What is the point of Jason asking Kaneki to count backwards by 1000-7? What is the point of asking Kaneki the question 1000-7 at several points during his torture?

Is there some character development behind the reason hid did that? Or is it a known method of torture?
2 reasons:


First one being so that Kaneki doesn't go insane
To keep him mentally aware so that he constantly feels pain instead of trying to ignore it. By keeping him mentally engaged it prevents Kaneki from ignoring the constant pain cycle (although he later goes on to say that it helped him keep his mind on something else besides the pain - linking back to bullet 1, keeping him sane)


Source: Chapter 61 page 9 :)