German composer Karl-Heinz Stockhausen (1928-2007) has been among the leading avant-garde figures in German music since the 1950s. In spite of material difficulties, he studied in Cologne with Frank Martin and was subsequently strongly influenced by attendance at Darmstadt, where summer sessions contributed largely to the development of new music. He went on to study with Messiaen in Paris. Parallel to his work in electronic music, he explored the human element in performance, moving from total serialism, in which every aspect of a piece is controlled by a predetermined serial pattern, to a more flexible approach.