Visual Aids and Slides

The Slide Epidemic

Edward Tufte, the Yale professor who pioneered information design, has argued that PowerPoint is actively dangerous — that it reduces complex ideas to bullet points and encourages speakers to read from slides instead of engaging their audience. He pointed to the Columbia space shuttle disaster, where critical engineering concerns were buried in a dense PowerPoint hierarchy that obscured the severity of the problem.

Tufte's critique isn't that slides are always bad — it's that most people use them as a crutch rather than a tool. The default approach (open PowerPoint, type bullet points, read them aloud) is the single worst way to use slides. Audiences can read faster than you can speak, so the moment you put text on screen, they stop listening to you and start reading. This is called the redundancy effect — when identical information is presented in two channels simultaneously, comprehension actually decreases.

Principles of Effective Slide Design

One idea per slide. If a slide requires more than six words to understand, it's doing too much. The presentation researcher John Sweller demonstrated that working memory can only hold about four chunks of information at once. Every element on your slide competes for those slots.

Images over text. The picture superiority effect, documented by Allan Paivio, shows that people remember images six times better than words after three days. A single powerful photograph communicates more than a paragraph of text and lets the audience listen to you rather than read.

The assertion-evidence model. Developed by Michael Alley at Penn State, this approach replaces traditional title-and-bullets with a sentence headline (your key assertion) supported by a visual (graph, photo, diagram). Research shows audiences recall 20% more from assertion-evidence slides than from conventional formats.

Dark backgrounds for large rooms, light backgrounds for small rooms. This isn't aesthetics — it's visibility. In a dimly lit auditorium, white backgrounds create glare. In a bright conference room, dark backgrounds wash out.

Worked Example: Fixing a Bad Slide

Suppose your key point is that renewable energy costs fell sharply. Here is the same content in three slide formats:

The assertion-evidence version does the work: the audience grasps the claim in one second and spends the rest of the time listening to you explain why it matters.