How visual concentration closes our ears to the world



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We all know what it's like to feel like we're being ignored because a certain someone's attention is being inexorably drawn away by the TV, radio or computer. We also know how frustrating it can be to miss a crucial train announcement because that new book or newspaper is so darned engrossing. It might be more than just inattentiveness. According to a new study published in the Journal of Neuroscience, concentrating attention on a visual task can render you momentarily "deaf" to sounds at normal levels.


Thought experiment

The new study from University London (UCL) suggests that the senses of hearing and vision share a "limited neural resource" — in other words, what you give to one, you take from the other. For the study, 13 participants were given brain scans while engaged in a demanding visual task. The ability of people to detect sound during these tasks was significantly impaired even though the sounds were clearly audible and were noticeable when the visual task was easy. While it was fully occupied with this visual input, that is, the brain's response to sound was significantly reduced.

The phenomenon of "inattentional deafness," — where we fail to notice sounds when concentrating on other things, has been observed before. However, this is the first time researchers have been able to determine that the effects are driven by mechanisms in the brain that occur at a very early stage of sound processing. By measuring detailed, real-time brain activity using magnetoencephalography (MEG), the team identified the process that makes us "deaf" to the sounds which we'd normally be aware of.


Miles away

"This was an experimental lab study that is one of the ways that we can establish cause and effect," explains study co-author Dr. Maria Chait of UCL's Ear Institute. "We found that when volunteers were performing the demanding visual task, they were unable to hear sounds that they would normally hear. The brain scans showed that people were not only ignoring or filtering out the sounds, they were not actually hearing them in the first place." Chait's colleague and co-author, Professor Nilli Lavie, adds:"Inattentional deafness is a common experience in everyday life, and now we know why. If you try to talk to someone who is focusing on a book, game or television program and don't receive a response, they aren't necessarily ignoring you, they might simply not hear you!"

"This has more serious implications in situations such as the operating theatre," Lavie says, "where a surgeon concentrating on their work might not hear the equipment beeping. It also applies to drivers concentrating on complex satnav directions as well as cyclists and motorists who are focusing intently on something such as an advert or even simply an interesting-looking passerby. Pedestrians engaging with their phone, for example texting while walking, are also prone to inattentional deafness. Loud sounds such as sirens and horns will be loud enough to get through, but quieter sounds like bicycle bells or car engines are likely to go unheard."