Psychologists Study the Effects of Diagram Orientation On
Comprehension. The orientation of a diagram on the page of a textbook may seem
inconsequential, but it can have a significant impact on a reader's ability to
comprehend the information as presented, according to a team of researchers at
UC Santa Barbara, Vanderbilt University, and West Carolina University. Their
findings appear in a recent issue of the journal Bioscience.
Focusing on variously formatted cladograms -- also known
as phylogenetic trees -- the researchers found that two diagrams may contain
the same information, but they aren't necessarily equivalent in terms of how
the information is interpreted. "In Western culture, we read from left to
right, so we naturally come to a diagram with that behavior," said Andrew
T. Stull, a researcher in the Department of Psychological & Brain Sciences
at UCSB and an author of the paper. "The important point in this research,
however, is that how efficiently a student comprehends the information
presented in the phylogenetic tree depends on how the tree is angled."
As it turns out, when a diagonal tree extends from tips
on the left to the root on the right, and the trunk angles downward to the
right-hand side, the information is more easily accessible. "The way we
interrogate the tree is first culturally based -- left to right -- and the
strong diagonal line tends to make us flow one way or another," said Stull.
"But that combined effect influences the accuracy, or how we're able to
use the tree effectively."
Although images in textbooks generally represent phylogenetic trees with trunks angling up and to the right, research shows that students have better comprehension when the trunks angle down to the right. (Credit: UCSB)
However, most textbooks depict the diagonal cladogram in
the upward orientation, Stull noted. "Many artists draw the diagram in an
inefficient and potentially confusing way," he said. "Artists have a
tendency to draw it at the upward angle, not realizing they'd communicate the
information better if they angled it downward."
The researchers used a phylogenetic tree for their
research because it is very important for a process called tree thinking.
"It's the idea that from an evolutionary perspective, there is a
distinctive relationship between taxa," said Stull. "It's not just
that things line up together on a tree, but you can infer certain biological,
physiological, and pharmaceutical commonalities that might be relevant. There
are a lot of things you can do in knowing how all of life is organized, and
each organism's relation to everything else."
Drawing them in tree form, Stull continued, should help
teach students the relationships between organisms, and to anticipate the
valuable information those relationships can provide.
The researchers used eye-tracking technology to carry out
their research. They showed test subjects one tree, and then another, and asked
them to determine whether or not they were the same. "In order to answer
the question, they had to interpret the two images," Stull explained.
"Then we took all the eye positions. What we found is that when people
studied the tree with the upward diagonal trunk, they were less accurate than
when the tree followed the downward diagonal."
Why the directional angle makes a difference may have to
do with how organisms represented by the individual branches relate to their
closest common ancestor and to those with a more distant common ancestor.
"With upward angled trunks, it may be because they [students] are thinking
of it from the root up," Stull said. "But it's more efficient to
think of it from the branches down. So, from an artistic perspective, it makes
more sense to build it that way. With that orientation, the user doesn't have
to deconstruct it in order to access the information."
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