  Textbooks in applied mathematics often use graphs to explain the meaning of
formulae, even though their benefit is still not fully explored. To test
processes underlying this assumed multimedia effect we collected performance
scores, eye movements, and think-aloud protocols from students solving problems
in vector calculus with and without graphs. Results showed no overall
multimedia effect, but instead an effect to confirm statements that were
accompanied by graphs, irrespective of whether these statements were true or
false. Eye movement and verbal data shed light on this surprising finding.
Students looked proportionally less at the text and the problem statement when
a graph was present. Moreover, they experienced more mental effort with the
graph, as indicated by more silent pauses in thinking aloud. Hence, students
actively processed the graphs. This, however, was not sufficient. Further
analysis revealed that the more students looked at the statement, the better
they performed. Thus, in the multimedia condition the graph drew students'
attention and cognitive capacities away from focusing on the statement. A good
alternative strategy in the multimedia condition was to frequently look between
graph and problem statement, and thus to integrate their information. In
conclusion, graphs influence where students look and what they process, and may
even mislead them into believing accompanying information. Thus, teachers and
textbook designers should be very critical on when to use graphs and carefully
consider how the graphs are integrated with other parts of the problem.
