How might investigating mathematical tasks through digital media influence students' learning trajectories, and hence their mathematical thinking? This article reports on elements of an ongoing study that examines how engaging mathematical phenomena through digital pedagogical media might influence understanding. As the students sought interpretations and explanations, they frequently negotiated investigative pathways based on the visual feedback they received. Unexpected visual output, encountered when students engaged in mathematical investigative tasks using spreadsheets, evoked tensions which influenced their learning trajectory. These cognitive visual perturbations often stimulated dialogue, which in conjunction with the associated activity, fostered mathematical thinking, the formation of informal conjectures, and hence a reshaping of their understanding.