Myth Information: Is Human Hearing That Mysterious?

This is a post about human hearing, technology, science writing, and internet services. Have you ever wondered how persistent myths get started? I think we might have an incipient instance starting up as of a few days ago (2019-06-18). On ‘How To Geek’, Andrew Heinzman takes on the question, ‘Why do noise-canceling headphones hurt my ears?’.

The takeaway from Heinzman:

Remember how ANC headphones aim to cancel out low-frequency ambient noises, like the sound of an engine? Sometimes, this can trick your brain into perceiving a change in air pressure.

Of course, your brain isn’t actually receiving any feelings of pain or discomfort. So, it starts to emulate those feelings to encourage you to pop your ears. Since popping your ears doesn’t resolve the lack of low-frequency ambient sound, the sense of pain and pressure can increase until you take off your ANC headphones.

I can neither confirm nor deny a bit of that. It might even be true. More on that later.

My beef on initially reading the article had to do with Heinzman’s run-up to that, which was pitched as an explanation of how human hearing and air pressure interact, including a mini-lesson on anatomy. Here’s the bit that got me going, from the ‘Why Do My Ears Feel “Pressure” On an Airplane?’ and a part of the following section…

Most people describe the feeling of ANC headphones as a sort of “pressure” on the ears, like the changes in atmospheric pressure from ascending in an airplane or diving deep into the ocean. So, it’s important to understand how air pressure works (and its relationship with sound perception) before we try to figure out why ANC headphones put “pressure” on your ears.

Atmospheric pressure (also called air pressure and barometric pressure) is the force extended on a surface by its atmosphere. Gravity from our Earth is constantly pulling atmosphere down, so the air in low altitude climates (the bottom of the ocean) is denser than high altitude climates (a mountaintop or an airplane in flight).

Now, atmospheric density isn’t what causes painful pressure in your ears. That feeling of “pressure” is caused the difference between the air pressure of your inner ears and the air pressure of your environment. If you’re at a high altitude, then the air in your ears wants to escape. If you’re at a low altitude and under a ton of pressure, your inner ears need more air so that they won’t collapse. When you “pop” your ears, you’re just equalizing your in-ear air pressure with the air pressure of your environment, and the feeling of “pressure” goes away.

But your brain doesn’t just rely on ear pain and headaches to determine when there’s a change in atmospheric pressure. It also looks at how much your middle ear vibrates.

When you first go up in an airplane, your ear has more air density than your environment. As a result, your inner ear is a bit like a balloon, it’s under a lot of pressure, and it doesn’t vibrate much. This lack of vibration results in decreased low-frequency hearing, so your brain tends to operate under the assumption that a loss in low-frequency hearing indicates a change in atmospheric pressure. (This is also the reason why you can hear better in a plane after popping your ears.)

And that, given a further day of stewing, reminds me of a second pseudo-explanation, one by Monty Python.

I’m afraid he’s suffering from what we doctors call “whooping cough”. That is the failure of the autonomic nervous section of the brain to deal with the nerve impulses that enable you or I to retain some facts and eliminate others.

[…]

The human brain is like an enormous fish. It’s flat and slimy, and has gills through which it can see. Should one of these gills fail to open, the messages transmitted by the lungs don’t reach the brain. It’s as simple as that.

But wait, you might say, why a second pseudo-explanation and a second day of stewing? I saw a link to the article the day after its publication online, and I prepared a comment to the article in Disqus. I mentioned a first pseudo-explanation in that, as well as rattling off a rejoinder on how the anatomy and pressure interact. When I checked a bit later for comment, though, my comment wasn’t there. I looked on Disqus, which had a notice on the comment that it was recognized as spam. I clicked the “This isn’t spam” button, and there’s a message that they will work on fixing that. It still isn’t showing up at “HowToGeek”, though, so I thought I’d make my response where I know it will actually be visible.

Here’s the original comment as I entered it in Disqus.

“”” (This is also the reason why you can hear better in a plane after popping your ears.)
“””
I had a photography instructor who told our class that reciprocity failure was due to photons becoming less energetic as it got darker. You could construct right-action for compensation out of that explanation, but the explanation itself was codswallop. Similarly, there are certain phenomena described correctly in this article, but some of the “here’s why” makes me cringe. (And I may make others cringe as I try to do this technical bit from memory.)

We humans share the general mammalian mechanism for hearing, which itself can be seen as an elaboration of what fish have (which is pretty similar to our inner ear). For our physical bits, we have the outer ear (pinna, auditory canal, and tympanum (eardrum)), the middle ear (gas-filled volume with Eustachian tube, ossicular chain of stapes, incus, and malleus, associated muscles and tendons) which is the region between the tympanum and the inner ear, and the just-mentioned inner ear (of which we are most concerned with the cochlea and its oval window).

