Health & Wellness

Your brain can't swipe and hear at the same time, scans show

Your loved one, friend or colleague is immersed with the smart phone and seems to be totally ignoring what you're saying. Don't get angry: it's not on purpose.

A new study shows that people who are focused on visual tasks actually can’t hear what's going on around them because hearing and vision tap the same brain regions, according to a report published Tuesday in the Journal of Neuroscience.

The researchers have dubbed this hearing deficit: inattentional deafness.

“You may think that the person is ignoring you,” says study coauthor Nilli Lavie, a professor of psychology and brain science at University College London. “But their brain just can’t respond to your voice. So you shouldn’t take it personally.”

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The more taxing the visual task, the less likely the person is going to hear what you are saying. It’s why, Lavie says, people reading a book on a train often don’t hear their stop called.

It’s also why surgeons need someone to keep track of the beeps and buzzers of monitoring equipment when they are operating.

“They’re going to be focusing on the operation and they might not hear alarms,” Lavie says. “So you need a different person who is in charge of listening.”

Similarly, if you’re in a meeting at work and talking to a colleague who is looking over some data or a report, don’t assume that what you’ve said has been heard, Lavie counsels.

Lavie and her colleagues suspected that the brain might have problems multitasking when it was given a visual task that required concentration.

They told 13 volunteers that their study was just looking at reaction times. The volunteers were asked to view a computer screen and tap a key when certain letters flashed up. In each iteration, the letters were on the screen for less than a quarter of a second. In the difficult version of the task, many letters were on the screen at the same time. In the easy version, there was just one letter along with some circles.

All volunteers wore headphones, which periodically played tones.

“When the task was easier we could see a brain signal indicating they could hear the tone,” Lavie says. “When it was difficult, we saw a reduced signal in the auditory cortex.”

The reason we can’t multitask hearing and vision is these two senses share access to a part of the brain, the association cortex, whose job it is to integrate all incoming information.

In reality, this ability to shut out sound when we are focusing on a visual task “is an asset,” says Dr. Peter Whybrow, a psychiatrist and director of the Semel Institute for Neuroscience and Human Behavior at the University of California, Los Angeles and author of “The Well-Tuned Brain: Neuroscience and the Life Well Lived.”

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“The brain switches from one task to another,” Whybrow says. “It doesn’t do two things at once just as this study suggests.”

That's something people seem to have trouble accepting in our modern world, Whybrow says.

The only time the brain can do two things at once is when one of those things is something we do out of habit.

“The brain is terribly efficient largely because it runs 80 percent on habit,” he explains. “And habit is a totally different system of wiring than conscious awareness. If I’m walking around the garden while I’m talking to you on the phone I don’t have to think about how to walk.”

Whybrow’s advice to those who’ve been accused of being rude when they’re staring at their phones and don’t hear what a friend or loved one says: “put down the phone.”

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