Seeing with your tongue! - emerging models of the brain's amazing flexibility
We often think of brains as having separate sections for separate senses. For example, there's an auditory cortex for hearing, and a visual cortex for seeing, and so on.
But as per emerging models of the brain, there is nothing fundamentally different between these regions.
The neurons involved in the auditory cortex serve to process sound because they're connected (indirectly) to ears, not because they're specialised for processing sound. If the same neurons were connected to eyes, they'll be able to process visual input.
This was experimentally verified in an MIT study where data coming from a ferret's eye was redirected to it's auditory cortex (which usually receives sounds). The result was that the auditory cortex rewired itself to resemble the visual cortex and the ferret was able to "see" well enough.
Under this model, the brain is a general purpose computing device which can "make sense" of any data stream supplied to it by performing standard operations on it.
That's why, even if you supply a video data stream to a person's tongue (each pixel of video causes a small electric shock on a specific location on the person's tongue), the person is ultimately able to make out distance, shape, size, etc of what's displayed in the video.
That person is literally seeing with her tongue!
At first, she's confused and the signals seems a total mess, but soon, the mind starts extracting patterns from the data, which is then conveyed to the conscious mind as something similar to sight.
Mice are naturally colour blind but if you add a color receptor gene, their minds are able to interpret this new input and allow color vision. It's yet another incredible demonstration of the idea that brains can not only interpret input from "standard" senses, but also novel ones that evolution had never provided us with.
Several such experiments have now been done and the whole phenomenon is called "sensory substitution". It's not a new thing, but recent advancements in electronics and computing power are making practical application of such technologies nearer to reality
(Summarised from David Eagleman's excellent book, "Livewired")