2005-05-27 - 10:20 p.m.

On the internal soundtrack: "Killing in the Name", Rage Against the Machine

Brkvw asked me a question about my hearing earlier today (from this thread in PJammer's journal), and my answer got long-winded (surprise!) so I decided to put the answer here.

My hearing loss ranges from 60dB in both ears at 250 hertz to 80/95dB at 500 hertz and then is in the 100-110 range or nonexistent as the frequencies get higher, with an odd bounce back up to 90dB at 8000 hertz. There are some frequencies where I will feel my eardrum vibrating (it tickles) with the loudness of the sound but I cannot actually hear the sound itself.

As I understand it, the "dB" measure tells you how loud a sound must be in order for me to hear it, and a person with perfect hearing can hear a sound at the threshold of 0dB, the beginning of the decibel scale.

To put that in perspective, here are some sounds and the approximate decibel level:

loud music in a club - 100 dB
average street traffic - 85 dB
conversation in a quiet living room - 60 dB
sounds in a library - 35 dB

So basically, I can just barely hear male low-pitched voices at a conversational level with some personal space, but a girl needs to be talking right in my ear for me to even be able to hear her voice at all. Higher-pitched sounds (whistles, little kid's voices) I cannot hear at all.

Without hearing aids, my world is essentially silent except for the occasional unmuffled car engine, a jet passing over head, doors slamming, or somebody dropping something big and heavy in the same room.

Thank goodness, however, for technology. I heart technology. With my hearing aids, I am now able to hear those girls' and little kids' voices, sometimes even if they are in the other room. I can hear the full range of normal speaking voice (the sounds you make with your larynx, that is -- more on that in a moment).

What the hearing aids do is amplify the sounds I have the capability to hear. We know already that in order for me to just just barely hear a 500 hertz tone, it has to be about as loud as average street traffic (freaky thought!). So my hearing aids give the frequency an 85-dB "boost", bringing the sound into a range that I can hear.

The best part about my new digital hearing aids is that they give different frequencies different "boosts". The higher frequencies are boosted more than the lower ones where my hearing is less damaged. Older analog hearing aids had to amplify all frequencies equally (basically like turning up the volume on your stereo), which meant that I could only amplify as much as it was comfortable (and non-damaging) to hear the low frequencies, where my hearing is better. This meant that the higher frequencies were not getting amplified as much as I needed. Now I get the maximum boost possible within each of 16 "channels" of frequencies.

So you see, this is enough for me to hear enough of music to enjoy it. I can hear drums, bass viol, cello, bass guitar, and some of the lower notes of horns and electric guitar (can't hear the high notes well enough to appreciate Jimi Hendrix, dammit). I can "hear" -- but can't distinguish the pitch of -- flutes and upper violin notes.

HOWEVER.

The catch is that hearing aids do not give you "normal hearing". In particular, there are some frequencies that, even with hearing aids, I still cannot hear. Among these frequencies are the small breathy sounds that people use to make consonants. Some consonants are not even voiced! "K" and "G" are made with a similar closing of the throat, but the "G" is voiced, and the "K" is not. If you said "could" and "good", I would be able to tell that they were two different words because one had a voiced consonant in the beginning and the other didn't.

But even though the "G" is voiced, so are "B" and "D", and I cannot tell, by listening, the difference among them, because all I can hear is the voice, not the sound you make with your teeth, lips and throat that distinguish among them. In fact, I'm even skeptical that YOU can distinguish, because that just sounds impossible. ;)

Now I'll borrow from an old post of mine to explain how this works:

So I'm walking around hearing a lot of vowels and very few consonants, my own personal hangman/Wheel of Fortune game, except I have to buy consonants, not vowels. The context of a conversation has a function similar to the "hint" you get on the Wheel of Fortune show.

Lipreading fills in the blanks to a good extent. "B" doesn't look a damn thing like "L" or "K". (Unless, of course, the person mumbles or has what we call "Connecticut lockjaw" and won't move their jaw much when they talk. Let's not get me started on people like that.)

On the other hand, "B" DOES look a lot like "P" and "M". If you plug your ears and have somebody say to you the following nine words:

bad bad ban mat mat man pat pad pan

you'll notice that they look like they're just going "ba ba ba" repeatedly (or is that "ma ma ma"?).

So there's a lot of mental shuffling going on, trying on different possibilities to see what fits in the context of the conversation. Lipreaders depend very, very heavily on context. I might not be able to comprehend a sentence someone says out of the blue, but if we're already talking about a specific subject, it helps a lot with the guesswork.

If I know a person very well or what they say to me is very predictible based on context, I can understand short phrases without looking at the person. If I'm standing in front of an open refrigerator and my husband says "Can you hand me a Coke?", I'll hear it. If he starts randomly talking about his day at work, I probably won't understand a word.

One of the oddest things I've caught myself doing is the mental work that goes into deciphering something said from across the room without me seeing the speaker. I have a jumble of meaningless vowel sounds in my head, and I hold onto them -- including tone and inflection -- and my mind starts racing through the possible things the person could be talking about given the topic of conversation at the time. About 5-10 seconds later, when I hit on the right guess, suddenly all the pieces fall into place and I realize exactly what they said, word for word, by fitting the topic to the jumble of sounds I was holding on to.

It's really, really freaky. Even more freaky is how speedy and subconscious the process is. It's very similar to how sometimes I'll fall asleep working on a mental problem of some sort, and when I wake up in the morning I know the solution. It's like my brain is working overtime without any help from my consciousness.

I think I am also extremely lucky in that I have something of a knack for languages. My brain seems to be pretty open to the idiosyncrasies of other languages and doesn't try to map them directly to English. This same openness probably helps with all the context-driven guesswork of lipreading. I think sometimes other people with similar hearing losses have more difficulty deciphering spoken English, in which case I can understand why they might want to isolate themselves in an ASL community.

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