Fifty years ago in Washington D.C., Martin Luther King Jr. departed from his prepared remarks and delivered a speech that left an indelible mark on the American conscience. No PowerPoint, no technology — just imagery and cadence. He watched his audience, not a screen.

In an age where so many of us rely on technology and PowerPoint presentations, the most effective communicators understand that, to persuasively present ideas, you have to understand your audience and react to signals sent to the presenter in real time.