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I am curious as to what current research shows regarding why scraping noises such as fingernails on a chalkboard, a knife/fork scraping against a plate, metal grinding against metal or stone etc are so intolerable to humans. In doing some initial research for this I read the wikipedia article on Sound of fingernails scraping chalkboard (there's a wikipedia article on everything!) but I am looking for more references or updated research.

From the reading I have done, there seems to be two competing theories:

  • The sound is reminiscent of the warning calls of primates and triggers an evolutionary response left over from an earlier age designed to protect us from predators
  • The sound hits a resonante frequency of the inner ear which causes it to be particularly intolerable

To me personally the first theory makes very little sense. Hearing the warning calls of primates does not personally trigger anywhere near the same feelings of extreme frustration and irritability that I feel when I accidentally scrape my knife on my plate. Furthermore the feelings caused by the "nails on a chalkboard" sound do not at all trigger a fight-or-flight response or put me on edge as a loud noise or something that startles me does. If anything it is almost paralyzing, which seems counter to the evolutionary theory.

How accurate is the wikipedia article? Is there any newer / more widely accepted research available on what causes the sound of "fingernails on a chalkboard" to be so intensely awful to human beings?

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The feeling I have when I hear chalk screeching on a chalkboard is very similar to the feeling I have when my baby cries (I think more research should be done by people with children, it would be enlightening). – what Aug 19 '13 at 9:45
@what that is an interesting insight - I wonder if there is a connection in that respect? As for your point in parentheses, that indeed would be interesting (and no, I don't have any children). – user3554 Aug 19 '13 at 10:04
Okay, let's say it has an evolutionary cause as suggested by the theory. What the makes me curious is, If we were to find people on earth who do not react adversely to it and further select people who are "normal" (with no hearing problems, psychological problems or any other irrelevant to our experiment), it would probably be a very small percentage. So, in that percentage, can we say, they have evolved to the "next generation" humans compared to us. Or, is it that, the average percentage for any such characteristics has, is and will remain the same forever.(The balance of probability) ? – pulp_fiction Oct 3 at 5:29

5 Answers 5

My initial thoughts are that the sound produced a dissonant sound, that is (from the link):

"An unstable tone combination is a dissonance; its tension demands an onward motion to a stable chord. Thus dissonant chords are 'active'; traditionally they have been considered harsh and have expressed pain, grief, and conflict."

—Roger Kamien (2008)

According to the article "Psychacoustics of a chilling sound", (Halpern et al. 1986), it is the low frequency components of the sound that cause the most discomfort. In their tests, removing the low frequency part in a digital simulation, made the sound a bit more bearable.

In the conclusion of the article, there is some support for the Wikipedia article that Josh Gitlin linked to in his question:

the complex acoustic stimulus pictured in Figure I very closely resembles some of the spectrograms of warning cries emitted by macaque monkeys (Green, 1975). As another possibility, the signal may be similar to the vocalizations of some predator.

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Hmmm, dissonance, very interesting, thanks! I'll do further reading on this and will likely have followup questions. I still feel like the relationship to a predator doesn't compute to me as it doesn't trigger anything like fear/fight-or-flight, but I could easily be wrong there because I am basing my beliefs on pretty much zero empirical evidence ;-) – Josh Gitlin Aug 15 '13 at 21:48
@JoshGitlin as an aside, as a teacher, this sound has no effect on me at all. Interestingly, just the mention of scratching a blackboard is often enough to bring students in line. The dissonance is a personal theory of mine, based on the definition (above) - I tend to agree with your assumption about the predator relationship for the same reasons. I look forward to more questions! – user3554 Aug 16 '13 at 8:15

Furthermore the feelings caused by the "nails on a chalkboard" sound do not at all trigger a fight-or-flight response or put me on edge as a loud noise or something that startles me does. If anything it is almost paralyzing, which seems counter to the evolutionary theory.

Yes, I agree, it seems to, however what about the fainting goats? We could have traits which aren't advantageous, yet we were able to survive in spite of them. Like the goats.

