The natural aging process affects not only
the ability to detect sounds at soft levels (hearing thresholds) but also the ability
to understand speech at typical conversational volume.
No single factor is the cause of presbycusis, or age-related hearing loss, in hearing
ability.
Changes are seen throughout
the hearing system.
Many people who suffer from sensory presbycusis report that they hear speech, but
have difficulty understanding, particularly in the presence of background noise.
Because
presbycusis results in permanent sensorineural hearing loss, hearing instruments
are the treatment of choice.
Many older
adults do not report any hearing difficulties in quiet situations or for one-on-one communication. Even if a hearing loss
is present, they will seem to be able to get by.
However, in environments with lots of noise or echo (reverberation), older
adults identify fewer words correctly than younger adults with equivalent hearing.
When listening
to speech, sounds are available for only a few fleeting moments before they disappear,
and within that timeframe, the listener is expected to understand what has been said. Age may affect one’s ability
to process rapidly changing auditory information.
The central auditory system coordinates information
between the ear and brain.
It plays an important role in processing complex information such as understanding
speech in the presence of background noise or detecting differences in signal loudness
or duration.
Deterioration of neurons in the central auditory pathways (the pathways that transmit
information from the cochlea to the auditory cortex in the brain) may limit an individual’s
ability to separate out important components of complex stimuli.
It has also been suggested that changes in global cognitive ability may underlie
some aspect of the speech perception difficulties.
These are changes in cognitive skills
such as memory and attention, independent of hearing ability.
Investigators have suggested that reductions in working memory and other
facets of cognitive function may impact word recognition ability.
There is some evidence to suggest that memory performance declines for older adults
with hearing loss because of increased demands on attention.
It is possible that hearing loss places
more demands on auditory attention when distracting signals are present.
In studies of working memory and brain imaging,
researchers found older adults activated more brain regions than young
adults for the same task.
This has led some researchers to speculate that older brains activate new areas
in order to compensate for declines in other areas.
This highlights the potential for brain plasticity (the ability of the brain
to learn and change) across the life span.
Kathleen M. Cienkowski, Ph.D., CCC-A is an
assistant professor
in the Department of Communication Sciences at the University
of Connecticut
in Storrs, Connecticut.
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