Modern workers might find it hard to believe that multitasking is a relatively new idea.

For most of us, the need to accomplish many things at once seems like a given. But, believe it or not, the concept of multitasking didn’t crop up in the workplace until around the time that every desk got a computer.

Our computers (and now our cell phones) are one-stop shops for communication, research, word processing—you name it. Most desktops can generate a report, download e-mail, and support a videoconference all at the same time, without skipping a beat.

These machines have become so central to our lives that it makes sense we have come to see ourselves in their image. If our computers can juggle three or four things at once, well, so can we.

Seeds Of Doubt

Or can we?

In the 1990s, multitasking became recognized as an attribute—even a requirement—in the workplace. But as it became a buzzword in the business world, psychiatrists wondered if the human brain was really up to the task.

That skepticism quickly spread outside the laboratory as many states made it illegal for drivers to hold cell phones while on the road. Multitasking became widely recognized as dangerous, at least from behind the wheel.

By 2010, The New York Times was reporting on the hazards of what it termed “lower-stakes multitasking”—that is, using a cell phone while walking. Anecdotal evidence included firsthand accounts from people so absorbed in their phone conversations that they sustained injuries from walking into windows and cars.

Meanwhile, researchers at Western Washington University discovered that pedestrians on a call were far less likely than their phone-free counterparts to see a clown on a unicycle.

If those callers didn’t notice a flashy clown, how much work can we really accomplish as we, say, compose an e-mail, send an instant message, make coffee and prepare for a meeting … all while we’re on a call?...