Thursday 1 September 2011

Reverse Slope Hearing loss - Good article and explanation from a patient.

The Bizarre World of Extreme Reverse-Slope
(or Low Frequency) Hearing Loss
(short, abridged version)

(Click here to read the complete, unabridged version)
© April 2007 (latest revision August 2007), by Neil Bauman, Ph.D.
Table of Contents
Imagine a person with a hearing loss so severe he can’t hear thunder rumbling overhead, yet, at the same time, he has hearing so acute he can hear a pin drop; or imagine a person that can’t hear you talking just 4 feet away, yet clearly hears a whisper from across a large room; or imagine a person that can’t hear a car motor running right beside him, yet can hear a single dry leaf skittering along in the gutter 50 feet away.
“Impossible,” you say, “a person could never have such good and bad hearing at the same time!”
Surprise! It’s true. Welcome to my world—the bizarre world of people with extreme reverse-slope hearing losses.

What Is Reverse-Slope (or Low Frequency) Hearing Loss?

Hearing losses are sometimes classified according to the shape they form on an audiogram. They commonly go by strange names such as ski-slope loss, cookie-bite loss, flat loss, reverse cookie-bite loss and reverse-slope (or reverse curve) hearing loss. (My article Kinds of Hearing Losses explains these different hearing losses and illustrates the various shapes they form on audiograms.)
   Fig. 1.  Severe ski-slope
By far the most common kind of hearing loss is the typical ski-slope loss where the line on the audiogram slopes down to the right (Fig. 1). In contrast, a reverse-slope loss (as its name implies) does the reverse and slopes upto the right (Fig. 2).
   Fig. 2. Severe reverse-slope
As a result, this kind of hearing loss is sometimes referred to as an up-sloping loss, a rising loss, or  low-frequency hearing loss, but by far the most common name is the reverse-slope (or reverse-curve) hearing loss.
   Fig. 3.  Mild reverse-slope
Don’t make the mistake of thinking that all reverse-slope losses are the same. Nothing could be further from the truth. There is an enormous difference in hearing between a mild, gently-sloping reverse-slope hearing loss (Fig. 3), and a severe or profound steeply-sloping reverse-slope loss (Fig. 4), just as there is between the various degrees of ski-slope hearing losses.
For practical purposes, we can group reverse-slope hearing losses into three basic classes.

  Fig. 4.  Neil's severe reverse-slope loss
               at age 21
Class 1.     The most common form of this relatively-rare loss is a gently up-sloping line in the standard audiometric frequencies between 250 and 8,000 Hz (Fig. 3). In this class, the worst low-frequency hearing loss typically lies somewhere between mild and moderately-severe. Class 1 curves are often seen in the beginning stages of Meniere’s disease.
Class 2.     Rarer, is a fairly-steep up-sloping line in the standard audiometric frequencies. In this class, there is a moderate to severe hearing loss in the frequencies below 1,000 Hz, but at the same time, hearing becomes virtually normal somewhere in the range of 2,000 to 6,000 Hz (Fig. 2). It is in Class 2 that the differences between reverse-slope losses and ski-slope losses really become apparent.
Class 3.     The rarest form of the reverse-slope loss reveals a steep up-sloping line ranging from severe to profound hearing loss (70 to 110 dB) in the low frequencies to incredible hearing in the very high frequencies (those frequencies above 8,000 Hz) (Fig. 4).
Years ago (when I was in my early 20s) my hearing ranged from 75 dB at 1,000 Hz to -30 dB in the frequencies above 16,000 Hz (Fig. 4). (Note: numbers above the 0 dB line represent super-acute hearing, and are expressed as negative numbers.) Since I could easily hear “silent” dog whistles, some said I had “dog ears” hearing.
It is here in Class 3, with its incredible range of over 100 dB between the faintest low-frequency sound heard and the faintest high-frequency sound heard, that truly bizarre hearing is the most pronounced. Since my hearing loss spanned an incredible range of 105 dB, no wonder people were always confused about what I could, and could not, hear!
For example, my former mother-in-law wouldn’t believe my hearing was as bad as it was because she would whisper when she didn’t want me to hear something, and I would easily hear her. (She never caught on that if she just spoke in a normal voice, I wouldn’t have understood a thing!) (Back to Table of Contents)

How Common Are Reverse-Slope (or Low Frequency) Hearing Losses?

