Graphics have a variety of functions, which include decoration, representation, organization,
interpretation, and transformation (Carney & Levin, 2002). Unfortunately, not all visual
displays will cause the same degree of improvement in comprehension and retention.
Therefore, research on the impact of visual representations sometimes leads to contradictory
results in which the value of these representations is called into question (Harrison &
Treagust, 2000). Concepts can be represented pictorially in numerous ways and not all will
be equally understood (Pozzer-Ardenghi & Roth, 2005). As with verbal communication,
illustrations have to be ―read.‖ In order to bring about more consistent improvement in
knowledge acquisition, researchers have explored what factors enhance the readability of
illustrations.