an MSI scan or infrared scan and seeing that certain things happen in the brain electrically and thermally when the subject is "concentrating" or working out a math problem or sleeping or rutting, etc.. We know that "things happen" in the brain when we do these things--but have no clue as to what is going on or why. It's kind of like middle-ages physicians noting that people's skin temperature was elevated when they got sick--but having no clue as to why that was happening--right before they attached the leeches that would often kill their patients, in order to suck out the "ill humors"...
Among the more interesting recent theories as to consciousness I've read is the idea that consciousness is "quantum" (as in quantum mechanics), which neatly provides us with a way to "feel good" about the fact that we cannot understand much of anything about the function and structure of the mind. Certainly, it operates in a manner we are unable to grasp rationally, as is true of the "axioms" of the quantum realm (which are that there are no axioms, basically), but I tend to think that 75-100 years ago other scientists might have said that the brain is the physical seat of the mind, and not the mind itself (which they might have called "spirit" among many choices), which strikes me as pretty much exactly the same thing as the "quantum" theories I read today. The human mind always seeks to label and quantify that which it cannot understand so as to provide itself with the illusion that it understands it, as in "that's spiritl," or "that's quantum," etc...
Anyway--the idea of tapping directly into the brain to feed it signals like your 3d-card is wired to your monitor--is pure SF, imo, as I think that we understand so little about the brain itself that we might imagine such a thing as practically workable in the first place. Fascinating subject, though, and interesting to think about.
One last example: remember when Rush Limbaugh went deaf, and underwent a cochlear implant which has restored his hearing? It was successful because enough of the auditory nerve remained so that the implant could become attached. However, often cochlear implants simply don't work, and the reasons are theoretical: one such theory is that some people lose hearing because the mechanism inside of the brain which decodes the auditory nerve impulses from the ear is damaged, or else the mechanism in the brain which mixes the decoded auditory stream into the stream of consciousness is damaged or degenerated. Similar concepts apply to blindness. As we know so very little about the brain, there is nothing that can be done in those cases.
I'd be interested in hearing from anyone who might have some more recent info on this topic to share.