Watch Out! Visual Concentration Can Leave You Temporarily ‘Deaf’

— -- Next time your friend ignores you while concentrating on their mobile device, you might want to tap them on the shoulder – they may not have even heard your voice.

Researchers at the University College London have found that the brain’s senses of vision and hearing share a limited processing capacity, so the brain is often forced to choose between them.

In a small new study published in the Journal of Neuroscience, 14 people attempted visual tasks of increasing difficulty while sounds were played in the background. All the while, researchers monitored their brain activity.

During the more demanding visual tasks, the brain’s early response to sound was dampened. The researchers believe the participants were not just ignoring the sounds; they actually did not hear them.

“In order to hear, we don’t just need our ears to be operating; we need our brain to respond to the sound,” said study author Nilli Lavie, professor of psychology and brain sciences at the University College London. “If our brain doesn’t respond because our attention is fully taken by another task, then we experience deafness.

“We have confirmed an experience that people commonly report, that they may fail to notice a sound when they are concentrating. It’s because the brain signal related to hearing is significantly reduced during more demanding visual tasks.”

Importantly, this brain signal occurs very quickly after the sound occurs – in less than one-quarter of a second – which indicates that the early stages of perception are affected.

The study is not the first research to find that our brains may be easily overloaded in such a way.

“We can fail to notice things that are right in front of us when we are focusing our attention on other things,” said Daniel Simons, professor of psychology at the University of Illinois and author of the bestselling book on human attention, “The Invisible Gorilla,” who was not involved with this study. “When you are distracted by something visual, you may not hear something that is auditory.”

Such a distraction can lead to problems. A surgeon concentrating on an operation might not hear the equipment beeping in the background. Or a driver, focused on the road, might not hear an approaching bicycle bell ringing.

Bottom line: We might not be as good at multitasking as we think, and the brain’s hard wiring is to blame.

Dr. Jennifer Hoffmann is a resident physician specializing in pediatrics at Boston Children’s Hospital and Boston Medical Center in Boston.