Researchers from Southampton, England found the following: People combine parts of a word that were on average two letters apart. That means that two eyes basicilly won't work in harmony. When we read our eyes lock on to different letters in the same word instead of scanning a page smoothly from left to right as previously thought.
If these findings can help us writing better ad copies is a question that I cannot answer. Still research like this shows us that the current eyetracking studies have still room to improve.