I will add that this effect is broader than just reading aloud. Memory is incredibly tied to place and time - everytime you try to memorise abstract information you are mostly remembering your location and events going on in the background (birds chirping in the trees, dog barking, light streaming through the window, the room temperature, etc, etc).

If you really want to remember abstract information try to vary the background environment as much as possible. Go over the material in as many different locations as possible, with as many different outside cues as possible. Doing this the different environments cancel out leaving only the information you want to remember.