Avoid ‘cognitive backlog.’
In the early 1980s, researchers found that people suffer from “cognitive backlog.” Simply put, information acts like weights–the more you pile on, the more likely you are to drop everything. A 5-minute lecture produces a relatively small amount of cognitive backlog, while a 30-minute lecture produces a relatively large amount of cognitive backlog.
In addition to cognitive backlog, your audience has a short attention span that will seek out alternative stimulation, regardless of how captivating you think your PowerPoint might be. In other words, the brain gets bored really easily.
Biologist John Medina studies how the brain processes information. Medina has found that–given a topic of moderate interest–people will begin to tune out after approximately 10 minutes. Now, that doesn’t mean you should end your presentation after 10 minutes, but it does suggest that you should re-engage the audience at the 10-minute mark. Showing videos, giving a demonstration, and telling stories are simple ways to bring your audience back from their daydream.
Spending 10 minutes on a new business pitch may not give you enough breathing room to flesh out your idea. On the other hand, spending too much time results in cognitive backlog, which makes it hard for your audience to remember your key points. And that brings us back to the TED Talk rule of 18 minutes. Eighteen minutes is the Goldilocks zone of presentation length. It also forces you to really think about every word and to clarify your argument.
Rest assured, you can accomplish a lot in 18 minutes. John F. Kennedy persuaded a nation to reach for the moon in 18 minutes at Rice University in 1962. Steve Jobs gave one of the most popular commencement speeches of all time in 15 minutes at Stanford. And in a TED talk that’s been viewed more than six million times, historian David Christian explained the history of the world in 18 minutes. That’s a lot of ground to cover, but Christian managed to do it.
PUBLISHED ON: FEB 21, 2017