chords, but at all times a good improviser must follow the changes. ... [However], a jazz musician really has several options: he may reflect the chord progression exactly, he may "skim over" the progression and simply elaborate the background harmony, or he may fashion his own voice-leading which may clash at some points with the chords the rhythm section is playing. Contemporary classical music With the notable exception of liturgical improvisation on the organ, the first half of the twentieth century is marked by an almost total absence of actual improvisation in contemporary classical music. Since the 1950s, some contemporary composers have placed fewer restrictions on the improvising performer, using techniques such as vague notation (for example, indicating only that a certain number of notes must sound within a defined period of time). New Music ensembles formed around improvisation were founded, such as the Scratch Orchestra in England; Musica Elettronica Viva in Italy; Lukas Foss Improvisation Chamber Ensemble at the University of California, Los Angeles; Larry Austin's New Music Ensemble at the University of California, Davis; the ONCE Group at Ann Arbor; the Sonic Arts Group; and Sonics, the latter three funding themselves through concerts, tours, and grants. Significant pieces include Foss Time Cycles (1960) and Echoi (1963). Other composers working with improvisation include Richard Barrett, Benjamin Boretz, Pierre Boulez, Joseph Brent, Sylvano Bussotti, Cornelius Cardew, Jani Christou, Douglas J. Cuomo, Alvin Curran, Stuart Dempster, Hugh Davies, Karlheinz Essl, Mohammed Fairouz, Rolf Gehlhaar, Vinko Globokar, Richard Grayson, Hans-Joachim Hespos, Barton McLean, Priscilla McLean, Stephen Nachmanovitch, Pauline Oliveros, Henri Pousseur, Todd Reynolds, Terry Riley, Frederic Rzewski, Saman Samadi, William O. Smith, Manfred Stahnke, Karlheinz Stockhausen, Tōru Takemitsu, Richard Teitelbaum, Vangelis, Michael Vetter, Christian Wolff, Iannis Xenakis, Yitzhak Yedid, La Monte Young, Frank Zappa, Hans Zender, and John Zorn. Contemporary popular music Psychedelic- and progressive-rock music British and American psychedelic rock acts of the 1960s and 1970s used improvisations to express themselves in a musical language. The progressive rock genre also began exploring improvisation as a musical expression, e.g. Henry Cow. Silent-film music In the realm of silent film-music performance, there were musicians (theatre organ players and piano players) whose improvised performances accompanying these film has been recognized as exceptional by critics, scholars, and audiences alike. Neil Brand was a composer who also performed improvisationally. Brand, along with Guenter A. Buchwald, Philip Carli, Stephen Horne, Donald Sosin, John Sweeney, and Gabriel Thibaudeau,