They are prey to a form of stuttering known as thrashing, in which resources are swapped back and forth among tasks so rapidly that no work gets done. The human analogy to thrashing may pertain to memory. When immersion is impossible, focus minimal, and switching rapid, it may be that a crucial step in the binding of memories has been omitted.
It certainly looks as though multitasking impairs your memory. You cannot remember anything because you haven't concentrated on it long enough to penetrate your head.
He also talks about air traffic controllers but they don't work 8 hours straight. They are on a up and down schedule of a hour up and an hour down to rest and recuperate, it is a hard job.
I have noticed in myself that I am more productive when I can concentrate for a couple of hours on a single topic rather then thrashing and not being able to remember what I did all day.
I guess that explains why one of my schoolmates did so poorly, he may have been ADD though it was before ADD was discovered, He would work on all his homework at once: math english, geography all at the same time. He was trying to do his homework faster but all he did was fail.
I have organized my day to be more concentrative.
An hour of reading to warm up the old grey cells.
Two-three hours for flow time on the most important things.
Then all the communications stuff: phone, email, RSS, web, and the rest after I have got something done.
That is far more productive then the old way which started with email and left me feeling scatterbrained and pulled in a thousand directions all day. I was reacting to the day and the interruptions rather then acting on them.