University of Maryland : "Could you repeat that?" The reason you may have to say something
twice when talking to older family members at Thanksgiving dinner may
not be because of their hearing. Researchers at the University of
Maryland have determined that something is going on in the brains of
typical older adults that causes them to struggle to follow speech
amidst background noise, even when their hearing would be considered
normal on a clinical assessment.
In an interdisciplinary study published by the Journal of Neurophysiology, researchers Samira Anderson, Jonathan Z. Simon,
and Alessandro Presacco found that adults aged 61–73 with normal
hearing scored significantly worse on speech understanding in noisy
environments than adults aged 18–30 with normal hearing. The researchers
are all associated with the UMD’s Brain and Behavior Initiative.
"Evidence of degraded representation of speech in noise, in the aging midbrain and cortex"
is part of ongoing research into the so-called cocktail party problem,
or the brain’s ability to focus on and process a particular stream of
speech in the middle of a noisy environment. This research brings
together the fields of hearing and speech science, neuroscience and
cognitive science, electrical engineering, biology, and systems science.
The
study subjects underwent two different kinds of scans to measure their
brains’ electrical activity while they listened to people talk. The
researchers were able to see what the subjects’ brains were up to when
asked what someone was saying, both in a quiet environment and amidst a
level of noise.
The researchers studied two areas of the brain. They
looked at the more ‘ancestral’ midbrain area, which most vertebrate
animals—all the way down to fish—have, and which does basic processing
of all sounds. They also looked at the cortex, which is particularly
large in humans and part of which specializes in speech processing.
In the younger subject group, the midbrain generated a signal that
matched its task in each case—looking like speech in the quiet
environment, and speech clearly discernable against a noisy background
in the noise environment.
But in the older subject group, the quality
of the response to the speech signal was degraded even when in the
quiet environment, and the response was even worse in the noisy
environment.
"For older listeners, even when there isn’t any noise, the brain is already having trouble processing the speech," said Simon.
Neural
signals recorded from cortex showed that younger adults could process
speech well in a relatively short amount of time. But the auditory
cortex of older test subjects took longer to represent the same amount
of information.
Why is this the case? "Part of the comprehension
problems experienced by older adults in both quiet and noise conditions
could be linked to age-related imbalance between excitatory and
inhibitory neural processes in the brain," Presacco said. "This
imbalance could impair the brain’s ability to correctly process auditory
stimuli and could be the main cause of the abnormally high cortical
response observed in our study."
"Older people need more time to
figure out what a speaker is saying," Simon noted. "They are dedicating
more of their resources and exerting more effort than younger adults
when they are listening to speech."
"Often we will hear an older person say, ‘I can hear you, I just
can’t understand you,’" said Anderson. "This research gives us new
insight into why that is the case."
This eroding of brain function appears to be typical for older adults
and a natural part of the aging process. The researchers are now
looking into whether brain training techniques may be able to help older
adults improve their speech comprehension.
Simple courtesies can
help, too. Since being able to see as well as hear someone speaking
helps with speech processing, it’s a good idea to look directly at older
adults and make sure you have their attention before talking with them.
"The older brain just drops part of the speech signal, even if the
ears captured it all just fine," said Simon. "When someone can see you
speaking, instead of only hearing you, their visual system can sometimes
make up for that loss."
Holding conversations in a quiet environment helps as well.
"The main message is that the older adults in our study have normal
hearing as measured on an audiogram, yet they have difficulty
understanding speech in noise because the timing aspects of the speech
signal are not being accurately encoded," said Anderson. "Because they
have normal hearing, talking louder does not help. So if someone is
having trouble understanding you in a noisy restaurant or in a crowded
room, it is most important to speak clearly at a normal or slightly
slower than normal rate. Your older loved ones will appreciate this
courtesy during the upcoming holidays!"