A friend of mine down in Singapore, Jim Quirk, was telling me this week about a great professor he had back in college. The professor was Dr. Nobel Peterson at the University of New Hampshire. As you can see from this link, he was beloved by his students for being such an outstanding teacher. Here's what my friend had to say about his professor's teaching style:
"...at the precise time for the class to start, the lights went out and suddenly an explosion, and through the smoke appeared Dr.Peterson dressed like a cross between the Arabian Nights and Harry Houdini complete with Cape, Wand, Turban, etc. and we began with the formation of the earth and off we go — every class began with the point of the days lectures.
"Next I was very surprised to find he would never lecture for more than 7 minutes without a break. As he said, after that point you've stopped listening so why carry on? During the 3-minute breaks he would play excerpts from Bob Newhart albums. Needless to say, the class time would fly by and he always left you wanting more. All this was done with overheads and a simple phonograph — imagine what he could have done with today's technology."
I often say that whatever the actual time may be (for audiences to maintain concentration), it is certainly far less than the typical presentation or lecture today. I like the idea of a "seven minute rule." This does not mean you have to stop everything and play a comedy CD or tell a joke, etc. But it is very good advice to plan for your presentation to change gears about every seven minutes or so.
For example: You could show a short video clip to demonstrate a point. Handout an activity in which the audience participates. Take questions to make sure the audience understands you so far, or get examples/personal anecdotes from the audience related to your point. Exhibit a graphic that illustrates your point (in PPT or some other medium). Hit the "B key" in PowerPoint (screen goes blank), move to the center, smile, and tell a very short story that supports your theme or point. Use physical props if appropriate, and on and on.
In a statistics class in grad school, my professor brought in a huge gumball machine filled with hundreds of colored gumballs to illustrate issues related to sampling. Brilliant! The lecture was more meaningful, engaging and memorable. We learned the stuff while having fun. Rather than lecture on and on about sampling, she lectured a bit, told stories, and came back to the gumball machine from time to time.
The point? If you are speaking for 20 minutes or 120 minutes, you must break the time up...after seven minutes or so, they probably are not listening anyway, so for who's benefit are you speaking then?