Presbycusis: THE TROUBLE WITH TREBLE
By far, the most common hearing loss is called Presbycusis. It sounds a bit like Presbyterian, doesn’t it? Presbyterian means church of the elders. Presby is Greek for the word elders. At about age 40, one has difficulty seeing close up. This is called Presbyopia, which means vision of the elders. Presbycusis means hearing of the elders. At around 65 years of age, many people say they can hear, but just have trouble with clarity of speech. The complaint will be “People are mumbling. I can hear, but just cannot always understand what’s being said.” Conversations one-on-one, and in quiet, won’t be too difficult. Hearing problems will occur, however, when someone is speaking from another room, or when the face of the talker cannot be seen, or when there is competing background noise.
Why is this? With Presbycusis, hearing for low-pitched (bass) sounds is typically better than hearing for high-pitched (treble) sounds. The degree or amount of treble hearing loss does not have to be very much to cause difficulty. In fact, the treble hearing loss is usually moderate in degree.
The diagram shows a hearing test (audiogram) commonly found with Presbycusis and explains why treble hearing loss causes difficulty distinguishing words that sound alike. The numbers along the top indicate pitch. Bass on the left and treble is on the right. In music, 125 is low C, 250 is middle C and 500 is high C. As you look toward the right, the numbers continue to double. Each time they do, the pitch goes up one octave. Within the range of human hearing, music is relatively low in pitch. Going down the side of the audiogram are decibels of loudness. Zero (0) means very soft, 50 to 60 is about the loudness of normal conversational speech, and 120 is very loud.
Hearing testing is done under headphones. This way, the left and right ears are tested separately. The Xs represent the softest decibel level it took for the left ear to just barely hear all of the octave tones; the Os represent the same thing for the right ear. With normal hearing, these would lie along the top, because with very few decibels, all the pitches from low to high would be heard. Presbycusis usually shows fairly good hearing for bass sounds, with a moderate degree of hearing loss for the treble sounds.
Now look at the letters of speech across the audiogram. These are laid out as they would be with normal conversational loudness. Note that the speech sounds on the left (all the vowels and some consonants) are louder, and also lower in pitch, than those on the right. For someone with Presbycusis, these are quite easy to hear. On the other hand, consonants like S, TH, F,K, T, CH, SH are not only higher in pitch, but also quite soft. Someone with Presbycusis will have difficulty hearing these sounds.
So what? Well, every word has at least one vowel. In English, we have only five to six vowels (A,E, I,O,U and sometimes Y). There are thousands of words but they all have to share some five to six different vowels.
If speech were currency, vowels would be cheap; they’d be the nickels. Vowels tell only that speech is spoken. Think about this list of words: Sat, Fat, Cat, Hat, Chat; all of them share the vowel but those soft, high-pitched treble consonants determine what these words are.
People with Presbycusis have difficulty hearing high-pitched treble speech sounds and so they have trouble hearing which one of those words was said. They’ll rely on their eyes and on the context surrounding the words in question to help along in conversation. This can be rather tiring. Is it any wonder that they feel out of it and want to simply be left alone? This is not living the quality of life that they deserve. We should do something about it. The good thing here is that with good, trebleemphasis hearing aids, we can.