How to learn while you sleep (using sound)

"It turns out there actually are a few things you can learn - or at least improve your grasp of - while you snooze. Most of them depend on one thing: sound. "

According to the article, some learning categories that might be improved by sounds during sleep are:

  • Foreign words
  • Musical skills
  • Where you put something
  • Special memories

Has anyone tried doing something like this, like playing the sounds of foreign languages while you sleep?