First, correct the most fundamental role confusion: slides exist to aid you (the speaker), not to move everything you want to say onto the screen.

Garr Reynolds (*Presentation Zen*) and Nancy Duarte (*slide:ology*) both stress that a slide is a 'glance medium' — a slide should be graspable in about 3 seconds, after which the audience hands their attention back to you, the person.

So the principle is: **put what should be *seen* on screen (an image, key data, a single claim), and *say* what should be heard (the explanation, the story, the connections).** Piling whole speaker notes or big blocks of text onto the screen lets the slide steal your role; anything that needs detailed text should be handed out as a post-talk handout, not stuffed into the live slides.

The redundancy principle (Mayer 2009): don't turn on-screen text into the words you're already saying.

Cognitive psychologist Richard Mayer found that people learn better from 'graphics + narration' than from 'graphics + narration + on-screen identical text.'

Why: when the on-screen text nearly repeats what you're saying, the audience's visual and auditory channels are occupied twice by the same information, and they end up reading the screen instead of listening to you — which actually splits attention and raises cognitive load.

What to do: keep only keywords / images on screen, not full sentences; deliver the explanation with your voice, and don't force the audience to choose between reading and listening.