This is such an obvious thing, and yet I see it all of the time when someone is using PowerPoint.
“If someone throws text up on a screen, you’ll read it. You have no choice but to read it. You don’t choose to read it. You do it at a much deeper cognitive level of automaticity. Text –> Read. Ask a colleague not to read what you’re about to show them, then hold up a piece of paper with a word on it. They’ll read it because they can’t not read it. It’s what we do. Now, if you’re saying anything other than the text on your screen, your audience is receiving two competing messages and asking their cortices to multitask. We are not wired for that. If both messages are important, you will be losing some of the information from one or both sources you’re trying to transmit.”
The number of people who can read one thing and listen to another is very small. It might be zero. Our brains can’t process two different things that require our understanding simultaneously.
Of course, that also doesn’t mean that you just read your slides. That’s just boring. No one likes boring either.
Visuals. It’s all about the visuals.