Repetitive music largely developed in the United States during the 1960s, a period when the influence of different oral musical traditions (jazz, traditional Oriental and African music) came to the fore. The composers of repetitive music are close to the minimalism of La Monte Young, whose origins lie in the serial music of Anton von Webern. Repetitive music uses resonance, varied repetitions of cyclical formulas that become increasingly unsynchronized, and a rhythm with a regular beat. The music is conceived as a gradual mechanism of change over an extended period of time. The main representatives of this musical current are Steve Reich, Philip Glass, Terry Riley, Jon Gibson, and Laurie Spiegel. Riley's works are based on simple harmonic and rhythmic models; the repetition, seemingly unchanging, nonetheless reveals a perpetual movement. Reich uses the principle of repetition generate an evolving sequential process. Glass adds rhythms to the melodic line in pursuit of continuity, unity, and broader musical texture. For these three composers, repetition becomes a system of composition, as it was for Andy Warhol during the same period of time, but in the context of the visual arts.