For more than a century scientists have known that individuals who are tested on material are more likely to remember it than those who simply study. But questions remain about why that is the case. Kent State University psychology researcher Katherine Rawson argues that part of the explanation is that testing gets people to come up with better keyword clues, which bridge the gap between familiar and new information—and it strengthens ties between these keywords and the newly learned information.

Rawson and former graduate student Mary Pyc asked 118 college students to learn four dozen Swahili words by matching them with their English counterparts, such as wingu, which means “cloud.” After an initial study period, half were given practice tests before studying the words a second time, and half restudied the words without taking a practice test.

As expected, students in the practice test group were better at remembering the word pairs during a final exam a week later. But Rawson and Pyc also asked students to tell them their keywords—for instance, “bird” might serve as a bridge between wingu and cloud—and they revealed that the people in the practice test group not only remembered more of their keywords, but they were more likely to have changed their keyword before restudying the word pairs than those who had not been tested. As the researchers reported in Science last October, these results suggest that testing improves memory by strengthening keyword associations and weeding out clues that do not work.