Brief training regimen redefines upper limits of attention

Scientists have used a simple training program to break through what was believed to be a fundamental limitation of the human brain — the ability to perceive two items when they are presented in rapid succession, less than half a second apart. The findings suggest new treatments for those with attentional deficits following a brain injury or during the progression of a neurodegenerative disease. They could also lead to a way for people with normal attention to perceive the world better.

Think of all the times you’ve heard someone say “It came out of nowhere.” There’s a reason that happens to us so often: About 20 years ago, scientists conducted experiments showing that humans are very bad at seeing two objects when they appear less than half a second apart. So when a driver veers into your lane from the left just after a bicyclist swerves from the right, there’s a good chance you’ll be slow to react to the car because you simply don’t see it right away. This phenomenon is called “attentional blink” because there is a period after we focus on a first object that a second object goes unseen — as if we are blinking.

Since its discovery, scientists have worked hard to shrink the period of the attentional blink — or to eliminate it altogether — with the goal of turning our brains into more efficient and productive visual processing machines. But they have had little success.

Now, in a new study published in the July 9 Proceedings of the National Academy of Sciences, researchers have finally eliminated the attentional blink.

The scientists, from Boston University, Brown and Harvard, had people view a rapid series of white letters on a black background on a computer screen. During every experiment, two numbers would pop up amidst the letters. In some experiments, the subjects saw two numbers separated by 200 milliseconds, and in other experiments, they were separated by more than 500 milliseconds, or half a second.

As expected, all the subjects had trouble seeing the second number when it was 200 milliseconds apart from the other number, but little difficulty doing it when they were more than half a second apart.

But then the researchers used a clever training technique — they turned the second number red, making it more visually salient. Suddenly people began to see it.

The real proof that the training had removed the attentional blink came after training was over, when the researchers turned the red number back to white. After only a single day of training, the subjects were able to see the second number just as well when it was 200 milliseconds after the first number as when it was half a second after.

And when the researchers brought the participants back a few months later, they found that the effect persevered. After only three total days of training with the red numbers, it appeared that their brains had fundamentally changed the way they perceived the visual world.

So what had the training actually done to these brains? The researchers used functional magnetic resonance imaging (fMRI) tests to show that the changes appeared to occur in so-called higher-level areas of the brain, areas like the prefrontal cortex that have evolved most recently. These changes, the researchers hypothesized, did not change what visual information reached the brain but rather allowed the participants to switch their attention from one target to another more rapidly.

If these laboratory experiments translate to everyday life, the researchers suggest that people with deficits in attention — which have been revealed in people with ADHD, brain injuries and neurodegenerative diseases alike — may soon have a way to restore the ability.

-- For the Science Now blog