The vertical edge shape contrast has also been noted to have an effect on comprehension (as in ragged right vs full justification). A few resources/papers:
The TL;DR version for those who don't want to bother with the links:
Full justification creates "rivers" of white space (effectively spaces above and below that partially line up forming a white line snaking down part of the page).
The eye has a tendency to follow these down the page which leads to either skim reading (you just resume reading where the river stops) or having to go back and reread and not get caught by the river this time.
Either obviously compromise the information you're taking in.
http://onlinelibrary.wiley.com/doi/10.1111/j.1467-8535.1986.... http://kaiweber.wordpress.com/2010/05/31/ragged-right-or-jus... http://www.eric.ed.gov/ERICWebPortal/search/detailmini.jsp?_...