The "speech suppression effect of PowerPoint"

No substitute for simply talking to the audience


A slide from the Munich study with 35 words caused speech suppression in the lecture.
The only reason for bringing people together in any form of speech, lecture or presentation—whether in the room or via Zoom—is to listen to someone share something of value.

Without a speaker, lecturer or presenter, there simply cannot be a speech, lecture or presentation. Slides and decks are not presentations. They are written documents. If you don’t need to gather together, send an e-mail or a text. Send the slides. Write an article. Or post an item to social media.

Researchers at Ludwig-Maximilians-Universität München, led by Professor Christoph Wecker, tested two types of slides—what they called “regular” and “concise” slides—versus a control group of simply talking to the audience. They then tested the audience’s understanding and retention of what was presented.

The researchers concluded that the retention of oral information was significantly lower during lectures that used regular slides compared to lectures without slides, and that simply talking to the audience led to greater overall retention of the information presented.

Professor Wecker calls this a speech suppression effect. If you buy into the argument that presentation value comes from what the presenter says (otherwise, why have a presentation?), suppressing spoken information is counterproductive. Significantly less of what is presented makes it to the long-term memory of the audience, which negatively impacts communication effectiveness.

Unless, of course, the purpose was something other than having the audience remember what was presented.

But Professor Wecker and his team went a step further. If the audience loses a large portion of what’s said while slides are shown, is there an offsetting gain to using slides? In other words, if slides take away from communication effectiveness in one area, do they add value somewhere else?

Dr. Wecker’s team determined the answer to both questions is an unequivocal no. “It is remarkable, however, that this ‘suppressive’ effect of regular slides,” they said, “could not be demonstrated to be the downside of a trade-off in favour of the retention of information on slides.”

When presentations use what the researchers call regular slides (of precisely the same density—the same number of letters and words—as the slide above), audiences lose huge portions of what is said. And the communication effectiveness lost by showing slides is not regained anywhere else, leading to a net negative impact of using slides.

I changed the words on the slide into gibberish, but this was the exact density of a slide in the study. With about thirty-five words each, Professor Wecker’s regular slides are almost identical to the six-by-six guideline (six lines of text with six words per line) that many presenters have adopted as a rule of thumb. Dr. Wecker demonstrated that the six-by-six approach significantly decreases a presenter’s ability to move information to the long-term memory of the audience.

Words on slides simply do not work. The more the audience has to read, the less they hear. The less they retain. Period.

Even a slide with 13 words impeded the communication process. But Professor Wecker’s team didn’t stop there.
They also tested what they called concise slides. This test, using slides identical in density to the slide shown at the right (for which I’ve changed the words to gibberish once again), contained six slides (four fewer than the presentation with standard slides): a title slide, a structural slide, and four additional slides. None of the concise slides contained more than seven lines (excluding the heading) or five bullet points. The example on this page has twelve words.

The researchers also used “black” slides between the regular slides, removing all information from view. However, while the concise slides improved communication outcomes when compared to standard slides, nothing worked better than removing slides from view and simply talking to the audience. Bullet points, even those as skimpy as the twelve words shown on this second slide, overload working memory.

What does this mean for you? You have a choice. You can continue to show bullet points, quotes, sentences, charts, graphs and paragraphs to the audience while you’re talking. If you do, the message is one hundred percent clear: your communication effectiveness will be negatively impacted. The audience will be less likely to remember anything.

Alternatively, you can choose to set yourself and your ideas apart by focusing on having a conversation with the audience. Use notes to keep yourself on track and on time when you deliver your presentations. But don’t show your notes to the audience.

When you need a visual to aid understanding, use it. But when it’s no longer needed, remove it from view and carry on the conversation.

It is your best hope for having your ideas remembered after they have left the room or signed off Zoom.

most critical presentation skill

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