[research at the University of NSW, Sydney, Australia, claims the human brain processes & retains more information if it is digested in either its verbal or written form, but not both at the same time.][1]
more of the passages would be understood & retained if heard or read separately. “The use of the PowerPoint presentation has been a disaster,” Professor Sweller said. “It should be ditched.”
[1]: http://infosthetics.com/archives/2007/04/powerpoint_bad_for_brains.html