The human brain is always multitasking. That doesn't mean we're good at it - National Post

Workers in the health-care field are constantly multitasking because they have to. But the brain can't focus on two things at once. Photo by Getty ImagesArticle contentThe human brain switches its attention constantly because it can’t focus on two things at once. Multitasking works until a task needs concentration.

Two tasks can run simultaneously, unless they need the same part of the brain or body. Walking and chewing gum, for example, can be done at the same time because they use different body parts and don’t require a lot of concentration. But texting and driving both need the same pair of eyes.

And the front of the brain, which handles focus, does one thing at a time, so tasks that need it take turns. This is when multitasking takes a toll. It’s called switch cost, when the brain takes a moment or two to recover from switching between information competing for attention,

Reading while someone talks to you can feel like doing two things at once. But John Paul Minda, a psychology professor at Western University, said much of what people call multitasking comes down to the brain switching between sources of information. And there is always some cost to that, he said.

The human brain takes in lots of things at once, “because we don’t know what the important information is until we’ve processed it,” he said. “The idea of jumping around is just something that your brain does whether you want it to or not.”

People who multitask a lot and think they are good at it are actually worse at it when they need to focus on two things. That’s because “you’re kind of used to shifting your attention really quickly,” Minda said. Each shift takes “a few seconds or half a second” to recover, he said.

Maximilian Riesenhuber, a professor of neuroscience at Georgetown University Medical Center, said some multitasking comes naturally and others, like tying your shoes while you talk, can become automatic with practice. “You can walk and chew gum, right? I mean, some things we can do naturally in parallel.”

Riesenhuber, along with Patrick Cox, an assistant professor of psychology at Lehigh University, led a study published this year in the Journal of Cognitive Neuroscience that tested whether practice could make a new task automatic. The 11 people in the test practiced sorting pictures of cars into two groups on a phone app, more than 30,000 times over five to 10 weeks. Brain scans were taken before and after the test.

Before the study, Riesenhuber said the accepted view was that practice made people better at switching between tasks, while the prefrontal cortex, at the very front of the brain, kept doing the work. After the test, the scans showed the sorting-cars task had moved to the temporal cortex, a region he said “does a lot for vision.”