Esoteric, almost OT: stapedius reflex (aka"acoustic ref

[chconnor]

[Edit: I probably should have posted this in "listening to other music"... ?]

Ok, for background: http://en.wikipedia.org/wiki/Acoustic_reflex

We all know that prolonged exposure to loud sounds can tire this reflex, resulting in more hearing loss, and that the non-instant reaction time of the reflex is why it's crucial to wear hearing protection if you're a carpenter or metal worker (hammering), etc etc.

But what i'm amazed about is this factoid:

The stapedius reflex is also invoked when a person vocalizes. In humans, the vocalization-induced stapedius reflex reduces sound pressure levels reaching the inner ear hair cells by approximately 20 decibels.

20dB ?? That seems like an awful lot. According to the article it can be induced by humming, and they suggest it as an additional protection against hearing loss: hum just before and while hammering, etc.

If i listen to some music and hum, it certainly doesn't seem as if anything is attenuated 20dB... in fact, it sounds totally unaltered... which suggests to me that either the perceptual processing of the sound compensates for the physical attenuation, or that my stapedius ain't stapedin'.

Any thoughts on this? The wiki article isn't well-sourced, and i haven't dug around looking for other articles yet, but thought i'd throw it up here.

-c

[Snarl 12/8]

I was listening to music while I was reading that.
I hummed and noticed a drop in volume.
It really felt psychosomatic to me though.

[MoreSpaceEcho]

can you go hammer a couple hundred nails sans earplugs, see if humming makes it quieter and report back to us? kthx.

[chconnor]

can you go hammer a couple hundred nails sans earplugs, see if humming makes it quieter and report back to us? kthx.

In defense of the Wikipedia author(s), i didn't at all get the impression that they were suggesting it as front-line hearing protection, just that they were pointing out that it apparently has an appreciable impact on the damage that could be done to your hearing; i.e. that it's not just a perceptual drop in level. Anyway, I'm mainly curious to know if others perceive any drop in level in their own heads... i feel better asking audio geeks than asking my non-audio-geek friends who aren't used to listening for such things (although 20dB shouldn't be all that subtle...) Snarl noticed a drop, but possibly psychosomatic... again, seems like 20dB would be more decisive. I think i'm going to have to google around a bit...

-c

[vvv]

I wonder if it may be a physiological side-effect, like a change in pressure on the eardrum ...


DISCLAIMER: I am not a doctor, and I have never played with one on TV.

[chconnor]

I wonder if it may be a physiological side-effect, like a change in pressure on the eardrum ...

The acoustic reflex is, generally, a physiological reflex. What i'm on about is that they say it's a physiological drop in 20dB, which seems extreme.... do i have my math right? Wouldn't that be a bit more than 8x quieter?

Anyway, all from Wikipedia:

When presented with a high-intensity sound stimulus, the stapedius and tensor tympani muscles of the ossicles contract. The stapedius pulls the stapes (stirrup) of the middle ear away from the oval window of the cochlea and the tensor tympani muscle pulls the malleus (hammer) away from ear drum. The reflex decreases the transmission of vibrational energy to the cochlea, where it is converted into electrical impulses to be processed by the brain. The acoustic reflex normally occurs only at relatively high intensities; activation for quieter sounds can indicate ear dysfunction and absence of acoustic reflex can indicate neural hearing loss.

and:

The stapedius reflex is also invoked when a person vocalizes. In humans, the vocalization-induced stapedius reflex reduces sound pressure levels reaching the inner ear hair cells by approximately 20 decibels. The stapedius reflex causes an acousto-mechanical increase in impedance.

and:

Humming when you don't want to hear someone else really works ? and the reason is the stapedius reflex. While rude, the behavior provides the opportunity to make two points: first, the effect is active, not passive; second, and a more subtle point, is that the reflex is not a psychological effect or perceptual masking effect or a question of poorer signal-to-noise ratio when "noise" is boosted. The effect is not that of a sound seeming less loud; rather, the effect is that less of the sound waves is transducted into the inner ear ? thus causing less bending of the hairs of the hair cells.

[Snarl 12/8]

In my defense, I would argue that anyone reading this and then humming while listening who perceives a drop might be subject to their own expectations. I'm having trouble figuring out a "double blind" way of doing this. Especially to myself. Should I sit on my arm for half an hour and then call it "the stranger?"

Anyway, I'm wondering about these seemingly carefully chosen words "reduces sound pressure levels reaching the inner ear hair cells by approximately 20 decibels" I know there are all kinds of "db" scales, dbv, dbu, etc. Maybe what they're talking about there doesn't result in an 8x perceived reduction in a hummer's brain pan.

[chconnor]

In my defense, I would argue that anyone reading this and then humming while listening who perceives a drop might be subject to their own expectations. I'm having trouble figuring out a "double blind" way of doing this.

For sure. That's why i was interested in audio folks' experiences with it... I feel like if I'm listening to track A and I play track B, I'd notice if track A dipped even a couple dB, much less 20, so I was hoping I could do the same in my head (track A = music, B = hum). But it may be beyond the reach of mere mortals.

Anyway, I'm wondering about these seemingly carefully chosen words "reduces sound pressure levels reaching the inner ear hair cells by approximately 20 decibels" I know there are all kinds of "db" scales, dbv, dbu, etc. Maybe what they're talking about there doesn't result in an 8x perceived reduction in a hummer's brain pan.

I assume they mean dB-SPL, since it's air they're talking about. In re-thinking and re-researching it: 20dB is only about four times the "loudness" (10dB per doubling of loudness, which of course is partially subjective and based on frequency and A/B/C-weighting, etc etc). Even so, 4x is substantial... but maybe that's the max reflex, when you're full-out screaming at your hammer.

Assuming the reflex is proportional to the loudness of humming, I've been trying to hum louder and listen for changes in the apparent music level, and sometimes it seems like I can hear a drop. Mostly not, though. Maybe for whatever psychoacoustic/physiological reason it's just not fair to expect it to be as noticeable as when doing the "track A / track B" experiment described above.

-c

[Burnt Ernie]

Question-Do the Cilia(? -hairs in your ears) face in (towards brain),or out(facing earhole)? Are they randomly angled? Could it have something to do with air passing out ears/sinuses while exhaling?

[chconnor]

Question-Do the Cilia(? -hairs in your ears) face in (towards brain),or out(facing earhole)? Are they randomly angled? Could it have something to do with air passing out ears/sinuses while exhaling?

http://en.wikipedia.org/wiki/Stereocili ... ner_ear%29
http://en.wikipedia.org/wiki/Ear_canal

They are immersed in a fluid in the cochlea... and note that inhaling/exhaling doesn't send air through the ears unless you've ruptured your eardrum, and even then it would have to get through your Eustachian tube (which it can, but it's normally closed unless you intentionally open it, or sometimes when yawning, or if you close your mouth, pinch your nose, and blow, etc.). The ear sure is amazing.

But again, the physiology of how the attenuation happens is well understood, i'm just wondering about the magnitude of it (20dB), and i'm having trouble noticing it (at all) in my own experience.

-c

[vvv]

As a fan of loud music, I knew there was a reason I have always loved hummers.

Wait ...