Multitasking Has Its Limits
Study shows brain can only perform two complicated jobs at one time
THURSDAY, April 15, 2010 (HealthDay News) -- For those who think they can juggle several tasks at once with ease, new research from France suggests that humans may not be able to perform more than two complicated jobs at one time.
That doesn't mean you can't walk and chew gum simultaneously, but it probably means you can't talk about astrophysics on the phone while doing your taxes. And you definitely can't add solving calculus equations to the mix, at least if you want to perform any of these tasks with some proficiency.
"They are suggesting that you can only handle two things at once, but they're cognitively demanding tasks," said Mark Mapstone, an associate professor of neurology at the University of Rochester Medical Center in Rochester, N.Y.
The reason: The human brain has two lobes that divide the responsibility equally when two tasks are being carried out at the same time.
"Three-tasking [overwhelms] the capacity of human frontal function. Dual-tasking is alright," explained study co-author Etienne Koechlin, whose research appears in the April 15 online issue of Science. "Human higher cognition is dual in essence, which can explain why people like binary choice and have difficulties in multiple choices [people can easily switch back and forth between two options before making a decision, but not across three alternatives]."
The results could eventually have some real-world applications.
"Frontal lobe function is the most fragile human brain function, and is altered in aging and impaired in most neuropsychiatric diseases [schizophrenia, autism, dementia, depression]," said Koechlin, a professor with the French National Institute for Health and Medical Research in Paris. "Understanding how the frontal lobe function works is fundamental to understanding cognitive aging and the nature of neuropsychiatric mental alterations."
The work could also have "important practical applications to areas such as traffic safety [e.g., air traffic control, or driving while using a cell phone], and neurological disorders such as dementia where the ability to multitask is lost," added Dr. Fatta B. Nahab, an assistant professor of neurology at the University of Miami Miller School of Medicine.
"Knowing our limitations is [being able to] not overwhelm them, so in a business like air-traffic control, you would want to limit the number of tasks everyone is responsible for and divide the responsibilities across those people," Nahab said.
These authors used functional MRI to study the brains of people while they were performing fairly complicated tasks involving letter sequencing.
In the first scenario, volunteers were asked to alternate between two different tasks. In the second scenario, participants were told to postpone one task while completing the other one.
The most surprising finding, Koechlin said, was that when volunteers postponed a task, rather than substituting one for another, the two frontal lobes lit up as they focused on the one task.
Introducing a third task increased the error rate.
"This inferred that the brain was inherently unable to do three tasks simultaneously, so the assumption is because we have two hemispheres [of the brain], we are able to do two tasks at the same time," said Dr. Michael Hutchinson, an associate professor of neurology at NYU Langone Medical Center in New York City.
"It happens as if each frontal lobe is pursuing its own goal!" Koechlin said. "This finding . . . suggests that the frontal function cannot keep track of more than two goals/tasks at the same time."
Stanford University has more on the perils of electronic multitasking.