This article presents two studies investigating how computer interface affordances influence basic cognition, including ideational fluency, problem solving, and inferential reasoning. In one study comparing interfaces with different input capabilities, students expressed 56% more nonlinguistic representations (diagrams, symbols, numbers) when using pen interfaces. A linear regression confirmed that nonlinguistic communication directly mediated a substantial increase (38.5%) in students' ability to produce appropriate science ideas. In contrast, students expressed 41% more linguistic content when using a keyboard-based interface, which mediated a drop in science ideation. A follow-up study pursued the question of how interfaces that prime nonlinguistic communication so effectively facilitate cognition. This study examined the relation between students' expression of nonlinguistic representations and their inference accuracy when using analogous digital and non-digital pen tools. Perhaps surprisingly, the digital pen interface stimulated construction of more diagrams, more correct Venn diagrams, and more accurate domain inferences. Students' construction of multiple diagrams to represent a problem also directly suppressed overgeneralization errors, which were the most common inference failure. These research results reveal that computer interfaces have communications affordances which elicit communication patterns that can substantially stimulate or impede basic cognition. Implications are discussed for designing new digital tools for thinking, with an emphasis on nonlinguistic and especially spatial representations that are most poorly supported by current keyboard-based interfaces.