Johnston began as a traditional composer of art music before working with Harry Partch. He helped the senior musician to build instruments and use them in the performance and recording of new compositions. Partch then arranged for Johnston to study with Darius Milhaud at Mills College. In 1952, Johnston met Cage, who invited him to come to New York to study with him in the summer. Though Johnston decided he did not have sufficient time to prepare for such studies, he did go to New York for several weeks and assisted, along with Earle Brown, in the production of Cage's eight-track tape composition, "Williams Mix".