Sound is transduced to neural activity in the cochlea. The hair cells on the basilar membrane do that job. This is all essentially bony structure and cartilage with fluid inside. This works great for fish underwater. Sound energy, though, is not efficiently transmitted at gas/fluid or gas/solid boundaries. It’s about a 30 dB re 1 microbar hit or about 1/32nd the energy IIRC (I used to do a lot of calculations for underwater acoustics, whose scale is dB re 1 micropascal, not quite the same thing.). That’s pretty significant. If you want to hear well in air, you have to do more than expose a surface of the cochlea to the outside.

So our system basically adds an air-compartment with hard bits that link the tympanum and the oval window on the cochlea. When everything works, the compression/rarefaction pressure changes of sound energy in air outside makes the following things happen. The tympanum moves. The area of the tympanum is what puts a limit on how much energy can be exploited for that movement. As a source says (from memory), sound produces large-volume movements in the tympanum. That’s going to be relative to the other end-point. That bony chain moves with the tympanum, and with the usual mechanics of lever-action, converts those larger displacements seen at the tympanum into smaller displacements of greater force pushing and pulling on the oval window. The fluid inside the cochlea then is moved more efficiently, and hearing sensitivity is improved. The function of the middle ear is described as impedance-matching between the two different media for sound transmission.

But we are interested in what happens when it doesn’t work. “Popping your ears” has a name, the Valsalva maneuver. The Eustachian tube is a small passageway for gas that goes between the middle ear and the esophagus. Usually, nothing special must be done to allow equal pressure to exist within the middle ear and the outside environment. But fast pressure changes and a compromised Eustachian tube can lead to a pressure imbalance. And when the pressure is not in balance, the tympanum is not as compliant a surface: it can’t move as well when there is a constant pressure differential between its inside and outside surfaces. (The varying pressure differential due to a sound signal, though, is why it exists.) The Valsalva maneuver at least temporarily opens the Eustachian tube so gas can come closer to a balance between the middle ear and the outside. The article is right that there is a ‘lack of vibration’, or more precisely, a reduction in the amplitude of vibration, but the structure at issue in this is not the inner ear, it is the tympanum. The Valsalva maneuver changes the inner ear not one little bit (or at least none that I know of). And the pressure differential commonly causing pain also has nothing to do with the inner ear: it is the much more commonly experienced pressure differential between the middle ear and ambient environmental pressure that is the problem, and the tympanum that is the locus of one’s pain on experiencing a constant (or changing at some longer timescale than acoustic signals) pressure differential between the middle ear and the ambient pressure. The inner ear doesn’t have gas and doesn’t need air to keep you from feeling pain.

That’s the broad-brush version of it, or the bits as I recall them. I thinks there’s more going on than the article would lead a casual reader to believe. Anybody who would care to take the pedantry further probably has plenty of scope to do so.

Heinzman helpfully gives three sources. However, none of them address the matter of a particular, confirmed mechanism for what happens in a certain demographic of people who have sensations of pressure or pain with use of ANC headphones. So pretty much everything in Heinzman’s authoritatively-stated conclusion looks to me to be entirely speculative.

The Wikipedia article notes the technical challenges increase for active noise cancellation (ANC) with increasing frequency, but it doesn’t make the claim that makers of ANC headphones do not attempt to do so. It’s one thing to know that an engineering challenge exists and another to know that particular instances of the technology actually avoid problem areas. There’s nothing behind the claim that no pain is detected peripherally and is entirely a figment of the brain’s processing. There’s no discussion in the sources of people’s brains making things up to result in a particular behavioral sequence. There is no quantification of degree or amount of pain experienced over time with ANC to establish an upward trend. To go back to Monty Python, there’s not a sausage. I don’t see any of that being ruled out, though, so as far as I can go is noting that it appears to be speculation. Maybe Heinzman didn’t share all his sources and everything is covered in something he has and I haven’t found. That’s possible. But it seems to me that if one is going to do science writing with some sources revealed, you really ought to provide all the sources that actually support your summary or conclusion.

Stepping back to Heinzman’s background explainer, though, what is weird is that Heinzman’s sources don’t get any of the underlying anatomy and physiology wrong that I can see. The bits about inflatable, collapsible, vibrating inner ears appear to be his very own inventions. Will they become a new part of pop culture? We are here at the outset of a potential new myth, and I feel like it needs to be marked as “Busted”, but have no idea whether I can accomplish that. Disqus unhelpfully reports the same thing about ‘spam’ status whether its own automated routines do the categorization or whether a client site’s moderators do it, so I can’t tell whether it’s just glitchy software at Disqus or someone at ‘HowToGeek’ who was hoping I’d just go away.