A University of Illinois professor says people don't need to feel guilty about checking personal e-mail, chatting with co-workers or addressing other minor distractions throughout the workday.

Brief diversions might actually help people concentrate and improve their performance on more important tasks, says Alejandro Lleras, who wrote a study on the topic for the journal Cognition.

Lleras' research seems to contradict long-standing theories that attention is a finite resource that runs out after a lengthy period of focus. Attention is more like a gas tank that refills during short breaks from the task at hand, according to his study.

"When you are distracted, it doesn't mean you aren't paying attention to anything," he said.

Lleras based his theory on the idea that our senses become used to stimulus. Take a room that smells strongly of coffee. If you stay in the room all day, the scent goes away because the brain is trained to respond to differences and not constants in the environment.

The same can be true of the thought process. Sustained attention to a thought can cause that thought to disappear. But if you are given something else to think about, the original thought will seem fresh when you return to it.

To prove his theory, Lleras had 84 students focus on various numbers flashing on a computer for an hour. One group received no breaks or distractions, and their attention spans waned after 20 minutes. Other groups that received diversions sustained their concentration.

"It's unrealistic to expect people to focus at high levels for a long period," he said. "It's important to create an environment where it's OK to take small breaks."