Motherwell's intense engagement with spontaneously painted works on paper found a particularly rich vein in the Lyric Suite drawings. These were executed in a burst of inspiration during the spring of 1965, when he did over six hundred automatist compositions in ink on rice paper, just letting the forms pour out of him, with no correction or revision, as a prod to his powers of invention. Taken together, these explorations of pure abstraction were like a series of musical themes and variations - to Alban Berg's Lyric Suite, which Motherwell listened to while he was doing them.  You can listen to Berg's Lyric Suite in the video link.