This article explores how the POEMFIELD series of computer animations, created by Stan VanDerBeek and Kenneth Knowlton between 1964--70, consciously mines a terrain between visibility and invisibility, drawing numbers and letters into cascades of representation simultaneously pictorial, linguistic and schematic. Skating the border of legibility, the animations exhibit a double vision of text and image, code and picture and, in so doing, work to figure a larger, epistemic question of computational visibility at the close of the mechanical age'. The subtitle of the MoMA 1968 exhibition -- The Machine' -- marked the emergence of a computational model in which mechanical animation would no longer be visible to the human eye. The resulting crisis of visibility takes on a particular importance in light of the model of the graphical user interface' being explored at that time. In the POEMFIELD series, VanDerBeek and Knowlton attempt to convey both the complexity and the promise of this emerging paradigm of layered pictoriality, language and code.