Human nature to keep jumping from one thought to another is one of the reasons that photoreading is so effective. You go in with a question and look for that answer. Thats why it is stressed to have a purpose for reading and knowing what you want from the text. If you don't know what you want how can you concentrate with focus?
It is also the reason it is strongly advised to stick to time frames when activating. It disciplines your concentration and focus. If you habitually go over the time you set for yourself your mind will go back droping concentration. Also remember to take breaks every 30 minutes definately after 50 minutes of studying and reading this allows your mind to intergrate what you have collected. Pointless having focus to the exclusion of the intergration process.
Alex