Posting in Technology
Why hearing aids are frustratingly imperfect and continue to be a tough challenge for technology to solve.
Hearing aids have improved greatly over recent years, but they continue to be a surprisingly frustrating experience for new wearers. Sure today’s hearing aids are tiny, nearly invisible in fact, and they amplify sound and are able to present a higher range of frequencies, but they have not solved the problem of amplifying the sounds we just don’t want to hear. For new wearers the crumpling of a paper bag on the other side of a room can sound like a jackhammer.
To explain why this is such a huge challenge for technology, Smart Planet spoke with an expert in psychoacoustics, the study of how the brain perceives sound. Andrew J. Oxenham is a psychologist and hearing expert at the University of Minnesota.
SmartPlanet: Why can’t hearing aids work like glasses, and simply grant us healthy hearing?
Andrew Oxenham: Glasses compensate for lenses that aren’t focusing properly. With the ear it’s different. The ear works by analyzing sound and breaking it into different frequencies. And with many forms of hearing impairment it’s this frequency selectivity that is impaired.
SP: What does that mean?
AO: What that means is that the ear doesn’t filter as well as it did before. So instead of having very sharp tuning to filter out different frequencies the filtering becomes much broader and there is no real way of compensating for that. You can’t sharpen the filters or you can’t pre-process sound so it’s sharp. It’s like a broken TV set. You can process the signal going into the TV as much as you like but you still won’t get a clear picture of the output.
SP: So have hearing aids improved recently?
AO: Recent hearing aids have made a lot of progress, like being able to present frequencies of up to 6000 Hz as opposed to limited frequencies up to about 4000 Hz.
AO: By using digital signal processing, and a lot more computing power on a lot smaller chip.
SP: You mean it’s due Moore’s Law?
AO: Yes that is right.
SP: I didn't realize that.
AO: Well that's not all. Another big leap has been with the directional hearing. They can focus the microphones toward the front and filter out a lot of the sound coming from the side and back. And that is a fairly simple technique, but it involves signal processing that wasn’t possible with earlier hearing aids.
SP: I understand from hearing aid wearers that ambient sound is horribly distracting for them. A paper bag being crumpled across a room sounds screechingly loud. Why?
AO: This is common complaint of people who recently start wearing a hearing aid. Their hearing has deteriorated, often without them being completely aware of it, over a period of time. Then they are fitted with a hearing aid and they hear sounds they've got used to not hearing. The sounds are suddenly annoying and distracting. It’s a contrast effect. For a long time and suddenly they are now amplified and you can hear them and they become distracting.
SP: So it’s a perception thing? That is sourced in the brain’s ability to analyze sound?
AO: It's a complex interaction between the ear and the brain. The ear sends signals up to the brain, and we also know the brain does an awful lot of processing and on top of that, and then sends signals back down to the ear. These signals change the way the ear accepts input. This is partly why hearing aids are not perfect. Because the hearing aid is not part of that natural feedback loop. There’s no way with current aids that the brain can interface with a hearing aid directly to change its characteristics.
SP: To deal with background noise there are things called “hearing loops.” What are they?
AO: These are systems that are set up within places like concert halls and churches that interface directly with the hearing aid. It's like sending a radio signal to the hearing device.
AO: The idea is that this hearing loop picks up the sound directly from the microphone in front of a speaker. Say you're in a church and the priest is talking into a microphone. Normally we hear the sound acoustically through the airwaves. If you are wearing a regular hearing aid the microphone will pick up the sounds on the airwaves but that is together with all the background noise and reverberation in the church. With a hearing loop it sends the signal directly from the microphone to the ear and bypasses all the acoustics in the building itself. So the ear is getting a much better, clearer and cleaner signal of what's coming into the microphone.
SP: Where else could we use hearing loops?
AO: Concert halls, movie theaters.
SP: Why are we now fitted with two hearing aids, as opposed to one? And how does this help our hearing?
AO: It's only recently that people have routinely been fitted with two hearing aids. Often people only got one. The way we localize sound, to know where the sound is coming from, is the brain comparing the signals coming in at the two ears. So if it's slightly louder on one side then the brain knows the sound is coming from that side. But more importantly it's the time of arrival difference between the two ears. If you think about a sound coming from the right. The sound will reach your right ear a little bit before it reaches your left ear. We are talking about millionths of seconds. But your brain needs two ears to make a distinction. If you only have one you lose that ability to localize sound. And it's also an important part of filtering out sound and noise. The brain can determine if there is speech right in front and background noise in back of and to the side. And the brain can use those differences in localization to help to make the speech more intelligible.
SP: So the biggest technical challenge is developing hearing aids that can focus on what we really need and want to listen to. How are we going to solve this problem?
AO: We are hoping through even more sophisticated signal processing schemes that we'll be able to work on artificial source segregation and that means is analyzing the signal that is coming in and figuring out what is speech and what isn't, and only presenting to the ear the wanted signal.
