A new study shows that subconscious signals interfere with concentration, causing people to become easily distracted and falter on even the simplest of tasks.

When people concentrate, they focus on the task at hand and filter out information irrelevant to what they are doing. A new report, however, published in this week's Science, says that sometimes unrelated info slips through, even if it is not consciously processed. "Our results contradict the general view," says lead author Yoshiaki Tsushima, a graduate student in psychology at Boston University.

Tsushima and his colleagues performed a series of experiments that show how bits of irrelevant information sneak past people's attention-focusing mechanism. Study participants were told to report the pair of numbers in a string of six letters and two numerals that they saw on a computer screen, and to ignore the dots bouncing around them. Some of the dots moved about randomly and others traveled in fixed directions.

Sounds simple. However, ignoring the dancing dots turned out to be easier said than done. The participants did well on their task when less or more than 5 percent of the dots moved in specific patterns, but their success rate dropped off at around 5 percent. This is because, researchers say, at 5 percent the pattern was apparently below the threshold of conscious awareness, but the subjects still picked it up subconsciously. "Invisible signals distract," Tsushima explains. The subjects did not pick up on any pattern in movement below 5 percent. In one fixed-direction pattern above 5 percent, they noticed the dots but were able to ignore them.

In one of the experiments, the researchers measured participants' brain activity during the computer test. They primarily focused on the visual cortex and the lateral prefrontal cortex, because those are the areas of the brain that filter irrelevant stimuli. Their goal: to determine how subliminal signals, which can be distracting, are processed. When 5 percent of the dots moved coherently, the visual cortex was activated, though the signal was computed only subconsciously: the lateral prefrontal cortex was not activated. The reason, researchers say, is that the signal was able to sneak by that attention-focusing part of the brain, thus allowing subjects to be distracted; the subliminal signal was too weak for the lateral prefrontal cortex to pick up and block.

When people are distracted, they have fewer resources to allocate to what they are doing and, as a result, their performance suffers, the scientists say. They speculate that stronger messages prompt the lateral prefrontal cortex to jump into action, batting back the potentially distracting signals.