They need to study the difference between familiar and unfamiliar words. They probably note this in the conclusion of the actual paper. I speculate that unambiguous and familiar words are recognized whole (in the same way a chess master recognizes the pattern of the whole board), and kids and adults finding a new or ambiguous word look at each letter and pause there to figure it out (like a chess novice looks at each piece and can only anticipate the next move).
I hope this work isn't used as ammunition in the whole word vs phonetics holy war.
The article doesn't really explain how reading occurs, although perhaps the original paper does. All the article says is that your eyes sometimes look at different spots.
I've also heard that a classic way for speed-reading is to then focus on the middle of each line of test. This minimizes eye movement and relies on your peripheral vision to read faster.
Most speed reading courses are based on theories as solid as air. Peripheral vision does matter in comprehension, but that doesn't make them suited for the bulk of information processing, let alone rely on them. When you actually take in information from the periphery you usually piece it together from imperfect cues, which suffices for waffly material but won't work if you're reading a textbook. Duh, you say, but the amazing courses will tell you it works for everything, and people believe it!
The read-between-the-line thing, AFAIK, is just supposed to make your eyes backtrack less, which lessens fixations. More fixations = slower reading; it doesn't matter where you place your eyes.
I read a paper that talked about the difference between dyslexic reading and normal reading. The researchers found that dyslexic people actually see too much at once and that by forcing them to focus on a smaller region of text (by, for example, having them read through a small hole in a piece of paper), they had much better performance. With consistent drills, they could even read without the mask.
Kim Peek ( http://en.wikipedia.org/wiki/Kim_Peek ) supposedly reads two pages at the same time, left page with left eye, right page with right.
I hope there is some followup study on split-brain patients.