The Folly of Multitasking

Posted by Ricki Sharpe on May 31, 2007  
Filed Under Work Behaviour

How often have you seen Multitasking advertised as an essential requirement for a job, or perhaps the ability to juggle many balls at once? How effective do you think you are doing two things at the same time? e.g., checking email while talking on the phone, driving while answering a mobile phone, watching television while reading, or studying while listening to your favourite music.

You probably think that multitasking is a necessary part of life, and most of the time you get away with it. (Throwing in a load of laundry while talking on the phone, or driving while listening to the radio.) Human beings have always had the capacity to attend to several things at once, but how effective are we in doing it? Did you know, for instance, that losing a half second of time to task switching can make a life-or-death difference for a driver on a mobile phone travelling at 50 kph.

While much of brain activity remains uncharted, substantial literature exists on how the brain handles multitasking. And basically, it does not. Doing more than one task at a time, especially more than one complex task, takes a toll on productivity. Researchers who study what happens when people try to perform more than one task at a time have found that the brain was not designed for heavy-duty multitasking. They note that in some operations, say air-traffic control, mental overload can result in catastrophe.

When people try to perform two or more related tasks either at the same time or alternating rapidly between them, errors go way up, and it takes far longer, often double the time or more, to get the jobs done than if they were done sequentially. David E Meyer, Director of the Brain, Cognition and Action laboratory at the University of Michigan says: “The toll in terms of slowdown is extremely large, amazingly so. The bottom line is that you can’t simultaneously be thinking about your tax return and reading an essay, just as you can’t talk to yourself about two things at once.”

Even when we switch completely predictably between two tasks, we are still slower on task-switch than on task-repeat. Moreover, increasing the time available between switching for preparation reduces but does not eliminate the cost of switching.

Surprisingly, it can be harder to switch to the more habitual of two tasks. In one experiment people had to name digits in their first or second language, depending on the colour of the background. As one might expect they named digits in their second language slower than in their first when the language repeated. But they were slower in their first language when they had to revert back to that language.

As tasks get more complex, we lose more time during switching. In addition, we take more time when switching to tasks that are relatively unfamiliar. We get up to speed faster when we switch to tasks we know better.

In addition to reconfiguring control settings for a new task, there is often the need to remember where you got to in the task to which you are returning and to decide which task to change to, when.

What the Research Means

Although switching costs may be relatively small, sometimes just a few tenths of a second per switch, they can add up to large amounts when people switch repeatedly back and forth between tasks. Thus, multitasking may seem efficient on the surface but may actually take more time in the end and involve more error. Mental blocks created by shifting between tasks can cost as much as 40 percent of someone’s productive time. Real problems arise when switching costs conflict with environmental demands for productivity and safety.

Understanding the hidden costs of multitasking may help people to choose strategies that boost their efficiency above all, by avoiding multitasking, especially with complex tasks. For example, losing just a half second of time to task switching can make a life-or-death difference for a driver on a mobile phone travelling at 50 KPH. During the time the driver is not totally focused on driving the car, it can travel far enough to crash into an obstacle that might otherwise have been avoided.

Understanding switching costs and the light they shed on behaviour may help to improve the design and engineering of equipment and human-computer interfaces for vehicle and aircraft operation, air traffic control, and many other activities using sophisticated technologies. We need to design jobs and develop expectations that allow people to concentrate on one thing at a time, particularly for older workers. Young children do not multitask well, nor do adults over 60.


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