touching the area at the back of the head triggers that part of the brain into action. You might even notice some activity there. It helps to just put some of your awareness there. You can imagine yourself standing behind you while you are reading or you can simply imagine the weight of the tangerine there. Whenever you feel your attention drifting away from reading or you feel that you have slowed down just become aware again of the 'weight' of the tangerine at the back of your head.
Actually touching the area will help to give you a sensation to focus on. Play with it and see what works best for you.
I personally found going through the motions tossing the tangerine from one hand to the other, smelling it, imagining it's colour before I placed it at the back of the head the first helped a lot in putting my awareness. Now I just need to think of it there when I read or write 
Alex