Mild reverse-slope hearing losses are relatively rare. However, extreme reverse-slope hearing losses like mine are much rarer still. Dr. Charles Berlin, formerly head of the Kresge Institute in Louisiana, one researcher that has studied this kind of hearing loss fairly extensively, estimates that out of the roughly 31 million hard of hearing people in the USA, there are 3,000 plus people that have my unusual kind of reverse-slope hearing loss. (Back to Table of Contents)

Causes of Reverse-Slope (or Low Frequency) Hearing Losses

When people think of causes of reverse-slope losses, typically they think about Meniere’s disease. Classic Meniere’s disease does indeed often, but not always, result in a reverse-slope hearing loss (Class 1 curve), at least in the beginning stages.
However, probably the most common cause of reverse-slope hearing losses, particularly in Classes 2 and 3, is of genetic origin. Hereditary losses often seem to run in our families.
Reverse-slope hearing loss has run in my family for the past four generations. Those that I know of include my maternal grandfather, my mother, myself, my brother, my younger daughter and my brother’s older son. I know of a number of other people who also have reverse-slope hearing losses running in their families—some also for the past 4 or 5 generations.
It appears that extreme reverse-slope hearing losses are a dominant genetic trait. It certainly is in my family. Each person born in my family has a 50% chance of having this kind of hearing loss.
Another interesting characteristic of severe or extreme reverse-slope hearing losses such as mine is that they seem to be non-syndromic—that is, they don’t have any other conditions or syndromes associated with them.
In addition to Meniere’s disease and genetic mutations, various childhood diseases are thought to occasionally result in reverse-slope hearing losses. As Judith explained, “My hearing loss apparently was the result of measles at the age of 2.” Debbie’s daughter “was not born with a hearing loss, but acquired it from complications of chicken pox” also at age 2. (Back to Table of Contents)

How Reverse-Slope (or Low Frequency) Hearing Losses Progress

Whether reverse-slope losses get worse with time depends on what caused the loss in the first place. (Back to Table of Contents)

Meniere’s Disease

One of the characteristics of Meniere’s disease is that it typically results in a progressive, fluctuating, step-wise hearing loss. Thus if you have Meniere’s disease, initially you may have a Class 1 type of reverse-slope loss. Over time, as your Meniere’s Disease progresses, you will likely find that this reverse-slope loss slowly evolves into a reverse cookie-bite or flat loss, and ultimately into some degree of a severe or profound ski-slope loss. (Back to Table of Contents)

Hereditary losses

With hereditary reverse-slope losses, we seem to go through three distinct stages.
Stage 1: The first stage occurs from birth to around 5 years of age. It appears that although there is some degree of hearing loss at birth, hearing in the lower frequencies rapidly decreases until around age 5 or so.
Furthermore, it seems that because of our excellent high-frequency hearing, and because of our excellent speechreading skills at a very early age (of which our parents are typically totally unaware), our hearing losses do not become apparent until something happens to drive home the fact that we cannot hear well.
For example, my parents didn’t discover I had a hearing loss until I was about 4 or 5. One day my dad, who was standing behind me where I couldn’t speechread him, asked, “Do you want to come for a ride in the car with me?” I totally ignored him, and continued playing on the floor. He knew something was wrong because I loved riding in the car! (It was a ‘29 Buick back in those days.) Another time he asked me if I wanted some ice cream—which I still love—and again I ignored him. It was at this point that my parents had my hearing tested and discovered I had a severe hearing loss!
Stage 2: The second stage begins around age 5 and continues without significant change to around age 50 (if there are no other factors involved such as hearing loss from noise damage, or from taking ototoxic drugs, for example). Thus, once we learn to adapt to our strange hearing losses, our coping strategies can remain the same for most of our lives.
   Fig. 5.  Average  (ski-slope) hearing loss
                curves with increasing age
Stage 3: The third stage kicks in about age 50 and continues for the rest of our lives. This is not really our reverse-slope hearing loss progressing, but rather, the effects of aging dramatically impinging on our precious high-frequency hearing. Here’s what happens.
As people age, they typically begin to lose their high-frequency hearing. This happens slowly and insidiously over many years. Fig. 5 plots “average” curves showing increasing high-frequency hearing loss from ages 40 (top line) to age 80 (bottom line).
Notice that people with the typical ski-slope losses have already lost their high-frequency hearing (but retain their low-frequency hearing). Thus as they age, they don’t have much high-frequency hearing left to lose.
   Fig. 6.  Progression of Neil's reverse-
                slope loss at age 59
In contrast, those of us with extreme reverse-slope losses have most of our residual hearing in the high (and very high) frequencies, yet it is these very frequencies that people typically lose as they get older. As a result, somewhere around age 50 or so we begin to notice a significant drop in our hearing. Our reverse-slope losses rapidly begin to flatten, and in time become more or less “flat” curves.
For example, between ages 50 and 60, I lost much of my excellent high-frequency hearing. You can verify this by comparing my audiogram taken at around age 21 (Fig. 4) with my current audiogram (Fig. 6) taken at age 59.  As you can see, I have lost much of my high-frequency hearing. (In fact, I am following the same hearing loss pattern my mother went though as she aged.) (Back to Table of Contents)

