Some people suspect that a multitasking lifestyle has changed how they think, leaving them easily distracted and unable to concentrate even when separated from computers and phones. Their uneasiness may be justified.

In several benchmark tests of focus, college students who routinely juggle many flows of information, bouncing from e-mail to web text to video to chat to phone calls, fared significantly worse than their low-multitasking peers.

Other studies have focused on multitasking's immediate effects — children doing worse on homework while watching television, office workers being more productive when not checking email every five minutes.

"We wanted to ask a different question," said Clifford Nass, a Stanford University cognitive scientist. "What happens to people who multitasking all the time?"

In a study published Monday in the Proceedings of the National Academy of Sciences, Nass and Stanford psychologists Anthony Wagner and Eyal Ophir surveyed 262 students on their media consumption habits. The 19 students who multitasked the most and 22 who multitasked least then took two computer-based tests, each completed while concentrating only on the task at hand.

First, they had to remember the briefly glimpsed orientations of red rectangles surrounded by different numbers of blue rectangles. In the second task, they were asked to categorize a random string of words, and then to do it again without categorizing words that were preceded by a beep.

In a third test, a different group of 30 high- and low-multitaskers were asked to identify target letters on a screen. As the test was repeated, they had to remember whether letters had also been targeted in earlier trials.

In every test, students who spent less time simultaneously reading e-mail, surfing the web, talking on the phone and watching TV performed best.

"These are all very standard tasks in psychology," said Nass. "In the first, there's lots of evidence that if people do poorly, they have trouble ignoring irrelevant information. For the second task, there are many demonstrations that this is a good reflection of people's ability to organize things in their working memory. The third task shows how fast and readily people switch from doing one thing to another."

As for what caused the differences — whether people with a predisposition to multitask happen to be mentally disorganized, or if multitasking feeds the condition — "that's the million dollar question, and we don't have a million dollar answer," said Nass.

Wagner next plans to use brain imaging to study the neurology of multitasking, while Ness wants to look at the development of multitasking habits in children.

"The causality question is enormous here," he said. "There's a lot of social pressure to multitask. You're getting tweets, e-mails, IMs from multiple people at once, and the web offers unbelievable opportunities for text and video. It may be thrust upon you."

Citation: "Cognitive control in media multitaskers." By Eyal Ophira, Clifford Nass, and Anthony D. Wagner. Proceedings of the National Academy of Sciences, Vol. 106 No. 33, August 25, 2009.

Image: Flickr/TotalAldo

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