Researchers at the Max Planck Institute for Cognitive and Brain Sciences, Leipzig, Germany, have discovered that changes in brain waves compound hearing problems in older adults. The researchers have found that the hearing difficulties older people experience are due to more than hearing loss–the difficulties are also due, most likely, to changes in the brain’s alpha waves, whose adaptation to altered hearing situations improves speech comprehension.

The elderly often complain about hearing difficulties, especially in environments where there is background noise. According to a January 28, 2015 study article published in The Journal of Neuroscience from scientists at Max Planck Institute, our brains are constantly active with our efforts to perform various tasks. The currents flowing in the brain during these tasks can be measured using an electroencephalogram in the form of voltage fluctuations on the scalp. The research team at Max Planck was most interested in studying the brain’s alpha waves because, in hearing tasks, the strength of alpha waves indicates the listening effort of the listener.

In a study headed by scientists Jonas Obleser and Malte Wöstmann, the team recorded the alpha waves of study participants who were 20-30 years old, and study participants who were 60-70 years old, while they were performing a hearing task. According to the article, participants listened to 2 spoken numbers and had to indicate by pressing a button whether the second number was higher or lower than the first. The numbers were presented in background noise to simulate hearing environments that are typically encountered in everyday life. To prevent the results from being skewed by variations in the individual hearing performance of the ear, the scientists reportedly tested the hearing acuity of all participants prior to the task and adapted the speech material to the requirements of each individual. This made the task equally difficult for younger and older participants.

While the participants were solving the number task, the researchers triggered the modulation or adaptation response in the participants’ alpha waves by manipulating the acoustic quality of the speech signal. The researchers report that they also intentionally varied the predictability of the task’s solution. They found that both older and younger participants had similar outcomes when completing the task, until the acoustic quality was changed. When the acoustic quality was changed, the older study participants benefitted to a greater extent from better quality, completing the task more quickly.

The researchers discovered that the major significance of acoustic quality for older participants was also reflected in the alpha waves. With better speech quality, the amplitude of the alpha waves in the group of older participants was significantly lower than among the younger ones. Attention in old age apparently shifts to acoustic aspects of the speech signal, according to the researchers. Additionally, the results of a survey given to the participants asking them to estimate their own difficulty in listening to speech in the presence of background noise also point to the importance of alpha waves.

Participants whose alpha waves adapted better to the acoustic quality of speech and to the predictability of speech in the experiment found it easier to listen despite background noise. “The modulation of the alpha waves therefore influences speech comprehension in everyday hearing situations,” said Wöstmann. The researchers believe that these research results open up new opportunities for further studies that explore how a hearing aid might be adapted to a listeners’ brain activity to improve speech comprehension in challenging listening environments.

Source: Max Planck Institute for Cognitive and Brain Sciences

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