Abstract
We argue that people compare values in graphs with a visual routine - attending to data values in an ordered pattern over time. Do these visual routines exist to manage capacity limitations in how many values can be encoded at once, or do they actually affect the relations that are extracted? We measured eye movements while people judged configurations of a two-bar graph based on size only ("[short tall] or [tall short]?") and contrast only ("[light dark] or [dark light]?"). Participants exhibited visual routines in which they systematically attended to a specific feature (or "anchor point") in the graph; in the size task, most participants inspected the taller bar first, and in the contrast task, most participants attended to the darker bar first. Participants then judged configurations that varied in both size and contrast (e.g., [short-light tall-dark]); however, only one dimension was task-relevant (varied between subjects). During this orthogonal task, participants overwhelmingly relied on the same anchor point used in the single-dimension version, but only for the task-relevant dimension (e.g., taller bar for the size-relevant task). These results suggest that visual routines are associated with specific graph interpretations. Responses were also faster when task-relevant and task-irrelevant anchor points appeared on the same object (congruent) than on different objects (incongruent). This interference from the task-irrelevant dimension suggests that top-down control may be necessary to extract relevant relations from graphs. The effect of visual routines on graph comprehension has implications for both science, technology, engineering, and mathematics pedagogy and graph design.