An article in this week's New Yorker magazine called "Seeing with Your Tongue" by Nicola Twilley explores the topic of sensory substitution. There has been a great deal of research over the years about the parts of the brain that are used to perform certain tasks and how this does or does not change in someone who is blind. The article discusses BrainPort, a technological device that allows people to "see" using their tongue. Erik Weihenmayer is among those who has tried BrainPort and he describes how he has used it when climbing (although not on Mt. Everest). Another sensory substitution device, called vOICe, turns visual information into sound.
Twilley examines the role of the brain in all of this, noting that "the BrainPort’s inventor, the neuroscientist Paul Bach-y-Rita, put it, 'You don’t see with the eyes. You see with the brain.'"
In the video below, Erik Weihenmayer demonstrates how BrainPort works.