Interesting. I don't think I agree with this example, though: He might, for example, ask students to recite the letters A through J as fast as possible, and th

Interesting. I don't think I agree with this example, though: 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. That's not a fair comparison. When I quickly recite the numbers from 1-10, I'm not figuring out which number comes next each time, I'm reciting an incredibly well-rehearsed script I have memorized. Same with the letters. I could memorize the sequence A-1-B-2-... Then I bet I would be able to recite it in 4 seconds. To better capture the "switching time" that purports to demonstrate, you'd need to interleave two tasks which each require that kind of "next step" generation. e.g. Time someone giving every other letter and the square numbers, for instance. It's pretty easy to determine the sequence for each of those, and it's unlikely that someone's memorized the whole thing already.