Can you count to ten? Can you pat your head? Can you rub your tummy? Can you read? Of course you can. So, do each of these simple task right now, together. Or at least try. Come on! They are simple tasks. Now try reading, listening, writing and thinking all at the same time. Tricky eh? This is due to cognitive load. Your amazing brain is able to read and listen and write and think but not all, at full capacity, at the same time. This is why, for an audience, bulletpoints fail.
In a presentation, if there is text on a screen the audience will, without fail, read this. The reading will be out of synch with the speaking and these two processes are done in separate parts of the cortex. Adding further load to the system such as writing will necessarily cause the quality of the processes to drop. Realistically, no-one is actually able to read and listen at the same time and as soon as one attempts to write at least one of the other processes is lost, like the hypnotised chicken. Most importantly there is no cognitive space to think, question, challenge, expand or remember.
In a standard “powerpoint” presentation there are therefore four, independent processes running, at the very least. Whilst one may be able to count to ten, pat one’s head, rub one’s tummy and read, it is simply not possible to do them all at once, cognitive load. This is part of the science of powerpoint fail.