Vertical columns of background have, until ligatures, been a bullet proof means for brains to delineate characters. Is it possible to figure out with an increased cognitive load? Yes. Is it exactly as easy as without? No.
I'm confused, because I can delineate the characters in your comment fine, and this is with my browser's default sans-serif proportional typeface. I tend to read English text left-to-right, though, so if others are more comfortable reading top-to-bottom (or bottom-to-top, or middle-out), then my apologies.