Well whenever that happens to me I stop. Then I focus on reading one sentence and I think about it how it relates to the title and what I've read before, not trying to memorize it. After that I continue, but if you need memorization help go towww.luminosity.com
Also make sure your understanding what you read, not just word calling. Think about other stuff you know that might relate to what your reading. With the focus part I put my head in my hands with my palms against my temples, and my fingers in my ears. That cancels out noise, and if I get a headache it helps. Then I just read the passage at my own speed, after that I go onto the questions. If I get to one I don't know I hold my finger on that page, then find the answer in the passage.I hope I helped, sorry it's a little long!