NARRATOR：

Listen to part of a lecture in a psychology class.

FEMALE PROFESSOR：

For decades, psychologists have been looking at our ability to perform tasks while other things are going on- how we're able to keep from being distracted and what the conditions for good concentration are.

As long ago as 1982, researchers came up with something called the CFQ- the Cognitive Failures Questionnaire.

This questionnaire asks people to rate themselves according to how often they get distracted in different situations, like um, forgetting to save a computer file because they had something else on their mind, or missing a speed-limit sign on the road. John?

MALE STUDENT：

I've lost my share of computer files, but not because I'm easily distracted. I just forget to save them.

FEMALE PROFESSOR：

And that's part of the problem with the CFQ. It doesn't take other factors into account enough, like forgetfulness.

Plus, you really can't say you're getting objective, scientific results from a subjective questionnaire where people report on themselves.

So it's no surprise that someone attempted to design an objective way to measure distraction.

It's a simple computer game designed by a psychologist named Nilli Lavie.

In Lavie's game, people watch as the letters N and X appear and disappear in a certain area on the computer screen.

Every time they see an N, they press one key; and every time they see an X, they press another.

Except other letters also start appearing in the surrounding area of the screen- with increasing frequency- which creates a distraction and makes the task more difficult.

Lavie observed that people's reaction time slowed as these distractions increased.

FEMALE STUDENT：

Well, that's not too surprising, is it?

FEMALE PROFESSOR：

No, it's not. It's the next part of the experiment that was surprising.

When the difficulty really increased, when the screen filled up with letters, people got better at spotting the Xs and Ns.

Uh, why do you think that happened?

MALE STUDENT：

Well...maybe when we're really concentrating, we just don't perceive irrelevant information; maybe we just don't take it in, you know?

FEMALE PROFESSOR：

Yes, and that's one of the hypotheses that was proposed- that the brain simply doesn't admit the unimportant information.

The second hypothesis is that yes, we do perceive everything, but the brain categorizes the information... and whatever's not relevant to what we're concentrating on gets treated as low priority.

So Lavie did another experiment designed to look at this ability to concentrate better in the face of increased difficulty.

This time she used brain-scanning equipment to monitor activity in a certain part of the brain: the area called V5, which is part of the visual cortex- the part of our brains that processes visual stimuli.

V5 is the area of the visual cortex that's responsible for the sensation of movement.

Once again, Lavie gave people a computer-based task to do: they had to distinguish between words in upper and lowercase letters, or-even harder- they had to count the number of syllables in different words.

This time the distraction was a moving star field in the background- you know, where it looks like you're moving through space, passing stars?

Normally, area V5 would be stimulated as those moving stars are perceived, and sure enough, Lavie found that, during the task, area V5 was active, so people were aware of the moving star field.

That means people were not "blocking out" the distraction.

FEMALE STUDENT：

Wait, so doesn't that mean that the first hypothesis you mentioned was wrong?

The one that says we don't even perceive irrelevant information when we're concentrating?

FEMALE PROFESSOR：

Yes, that's right... up to a point. But that's not all.

Lavie also discovered that as she made the task more difficult, V5 became less active.

So that means that now people weren't really noticing the star field at all.

That was quite a surprise, and it proved that the second hypothesis, that we do perceive everything all the time, but the brain categorizes distractions differently... well, that wasn't true either.

Lavie thinks the solution lies in the brain's ability to accept or ignore visual information.

She thinks its capacity is limited. It's like a highway: when there are too many cars, traffic is stopped. No one can get on.

So when the brain is loaded to capacity, no new distractions can be perceived.

Now, that may be the correct conclusion for visual distractions... but more research is needed to tell us how the brain deals with,say, the distractions of solving a math problem when we're hungry, or when someone is singing in the next room.