Brief interruptions spawn errors in surprising quantity

Short interruptions and distractions - like from emails, mobile phone notifications etc - have a surprisingly large effect on one's ability to accurately complete a task, according to new research by Michigan State University psychologists.

The study set out to quantify the extent of the known effect and found that interruptions averaging 2.8 seconds long doubled the error rate, while interruptions averaging 4.4 s long even tripled the error rate.

Brief interruptions are ubiquitous in today's society, from text messages to colleagues poking their head in the door and interrupting an important conversation. The ensuing errors lower productivity in general, but can be even dangerous when they affect professionals such as airplane mechanics and emergency room doctors, said Erik Altmann, lead researcher on the study.

"What this means is that our health and safety is, on some level, contingent on whether the people looking after it have been interrupted," said Altmann, MSU associate professor of psychology.

The study, funded by the U.S. Navy's Office of Naval Research, is one of the first to examine brief interruptions of relatively difficult tasks.

The study participants (300 college undergraduates) were asked to perform a series of tasks in a specific order, such as identifying with a keystroke whether a letter was closer to the start or the end of the alphabet. Even without interruptions, a small number of errors in sequence were made.

Sometimes participants were interrupted and told to type two letters - which took 2.8 seconds - before returning to the task. When this happened, they were twice as likely to mess up the sequence.

Altmann said he was surprised that such short interruptions had a large effect. The interruptions lasted no longer than each step of the main task, he noted, so the time factor likely wasn't the cause of the errors. Also, non-sequence errors showed no interruption effects

"So why did the error rate go up?" Altmann said. "The answer is that the participants had to shift their attention from one task to another. Even momentary interruptions can seem jarring when they occur during a process that takes considerable thought."

One potential solution, particularly when errors would be costly, is to design an environment that protects against interruptions. "So before you enter this critical phase: All cell phones off at the very least," Altmann said.

Note that some types of interruptions may have larger effects. For example, a study of media multitasking by Boston College researchers found that being in a room with both a television and a computer was particularly distracting. And trying to do two visual tasks at once hurt performance in both tasks significantly more than combining a visual and an audio task, Ohio State University researchers found.