How Sleep Helps Memory

According to this article, researchers in Germany did a study on sleep and memory. They had a group of people, and made these people memorize cards with animals and objects on them. They then took half the people, let them take a nap, and took the other half and made them memorize an entirely different set of cards. The study showed that the people who took a nap were 25% more accurate at remembering the first set of cards. However, I do not believe this study was very efficient at directly comparing memory between people who took naps and people who didn't. Because the people who did not take a nap also had to memorize more cards, which must have a large effect on their memories. If these people were just given the test again having not taken a nap, and never having to memorize a new set of cards, the research would be more accurate in determining the real effect of naps on memory.