well, there is one thing (a bit OT here): it’s quite easy: make a little noise with the tongue or use a small impulse machine that sends out audio pulses. even a blind person on a bike can train to hear the street and even go on a mountain trecking tour just using your ears and sending out acoustig signals just like bats do. for those, who wantz to know more: google for Dan Kish + blind and word like bat or sonar and you find some info. It may help other blind people to have a better life in this world.. it works, no joke! link for blind ones..
I am not blind but I really like people telling people things like this..