There are just some sounds that make everyone cringe. Nails on a chalkboard, metal dragged on metal, children screaming, those sounds have the power to make us cringe even remembering them and make us think that skipping the audiologist would be just fine (but don’t do it!).
But why do some sounds give us the chills and others are just fine? To understand, we need to first talk about why the ear is shaped the way it is.
Ears Shaped For Sounds
Our ears are shaped to pick up a certain range of sounds. From the curved upper ear to the inner ridge, our pinna (outer ear) does much of the initial work in catching sounds.
Think about it. How many times have you cupped a hand around your ear to catch a far-away sound? You instinctively add surface area to your outer ear so that you can extend your sound catching range.
Those without outer ears or have their outer ears damaged, have a shorter range of hearing. As for aging ears, though as we age our ears will continue to lengthen due to gravity, this change is gradual enough that it will not noticeable distort hearing. Though popping on some elf costume ears may have a distorting effect on your hearing.
However, our pinna are simply sound catchers, not interpreters. So something else it telling us that screeching sounds need to send chills down our backs.
Making Sense Of Sounds
After the pinna has caught a sound and sent it down the ear canal, through the middle and inner ear to reach the auditory nerve, that nerve takes the sound to our brains. Damage to the middle or inner ear may cause you to need a hearing aid to help sounds reach the auditory nerve.
Brain imaging scans have shown that when an unpleasant sound reaches the brain, the amygdala is the one to process the sound.
However, the amygdala is also the part of the brain that controls survival instincts and emotions like fear. When primitive humans with the right pinna heard high screeching sounds, their brains likely interpreted them as dangerous. Those humans that acted correctly survived to have children which passed the instinctual dislike of certain sounds on to future generations.
Normal human hearing has a range from 20-20,000 hertz (Hz). However, anything that falls into the 2,000-5,000 Hz range is perceived as unpleasant. For a reference point, most human speech falls between 85-255 Hz, so it is not hard to imagine how higher frequency noises can provoke adverse reactions.
So the next time you get a chill from someone scraping their fork on their teeth, you can probably thank your caveman ancestors for that.
