Reading a graph is like reading a paragraph

Vision provides rapid processing for some tasks, but encounters strong constraints for others. Although many tasks encounter a capacity limit of processing 4 visual objects at once, some evidence suggests far lower limits for processing relationships among objects. What is our capacity limit for relational processing? If it is in- deed limited, then people may miss important relationships between data values in a graph. To test this question, we asked people to explore graphs of trivially simple 2x2 datasets, and found that half of viewers missed surprising and improbable relation- ships (e.g., a child’s height decreasing over time). These relationships were spotted easily in a control condition, which implicitly directed viewers to prioritize inspect- ing the key relationships. Thus, a severe limit on relational processing, combined with a cascade of other capacity-limited operations (e.g., linking values to semantic content), makes understanding a graph more like slowly reading a paragraph than immediately recognizing an image. These results also highlight the practical impor- tance of ‘data storytelling’ techniques, where communicators design graphs that help their audience prioritize the most important relationships in data.