A friend shared this yesterday. Brain compass implant gives blind rats psychic GPS - life - 02 April 2015 - New Scientist (Almost boycotted it due to the word 'psychic').
Somehow interesting (I haven't read the paper proper, only the web post, as usual with these quick notes) but I wonder if they tried to block the GPS signals to see if the mice went 'blind' again. (I would presume this was indeed tested.) As noted in the New Scientist it is not quite clear how this works; but in many ways I am not surprised if it does.
I do think however that the question about what the mice 'see' is most likely nonsensical, even if the GPS input is to the visual cortex. I'd guess what we'd usually call seeing in a non medical/technical sense is a rather messy sensation from signals in the eye and brain. Host dependent. More strictly seeing could of course be defined as activity in the visual cortex, where by the GPS enabled rats do see… but then the answer to the question becomes the corresponding activity.
I am sure neuroscientists have a proper definition, and possibly already a proper answer to that question if there is one.
In any case, what stays with me after reading this is asking myself the question of how the mice as whole were changed by the new 'sense'. And, perhaps a small part of me wonders if it was really necessary.