Thornton's first 16mm film, X-Tracts was made in collaboration with cinematographer Desmond Horsfield. The film consists of complex and rapid patterning of sound/image segments that are structured by a formal mathematical schema that determines duration, interaction, and progression. Moving beyond the critiques of the cinematic apparatus and its analogy to language that were central to that time (Hollis Frampton's Hapax Legomena or Paul Sharit's T:O:U:C:H:I:N:G, for example), Thornton expands into the territories of rhetoric, cognition, and linguistics. Composed of a cut-up reading of Thornton's high school diary paired with images of the filmmaker, fragments of the body in motion or at rest, and just-occupied spaces, X-Tracts seems both to defy and propose an autobiographical narrative. The film has been described by Chrissie Iles, curator at The Whitney Museum of American Art, as the "missing link" between the structuralists and the introduction of a more narratological tendency in experimental film practice.