When you go to sleep tonight, put a book under your pillow. When you wake up tomorrow morning, you'll have its contents memorized.

OK, so that probably won't work.

But don't lose hope just yet: 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.

Here are some of the skills you may be able to sharpen in your sleep:

Flickr/Giuseppe Milo

1. Foreign words In a recent experiment, scientists had native German speakers start learning Dutch, beginning with some basic vocab. Then they asked them to go to sleep. Unbeknownst to the dozing Germans, while they slept, the researchers played the sound of some of those basic words to one group of them. The other group was exposed to no such sounds. Later on when they were tested on the words, the group who'd listened to them overnight was better able to identify and translate them. To make sure the findings were tied to sleep — and not just the result of people hearing the words — they had another group listen to the words while they did something else while awake, like walking. The walkers didn't recall the words nearly as well as the sleepers.

Flickr/Zlatko Vickovic