Anyone watching two things at once is bound to miss something. Now research in this week's issue of the journal Nature reveals that your attention, when caught up in a challenging activity, will lapse for even the simplest additional tasks. But a companion paper suggests that your ears can come to the rescue, helping the brain handle two streams of information quickly and reliably. Where fast reactions are critical--as in jet planes--engineers may want to present some information to the ears as well as the eyes.
Researchers have already shown that performing one visual task, such as spotting an "L" in a rapidly flashed series of letters, will cause you to lose track of another task for about a half second. But psychologists thought that very simple tasks would be immune to this delay. Not so, says Julian Joseph, of the University of Nevada, Reno. He and his colleagues displayed a dozen striped balls on a computer screen and asked subjects to pick out the one that was oriented differently. The researchers tried to distract subjects from this simple task with a harder one--picking out one white letter from a rapidly flashed series of black letters. When the letter appeared at about the same time as the oddball, a subject's ability to pick out the ball dropped off dramatically--from 90% to about 65%.
There's hope, though. John Duncan of the Medical Research Council in Cambridge, United Kingdom, and his colleagues have proved that visual and auditory information don't distract from one another, enabling the ears to pick up the slack. They asked people to pick out a word that occasionally appeared amid a series of meaningless letter strings. When the subjects had to cope with two series of letter strings displayed simultaneously on a screen, they were only about 70% accurate at picking out two words that appeared half a second apart. When the researchers adapted one of these tasks for the ears, the accuracy improved to about 85% to 90%, even when the two signals were just a tenth of a second apart.
"It's a nice clean demonstration of something that most people in the field could agree on, but couldn't prove," says Jeremy Wolfe, a cognitive scientist at Brigham and Women's Hospital in Boston. The new findings should also be useful to airplane cockpit designers, Wolfe adds. The research from Duncan's lab, for instance, might warn designers away from trying to overlay two types of visual input on the same screen. "It's probably easier to tell someone to look at one thing and listen to another than to look at two things at the same time," he says.