Never done it with a text book however I have done a similar experiment. By accident actually. I was dubbing a video lecture and had the monitor going while watching the news on TV. I later watched that video and was amazed at how ahead of what he was talking about and I did understand the information at a deeper level. The interesting thing was the sound was off. I am strong lip reader so that particular experience may not work for most people.
It's definitely worth thinking about.
Alex