SP: How are you going to distinguish between a wanted signal and just plain noise?
AO: The assumption is that what you really want to listen to is speech, and so there are certain acoustical aspects of speech that we can recognize and there are certain acoustical aspects of noise that are different from speech. So if you can get your algorithm to distinguish between speech and noise that will help you towards filtering the unwanted signal.
SP: Could brain-computer interface be part of the hearing aid systems of the future?
AO: That could possibly be a direction for the future. Where the hearing aid is tapping into brain responses to pick up the signal the person wants to pay attention to.
SP: When are we going to solve this problem of distinguishing a wanted sound from noisy ambient background?
AO: It's an ongoing process with incremental steps and we will continue to see improvements in next 15 years.
Sep 9, 2011
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as a Long time hearing aide user myself it is interesting to know how the hearing aides techs have changes over the years I myself have tried serval diffrent companies until i finally found 1 that I will be sticking with in the area that i am in now if i was to move i will have to go through the process of it again but that is part of life for me as i had lost my hearing when i was a baby to high fevers for a month straight it is hard to deal with i know and it does takes time to get used to hearing things again when ur not used to hearing them
My late stepfather suffered hearing loss after being near-missed by a Luftwaffe bomb in 1940 - he died last year, which definitely would have made him a "long term user". He and I spoke about hearing aids often, and I was particularly interested by links between his complaints about them and research done as far back as the 1950's by E.Colin Cherry, for the Air Ministry. Cherry wrote about a metaphorical Cocktail Party; your entire conversation is centred on the conversation you're having with an old friend, when - on the far side of the room - someone mentions your name. The focus of your attention switches from your friend, to the conversation that mentioned you. Cherry demonstrated that parallel processing of TWO data streams is taking place; one "scans" background noise on a short loop, and discards the data if nothing interesting is picked up. If however it DOES hear something noteworthy, the OTHER stream is diverted to the new source. The processing takes place not in the ear... but in the brain. Cherry called it "Dichotic listening". My point being... my stepfather may have been a "long term user", but that doesn't magically convey an understanding of how hearing WORKS. His idea of "the perfect Aid" would have been something that replicated Cherry's cocktail party.
I'm dismayed to see Oxenham's comment re new technology that "the assumption is that what you really want to listen to is speech, ..." That's true much of the time, but sometimes aids that attend to speech would be a huge problem. I'm losing my hearing due to (possibly genetic) deterioration of my auditory nerves that started in my 30's, and I can confirm that there are many frustrating problems. One of them is background noise; this can be the paper bag crumpling that interferes with the conversation I'm trying to follow, OR it can be the person nearby whose speaking interferes with my ability to hear the singer's lines in a concert. I realize that developing hearing aids to address everyone's needs is a huge challenge, but please don't have as a working assumption that there's ANY one thing that everyone is wanting to hear all the time.
My hearing loss was caused by exposure to loud noises. The usual stupid stuff that young people do as well as a big dose of industrial noise. The hearing aid fix is to amplify the sounds around me so the "cure" just adds to the problem. For the last 25 years I have been growing increasingly deaf year by year. The fanciest, most high-tech, most powerful aids, the ones I have now, don't help much more than the first ones I had in 1986. I probably won't live long enough to see (hear) the direct brain interface.
As a lifelong user(birth or childhood) of hearing aids, I would like to know why the designers do not ask the real users (not those just suffering from adult onset hearing disabilities/impairment) about their take on the so-called "improvement" in the technology. Hearing present a difficult set of problems that can not be fixed by just one fit all piece of technology like glasses. Do not give those micro-nano computers total control over the level of hearing or automatic level adjustment. Let me decide what is comfortable or not! *GRR*
Scientists long hair cells basilar membrane cochlea translate sound waves electrical impulses brain processing. Different frequencies sound waves captured hair cells points membrane helps brain ... kral oyun
I have had hearing aids since 1995 and my initial experience was really bad. I was directed to in ear analog aids (no problem with analog, but digital was SO expensive then) and just had many problems. The people involved were not receptive to my needs. Moving forward, I now have digital aids and would not look back. The audiologist was great and spent severl sessions adjusting the signal processing as I found necessary. I suggest a new provider. In my area there have been MANY trials offered over the last year, but I'm happy where I'm at.
That's her officer! That's the woman that PUSHED me down the stairs. Play bridge....HA, you'll probably PUSH them off the bridge. And then, she had the nerve to come after me as I lay on the floor....barely breathing. No, not to ask me if I was alright.....she held up that damn cigarette---and asked me if I had a light!
Kral Oyun's failure to use verbs in his writing is perhaps an attempt to show what hearing loss seems like on paper.
I'm in the process of helping my elderly Mother get hearing aids and have seen sooo many adds and read soooo many bad reviews could you please tell me the name of your digital hearing aids. Thanks in advance.