By Jack Sharkey, March 24, 2014

Of the many annoying things we encounter on a regular basis, there are three or four sounds that rank at the top of our collective lists of the Most Annoying Things We Encounter On A Regular Basis. 

Here's an example:

 

That didn't bother you, you say? Try this:

 

Not yet? Well, if this next one doesn't get you, you might as well skip the rest of this piece:

 

Hopefully you're good and skeeved and annoyed right now. If not you may want to get your hearing checked in the mid-frequency range, or maybe your ear canal simply doesn't resonate at the frequencies you just listened to. Or maybe your amygdala (the most primitive area of your brain) is far too developed for your own good. 

 

Michael Oehler, professor of media and music management at the University of Cologne in Germany, and his colleague Christoph Reuter of the University of Vienna spent a good part of 2011 subjecting volunteers to sounds like the three you just listened to in order to gauge their responses and find correlations between the sounds.

 

What Oehler and Reuter found was that sounds in the frequency range between 2,000 and 4,000Hz are the ones that bother us the most. Of course, there are harmonics and other factors (more on the amygdala in a minute), but generally speaking, similarly produced sounds in lower (or higher) frequency ranges don't affect us in the same way. 

 

Because I depend on my ears to put food on my table, I get my hearing checked regularly so I'm aware when deficiencies have developed so I can compensate for them. I have a significant (.5db) dip in my hearing at 3,000Hz due to the fact that I grew up in the 70s and 80s before we regulated all the fun out of everything, so the noises in these videos (with one exception) don't really bother me too much (plus, 3,000Hz is almost dead-on in the frequency range where my first wife's voice was, so I'm thinking it was also a self-preservation loss-of-hearing). 

 

If we look at the chart below, we can see that 3kHz (the median in Oehler and Reuter's findings) is also within the frequency range of an awful lot of musical instruments, and when played correctly, all of them sound pleasing to us. So what's the deal? 

 

 

For some other reason, the fundamentals and harmonics created by fingernails on a chalkboard or fingernails scraped along the surface of an unwaxed car (my personal most-hated) make us want to smack teddy bears and otherwise throw tantrums.

 

Is it possible that our ear canals developed to resonate at particular frequencies to excite our amygdalae? And if so, why? And what does that have to do with why we hate those sounds so much?

 

Those are all good questions! Thanks!

 

Here's a somewhat abridged attempt to answer them.

 

Our amygdala is the place that processes the formation of emotional event memories, and to all of you college-types who took Psych 101, it's also the place where the FFF responses start (look it up, even though it's from science, FFF contains a bad word and, well, you never know how those type of things will be received). It seems the frequencies generated by things like fingernails on chalkboards and the like excite the connections between our auditory cortex and our amygdalae faster and more emphatically than the sounds emitted by your 5th grader's recorder, even though that noise probably currently ranks as your most annoying, but you have to be supportive so suck it up buttercup.

 

In spite of the fact that Mrs. Seibel was the meanest most scary teacher any second grader ever had, anywhere, in the history of the world, and that she did indeed run her nails along the chalkboard to keep me and the rest of my second grade class in line, there's probably more to this all than just my bad memories of second grade. But, before we completely discount Mrs. Seibel we should consider the fact that an unpleasant memory to a 2nd grader in the 20th Century is probably a lot milder than the memory of an early human whose entire tribe just got eaten by wolves or cheetahs or something, but it's a bad memory nevertheless.

 

Even though the human speaking voice ranges from around 250Hz to around 5kHz, the sound of a baby crying typically falls between 2k and 4kHz, as do other facets of human speech like yelling and screaming. Bingo. 

 

Since babies crying and the sounds of many of our most feared predators – and those who would be afraid of them – all fall in the frequency range between 2k and 4k Hz, it stands to reason that over time, our ear canals developed to specifically resonate (make louder) frequencies in that range as a prehistoric Spidey Sense to help us keep dingoes from eating our babies. 

 

So the next time someone scrapes their fork along their plate, go ahead and be annoyed, but also be thankful that you don't have to grab a club and a rock as you run out into the night to protect your cave from a wooly mammoth onslaught. Cringing at the sound of fingernails being scraped on a chalkboard is an evolutionary remnant of the time when danger lurked just outside the cave and the quicker we responded the better our chances of survival. So the next time you hear one of these offensive noises, after you're done cringing thank your ancestors for developing an auditory alarm system that made you possible.