Different parts of our brains process different signals. There's a section (cortex) that processes audio, and a different one that processes video. If you disconnect these parts of the brain from their inputs and instead cross connect the eyes to the auiditory cortex (in ferrets) it learns to interpret the visual signals. You can even do this in people: put a grid of electrodes on the tongue, connect them to the output of a video camera, and within 15 minutes people are seeing with their tongues (also, also).

I want to build this. The current potential needed is 5-15 volts, which is practical and reasonably safe. I need a flexible grid of electrodes, connected to something like an arduino, connected to some sort of camera. I think I could use a smartphone camera and use the smartphone to control the arduino. The part I don't currently know how to get or make is the electrode grid. It needs to be mouth-safe, and it would be nice if it were at least 10 electrodes on a side. The ones I see are way too small. I'd also need to figure out how to get that up to ~5V and controlled by the arduino, but I think there's a lot out there on thatt sort of thing.

It might be interesting to see whether there are other things that might make a better tongue-sense than sight. GPS location? Compass direction? Bus locations? Magnetic field strength? Weather predictions? How well would we internalize a sense we had not evolved to use?