The hippie legacy in literature includes the lasting popularity of books reflecting the hippie experience, such as "The Electric Kool-Aid Acid Test". In music, the folk rock and psychedelic rock popular among hippies evolved into genres such as acid rock, world beat and heavy metal music. Psychedelic trance (also known as psytrance) is a type of electronic music influenced by 1960s psychedelic rock. The tradition of hippie music festivals began in the United States in 1965 with Ken Kesey's Acid Tests, where the Grateful Dead played tripping on LSD and initiated psychedelic jamming. For the next several decades, many hippies and neo-hippies became part of the Deadhead community, attending music and art festivals held around the country. The Grateful Dead toured continuously, with few interruptions between 1965 and 1995. Phish and their fans (called "Phish Heads") operated in the same manner, with the band touring continuously between 1983 and 2004. Many contemporary bands performing at hippie festivals and their derivatives are called jam bands, since they play songs that contain long instrumentals similar to the original hippie bands of the 1960s.