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Understanding speech: How the brain and ear work together

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By Rex Banks, MA, CCC-A, Reg. CASLPO, Chief Audiologist

Many older adults with hearing loss struggle to understand speech in noisy environments, like restaurants, sporting events, and family gatherings. Most are told that this is simply one of the challenges of hearing loss. But what’s really going on between the ear and the brain during these noisy situations? Let’s take a closer look.

Hearing and cognition
It’s not unusual for older adults to experience changes in hearing and cognition, both of which cause difficulties in speech understanding and functional decline (i.e., a loss of independence in self-care capabilities), especially in noise or other environments where listening may be difficult.

As we age, the auditory system starts to break down, causing distortions in the cochlea (an organ in the inner ear which changes sounds into nerve messages and sends them to your brain). Studies have shown that those changes may play a role in reducing gray matter in parts of the brain that are sensitive to understanding speech. This leads to slower processing abilities and overall increased effort to understand speech.

This is a significant reason why older adults with hearing loss have difficulties in complex listening environments, with accents, with people who speak quickly, localizing speech, detecting environmental sounds or even hearing on the telephone.

When we think about hearing, we are referring to the cochlea’s ability to interpret the frequency and loudness of sound. Even with the use of appropriate amplification, like hearing aids, to address hearing loss, older adults may still experience problems with comprehension.

Comprehension issues are affected by cognitive variables such as working memory, reasoning, task flexibility, and problem solving, as well as the brain’s ability for planning and execution. These are called “executive functions” – all of which generally slow down as we age.

Processing information
In the world of audiology, we call the process where information travels from the ear to the brain a “bottom-up” approach to information processing. Basically, sound enters the outer ear and travels through the middle and inner ear where it is separated into useful bits of information which eventually travel up to the brain where labels and meaning are attached.

For years, this was how we thought information processing worked. However, there is a more holistic view which sees the brain and ear as working together. “Top-down” processing refers to how the brain makes sense of information that has already been brought into the brain by one of the sensory systems – in this case, by the ear. Some research suggests that as much as 15–20% of what we understand is accomplished through top-down processing.

There are several theories to explain this interconnectedness between the ear and the brain. One theory suggests that when information isn’t processed clearly in the cochlea, the brain has to work harder to identify words, which can deplete and reassign resources like memory, reasoning and attention, which help give meaning to speech. Top-down processing represents a more forward-thinking theory on how the brain and ear work together to process sound.

So what does all that mean for older hearing aid users? When older adults develop hearing loss, sounds they have been used to hearing over a lifetime become distorted. Hearing aids certainly add important cues that have been lost due to normal age-related hearing loss. However, for older adults to fill in the missing information from a partially-heard sentence, they will depend on their top-down processing to fill in the blanks. For this reason, hearing aids are an imperfect solution to a complicated problem. But while hearing aids cannot solve all communication difficulties, they can be very helpful when used with other communication devices and strategies.

Becoming a better communicator
The challenge of understanding in background noise is not just about the ear or the brain and certainly not just about the hearing aid: it’s really about how all these things come together.

People with hearing loss need to find an audiologist they are comfortable with to address their individual hearing concerns. The hearing aid prescribed by the audiologist has to be suited for the individual’s listening goals and provide appropriate amplification from the ear to the brain.

But there is more that people with hearing loss can do to improve their hearing experiences. Aural rehabilitation, use of effective communication strategies and even brain exercises may aid in providing extra support in becoming a more successful hearing aid user and better communicator.

This article originally appeared in the Fall-Winter 2015 issue of Vibes.

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