Research has shown that speakers who talked at a fast rate of 191 words per minute were considered more persuasive than slower speakers. And increasing rates of speed were considered more interesting to the studied subjects. So, if you want to persuade your audiences and appear interesting, just talk quickly. Right?

Even if you're delivering straight informational content, there's still a limit to how much of one kind of sensory input a person can process at a stretch. Think of a song you like. Often, the pattern of the first verse is followed by a the chorus variation, and this verse/chorus pattern is repeated and followed by a bridge variation--returning to the verse/chorus pattern to end the song. In popular music, the total elapsed time is about 3 minutes. Emotional songs that pull the heart strings are slow (like Whitney Houston's "I Will Always Love You" or Toni Braxton's "Unbreak My Heart"), and uptempo, patter songs that tell a story or convey information are fast (most songs by Gilbert & Sullivan, Eminem's "Lose Yourself").

So what does any of this have to do with business presentations?

The thing called "attention span" is your audience's ability to track what you're saying based on how you're saying it. So here's how to lose your audience's attention:

1. Only do one thing (all content or all slow or all one tonal quality)

2. Do one thing too long (15 minutes of slow content in a whisper)

3. Ignore the signs your audience needs you to do something new (fidgeting, browsing email, watching the clouds move outside the window)

And here's what to do about it:

Appropriate variation: If you're giving a 15-minute presentation and spend more than 3 minutes doing one of anything, you're spending too much time for too little effect. A well-constructed speech will have a deliberate layering of set-up, information, and transition. Each of these sections is for a different effect, and requires a variation of delivery. This might look like telling the board the high level headline, providing supporting data, and linking to the next area of critical content. Or presenting students with a provocation, fleshing out the concept, and posing a question to open further inquiry. Talk quickly and clearly when conveying data to keep up with the processing speed of the brain making pictures of your concepts. Slow down when communicating the emotional import of a story so that the audience can generate the feelings that will motivate them toward your call to action.
Useful segmentation: The best speakers follow classical story-telling structures--even if they are delivering financial reports to a corporate audience. Understanding the tolerance of your audience to long stretches of unvarying information is as critical as understanding the content they expect to receive. For most audiences, a good structure to use has short sections, with clear transitions and direct language, where each element builds on the preceding one.
Attentive conversation: Even if you are "broadcasting" a message from a stage, your audience is constantly participating with you. They are in "conversation" with you. The best speakers organize their content to calibrate audience feedback (laughter, groans, silence) to know how to lead the group where the speaker wants to take them.

The value to your audience is that you will use their time well, keep them engaged, and deliver content that is relevant to their needs. And they, as a result, will always love you. We hope.