I've escaped near-hits from cell-phone chattering drivers often enough to know that—as Sue Shellenbarger put it in the Wall Street Journal—multitasking makes you stupid. Multitaskers think their brains are buzzing along in cruise control as they listen to music, talk on the phone, surf the Net, and write an email all at the same time, but numerous scientific studies have shown that the brain is actually jerking from one task to another.

The research base underlying that conclusion has been developing for more than a decade. In one pioneering experiment (published in 1999), Canadian researcher Pierre Jolicoeur showed test subjects a computer display that flashed either an X or a Y. The respondents' job was simply to identify which letter. The task was easy, but it got harder when the people heard a tone played at the same time and they were asked to differentiate high and low pitches, while still naming the letters. With sound interfering, the X-Y task took longer and subjects made more mistakes. The brain has what Jolicoeur called "restricted attentional capacity." It can deal with only one set of inputs at a time.

This week, new research from Stanford added to the growing body of evidence that multitasking is madness. Clifford Nass and his colleagues asked students to fill out a questionnaire, estimating how often they multitasked with various media, including printed materials, television, computer-based video (such as YouTube or online TV episodes), music, nonmusical audio, video or computer games, telephone, instant messaging, Web surfing, and other computer-based applications (such as word processing). From those responses, the researchers calculated a score that differentiated low (infrequent) from high (habitual) media multitaskers.

The students then completed a battery of tests. In one, designed to measure how well they could filter out extraneous stimuli from the environment, the subjects had to look for changes in red rectangles while ignoring blue rectangles displayed on a computer monitor. The infrequent multitaskers scored well on the test, but the habitual multitaskers performed poorly. The blue rectangles distracted them. In another test, the students had to recognize whether they'd seen a letter before. Both groups got equal numbers right, but the high-media-multitaskers made more mistakes. They "remembered" things they shouldn't have, indicating-according to the research team-a diminished ability to filter irrelevant information from working memory.

You might expect, however, that frequent multitaskers proved expert at switching between tasks. After all, they get a lot of practice! But the Stanford study proved the opposite to be true. When asked to switch between classifying numbers as even or odd and classifying letters as vowels or consonants, the frequent multitaskers were slower than the low-multitasking students. The researchers suspect that the inability to filter out the previous (and now irrelevant) task may explain the slowdown.

So, add yet one more piece of evidence to a debate that's starting to look like no debate. Multitasking is not efficient, nor does it get more work done faster. Quite the opposite. One task interferes with another, so everything takes longer because the brain loses time--and accuracy--in repeatedly shifting its effort.

So, while I have no argument with TV, telephone, or computer, I'm convinced that one at a time is enough.


Sue Shellenbarger, "Multitasking Makes You Stupid: Studies Show Pitfalls of Doing Too Much at Once," Wall Street Journal (February 27, 2003), D1

Pierre Jolicoeur, "Restricted Attentional Capacity Between Sensory Modalities," Psychonomic Bulletin & Review (March 1999), 87-92.

Eyal Ophir, Clifford Nass, and Anthony D. Wagner. "Cognitive Control in Media Multitaskers," Proceedings of the National Academy of Sciences, August 24, 2009 (online early edition).

Most Recent Posts from Brain Sense

50 Years of United States Presidential Scholars

Students honored for high achievement offer lessons to parents and teachers.

Does Success Breed Success?

What happened when researchers bestowed success randomly?

Why We Smell Much Better Than We Thought

New research dispels the myth that humans have a poor sense of smell.