Multi-tasking Has a Downside

By Katherine Reynolds Lewis
c.2007 Newhouse News Service
Illustration by Monica Seaberry

We feel so efficient, listening to a teleconference while sorting e-mail and eating lunch at the same time. But experts warn that instead of completing three tasks in the space of one, we're really spending more time to achieve mediocre results.

"Research that's looked at multi-tasking shows that you can't do it well. No one can," said Kristin Byron, assistant professor of management at Syracuse University. "You're fighting the way your brain works."

The brain acts on just one task at a time. What we perceive as simultaneous multi-tasking is really rapid switching back and forth to keep different tasks going even if one is as simple as deciding to lift the sandwich for another bite.

It's like the classic vaudeville act of spinning plates. Your brain can set a task in motion, then another, and then another, before returning to pick up the first task, explained David Strayer, a psychology professor at the University of Utah in Salt Lake City. "If the demands of any given task aren't too taxing, you can get two, three, four plates going up, but at some point you're going to reach a threshold when they're going to crash."


You may avoid driving while talking on a cell phone because of the physical challenge of holding both phone and steering wheel. But Strayer's research shows hands-free cell phone use is just as dangerous while driving. The risk comes in toggling between the two mental demands.

Moreover, subjects in a recent study scored significantly lower on IQ tests they took while driving. "When your attention is taken away from a task, you are not going to perform it as smartly," Strayer said.

So does multi-tasking make us stupid?

It's not an outlandish conclusion. A 2005 study sponsored by Hewlett-Packard found the average worker lost 10 IQ points when interrupted by ringing telephones and incoming e-mails about equal to the cost of missing an entire night of sleep.

"Interruptions are time-consuming, and they are dangerous in the sense that they can lead to errors," said David E. Meyer, a psychology professor at the University of Michigan in Ann Arbor. "You are trying to feed information through various kinds of processing channels in the brain which have limited capacity and are really only available for one thing at a time."

Whenever we drop one task to perform another, we face "resumption costs" the time and energy it takes to orient ourselves when we return to the original task.

It's true that interweaving two lengthy tasks can take less total time than performing the tasks separately. But there's a price.

"A lot of tasks we have to do, there are little moments of gaps which you can steal for another task," said Hal Pashler, psychology professor at the University of California in San Diego. "The interesting hidden cost ... is that (we) may be strikingly unable to recollect what happened."

That's because the free moments in each task such as waiting for a partner to respond in a conversation appear to be used to store or consolidate memories. If we talk on the phone while checking e-mail, it's at the expense of downtime our brains need.

"The conversation plus the e-mail may take less of your life, but the cost is that tomorrow you may not know exactly what you said," Pashler said.

Thus, if you try to take in new material or facts while multi-tasking, you'll have a tougher time learning, said Russell A. Poldrack, psychology professor at the University of California in Los Angeles.

Does all this mean we should never check our Blackberries while waiting in line at the grocery store? Or even sip a cup of coffee while listening to a conference speaker? After all, multi-tasking is woven into the fabric of modern life. More than 85 percent of people multi-task, and 67 percent believe they do it well, according to a survey by Apex Performance, a Charlotte, N.C., training firm.

Fortunately, the experts give us some slack. "You can't say in every situation it would be better to always focus on one task," Poldrack said.

If you're a stock trader who has to respond quickly to a lot of information, it makes sense to monitor multiple televisions and computer screens at once, he said. It may not matter that the next day you're hazy about which news anchor said what.

Certain physical actions, like walking or eating, are so hardwired that they don't tax our brains much. There's certainly no harm in combining simple, low-stakes tasks, like folding laundry and watching television. And if background music energizes you to finish your work, that may outweigh the cost of your mind shifting between listening and crafting a report, Poldrack said.

Similarly, talking to an adult passenger doesn't hurt your driving the way that talking on a cell phone does, Strayer has found. That's because the person in your car is attuned to the driving environment, and will pause the conversation when a tricky maneuver approaches.

To the degree that tasks rely on similar processes, they are more likely to interfere with each other.

Talking on the phone and writing an e-mail is hard, because both involve language, Poldrack said. Trying to remember a phone number while someone reads off digits is tougher than if the person were chatting, said Gordon D. Logan, a psychology professor at Vanderbilt University in Nashville. And, Strayer observed, a warning "beep" is better than a light for alerting an airplane pilot who is visually monitoring a screen.

The answer is to choose carefully when you take on more than one job at once. For high-priority or complex tasks, you might want to shut down your e-mail, turn off the phone and close your office door. Apex Performance founder Louis Czoka even recommends that clients shut their eyes to focus on a teleconference.

This story was originally published Friday, February 23, 2007.