That's because it's the picture in the mind's eye of your listeners. If you succeed in putting it there, you'll drive your point home and keep it in their memories, long after your presentation's over. Helping them "see" what you're saying aids understanding and can help you persuade, without over-explaining or preaching.
Why do the mental pictures the audience members create work so well as visuals? Noted biographer Robert Caro says "the places in your mind's eye" help because you "will have succeeded in bringing the reader closer to an understanding of the character without giving him a lecture, will have made the reader therefore not just understand but empathize with a character, will have made the readers’ understanding more vivid, deeper than any lecture could.”
How can you make sure your audience has a mind's-eye picture as a takeaway? Here are some tactics:
- Give us the detail: Too much detail on a slide can cause the audience to check out, but details make the descriptions that create mental pictures. Tell us what the orphans you help are wearing when their adoptive parents pick them up, or share what the candy you manufacture tasted like when you first sampled it. In this TED talk about research on ice cores in Antarctica, we find out that the scientists have to keep the lab cold enough to keep the ice samples from melting--so they wear gloves heated in an oven to keep their fingers working, a detail I can picture, and remember.
- Make it concrete: This is no time for jargon, buzzwords and flowery adjectives. Use concrete nouns and active verbs, shapes, colors, temperatures, size, distance and whatever else will make that invisible visual seem more real to us. Help us smell those loaves of bread baking or hear the truck noises.
- Don't forget gesture: You can underscore a mental picture and make it memorable with a gesture. You don't need to act anything out, but a simple hand angling up to the ceiling can help us "see" a rocket take off, for example. Just don't overdo the gesturing. Your words count here.
- Plan where the picture belongs: As you're planning your presentation, give thought to the moment or moments when you want to create a mind's-eye picture. Does it arrive during a story? As an example supporting one of your key points? Are you explaining some data? Introducing yourself? Building sympathy for your cause? Starting a relationship with the audience? Make the invisible visual work, rather than just toss it in.