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Why Do Phones Cause "Inattention Deafness"?

Looking at the screen might interfere with the neural response to sound.

If your friend ignores your question while using a smartphone, he or she might be momentarily ’deaf', reports a new University College London study. Focusing on a smartphone or tablet might interfere with their neural response to sound.

The study, published in The Journal of Neuroscience, suggests that hearing and vision share a limited neural capacity. Brain scans from 13 volunteers found that when they were given demanding visual tasks—quickly identifying symbols on the screen—at the same time as sounds, the brain response to sound was significantly reduced. Their ability to detect sounds also failed more often.

“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," explained co-author Dr. Maria Chait, in a statement published in the Medical Daily.

This ‘inattention deafness’, in which sounds are ignored during attention elsewhere, has been observed before. However, this is the first report of brain activity in real-time using MEG (magnetoencephalography) that shows effects at an early stage of auditory processing, within the first 1/10 second after sound onset. The effect occurs in the auditory receiving area of the brain.

The complex MEG method allows you to detect both the location and time-course of neuronal activity in thousandths of a second, an advantage over the more common functional MRI brain scans. MEG is an extremely cool system--literally, since the magnetic sensors around the head need to be chilled more than 200 degrees centigrade below zero, to detect currents when a cluster of thousands of neighboring nerve cells become active.

To be sure, no effects are reported for the earliest response, in the first 1/100 second, after sound onset when neural responses travel from the auditory nerve upward to the auditory cortex. The effect holds for quieter tones rather than louder ones. The effect is brief, depending on the timing of the visual and auditory stimuli. And this is one study, rather than an all-purpose excuse for not paying attention.

But if inattention deafness occurs when a driver is reading from a GPS, or a surgeon is focusing on an operation, not hearing important information could have serious consequences, effects that may be possible although they were not tested. If similar results occur during a social situation while using a mobile device for email, texts, googling, or games, it adds to growing concerns about the effects of digital devices on conversation in the real world.

Reference: K. Molloy and others, Inattention Deafness: Visual Load Leads to Time-Specific Suppression of Auditory Evoked Responses.The Journal of Neuroscience, 9 December 2015, 35(49):16046-16054

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