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Note: This question has nothing to do with pressure change.

When I'm flying in an aircraft at cruising altitude, the monotonous sound often lulls me to sleep. I've noticed that just as I am on the verge of drifting off, the perceived sound volume drops significantly. I then notice what is going on and the thought awakens me a bit and the volume snaps back to normal. I verified that the actual noise in the airplane stays constant while this happens.

I always try to hold on to the state where the sound is quieter, but it is very difficult to do while at least a bit conscious. That's why I suspect that it could be part of the process human brain goes through normally when falling asleep. Perhaps it happens every time, but I do not notice because I only ever sleep in such a noisy environment when flying.

I asked a bunch of friends and some of them experience the same phenomenon. I was unable to find any relevant scientific literature mentioning it, though.

What causes this fascinating phenomenon? Does it have a name? Has it been studied?

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  • $\begingroup$ Cruising planes do throttle down sometimes which does decrease the sound level. Is it possible that the causality is reversed? That is, you are trying to sleep and are finally able to drift off when the noise level decreases. $\endgroup$ – Charles E. Grant Jun 22 '18 at 17:25
  • $\begingroup$ @CharlesE.Grant I have ruled that out. The actual volume stays constant the whole time. The people sitting next to me never perceived any change. If the plane's engines were throttling up and down like that, it would be called surging and the plane would be in big trouble. I am absolutely certain that this is something that happens to me, not the airplane. $\endgroup$ – JohnEye Jun 22 '18 at 22:29
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    $\begingroup$ Have experienced this myself. It is as if the part of the brain responsible for sensing or initially processing the sound falls asleep a bit faster than other parts involved in monitoring that sound consciously. Sound fades out then suddenly slams back to full volume along with full awakeness. $\endgroup$ – InsectSinger Jun 26 '18 at 0:02

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