The Blessing of Perfect Speech

One of the things that surprises many people is that all of us with severe reverse-slope losses have perfectly-normal or near-normal speech. Imagine a person that is essentially deaf, yet has flawless enunciation, perfectly-formed and well-modulated speech, all without having had any speech therapy. This is one of the blessings of having a severe reverse-slope hearing loss.
Shirley explains, “Because I have high-frequency hearing, my voice has never been affected by my hearing loss, although my hearing loss is profound.”
It’s the same with me. Because my speech is also indistinguishable from the speech of people with normal hearing, I’ve had many people refuse to believe how bad my hearing really is. Peggy, herself hard of hearing, after hearing me speak, exclaimed, “Do you realize that your speech is absolutely perfect? You must have worked very hard to perfect your tone like that, what with growing up hard of hearing.” The truth is, I’ve never had speech therapy. I’ve never needed it.
The real secret to perfectly-normal speech is hearing all speech frequencies, especially the high-frequency consonants such as “s,” “f,” “sh,” “ch,” “t,” and “th.”
When you can’t hear these sounds, it is very difficult to produce them properly. In fact, I can tell if a person has a profound loss just by the way they move their lips when they try to produce these sounds. Think how difficult, or impossible, it would be to learn to whistle if you couldn’t hear any of the sounds you were trying to produce. In like manner, correctly producing the above voiceless sounds depends 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 it, you don’t get this feedback so you don’t correct these sounds, and your poor speech reflects this.
Since those of us with severe reverse-slope losses hear these “voiceless” sounds the best, we use them correctly in our speech, and thus avoid the flat “deaf speech” patterns of many of those with severe ski-slope losses. (Back to Table of Contents)

