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National Public Radio/Morning Edition
Problems associated with multitasking (edited transcript)

August 6, 2001 Monday




MONTAGNE: Two thousand years ago a Roman sage said: To do two things at once is to do neither. Today it's more like 10 things at once. Scientists are learning more about how the brain deals with multitasking, and they even have a few practical suggestions. NPR's Joanne Silberner reports.

SILBERNER: You may be multitasking right now and not even realize it. You are if you're cooking breakfast or braking as the traffic slows while you're listening to MORNING EDITION. Maybe you're also on your cell phone. When you get to work, there'll be more. Looking at a spreadsheet while you're filing something away while worrying about your family or that lawn that needs mowing after work. How well can people do more than one thing at a time? David Meyer and his colleagues (Joshua Rubinstein and Jeffrey Evans) at the University of Michigan decided to measure the effects of multitasking. They asked several dozen student volunteers to switch back and forth between different types of arithmetic problems, multiplying and dividing, for example.

MEYER: If people had to switch back and forth between one of these tasks and another repeatedly, the time that they took to finish was quite a bit larger in comparison with how long it took when simply doing the same task over and over again.

SILBERNER: In other words, it might take them a minute to do 10 multiplication problems, but a mixture of 5 multiplication and 5 division problems might take an extra 15 to 20 seconds more than a minute. During task switching, the brain goes through an extra series of steps that take time and involve executive mental control, says Meyer.

MEYER: These executive control processes include ones that allow you to remember what your next task is supposed to be, enable you to get ready for doing the procedures that are going to be used next, and refocus your vision, your hearing, or whatever.

SILBERNER: Inside the brain, there's a price to pay. That's what Marcel Just of Carnegie Mellon University says. He put 18 volunteers into a brain imaging machine to see what parts of the brain they used when they listened to sentences while trying to mentally rotate visual objects.

JUST: We found that the amount of activation in the brain was substantially reduced for a given task if the task was being performed simultaneously with another one.

SILBERNER: Just had supposed that the different areas of the brain used for the two tasks wouldn't care that there was activity elsewhere in the brain, or that each area would have to work extra hard. The finding that each area worked less shows that there simply aren't enough resources in the brain to support both tasks simultaneously, he says.

JUST: It suggests that there's an overall constraint on how much work can be done in any given time, and parceling it out among brain parts doesn't get around that constraint.

SILBERNER: So apparently you don't get as much brain power aimed at either task. And multitasking takes more time than doing one thing at a time. Meyer's advice?

MEYER: If you can avoid it, don't multitask.

SILBERNER: If you have to do it, pick your tasks wisely, Just says.

JUST: Sure, have a conversation with the passenger in your car, but note to cut that conversation off sharply when the traffic becomes particularly demanding.

SILBERNER: Meyer has done studies that show that people can improve their multitasking ability with training -- at least with simple tasks. With practice, they can reduce the time it takes them to respond to a visual prompt on a computer while also listening for an auditory prompt through headphones.

MEYER: If you have people practice multiple tasks while giving various levels of emphasis to each task, then over a period of time, you can literally improve the efficiency of people's multitasking under these circumstances. In essence, it's a kind of mental yoga.

SILBERNER: But there's a limit. Meyer says workers and bosses tend to overestimate their ability to multitask.

MEYER: And as a result of making these false inferences with respect to how their mental processes work, people get themselves in deep trouble, both for predicting their own performance and the performance of others.

SILBERNER: That happens especially with cell phones, he says. Both multitasking researchers (Just and Meyer) oppose cell phone use, except in the simplest driving conditions: well-known roads with little traffic.

Joanne Silberner, NPR News, Washington.

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