by Neil Bauman, Ph.D.
Did you know that people born with extreme reverse-slope hearing losses, such as I have, generally have perfect speech? In contrast, people born with severe ski-slope hearing losses often struggle to produce acceptable speech, even after years of extensive speech therapy.
One lady told me: “My son has a hearing loss pattern similar to yours, and likewise has similarly-good speech.” Then she asked: “Could you explain how this works?”
Be glad to. Here is the secret why some people with severe hearing losses have perfect speech, while others with similarly-severe losses have “deaf” speech. Before I begin, let me explain the difference between a ski-slope loss and a reverse-slope loss. Both of these losses get their names from the shape of their curve on an audiogram.
The ski-slope loss is the common type of hearing loss most hard of hearing people have. A person with a ski-slope loss has an audiogram that looks like a ski hill–with the top of the hill on the left and sloping steeply down to the right. This means the person typically hears low-frequency sounds reasonably well, but cannot hear high-frequency sounds much if at all.
In contrast, a reverse-slope loss has the ski hill on the right and slopes steeply down to the left. Thus, this person doesn’t hear low-frequency sounds well, but has close to normal (or even abnormal) high-frequency hearing.
Now let’s link these differences to speech. I’m going to oversimplify things a bit so you can see how this works. Lower-frequency sounds (such as the vowels) give speech its volume. When you think about it, you’ll realize that the vowel sound is the loudest part of each syllable in English words.
High-frequency sounds (such as many of the consonants–but not all) give speech most of its intelligence. By this I mean that if you only hear the vowels, you hear a person talking, but it sounds like so much gibberish. However, by adding the high-frequency sounds, you make speech understandable or intelligible.
Lets take as our example the word “stop.” Stop is composed of 3 voiceless consonants–actually just air coming out of the mouth without any sound produced by the vocal cords–and one vowel that actually produces vocal sound. Thus:
S – air hissing between the teeth–a very high-frequency sound.
T – a burst of air released from behind the teeth–another high-frequency sound
O – a loud vowel sound produced by the vocal cords–lower-frequency sound.
P – a puff of air from the cheeks forced between the lips–another higher-frequency sound.
Now, if you have the typical ski-slope loss, where you hear low-frequency sounds quite well, and do not hear high-frequency sounds, when someone says the word “stop” all you hear is the short “o” sound, which sounds like “awe,” not “stop.”
However, if you have the extreme reverse-slope loss, where you don’t hear the low-frequencies well, but have excellent high-frequency hearing, you would hear the voiceless sounds of the “s,” “t” and “p” and, because the “o” is a loud sound, you would likely hear a bit of it too. Thus, you would hear the whole word correctly–assuming it was loud enough for you to hear it in the first place.
Now, since you hear all the individual sounds in this word, you also naturally produce them correctly when you speak. Thus, people with extreme reverse-slope losses typically have perfect speech without taking any special speech training, even though they actually don’t hear much speech unless it is amplified.
In contrast, the person with the typical ski-slope loss hears just the short “o” sound, so that is what they repeat. Consequently, their speech is “flat”–what I call “deaf” speech.
People with ski-slope losses typically need extensive speech therapy in order to learn how to make “voiceless” sounds such as the “s,” “sh,” “ch,” “t,” “th” and “f” sounds that give so much of English its intelligence. Such sounds are not easy to produce correctly if you can’t hear them. (Think how difficult or impossible it would be to learn to whistle a tune, or even whistle at all, if you couldn’t hear any of the sounds you were trying to produce.)
These voiceless sounds depend so much on aural feedback–meaning you listen to the sound you make, and if it isn’t “right on,” you immediately correct it. If you cannot hear these sounds, you don’t get this feedback. Consequently, you don’t correct these sounds. The result is poor speech.
Incidentally, if you have a reverse-slope hearing loss, many people will refuse to believe you can’t hear them because of your perfectly normal speech. It happens to me all the time.