Have you ever found it difficult to get the attention of someone engrossed in his smartphone, reading a book, playing a video game or watching TV? Don't worry, you have not been ignored - he probably just didn't hear you talking.
A new study in the United Kingdom revealed that concentrating and placing undivided attention into a visual task can make a person temporarily deaf to sounds coming from their environment. Experts at the University College London called this deficit "inattentional deafness."
In a study featured in the Journal of Neuroscience, UCL researchers explained that a person's sense of vision and hearing are located in a shared and limited region of the brain called the association cortex. Because of the limitation in processing capacity, the brain is forced to choose between the two senses and fails to multi-task.
"In order to hear, we don't just need our ears to be operating; we need our brain to respond to the sound," said UCL Professor Nilli Lavie, co-author of the study.
Lavie and her colleagues asked 13 volunteers to look at a computer screen and press a key when a certain letter pops up. The letters were flashed on screen for less than a quarter of a second. Some letters were on the screen simultaneously, while in another round, there was only one letter with circles on the screen. They all wore headphones that randomly played tunes.
Researchers conducted brain scans on the participants and found that when they were concentrating in a demanding visual task, their brain's response to sound was significantly lower.
There is also a higher rate of participants who fail to detect sounds during the demanding visual task, even though the sound is perfectly audible, researchers said. When the visual task was easy, participants were able to detect sounds with no difficulty.
Inattentional deafness can have serious implications, researchers said. A surgeon who is concentrating on his task might not hear the beeping of equipment. Drivers, cyclists and motorists who are focusing on complex directions may also fail to detect sounds.
Lavie said sounds such as horns and sirens are loud enough to be detected, but sounds such as car engines and bicycle bells are more silent and are most unlikely to be heard.
"You may think that the person is ignoring you," said Lavie. "But their brain just can't respond to your voice. So you shouldn't take it personally."
The Wellcome Trust-funded UCL research on inattentional deafness is not the first to examine the topic, but this is the first time that researchers measured brain activity by using magnetoencephalography (MEG) and discovered the mechanisms behind the deficit.