  A graph is an abstract model that represents relations among entities, for
example, the interactions between characters in a novel. A background story
endows entities and relations with real-world meanings and describes the
semantics and context of the abstract model, for example, the actual story that
the novel presents. Considering practical experience and prior research, human
viewers who are familiar with the background story of a graph and those who do
not know the background story may perceive the same graph differently. However,
no previous research has adequately addressed this problem. This research paper
thus presents an evaluation that investigated the effects of background stories
on graph perception. Three hypotheses that focused on the role of visual focus
areas, graph structure identification, and mental model formation on graph
perception were formulated and guided three controlled experiments that
evaluated the hypotheses using real-world graphs with background stories. An
analysis of the resulting experimental data, which compared the performance of
participants who read and did not read the background stories, obtained a set
of instructive findings. First, having knowledge about a graph's background
story influences participants' focus areas during interactive graph
explorations. Second, such knowledge significantly affects one's ability to
identify community structures but not high degree and bridge structures. Third,
this knowledge influences graph recognition under blurred visual conditions.
These findings can bring new considerations to the design of storytelling
visualizations and interactive graph explorations.
