What would be your best estimate of the number of people in the United States with significant hearing loss? You may be as surprised as I was to learn the answer: about 73 million, or approximately 1 in 5 persons. Moreover, the incidence of this loss increases over the lifespan, nearly doubling with every decade. By age 60, more than two-thirds of people are afflicted with hearing loss. Even more troubling is the well-established link between hearing loss and cognitive decline, impaired communication, and dementia.

According to the Lancet Commission on Dementia (2020), hearing loss in middle age and beyond is the single biggest risk factor for dementia. In 2023, the National Health and Aging Trends Study (NHATS) published findings that people older than 65 with moderate to severe hearing loss are afflicted with 61 percent greater prevalence of dementia compared to a similar group with normal hearing.

Degraded speech

Key to these associations between hearing and dementia is the concept of “degraded speech.” Actually, the term degraded speech is a misnomer: The speech is clear enough to those with normal hearing, but the perception of the speech is degraded in those with hearing loss, usually by background noise or electronic transmission.

Picture yourself in a frantically busy trattoria with voices bouncing off the tiled walls, ceiling, and floor. While you may hear the lion’s share of what your companion is saying, certain words may remain ambiguous. Did he say “safe lane” or “save lane”—you just couldn’t quite catch the f v distinction. In such a situation, the topic of conversation often provides the correct word choice. Was the conversation about traffic (safe) or finance (save)?

Such distinctions are perceived in the primary auditory cortex, located within the temporal lobe, which is concerned with the acoustic forms of speech (what you actually hear). Speech intelligibility, in contrast, is the responsibility of the temporal and frontal regions.

Under ideal circumstances, hearing, understanding, and replying to speech proceed smoothly, even in people with mild speech impairment. But conversations in everyday life don’t always occur under ideal circumstances; they often involve background noises such as crowds, loud music, or the clinking of glasses in a dining room or kitchen. Under such circumstances, even people with normal hearing must force themselves to concentrate in order to prevent mishearing.

Research by Connor Wild of The Brain & Mind Institute at Western University in London, Ontario, employed a PET scan, a measure of brain activity, to gauge how normally hearing people respond to speech that is unclear. Attention was increased, and additional portions of the brain became active. “Our findings unequivocally demonstrate that the extent to which degraded speech that is unclear is perceived depends on the listener’s attentional state.”

Simply put, a person with a hearing impairment has to expend more mental energy concentrating on and deciphering the words being said. As a consequence, those portions of the brain ordinarily used for thinking, analyzing, and responding to what is being said must now be used to correctly identify words.

As an additional effect, conversations in noisy settings often prove exhausting because of the increased mental effort needed to concentrate on another person’s speech.

Among the hearing impaired, speech misperceptions often lead to errors in understanding, which can trigger inappropriate responses that may, under certain circumstances, be interpreted as expressions of dementia.

Consider these three conversants in a moderately loud restaurant. They are talking about their favorite pets:

“I definitely prefer dogs. They are wonderful companions.”

“Since childhood, I’ve never been around anything other than cats. So, I guess I prefer them.”

“Me? I prefer vicious pets.”

“You prefer vicious pets!?” one of the two conversants—the one with impaired hearing—exclaims with astonishment.

“I didn’t say vicious pets; I said fish as pets.”

Although such mishearings may prove amusing to others, they are anything but amusing to the person with a hearing problem. In this example, “vicious pets” spurs the hearing-impaired conversant to disbelief, shock, and even a smidgeon of annoyance.

Social consequences of mishearing

Now consider the ramifications that are likely to result from these mishearing episodes.

When a hearing-impaired person does not hear what has been said and makes no comment, others may think the person just sits there staring blankly when spoken to. Such a behavior could easily be interpreted as either a sign of impaired hearing or, more likely in the elderly, an early sign of dementia.
When the hearing-impaired person erroneously hears something that hasn’t been said secondary to misperception resulting from degraded speech (the vicious pets example), responses can range from mild expressions of puzzlement to outright hostility.
When the hearing-impaired person responds sparingly in a free-flowing conversational exchange, secondary to the fear of making mistakes, social isolation is likely to follow. Social isolation is a universally recognized contributor to dementia.

As a result of these experiences, the hearing-impaired person is likely to keep conversations—particularly those involving several people at once—to a minimum.

Preventing the progression from hearing loss to dementia

Fortunately, this sad progression from hearing impairment to dementia can be interrupted. First, if you are experiencing significant difficulty, don’t try to hide it. Eventually, people are going to notice that you’re not “catching” some of the things said to you. By admitting upfront that you are experiencing difficulty, people are encouraged to take special efforts to increase their audibility by speaking louder, slower, and more precisely. Best of all, they may avoid lowering their voices at the tag end of a sentence (a frequent speech quirk that most of us display, especially when we are fatigued).

Second, consult a hearing specialist. Despite the high prevalence of hearing impairment, only 1 in 5 of hearing impaired people currently use hearing aids. If the specialist determines that you will benefit from hearing aids, purchase the best instruments you can afford, keeping in mind the World Health Organization’s conclusion that nearly twice the number of people with mild hearing loss go on to develop dementia compared to those without hearing loss. So, identifying and improving even mild degrees of hearing loss confers current and future benefits.