Today's students might be "media multitaskers" who are adept at juggling homework assignments while watching TV or instant-messaging their friends--but new brain research suggests that such distractions can affect the way people learn, making the knowledge they gain harder to use later on.

The study, published in the July 24 edition of the journal "Proceedings of the National Academy of Sciences," also provides a clue about why this happens.

"What's new is that even if you can learn while distracted, it changes how you learn"--making the learning "less efficient and useful," said Russell A. Poldrack, a psychology professor at the University of California, Los Angeles.

The study's findings could have important implications for today's students--and the educators charged with instructing them.

A study by the Kaiser Family Foundation last year found third-graders through 12th-graders devoted, on average, more than six hours per day to TV or videos, music, video games, and computers. That study referred to the current generation of learners as "media multitaskers," nearly one-third of whom said they chat on the phone, surf the web, send instant messages, watch TV, or listen to music "most of the time" while doing their homework (see story: Here).

As Poldrack explains it, the brain learns in two different ways. One, called declarative learning, involves the medial temporal lobe and deals with learning active facts that can be recalled and used with great flexibility. The second, involving the striatum, is called habit learning.

For instance, in learning a phone number you can simply memorize it, using declarative learning, and can then recall it whenever needed, Poldrack explained.

A second way to learn it is by habit: "punch it in 1,000 times, then even if you don't remember it consciously, you can go to the phone and punch it in," he said.

Memorizing often is more useful, he pointed out: "If you use the habit system, you have to be at a phone to recreate the movements."

The problem, Poldrack said, is that the two types of learning seem to be competing with each other, and when someone is distracted, habit learning seems to take over from declarative learning.

"We have to multitask in today's world, but you have to be aware of this," he said. "When a kid is trying to learn new concepts, new information, distraction is going to be bad, it's going to impair [her or his] ability to learn."

That doesn't mean Poldrack thinks a silent environment is essential--music can help in learning, because it can make the individual happier, he said.

But in general, "distraction is almost always a bad thing."

What Poldrack and his colleagues did was to use brain imaging to study the parts of the brain in use when 14 people were learning.