I don’t think so. Most isolation headphones block (or try to block) all frequencies fairly equally, and of course fail at that. The ones for musicians try harder. But they all tend to attenuate the highs most.
A gunshot is full-spectrum, so good ones for guns would try to be full-spectrum. In fact, in audio circles, starter pistols are used with microphones to generate the “impulse response” from an acoustic space, like Carnegie Hall, so that they can make a reverb unit sound just like Carnegie Hall. I bet they’d use a shotgun if they could get away with it!
The main reason you can still hear speech is that people are talking loud enough to be heard over the background noise. Your hearing system compensates for the overall reduction. Furthermore, in some cases (e.g., noisy bar with loud band) the reduction in all the sound reduces sound to a level where your ears are more acute – before those muscles kick in, for example.
I have read that crickets can do that. Their chirping is so loud that they would became deaf unless they disconnect something in their ears while they do it.
No, I can’t cite, it was a Finnish science magazine years ago.
I don’t know if it is what you had in mind, but the outer hair cells of the cochlea act as selective amplifiers of certain frequencies of sound. The amplification effect is probably actively tunable - i.e., the brain sets the mechanism to amplify those frequencies iti s currently interested in. Very likely, when levels are too high, this mechanism can be turned off (or tuned to other frequencies that are not so loud). Wikipedia does mention this, but only briefly and superficially.
Yes, but also eyelids (and blinking) play an important role in keeping the surface of the eyes wet, which they need to be. I believe that this, together with the protective mechanisms that you describe, are (as you imply) much more important than the ability to shut of visual stimulation. People can, and sometimes do, sleep with their eyes open (we had a thread on the topic a while back).
However, many species (though not humans) have transparent nictating membranes, that cover the moistening function as well as providing at least some degree of protection. I Believe, however, that all or most species with nictating membranes do have opaque eyelids too, and I am not sure why that is.
hearing is that much importent for humans ? Our ears can alert us of danger, so they’re open all the time. (Like from predators for animals and fire alarms and stuff). Just survival reasons, I guess.
Like all 70s boys, I daydreamed about being the Six Million Dollar Man. This was actually something I “looked forward” to being a useful function of my bionic equipment: being able to switch off my hearing completely, so, say, barking dogs wouldn’t disturb my sleep.
(Apologies for not adding anything pertinent to the previous replies, which have answered the OP quite well, I’d say.)