Even though it seems perfectly possible (though not logical) to be paralyzed by fear in response to a warning signal, I don't agree with the theory that the sound is indeed a warning signal.

In my experience with hearing fingernails on the chalkboard, its almost as if my teeth hurt. This leads me to believe it is not predators I'm fearing, but injury. It could be a fear by association produced from when I was very young and putting many different objects in my mouth. Some objects may have produced a similar sound and the sound was associated with pain. If you wish to survive in nature, its very important to have teeth, and injuring our teeth may be an especially important thing to avoid... not only if you expect to eat, but also attract a mate. A good smile is important.

In my search for references to back up my theory, I found this presentation, the author of which seems to agree with my assessment.

I also found at least one other person who claims to feel something in his teeth:

I feel the discomfort in my teeth and have always assumed the screeching is at the right frequency to build up uncomfortable vibrations in the teeth.

That is actually a random comment (pages 11-20 in the comments section at the bottom) to this article.

I don't agree that the sounds would have enough acoutical power to vibrate the teeth. I think the pain is merely imagined. Of course, that's my opinion, for what its worth. Since the prevailing theory is predator-based and not tooth-injury-based, I wouldn't expect to find any studies on the matter.

In addition to the evidence presented so far, I have another reason to doubt the predator theory. If the sound mimics the cry of danger and the response is instinctual, then why don't we all have the response? Out of 3 people contributing to this question, 1 has admitted "this sound has no effect on me at all." This argues in favor of my "fear by association" theory.

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very good points - particularly your final paragraph. – user3554 Aug 19 '13 at 10:05
Fainting goats were I believe actually bred deliberately as decoy animals: put one in your herd and if a predator ambushed the herd, the fainting goat would fall over and get eaten, distracting the predator from the rest of the herd. So no, fainting when startled isn't a survival trait without humans around to value and breed selectively for it! With humans around, though, it is in fact a survival trait. – Krysta Aug 22 '13 at 19:40
@Krysta That's an interesting bit of thinking, kinda like my cats who learned not to hunt in favor of begging at the door. But, how does one breed goats to fall over when scared instead of running? And how can I train my cats to do that? Running is usually what gets them killed in this modern world of automobiles. They see a car and immediately dash across the road. – Randy Aug 22 '13 at 21:01
Apparently the fainting trait (also called myotonia) is genetically quite simple. It shows up like any mutation, and some sharp goatherd realized its use and bred for the trait selectively. I think you have to be a catherd to do this in felines, though, and we all know how hard that is! ;-) – Krysta Aug 22 '13 at 21:06
@Krysta Opossums also have this trait of playing dead. So, who was herding the opossums? ;) – Randy Aug 22 '13 at 21:14

I don't understand why there's a bias to assuming that something that doesn't actually touch us can't cause pain. I assure you: the sound that Styrofoam makes is enormously painful to me. (And I grew up in the egg business, where I would have to plug my ears on a daily basis when my father or someone else had to do something with Styrofoam cartons. Ugh.)

We all have different tolerance levels for pain in other ways. The guys who go for Navy SEAL (or equivalent) training, or who play NFL football, clearly have a different tolerance for pain than I do. Why would anyone assume that this is different in terms of one's hearing?

The simplest answer is the best: some of us are caused actual pain when certain sounds are made, most likely because there are frequencies in the sound that we can perceive more or more clearly than others can. I'm an audiophile, and have lots of anecdotal evidence that I can hear higher-pitched sounds than my friends... my guess is that for those of us who have massively painful reactions to these sounds, our ears are genetically wired to be able to hear those frequencies far more clearly than those who aren't susceptible.

