I expect it would be some kind of a merge of the two (without severing the optic nerve that is) - neurons work by accumulation so you would effectively have the

I expect it would be some kind of a merge of the two (without severing the optic nerve that is) - neurons work by accumulation so you would effectively have the two realities summed - which would be neat for augmented reality. Two fully immerse you could close your eyes or put on dark glasses. A friend told me this is how visual hallucinations on LSD work ...