According to the National Institute on Deafness and other Communication Disorders, one in three individuals over the age of 60 and half of those over the age of 85 will have hearing loss. The hearing loss associated with aging is called presbycusis or high frequency, sensory neural hearing loss, caused by a deterioration of the VIII nerve. It is insipid and gradual. For most hearing impaired adults, their hearing loss began when they were in their late 40's or early 50's. It is binaural, permanent and invisible.
Common symptoms of presbycusis are:
1. "I don't have a hearing loss!" Denial is the number one symptom of age related hearing loss. Hearing loss has very strong connotations in our youth oriented culture of being OLD, and old is BAD. To admit hearing loss is to admit the loss of youth and vigor. Men are more commonly known to deny hearing loss.
2. "I hear just fine, it's just that everybody mumbles." In fact, they are right. Everybody does mumble - because we can. We spent a lifetime speaking rapidly, slurring our words and mumbling without it ever interfering with conversation. The normal ear is such a phenomenal sense organ, it can organize even the most distorted sounds into a comprehensible signal. We really don't need to speak clearly when speaking with someone with normal hearing. This will change, however, when speaking with someone who has a hearing loss.
3. "What?" This becomes such an automatic response when something isn't heard or understood that the hearing impaired adult won't even notice that they are using it in every other sentence in a conversation.
4. "What did he say?" This is a corollary to number 3. It is the common 'hearing aide' for spouses.
The sense of hearing is our most complex sense organ and probably the most poorly understood by the average person. The confusion comes from the fact that even someone with a severe, high frequency, sensory neural hearing loss can still hear. If an individual couldn't see, they would understand they had a problem with their vision. Logically, if they had a problem with their hearing they assume it would mean they couldn't hear, but they can. Consequently, it is natural for someone to deny they have a hearing loss even with severe presbycusis.
It is the very nature of our anatomy that causes us to lose high frequency sensitivity as we age. The VIII nerve is tonotopically arranged in the cochlea, our sense organ for hearing in the inner ear. As the nerve spirals around, the high frequencies are tuned at the basal end and the low frequencies resonate at the apical end. Sound waves impact the basal end initially and more forcefully and, like a sheet you shake out over a bed, the ripples decline in size as you get to the tip. After years of acoustic bombardment (or excessive noise exposure), the VIII nerve deteriorates more severely at the basal end of the cochlea. This results in the high frequency, sensory neural hearing loss of aging.
This loss of high frequencies has a predictable effect on communication. In an audiological evaluation, we measure hearing sensitivity - not acuity. The hearing threshold is the softest point at which a person hears 50% of the time. We are assessing only those frequencies which include the sounds of speech, from 250 Hz to 8000 Hz. At the lowest frequencies, sounds such as vowels, "b", "d", "g" are voiced. At the highest frequencies tested, sounds such as, "p", "t", "ch", "k" occur.
Here is the conundrum of high frequency, sensory neural loss. In the low frequencies, 90% of the energy of speech occurs, but these sounds contribute only 10% of the intelligibility. In the high frequencies, only 10% of the energy of speech occurs, but these sounds contain 90% of the intelligibility! Removing from audibility all or most of the high frequency speech sounds eliminates your ability to understand what is being said, even though you can still hear "fine." To the person with presbycusis, it will sound as if everyone is mumbling.
A distorted signal impacting an intact VIII nerve gets "smoothed out." We can fill in the blanks. It's like gluing together a broken mug. Even if you are missing the handle, when you're done, you can still tell it's a mug. If you have a distorted signal matched with a damaged VIII nerve, you aren't going to have enough pieces of the mug to glue together, so when it's done, you can't tell if it's a mug, a bowl, or an ashtray!
There are other serious communication issues caused by presbycusis. The most debilitating is the diminished ability to filter speech from background noise. If there are any auditory distractions in the room, such as other people talking or a television playing, understanding conversation can be almost impossible. Another side effect of high frequency VIII nerve damage is recruitment - an abnormal growth in loudness. If you intensify the volume of your voice slightly, to the patient with presbycusis, you will sound like you are shouting. Tinnitus is also common with this type of hearing loss. Not only will someone be struggling to hear you above the noise in the room, they will be fighting against the noises in their head.
One particularly damaging side effect of high frequency sensory neural loss can be an abnormally poor speech discrimination ability relative to the hearing loss. A speech discrimination test is part of a basic audiological evaluation. It measures the understanding of speech at optimal volume under optimal conditions. Normally, there is a 1:1 relationship between a person's level of hearing loss and their speech discrimination score. A mild-moderate hearing loss yields a mild loss in speech discrimination ability. For some individuals, and we don't always know why, a mild-moderate hearing loss might yield a severe speech discrimination deficit. Even under good listening conditions, this person will have extreme difficulty following a conversation.
There are many psychosocial issues for the individual with presbycusis which, when manifested, may be attributed to other causes depending on the professional lens through which they are being examined. It is amazing that older friends and relatives will be given a so-called thorough physical exam and there will be no evidence of audiogram in the chart. "Mr. Jones, how's your hearing?" "Fine, Doc." End of discussion!
Hearing loss is a major contributor to depression in seniors. They become so frustrated by
social encounters, going to the movies, talking on the phone, etc., that they will begin to withdraw and isolate themselves. They become angry, stressed, and cranky. Older adults with severe hearing loss are at higher risk for suicide. They suffer a loss of confidence, especially from the admonishments of their children, "Are you deaf?" "You only hear what you want to hear." They can appear to suffer from dementia because they may be answering a question that wasn't even asked. I once asked my Dad, "How's business?," and his response was, "Tickets?! What tickets?! No one told me I was supposed to pick up tickets!"
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