Ever hear a country tune that kept playing in your mind again and again?

"One of the great appeals of country music is that it's easy to remember because of repeated patterns," says Donald Shetler, a music professor at the University of Rochester. Rhythms repeat over and over, and three, four or five chords carry the harmony.Country music fans are usually at least 20 years old, he said, because the typical themes of this music - falling in love, mourning a lost love, working for a living - center around family life.