As we get older, our hearing gets worse, right? According to a new study, that may all depend upon what your definition of “hearing” is.
What we have always assumed was a failing of our ears as we age may actually be a function of wear and tear on our brains, instead. A team of scientists from the University of Maryland uphold that something is going on in the brains of older adults that causes them to struggle to follow speech amidst background noise. All that, even when their hearing would be considered normal on a clinical assessment.
The researchers 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 work was done as part of ongoing research into what has been called “the cocktail party problem,” that is, the brain's inability to focus on and process a particular stream of speech in the middle of a noisy environment.
Two groups were tested, one young and one old. The scientists analyzed two areas of the brain: the more 'ancestral' midbrain area, which most vertebrate animals have, which does basic processing of all sounds; and the cortex, which is rather large in humans and part of which specializes in speech processing.
The signals generated by the younger group's midbrain matched its task in each case. It looked like speech in both the quiet and noisy environments.
The responses to the signals in the older group of brains, however, was a different matter. 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 researcher Jonathan Z. Simon.
The neural signals recorded from the cortex showedthe scientiststhat younger adults could process speech well in a relatively short amount of time. Conversely, the auditory cortex of older test subjects took longer to represent the same amount of information.
"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," said researcher Alessandro Presacco. "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."
So what long has been viewed as older people becoming “hard of hearing” as in, having an ear problem, is actually borne of degrading brain function.
"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 researcher Samira 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."
The research was published by the Journal of Neurophysiology.