I dont drink seven cups a day....but this is what the "experts" claim. http://news.yahoo.com/s/afp/20090114/hl_afp/britainhealthcoffeepsychology
I don't drink a lot of coffee but I tend to hear voices a fair bit. Drinking that much coffee a day must have some side effects, so I wouldn't be surprised if this was one of those.
Those of us who drink 7 plus cups of coffee daily usually don't sleep much... sleep deprivation causes hallucinations too. I hope Durham Uni didn't spend too much on this research... it seems a kind of given too me.