Professor John Sweller, from the University of New South Wales School of Education, first came up with 'Cognitive Load Theory' in the 1980s. Most of his reasearch has been in the effectiveness of current teaching techniques. He has now produced evidence that PowerPoint presentations are impossible to take in if the information on the screen is the same as that which is spoken, because the audience’s attention will be split between the two.
'The use of Powerpoint presentations has been a disaster. It should be ditched. It is effective to 'speak to' a diagram because it presents the information in a different form, but it is not effective to speak the same words that are written."
"If you ever wondered why your eyes start glazing over as you read those dot points on the screen, at the same time the words are being spoken, it is because it is difficult to process the information if it is coming in the written and spoken form at the same time."
(modest cough)