Multitasking

Multitasking–doing several tasks simultaneously–sounds like a time management expert’s dream. What could be more efficient than, say, driving to work while talking to your secretary about the day’s meetings, or writing a report and dictating a letter while also catching the latest stock quotes on TV?

There’s just one problem–new studies show multitasking doesn’t work.

One study appeared in the August 1 issue of the journal NeuroImage. Dr. Marcel Just, a psychology professor and co-director of the Center for Cognitive Brain Imaging at Carnegie Mellon University in Pittsburgh, and colleagues used magnetic resonance imaging (MRI) to compare brain activity in people performing a single complex task with people performing two tasks at once.

The researchers found that when you do two things at once, brain power doesn’t increase to meet demand; in fact, it decreases, which means you perform each task more poorly than if you focused on it alone.

Active brain cells use more oxygen than inactive brain cells, and thus show up more clearly on MRI scans. Brain activity is measured in “voxels,” bits of tissue about the size of a grain of rice. The harder a region of a brain is working, the more voxels light up in the scan.

Previous research had shown that when a person attempts to, for example, visually track two objects at once, the region of the brain involved is actually less active than when that person visually tracks a single object. The new study shows that the same thing happens even when two different regions of the brain are in use.

The two tasks used in the study were language comprehension (specifically, understanding and responding to complex sentences), which uses the brain’s temporal lobe, and mentally rotating objects in space (volunteers were shown pairs of three-dimensional objects and asked to mentally rotate them to decide whether they were identical), which uses the parietal lobe. Eighteen volunteers had their brains scanned while performing one or both tasks. Each task, performed alone, activated 37 voxels in its respective region of the brain. But when both tasks were done at the same time, only 42 voxels activated, not 74.

Brain activity generated by mental rotation decreased 29 percent if the person was also listening to a sentence, and activity generated by listening to sentences decreased 53 percent if the person was also attempting mental rotation. The volunteers still successfully completed each task, but it took them longer.

This has implications for everything from cell-phone use while driving (talking and driving also use two different regions of the brain) to whether teenagers can really study effectively while watching TV or listening to music. And another study provides further ammunition for those who believe anything worth doing is worth your full concentration.

This study, led by Joshua Rubenstein, formerly of the University of Michigan and now with the Federal Aviation Administration, was published this month in the American Psychological Society’s Journal of Experimental Psychology: Human Perception and Performance. It found that multitasking is inefficient because whenever you try to do two things at once, you lose time as you switch from one to the other–and the more complicated the tasks, the longer the switch takes. That’s because each time you switch tasks you go through two distinct stages: deciding to do something new, and then turning off the mental rules needed to do the first task and turning on the mental rules needed to do the second.

Finally, a third new study focused exclusively on the using-the-cell-phone-while-driving type of multitasking and confirmed it’s a really bad idea. On behalf of the U.S.’s National Safety Council, researchers at the University of Utah put drivers in a car and had them brake and stop while also performing a variety of secondary tasks, such as changing radio stations, listening to the radio, listening to books on tape, talking on a hand-held cell phone and talking on a hands-free cell phone. The results: people using a cell phone (and it didn’t matter whether it was hands-on or hands-free) were much later braking for red lights–and much more likely to run them–than people who were just listening to the radio or a book on tape.

It seems the best way to perform multiple complex tasks is to do them one after the other, giving each your full concentration–especially if the tasks in question are driving a car and talking on the phone.

In other words, do us all a favor: pull over.

Permanent link to this article: https://edwardwillett.com/2001/08/multitasking/

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