A small number of blind people are adept at echolocating silent objects simply by producing mouth clicks and listening to the returning echoes. The neural architecture underlying the ability of aid-free human echolocation has been recently investigated in a study published in PLoS ONE. The authors conclude that "the findings suggest that processing of click-echoes recruits brain regions typically devoted to vision rather than audition in both early and late blind echolocation experts." "The study is a first step in understanding how the brain processes an ability that seemingly melds sound and sight." (Source: Article "Blind People 'See' Shapes, Navigate Using Echoes" on livescience.com)
The study is another brick in the foundation to the concept of brainplasticity or neuro(nal)plasticity (aka neuro-physiological plasticity). It basically says that the brain is able to reorganize itself on the physiological level to assign particular brain areas to functions for which they were not used before or for which they are not used for in other humans. In 2009 and in 2010 fantastic documentaries picturing the ideas from Norman Doidge's book were aired on German Arte TV respectively on Canadian CBC ("Neustart im Kopf" and "Changing your mind"/"The brain that changes itself") that showed how powerful that concept is and what it can mean to disabled people, both in terms of overcoming physical and mental disabilities. It takes a lot of training but you can teach your brain to build up neural connections that eventually can overtake the function of some damaged area or strengthen the function of existing areas.
For more information get Norman Doidge's book or have a look into the Google Scholar for papers on the topic.