From the 1970s, Ligeti turned away from sonorism and began to concentrate on rhythm. Pieces such as "Continuum" (1968) and "Clocks and Clouds" (1972–73) were written before he heard the music of Steve Reich and Terry Riley in 1972. But the second of his "Three Pieces for Two Pianos" (1976), entitled "Self-portrait with Reich and Riley (and Chopin in the background)", commemorates this affirmation and influence. During the 1970s, he also became interested in the polyphonic pipe music of the Banda-Linda tribe from the Central African Republic, which he heard through the recordings of one of his students.