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You might have experienced this a few times : when you listen to music and yawn, what you hear seems to transpose slightly.

Why does this happen?

I'm thinking it could be the tension of the eardrum that changes and leads to different vibrations.

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    I have not encountered this. Interesting to see whether this is common. – Doktor Mayhem Sep 22 '14 at 8:11
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    I think you actually answered your own question there, with the note about change in tension. – awe Sep 22 '14 at 8:34
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    I'm just guessing. It would be nice to have proof. – user13550 Sep 22 '14 at 8:35
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    Interesting. It doesn't happen to me as I don't listen to boring music!! – Tim Sep 22 '14 at 8:48
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    This is a really good question, but it doesn't have anything to do with music. Might better be asked on Physics or Biology. — "Change in eardrum tension" might be involved, but that hardly explains why you'd perceive a pitch shift. – leftaroundabout Sep 22 '14 at 12:20
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In The Physics and Psychophysics of Music: An Introduction by Juan G. Roedere, a footnote on page 107 reveals this gem:

...there is also a shift in pitch when the pressure in the cochlear fluid changes (e.g., pitch shifts perceived during yawning)...

And according to this Nature Physics paper, Mammalian pitch sensation shaped by the cochlear fluid, pitch shifts need not be purely cognitive constructs. In other words, physically changing the pressure in the cochlear fluid can affect pitch perception.

But these merely reveal a connection between the two events, what would the mechanism of pressure change be? The final piece is answering the question, "Does yawning increase the cochlear fluid pressure?" The answer can be found in any physiology textbook like this one here.

The Eustachian tube is normally closed, but it can be pulled open by yawning, chewing, and swallowing. Such opening permits air pressure within the middle ear to equilibrate with atmospheric pressure so that pressures on both sides of the tympanic membrane are equal.

And of course, changing the pressure around the ear drum causes fluid pressure inside the cochlea to change in a way we are all familiar with because that's how we perceive sound from our environment.

Ear anatomy http://med.stanford.edu/ohns/education/otologic_surgery_atlas/ear_anatomy/images/02.jpg

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Yes, I think you're on the right lines referring to a change in tension in the eardrum. More specifically, I suspect when you experience this, the yawn is equalising the pressure on either side of the drum. Think of the effect you get when sitting on an airplane as it comes in to land. As the pressure increases on the outside of your eardrum, the tension on the drum increases. Your sensitivity to higher frequencies decreases (that baby crying at the front gets less annoying!). Until you pop your ears - yawning being one of the best ways I find - everything sounds muffled, and your perception of pitch is slightly lowered.

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    I should've mentionned I have a problem hearing high frequencies (even if babies bother me ^^). When I start yawning, music transposes, but when I stop, music comes back to normal. If this was linked to air pressure, I think it wouldn't come back to normal and stay transposed. Maybe it's just my jaws's musles that tense the eardrum during the yawn. – user13550 Sep 22 '14 at 9:29
  • I take your point, and it may be that the yawn changes the shape of the ear canal in a way that puts tension directly on the drum. I would speculate, based only on my sense of how my own ears work, that pressure plays a greater part. For the duration of the yawn, the Eustachian tube is open and the pressure inside the ear is reduced. After the yawn, the pressure returns to normal along with your pitch perception. I mentioned the airplane as a more obvious example of the effect of changes in pressure. – Bacs Sep 22 '14 at 10:31
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The answers speculating about the eardrum are without merit as any changes regarding the eardrum may cause a change in the frequency response, making you hear some frequencies better or worse than before. But they don't change the frequencies as such.

Any change in the perceived frequency has to happen in the inner ear where frequency perception is situated and works via sound transmission in liquid. The velocity of sound in free liquids depends on density and the module of compressivity, both of which are not significantly dependent on the kind of pressure changes to be expected in the inner ear. So if we are talking about significant changes in the time sound takes to travel the inner ear tubes, it must be because of either geometric changes or because of momentary liquid circulation (which also forms the base for the sense of balance).

But I would expect this to trigger at best for rapid head movements. Yawning seems rather tame in contrast.

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