Brain Bottlenecks and Multitasking Myths: Shattering the Illusion

Believing you can multitask and actually doing it are two different things

By Peter M. Vishton, PhDWilliam & Mary
Edited by Kate Findley and proofread by Angela Shoemaker, Wondrium Daily

Multitasking is prevalent in our fast-paced lifestyle, and many people find pleasure in it. It can be invigorating to push your mind and body to their maximum capacity for processing information. However, Dr. Vishton explains why multitasking is largely counterproductive.

Close up of man multitasking using ipad
Multitasking produces a reduction in performance, whereas concentrating on one task at a time improves brain processing. Photo by TippaPatt / Shutterstock

Is Multitasking Really So Great?

Early research seems to endorse the benefits of multitasking, and we often feel like we can do multiple tasks at the same time. Yet this is largely a myth due to multitasking bottlenecks: a mental “traffic jam” that occurs when we perform certain actions simultaneously.

When we carefully assess people’s performance during multitasking, significant reductions in performance are found. In some cases, the drops in performance are dramatic. 

Perhaps more troubling, though, is how unaware we are of the drop. We can feel like we’re doing our best work while actually performing pretty badly.

Part of an old study involving expert typists, which on the surface presented multitasking in a favorable light, hinted at this problem even at the time it was originally performed. The typists could type written material while listening to other words and verbally shadowing, or repeating, them. 

However, if the typists had to type dictated words while also trying to listen to other words and verbally shadow them, then the task became tremendously difficult. It seems that there are certain limits to how well we can process different kinds of information streams simultaneously.

The human brain can perform many operations in tandem, but there are bottlenecks when our brain tries to process them. Certain brain utilities are essential to performing many behaviors, and these utilities can perform exactly one task at a time. 

Multitasking Bottlenecks

The problems with multitasking emerge directly from these bottlenecks. You might feel like you’re performing more than one task at a time, but the research shows that you are often just rapidly switching between two or more tasks to create the illusion of simultaneously performing multiple tasks.

Consider the task of writing something while also monitoring your incoming e-mail. You’re thinking about the topic of your writing, the structure of the document you’re composing, and how to compose the next sentence. This is an engaging task that pulls from a variety of different brain resources. 

While you’re doing that, a ping from your computer indicates that an email has arrived. You glance up and read that message, decide the e-mail can wait, and continue writing.

It feels like you’re doing those two things at the same time, but what you actually do is stop the thought processes that go with writing, switch to thinking about the email, and then return to the writing. That switch takes time and requires a substantial amount of brain resources to accomplish.

When Simple Is Hard

Many studies have involved giving a group of participants an hour to do a primary task such as writing or solving a set of problems. Half of the participants engage in monotasking—they just do the primary task. The other half of the participants also engage in a monitoring task, like monitoring incoming, very interesting email messages. 

That group that multitasks essentially always performs substantially worse than the monotasking group. They don’t feel like their performance was affected, but it always is.

Experimental psychologist Hal Pashler has done many well-regarded studies on multitasking bottlenecks. A hallmark of many of his experiments is not how difficult the multiple tasks have been, but, on the contrary, how simple. If you set up a pair of tasks such that they are really easy, but the two tasks both require the same underlying processing utility, then multitasking will produce clear differences in performance.

One of his studies involves asking people to make two very simple decisions at the same time. The participants sat in front of a computer. Every few seconds, the computer emitted a tone.

If it was a high-pitched tone, they pressed a key with the index finger of their left hand. For a low-pitched tone, they pressed the key under their middle finger.

A second task was introduced. Every few seconds, a letter was presented on the screen. Participants performed the actions with the same fingers for the letters A and B.

When these two tasks were combined, the participants had a much harder time performing them effectively than either of them individually. This is because the two tasks hit one of the key bottlenecks in the brain’s information processing system—the part of the brain that makes a decision about a particular piece of incoming sensory information. 

Pashler found even when study participants were given a lot of practice with the two tasks, while people became more efficient, the processes never got as fast as when the participant was engaged in a single task.

There’s simply an inevitable delay introduced if we have to switch back and forth between monitoring two different tasks. It’s an unavoidable aspect of how our brains are put together. 

We can alternate between two tasks quickly, and with practice that alternation can become very efficient, but there’s never a time when the switching back and forth becomes instantaneous. Additionally, there is never a time when you can truly be doing two tasks at the same time.

This article was edited by Kate Findley, Writer for Wondrium Daily, and proofread by Angela Shoemaker, Proofreader and Copy Editor for Wondrium Daily.
Image of Professor Peter Vishton

Peter M. Vishton is an Associate Professor of Psychology at William & Mary. He earned his PhD in Psychology and Cognitive Science from Cornell University. Before joining the faculty of William & Mary, he taught at Northwestern University and served as the program director for developmental and learning sciences at the National Science Foundation.