What It’s Like to Live with a Reverse-Slope (or Low Frequency) Hearing Loss

Having a Class 2 or 3 reverse-slope loss makes for some interesting experiences. Here are a few of the more bizarre things we hear, or don’t hear, and how we cope with it.
  • We don’t hear appliances running. Thus we have to put our hands on household appliances (fridge, washer, drier, furnace, etc) and feel the vibrations in order to know if they are running. However, we can readily hear the faint click of the relays from across a room as they kick in or out to start/stop these appliances, but we don’t know whether they just started or just stopped.
  • We hear whispers very clearly—even from across a room. In school, I used to hear kids whispering from across the classroom, yet couldn't hear the teacher talking only a few feet away. It always puzzled me that the teachers never heard all the whispering that to me was so loud. Since whispering seemed so loud to me, when I used to “whisper,” I’d actually use “low voice” (which to me sounded very faint as compared to whispering). To my chagrin, everyone around heard me “whispering.” My wife kept telling me to “whisper.” It eventually dawned on me that others couldn’t hear the whispers I so easily heard.
  • Since I can’t hear my car’s motor running, sometimes when I am parked I may try to start my car a second time thinking it hadn’t started. The suddenly-swiveled heads of the people nearby tell me that I just ground the gears on the starter—again! Now, I always look at the tachometer first. If it’s not reading 0, I leave the starter alone!
  • The screech of the wheels of trains on the tracks is so loud to me that it hurts my ears—yet to most people this is not even a loud sound. Imagine not being able to hear the loud roar of a train bearing down on you, yet getting headaches from the painfully-loud screech (to me) of the train wheels against the tracks as the train goes around a curve.
  • We can easily hear high-frequency sounds most people can’t hear. For example, I could easily hear the faint 15,734 Hz whine produced by the fly-back transformer of a TV from anywhere in the house, and even fromoutside the house, yet I had to put my ear about 6 inches from the TV’s speaker in order to understand any speech from it (if the volume was set to normal hearing levels).
  • To me, certain insects chirping from a block away (even just one insect) produce a racket loud enough to drown out the voice of a person standing almost nose-to-nose speaking. The “funny” thing (to me) is that people with normal hearing either can’t hear that insect at all, or only hear it very faintly!
  • We hear some birds singing and chirping away, but not others. For example, I have never heard the low-frequency sounds of an owl hooting or a Mourning Dove cooing (although I have a flock of Mourning Doves right outside my back door), yet I can easily hear a male hummingbird’s high-pitched angry squeaks as it chases off a competitor, or the wonderful trilling sounds it makes as it power dives to impress its prospective mate.
  • Although we have severe hearing losses in the speech frequencies, we can easily hear faint high-frequency sounds such as a pin dropping on a table or hard floor. Sarah explains, “I have a 60-80 dB reverse-slope hearing loss. I can hear a pin drop, but normally can’t hear thunder!” (Back to Table of Contents)

Practical Differences Between Reverse-Slope and Ski-Slope Losses

Although there are many coping skills that are common to all kinds of hearing losses, a number of the coping skills you typically read about were designed with the needs of people with ski-slope losses in mind. They were not designed for those of us with reverse-slope losses—yet people think we need these coping strategies, but we often need the opposite. Here are three examples.
1.     People with ski-slope losses don’t want you to speak louder, but clearer.
One of the “rules” when speaking to a hard of hearing person (really meaning those with ski-slope losses) is that you don’t “yell” at them, but speak slowly and clearly at your normal volume. This approach is totally wrong for those of us with reverse-slope losses. We need people to speak louder in order to hear speech in the first place.
If you have a ski-slope loss you hear the loud vowel sounds, but not the soft consonants. Thus you hear people talking with no problem, but because most of the intelligence of speech is in the consonants, you don’t understand what people are saying. To you, speech sounds muffled because you don’t hear the high-frequency sounds. Thus you primarily want more clarity, not more volume.
In contrast, those of us with reverse-slope losses hear the soft, high-frequency consonant sounds. To us, speech is thin, almost inaudible and often sounds like whispers. For example, as I approach someone talking, the first sounds I hear are the high-frequency voiceless “s” sounds. We do not really hear a person talking until we get very close so we can hear the “voiced sounds.” Thus we typically need more volume.
2.     People with ski-slope losses hear men better than women.
“Common wisdom” says that hard of hearing people hear men better than women and children. This is true for people with the typical ski-slope losses because they hear the louder, lower-pitched voices of men better. Women and children with their higher-pitched (and often softer) voices are much more difficult for them to hear and understand.
This “wisdom” is again totally wrong for those of us with reverse-slope losses. Since we hear the higher-frequency sounds best, we typically hear women’s voices better than men’s voices. I much prefer talking to women as their higher-pitched voices are more in tune with my ears. If men speak in a high falsetto voice I then hear them well too. It might sound ridiculous, but it works!
3.     If you have a ski-slope loss, low-frequency noise drowns out speech.
Loud low-frequency noise is the bane of people with ski-slope losses. Speech is lost in the racket caused by the noise in factories and mills, and by the air conditioning/heating fans in our homes, offices and schools, thus people with ski-slope losses have to shout over all the low-frequency noise around them. Since we don’t hear low-frequency sounds well, we clearly hear the people shouting. That’s one situation where I tell people (tongue in cheek), “You don’t have to yell at me. I’m not deaf!” By the same token, we often do not raise our voices enough in such situations so people with normal hearing can hear us talking over the low-frequency racket.
In contrast, we cannot hear speech through all the high-frequency sounds around us. The bane of our lives are nearby sounds such as running water, clinking cutlery, rustling and crumpling papers and people whispering. (Back to Table of Contents)

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