We explore the validity and applicability of educational and cognitive science theoretical frameworks for designing and evaluating data visualizations. Specifically, we are interested in using well-known frameworks from other domains to learn about how the subjective readability of a visualization relates to the perceived cognitive load required to acquire knowledge from it.
To that end, we conducted an online randomized study in which each participant performed learning tasks on two different data visualizations. One was presented in three successive parts, following the segmenting principle from the Cognitive Theory of Multimedia Learning, and the other was presented as a single image. Although most learners preferred the segmented style, this treatment did not significantly affect the overall mental effort they reported. Subjective measures of extraneous cognitive load, however, significantly and negatively correlated with visualizations' perceived readability measures.
In other words, if a learner found a visualization more readable, they felt it required less mental effort to parse relevant information from it for learning. In addition to a qualitative analysis of learners' preferences, we also contribute an interdisciplinary perspective on cognitive processing of visualizations and a discussion of implications for designing and evaluating data visualizations beyond educational contexts.
