This feeling of familiarity is, of course, known as déjà vu (a French term meaning "already seen") and it's reported to occur on an occasional basis in 60 to 80 percent of people. It's an experience that's almost always fleeting and it occurs at random.

So what is responsible for these feelings of familiarity?

Despite coverage in popular culture, experiences of déjà vu are poorly understood in scientific terms. Déjà vu occurs briefly, without warning, and has no physical manifestations other than the announcement: "I just had déjà vu!"

Many researchers propose that the phenomenon is a memory-based experience and assume the memory centers of the brain are responsible for it.