Defending the Truth

Several research reports, both recently published and not yet published, provide evidence of the limits of multitasking. The findings, according to neuroscientists, psychologists and management professors, suggest that many people would be wise to curb their multitasking behavior when working in an office, studying or driving a car.

These experts have some basic advice. Check e-mail messages once an hour, at most. Listening to soothing background music while studying may improve concentration. But other distractions — most songs with lyrics, instant messaging, television shows — hamper performance. Driving while talking on a cellphone, even with a hands-free headset, is a bad idea.

In short, the answer appears to lie in managing the technology, instead of merely yielding to its incessant tug.

“Multitasking is going to slow you down, increasing the chances of mistakes,” said David E. Meyer, a cognitive scientist and director of the Brain, Cognition and Action Laboratory at the University of Michigan. “Disruptions and interruptions are a bad deal from the standpoint of our ability to process information.”

The human brain, with its hundred billion neurons and hundreds of trillions of synaptic connections, is a cognitive powerhouse in many ways. “But a core limitation is an inability to concentrate on two things at once,” said René Marois, a neuroscientist and director of the Human Information Processing Laboratory at Vanderbilt University.

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The young, according to conventional wisdom, are the most adept multitaskers. Just look at teenagers and young workers in their 20s, e-mailing, instant messaging and listening to iPods at once.

Recently completed research at the Institute for the Future of the Mind at Oxford University suggests the popular perception is open to question. A group of 18- to 21-year-olds and a group of 35- to 39-year-olds were given 90 seconds to translate images into numbers, using a simple code.

The younger group did 10 percent better when not interrupted. But when both groups were interrupted by a phone call, a cellphone short-text message or an instant message, the older group matched the younger group in speed and accuracy.

“The older people think more slowly, but they have a faster fluid intelligence, so they are better able to block out interruptions and choose what to focus on,” said Martin Westwell, deputy director of the institute.

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In a recent study, a group of Microsoft workers took, on average, 15 minutes to return to serious mental tasks, like writing reports or computer code, after responding to incoming e-mail or instant messages. They strayed off to reply to other messages or browse news, sports or entertainment Web sites.

“I was surprised by how easily people were distracted and how long it took them to get back to the task,” said Eric Horvitz, a Microsoft research scientist and co-author, with Shamsi Iqbal of the University of Illinois, of a paper on the study that will be presented next month.

“If it’s this bad at Microsoft,” Mr. Horvitz added, “it has to be bad at other companies, too.”

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But the paper also found that “beyond an optimum, more multitasking is associated with declining project completion rates and revenue generation.”

For the executive recruiters, the optimum workload was four to six projects, taking two to five months each.

The productivity lost by overtaxed multitaskers cannot be measured precisely, but it is probably a lot. Jonathan B. Spira, chief analyst at Basex, a business-research firm, estimates the cost of interruptions to the American economy at nearly $650 billion a year.

That total is an update of research published 18 months ago, based on surveys and interviews with professionals and office workers, which concluded that 28 percent of their time was spent on what they deemed interruptions and recovery time before they returned to their main tasks.

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Slow Down, Brave Multitasker, and Don’t Read This in Traffic - New York Times