Wednesday, October 28, 2009

Sound Localization and Me

Yesterday while at work, I was sitting at the front desk when I started hearing a strange thumping sound. I could have sworn it was coming from behind me - where our public computers and fiction books are - but when I looked, there was nothing that could be making the sound. It continued for several minutes while I looked around, until I realized that the sound was actually coming from in front of me. It was the sound of a volunteer stacking empty boxes and lids on top of each other in our book sale area.

To any hearing person, this experience would be very foreign and unsettling. Hearing people have the ability, as do other animals, to localize sound and quickly determine where it is coming from. Most deaf and hard of hearing people, like me, find it difficult to localize sounds, a problem which can be annoying or even life-threatening. For example, when I am in a parking lot, I have to be very aware of my surroundings in a visual sense, because while I may be able to hear a car backing up or driving by, I can't tell where the danger is.

In school, I would often be walking across campus and hear what could have been my name (or perhaps not - I find I often mix the sound of my own name up with other sounds), but I absolutely could not tell where that person was coming from. I could either stop, look around, and move in a circle to attempt to identify the source, or I could assume it was a mistake, that I heard wrong, and continue on. This has continued - in a store, or at work, if I hear my name I have to stop whatever I am doing to localize the sound as best I can and then respond appropriately.

Last night I gave it a try. I closed my eyes and had Scotty (my husband) snap his fingers in a random location around my head. I had a lot of trouble with sounds in front of me and behind me, often answering the exact opposite. Sounds to the left and right were much easier, which makes sense, because my right ear has an extremely profound loss while my left ear is a little better, so I can tell the difference easier. Then I did the same thing to Scotty, who has normal hearing. His ability to reach out and immediately grab my hand upon the first sound he heard was startling. Like a superpower! This ability really is one of the cool things about our bodies we never think about.

So what can help a lack of sound localization? I couldn't find much. My own hearing aids, with Bluetooth connectivity to each other, are supposed to help by sending signals to each other over the course of the day, but I wonder if my right ear is so far gone that I can't use that feature to its fullest. Practice would probably help, if only to get me used to the varying ways that sounds can change dependent on their location. There's an interesting article on sound localization here, from PhysOrg.

9 comments:

  1. I *think* I read somewhere that localization comes from the very high frequency sounds because they have the shortest wavelengths and create the largest difference between left ear and right ear. A lower sound with a longer wavelength reaches both ears more simultaneously.

    It also has to do with the shape of the ears which hearing aids lose completely. All sounds from a hearing aid come from the the same place, the microphone that picks them up and the ear mold that delivers them.

    I've heard bilateral cochlear implant users claim that it helps with localizing sound, but not sure to what degree.

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  2. That's pretty interesting stuff. Since my right ear has a lot of loss, I think it just isn't picking up enough for there to be any difference... my left ear does all the work.

    I can see how cochlear implants might be better than aids in regards to localization.

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  3. this is so fascinating. My daughter has a lot of trouble localizing sounds as well and it can be scary for her. She hears a loud sound but can't figure out what it is or where it came from, so she freezes. You've just given me some good insight into what she's experiencing. thanks.

    And thanks for stopping by my blog and saying hello

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  4. Interesting blog. I have had similar experiences.

    At high frequencies it's the difference in intensity and at low frequencies (and the low frequency modulation of high frequencies such as tone bursts) it's the difference in timing that provide cues for localisation.

    I have open fittings and receive low frequencies undelayed and the low frequency modulation of high frequencies about 5 milliseconds later via digital aids. No wonder I can make 180 degree errors in localisation.

    Digital aids are great but this delay, which was not shared by analogue ones, is about five times the maximum delay experienced when a side-on sound travels the extra foot round your head. Does not compute, other than as a (single!)reverberation. The hearing aid industry has been in denial and AFAIK has not yet researched the impact of the switch to digital on localisation.

    Lack of localisation makes disattending to noise difficult and noise seems more intrusive and distracting. This was amplified for my mother when she she became blind overnight. In the absence of acoustic and visual localisation, every sound is "in your face".

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  5. I'm writing a paper on the feasibility of using Professor Edgar Choueiri's work to create better hearing aids, and I stumbled across this old post of yours. I figured I might share this article which outlines what he is doing, and briefly suggests that his new technique could revolutionize hearing aids.

    http://www.nj.com/news/index.ssf/2010/09/grants_in_princeton_alums_name.html

    "A common complaint among hearing-aid users is that the appliance reduces their ability to identify the location of a sound or a speaker, especially in a crowd. Choueiri said his technology restores that ability and he is now working on a way to reduce the circuitry to fit inside a conventional hearing aid."

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  6. Sound localization has always been a problem for me. I would actually get upset with people for calling out my name or a request because it would greatly confuse me as to where the sound was coming from. I am profoundly deaf in the very high frequency range. I also find that if too many of these instances occur simultaneously, I get quite dizzy.

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  7. As a teacher, as my hearing loss has become worse - even with aids - I find it harder and harder to localize "who's talking?" I have to work so much harder at watching the students. It's so frustrating ... and exhausting.

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  8. The pinna of your ear has a lot of importance in the localization process
    http://en.wikipedia.org/wiki/Pinna_%28anatomy%29

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  9. As has been mentioned good localization requires the use of your Pinnas...I use plural because it works best when you have both ears involved!...and unfortunately with Digital HAs the processing delay requires that both ears be fit in order to preserve the relative timing of the incoming sounds.

    To benefit from the acoustics associated with the Pinna the HA microphone needs to located at the entrance of the ear canal...historically this has meant a CIC or smaller instrument. There is now a miniBTE from the Netherlands that places both the microphone and the receiver in the ear canal...MaRIC technology in the Ytango. In principle it would seem like a good idea

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