Concentrating attention on a visual task can render you
momentarily 'deaf' to sounds at normal levels, reports a new UCL
(University College London) study funded by the Wellcome Trust.
The study suggests that the senses of hearing and vision share a
limited neural resource. Brain scans from 13 volunteers found that
when they were engaged in a demanding visual task, the brain
response to sound was significantly reduced. Examination of
people's ability to detect sounds during the visual demanding task
also showed a higher rate of failures to detect sounds, even though
the sounds were clearly audible and people did detect them when the
visual task was easy.
"This was an experimental lab study which is one of the ways
that we can establish cause and effect. We found that when
volunteers were performing the demanding visual task, they were
unable to hear sounds that they would normally hear," explains
study co-author Dr Maria Chait (UCL Ear Institute). "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."
The phenomenon of 'inattentional deafness', where we fail to
notice sounds when concentrating on other things, has been observed
by the researchers before. However, this is the first time that
they have been able to determine, by measuring brain activity in
real-time using MEG (magnetoencephalography), that the effects are
driven by brain mechanisms at a very early stage of auditory
processing which would be expected to lead to the experience of
being 'deaf' to these sounds.
"Inattentional deafness is a common experience in everyday life,
and now we know why," says co-author Professor Nilli Lavie (UCL
Institute of Cognitive Neuroscience) "For example, if you try to
talk to someone who is focusing on a book, game or television
programme and don't receive a response, they aren't necessarily
ignoring you, they might simply not hear you! This could also
explain why you might not hear your train or bus stop being
announced if you're concentrating on your phone, book or
newspaper.
"This has more serious implications in situations such as the
operating theatre, 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 passer-by. 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."
The paper, Inattentional
Deafness: Visual Load Leads to Time-Specific Suppression of
Auditory Evoked Responses, is published in the Journal of
Neuroscience.