You know that feeling you get when you step inside a new house or walk around a foreign city—places you know you’ve never been before—and you can’t help but think, I’ve done this already? Or maybe you are having dinner with a group of friends, discussing some current political topic, and you have the feeling that you’ve already experienced this very thing — same friends, same dinner, same topic. It’s déjà vu, and if you’ve never had it before, take it from us: It’s kind of creepy. It keeps on happening with me all the time.
Déjà vu is French word for “already seen,” and about two out of every three people experience the phenomenon at one time or another.
Despite being fairly common, “it’s not a widely studied subject,” says Alice Medalia, PhD, a professor of medical psychology at Columbia University Medical Center. And because déjà vu is a subjective experience—in other words, it’s difficult to induce in research subjects—testing the theories behind it can be tricky.