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 work day.

Brief diversions may 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 works at the university's Beckman Institute for Advanced Science and Technology in Urbana.

Lleras' research seems to contradict long-standing theories that 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 Lleras' study.

A loss of attention is not the problem.

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

Priests who meditate for hours don't concentrate solely on breathing or one object, he said.

"It's not that they don't get distracted, but that they're very good at dealing with the distractions and releasing themselves from them," Lleras said. "Good meditators will get distracted and get back to their main focus very quickly."

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.

Similarly, if you stare at one penny and place another coin 10 inches away, the penny in your will eventually disappear. If you blink or move, the second penny reappears because the change has jolted the brain.

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. Other groups were told to memorize numbers and wait for those numbers to pop up on the screen. The groups that received diversions, in the form of their memorized numbers popping up, sustained their concentration.

Other groups saw their attention spans wane after 20 minutes.

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