Blind echolocators see with the part of the brain built for seeing
A 2014 brain scan found something that should be impossible: sound lighting up the visual cortex like light does.
Some blind people navigate by making sharp clicks with their tongue and reading the echoes — identifying a parked car, a flagpole, a tree, by ear alone, well enough to ride a bike through a neighborhood. Researchers led by Lore Thaler recorded these clicks and their faint returning echoes with tiny microphones, then played the recordings back to the echolocators inside an MRI scanner in 2014.
The expected result was activity in the auditory cortex, since the input was, after all, sound. What showed up instead was activity in the primary visual cortex — the region that in sighted people processes light hitting the retina, doing essentially nothing when there's no light to process. In the echolocators, it lit up on cue, tracking the objects in the echoes as though it were looking at them. Sighted control subjects, played the same recordings, got no such activity anywhere, and couldn't tell a tree from a car.
This complicates a comfortable assumption: that a brain region is for a sense, permanently assigned by wiring at birth. It looks instead like the visual cortex is for a kind of computation — building spatial models of the world — and it will take that job from whatever sense actually shows up to supply the material. Sight was just the input light happened to provide.
The old philosophical puzzle about whether we can know what it's like to sense the world differently than we do assumed the senses were separate rooms. The echolocators suggest they're closer to the same room, wired for different doors.