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Hey, Matt: I want some information on multitasking. Everybody seems to be able to do it. Sometimes I’m on my computer and texting and doing my homework at the same time. How does my brain work when I do that? Is there a limit to the number of things a person can do at one time? How do I know if I’ve reached my limit on multitasking? — Busy BB, via email

How does your brain work when you multitask? Uh, not very well, sorry to say. It looks pretty impressive from the outside, all that frantic activity. Fools you into thinking things are buzzing along nicely. But your brain is sweating and nothing much is getting done well. And there’s a real simple explanation.

Once again we have to give thanks to the science guys, who’ve spent many hours and even more dollars probing the brains of busy people. And all the white coats have come to the same conclusion. The human brain can handle well a maximum of two tasks simultaneously. That’s it. Add another task, and things fall apart.

Our task-handling brain parts are in our frontal lobes, right where you smack yourself in the forehead when you’ve done something dumb. It’s the “goals and rewards” center. There are two of these, one in each lobe of the brain (remember, our brains are built in two side-by-side parts). Here’s how they work: You sit down at your desk, grab that trig book, and find the assignment. Then, of course, we have to pop in those iPod buds and fire up the tunes. Dig into homework. Okay. That’s two tasks. The two lobes are clicking along pretty well. Each lobe is handling its own task.

But suddenly your girlfriend sends you an IM. Aaak! Task number three. You switch from trig and tunes to girlfriend and your brain loses track of what’s going on. In fact, one of your first tasks (probably trig) gets dropped off the radar so your lobes can get back to their comfortable two-task limit (IM plus iPod). No lobe is handling trig.

IM over, you go back to trig, and the lobes have to rebuild the steps you took to get to wherever you were when girlfriend interrupted. It might not seem to take very long, but there is always a delay when the switch is made. So, multitasking is very inefficient. It’s been proved over and over. As much as people love multitasking, and as much as your boss loves to pile on the work, it’s a very bad idea.

Somehow, people think our brains can handle tasks in parallel; that is, all at once. No, no, our poor lobes handle things the way a computer does, in a linear, serial way. So, the more tasks you have, the more interruptions you have and the less progress and accuracy you achieve.

Unfortunately, recent research suggests that young people could develop a sort of addiction to multitasking. It might have something to do with a big brain rush or other kind of stimulation involved. The teens can’t concentrate unless several other things are drawing their attention. The jury’s still out on this one, but early tests indicate it could be true. Not a good trend.

See how this applies to driving and talking on a cell simultaneously? Driving is a very complicated activity that eats up all your lobular energy. Add a cell phone to the mix and you have a third task, so something in your driving is dropped from the radar. Maybe visual processing. Maybe your awareness of dangers. Tests have indicated that celling and driving cuts down on your peripheral vision, which means you’re less aware of any cars coming at you from the side. With enough practice, driving becomes a sort of automatic task, relieving your brain from having to process the activity in great detail. But phoning still reduces your safe-driving skills. Don’t bother to argue the point.

So, multitasking? Two’s plenty, three’s too much. End of discussion.

Dear Matthew: How many times can you recycle a piece of paper? — Anonymous, via email

According to the technical association of the paper pulping and recycling industry, you can reuse old paper five to seven times before it craps out. This sounds simple, but how can you tell how many times any individual cellulose fiber has been processed? Luckily, the fibers check themselves out when their time is done.

Paper is recycled by turning it back into its basic form — individual cellulose fibers — in big vats of water and chemicals. Young, studly fibers, on only their second or third go-rounds, maintain their long, springy form. Geriatric fibers are brittle and eventually shatter. These pieces are filtered out or skimmed off in the processing, before the new paper is made.

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