Omori, Takahide, Taku Ishii, and Keiko Kurata. 2004. Eye catchers in comics: Controlling eye movements in reading pictorial and textual media. In 28th International Congress of Psychology. Beijing, China.
A team of Japanese researchers perform two experiments examining eye-movements across comic pages to show that both page layout and balloon placement factor into how readily comic pages are read.
They found that, for an average of 8.5 panels per page, there are an average of 20.3 fixations. Most of their study focuses on panels that were skipped over for one reason or another, and examining modifications made to see whether they would still be skipped over.
There were two major changes that showed significant effects in decreasing the rates that they were skipped: balloon position and panel layout.
The first factor in skipping is if a panel is followed by another panel with dense text. They altered the "dense balloon panels" by distancing the balloon further away from the preceding panel. This change resulted in a significant reduction in the times that the preceding panel was skipped.
The other major factor was when panels were vertically stacked next to a long adjacent panel (what I call "blockage"). The lower panel was often skipped so the reading follows the horizontal path. When altering these layouts to make the panels horizontally arranged, the rate of skipping decreased. However, this phenomenon was only observed in a couple of scenarios (6 instances) and they don't mention how many of these skips lead to going back and rereading the skipped panel. They also don't state how many times "blockage" occured and didn't lead to skips.
Slight decreases in skipping were shown for moving characters' positions within a panel, though not to high percentages (significance is not shown).
Additionally, a recognition task asking whether various panels were or were not in the comic showed significant increases in accuracy for the modified versions. No differences were shown in accuracy of reading comprehension for the story.
While they state that their participants all had comic reading experience, I wonder the degree of "comic fluency" that they have. The desire to jump towards panels with dense text insinuates a focus more on text than on the visuals, which was characteristic of a naive comic reader's eye-movements compared with an expert reader in Nakazawa's eye-tracking study.
Further, this study supports an idea that "blockage" situations are harder to process (evidenced by the skipped panels). However, I have empirical evidence from my own experiments on page layout (to be posted soon hopefully) that following the vertical path of panels is the prefered reading path, and that preference for it does depend at least partially on expertise in comic reading. Also, their studies used only the results from 25 subjects (half seeing modified versions half not), whereas mine used 145, so looking at a broader populace would be good here.
Hypothetically, I could tackle this issue myself, since the lab next door to mine has an eye-tracker at my disposal. We'll see... I have a few other things on my plate right now.