Even Small Interruptions Can Lead to Mistakes


by Kayt Sukel

February 7, 2013

During the course of an average workday, you may face hundreds of middling interruptions. While trying to finish an important work project, your attention may be diverted by the quick ding of an incoming text message from your spouse, or perhaps by an impromptu face-to-face visit from your boss. We all know that interruptions have a cost—derailing your train of thought and leading to potential errors in your primary task. Yet it had been assumed only longer, more complicated interruptions resulted in significant mistakes. New research out of Michigan State University, however, suggests that even short, simple interruptions have the power to double the number of errors you make.

Only three seconds

Erik Altmann, a psychologist at MSU, has long been studying the ways interruptions can interfere with task performance.

“We’ve seen that the cost is quite high for task switching after an interruption, in terms of time and errors for all the tasks you may be switching between, but we didn’t know how long those interruptions had to be in order to result in those costs,” he says.

In a study published in the Jan. 7 issue of the Journal of Experimental Psychology, Altmann asked 300 undergraduates to complete a simple, computerized sequential task. Each participant was shown a string of characters and then asked to do things like pick out the vowels then the numbers then the red letters, etc., in a specific order. Occasionally, however, after inputting their responses, the computer screen would change, interrupting the primary task and asking participants to simply type a few characters they saw displayed. Immediately following the interruption, they went back to the first sequential task.

“What we saw was that people skipped steps or repeated steps at an elevated rate after the interruption,” says Altmann. In fact, the participants made mistakes twice as often when interrupted as they did when they were allowed to focus solely on the primary task. “These interruptions were only two-to-three seconds long and yet they were still really disruptive. That was a surprise to me.”

Michael Posner, a member of the Dana Alliance for Brain Initiatives (DABI) who has been studying the costs of attentional shifts for decades, says that three seconds is more than enough time to interfere with working memory and attention.

“When you are working on a task, you have to keep all of those things in mind that are involved with that task,” he says. “Once you are interrupted, you have to start from scratch and get all of that information back into working memory. It takes time and you may make errors while you are trying to get back on task.”

The interrupted brain

Why might there be such a high cost?  Adam Gazzaley, a neuroscientist at the University of California San Francisco, says that interruptions, unlike simple irrelevant distractions like loud music or a scratchy pencil, require a full shift of attention—and the reactivation of an important brain network once you go back to your primary task.

In a study published in the April 2010 issue of Cerebral Cortex, Gazzaley and colleagues used electroencephalogram and functional magnetic resonance imaging (fMRI) to look at what’s happening in the brain when you are distracted versus when you are truly interrupted. The group had participants do a simple delayed recognition task using photos of male faces. In the distraction condition, an image appeared—participants were told to ignore it as something irrelevant. In the interruption condition, however, participants were instructed to respond to the image after making a judgment of whether it was of a male older than 40 years. Using connectivity analyses, the researchers found that participants were able to maintain connectivity between the middle frontal gyrus and visual association cortex during the distraction condition. But when they were fully interrupted, those brain connections were broken.

“Your brain manages these two types of interference in different ways. In terms of distraction, it would seem that you maintain a network that is associated with your primary task and your success at essentially resisting the distractions is maintaining that brain network,” says Gazzaley. “But when you have an interruption, when you are actually multi-tasking, the network is broken and has to be reactivated before you can get back to that first task.”

The take-home

So in a world full of pinging inboxes and buzzing smartphones, what should we take away from this kind of research?

“I think most people don’t really have a very good idea of the specific brain mechanisms involved with attention and the difficulties involved with shifting it,” says Posner. “There are costs in time but also costs in terms of potential errors. People should be more aware of this.”

Gazzaley agrees. “We’re realizing that people are much more sensitive to interference than they think they are,” says Gazzaley. “And you can see the impact of these types of interference in the workplace, in the home, in education, with development, and with safety issues like driving. It’s not a small thing. And it’s only getting more complicated as very clever tech companies come up with more and more sophisticated ways of interrupting us throughout the day.”