Fascinating article about the effects of multitasking on learning from Chron. Higher Ed. (thanks @krelnik)

"I'm teaching a class of first-year students," says David E. Meyer, a professor of psychology at the University of Michigan at Ann Arbor. "This might well have been the very first class they walked into in their college careers. I handed out a sheet that said, 'Thou shalt have no electronic devices in the classroom.' ... I don't want to see students with their computers out, because you know they're surfing the Web. I don't want to see them taking notes. I want to see them paying attention to me."

Wait a minute. No notes? Does that include pen-and-paper note-taking?

"Yes, I don't want that going on either," Meyer says. "I think with the media that are now available, it makes more sense for the professor to distribute the material that seems absolutely crucial either after the fact or before the fact. Or you can record the lecture and make that available for the students to review. If you want to create the best environment for learning, I think it's best to have students listening to you and to each other in a rapt fashion. If they start taking notes, they're going to miss something you say."

Give Meyer his due. He has done as much as any scholar to explain how and why multitasking degrades performance. In a series of papers a decade ago, he and his colleagues determined that even under optimal conditions, it takes a significant amount of time for the brain to switch from one goal to another, and from one set of rules to another.

"I've done demonstrations in class," Meyer says, "whereby they can see the costs of multitasking as opposed to paying attention diligently to just one stream of input."

He might, for example, ask students to recite the letters A through J as fast as possible, and then the numbers 1 through 10. Each of those tasks typically takes around two seconds. Then he asks them to interweave the two recitations as fast as they can: "A, 1, B, 2," and so on. Does that take four seconds? No, it typically requires 15 to 20 seconds, and even then many students make mistakes.

"This is because there is a switching time cost whenever the subject shifts from the letter-recitation task to the number-recitation task, or vice versa," Meyer says. "And those extra time costs quickly add up."