Seeing with your ears

Here's a fascinating article about people who are blind that have learned to use echo-location to get around. Sample:

I am certainly not the first person to teach myself echolocation. In fact, human sonar has probably been around for as long as humans. There are two types of sonar: passive and active. Passive sonar exploits sounds made for other purposes to get a sense of the environment, and everyone does it to some extent. We can hear our voice change depending on the kind of space we are in, for instance.

Humans probably used to rely on echolocation far more in the days before artificial lighting, when we had to find our way round in the dark. The readiness with which people learn sonar suggests to me it may be an inbuilt skill.

This is a skill that can be taught. Very neat.