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Was it the pain of intensely loud sound (like a firetruck suddenly coming out from behind a building. Slap your hands on your ears!) Or was it the "horrible zing" of watching someone slide their finger along a knife blade. The sound seems to stab out along all your bones, must clench fists and jaw? Bad, but different than the ears-ouch-pain of extremely loud sounds? Or exactly the same as loud-hurt guns and firecrackers? – wbeaty Jun 28 at 21:41
Hmm... it's sudden like the fire truck you refer to, but much more painful. It's not merely a matter of volume... even the slightest squeak of it is painful, and certainly louder is more painful. It doesn't go through my whole body, really... I mean, I react, but the pain is localized to my hearing. That's the best way to describe it. Like most people with nails on a chalkboard. – Scott Jul 3 at 0:51

Mine is the evolutionarily ancient tooth-damage avoidance-response 2003 speculation article, but if I have it right, then toothed animals in general should experience it, not just primates. Maybe it goes all the way down the entire chain to octopi, snails, clams, any organism which needs to avoid radular-destruction when carefully trying to eat algae from silicate surfaces.

2012 research showed human fMRI to horrid glass-scraping noises, response located in amygdala and mediated by auditory cortex. With fMRI we need not rely on subjective reports.

Heh, be first to test non-humans, we can crack the mystery and share the igNobel!

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Welcome to Cognitive Sciences! Sorry for being skeptical - but - While the first part targets the question it is based on a link to a chatty blog with questionable credibility. The second part is nidely referenced, but does not address the question. – AliceD Jun 29 at 11:10
It's my pure speculation, and labeled as such. Wbeaty author, owner Also, sorry I was unclear, but there aren't two sections above. I reference fMRI articles to suggest eventual testing of non-humans for aversion response to chalkboard(etc.) sounds. If it ever turns out that other animals have similar avoidance, then the current theory has problems (current theory is, spectral peak of such noises are basically too loud, since that peak is matched to peak sensitivity of human ears.) – wbeaty Jul 1 at 2:31
CogSci reserves answers for scientifically sound answers. Speculations should be placed as a comment. You have enough rep to do so. – AliceD Jul 1 at 2:48

This may throw a spanner in the works but here is my personal experience with this, which might help someone. I have never been particularly sensitive to these sounds. Sure, nails on a chalkboard would get me, but not a knife on a plate for example. I recently changed my toothpaste from a standard Colgate toothpaste to Sensodyne Repair and Protect. Sensodyne leaves my teeth with a slightly chalky texture, and over the same time period I have noticed that I am suddenly ridiculously sensitive to all sounds of this nature. Even a hoarse voice on television nearly sent me over the edge. I've changed back to Colgate and my sound sensitivity has gone. I thought I should add this since so many people say that they seem to feel it in their teeth. I do not want to do the Sensodyne brand any harm. My own father is actually a dentist who highly recommends it. But it may not be for all people.

Here is my own semi-scientific theory about this. I have a side interest in earthquakes and, while scientists were looking into why some buildings get totally destroyed when others next to them are barely scathed, it has been suggested that each building has a specific frequency of it's own, and when that frequency is the same as the earthquake's waves it can be catastrophic. I can't remember which documentary I saw that suggested this. What if it's the same with our teeth? Maybe the fluoride residue coating that the one toothpaste leaves actually changed the frequency of my teeth so that I felt those sounds more.

If this is sounding strange to anyone, just think of how adding a bit more water to a wine glass changes the note or frequency when the rim is played. I've also noticed that with certain high notes my sofa actually vibrates, but volume doesn't affect it, just a certain pitch. So I do believe that every object has it's own frequency.

I do hope that even one person can be saved from this by just experimenting with different toothpastes.

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Welcome to Cognitive Sciences Danielle. We expect scientific answers on this site, so unfortunately I will need to remove this post eventually. Personal anecdotes not backed up by any scientific material do not constitute an answer on their own. – Steven Jeuris Oct 5 at 9:25
I realize that I can't provide the source material but there is some science in paragraph two. All science begins as a theory. I would welcome comments from anybody in that field who might be able to provide more on the subject. – Danielle Oct 5 at 23:43
Here is one of many links talking about the seismic frequencies of earthquakes and buildings. As I mentioned, all science begins as a theory. I am extrapolating to the scientific community that it might be the same with certain frequencies and teeth. – Danielle Oct 5 at 23:50
You can edit your answer to incorporate any useful new content into it, rather than using comments. – Steven Jeuris Oct 6 at 12:06
You can always edit your answer Danielle. I did not say comment. – Steven Jeuris Oct 7 at 9:09

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