CHALKBOARD SCIENCE: The unpleasantness of some chalkboard sounds has to do with their frequencies.
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Physiologically, why is the sound of fingernails on a blackboard so unnerving? Is this effect particular to human beings, or are other creatures similarly affected?
—Rowan Snyder, via e-mail
Neuroscientist Josh McDermott of New York University explains:
Probably a couple of factors combine to make such sounds unpleasant. The first, perhaps unsurprisingly, is the presence of high frequencies. The range between two and four kilohertz—approximately that covered by the highest octave of a standard piano—seems to contribute the most to the nastiness of the sound. It is unclear why people tend to find these frequencies unpleasant, but we know that noise-induced hearing loss most commonly occurs in roughly this region, so it is conceivable that the aversive reaction partly reflects the ear’s vulnerability.
The spectrum of screeching sounds is also much noisier than that of an instrument; that is, there is a strong random component to the sound. The noisiness probably results from the fingernails repeatedly catching on part of the chalkboard surface before sliding forward. This catching and sliding also causes rapid fluctuations in intensity, giving the sound a “rough” character.
Roughness is known to be unpleasant—car manufacturers, who aim to produce minimally unpleasant engine noise, for instance, find that smooth sounds with minimal variation in intensity are preferred by listeners over those that are rough. It’s a bit harder to say why sound roughness is considered unpleasant—as far as we know it is not harmful to the ears.
Some scientists have proposed that screeching sounds are acoustically similar to screams, a sound to which we might plausibly have evolved an aversion. If this hypothesis were true, one might expect to find similar reactions in nonhuman primates, which also produce screams. Thus far only one species of monkey has been tested, and it did not display the same aversive response to screeches that humans have. It may therefore be more appropriate to simply regard screeching sounds as a “perfect storm”—combining two properties that we know to be unpleasant, resulting in a single sound that is awful to listen to.
Note: This article was originally printed with the title, "Ask the Brains."
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28 Comments
Add CommentI was cringing the entire time reading this article, just from imagining the noise
Reply | Report Abuse | Link to thisPlease, they can't figure why smooth noises would be preferred over rough noises in a car? It wouldn't have anything to do with being alert to sudden environmental changes and the masking effect rough noises would have on noises that signal those changes? C'mon now!
Reply | Report Abuse | Link to thisTranslation:
Reply | Report Abuse | Link to thisWe don't know; here are some of my guesses, with the magic phrase evolutionary adaptation thrown in to give me credibility.
I was always wondering why some people react to this sound. I was always tolerant to it. Moreover, even did it on purpose to tease some classmates. So I guess this stuff isn't universal.
Reply | Report Abuse | Link to thisP.S. Some people also has goosebumps after the sound of a nail screeching a glass surface. Inexplicably though, I can't stand the sound of digging a hole in the earth with a wooden stick. Like kids do sometimes in a sandbox.
I think it has something to do with our interpretation of music.
Reply | Report Abuse | Link to thisI've never had a problem with the sound of nails on a chalkboard. It's a little annoying, but nothing terrible. I've always been amused and curious when watching other people cringe at this.
Reply | Report Abuse | Link to thisI think it is an evolutionary response to disorder: how can we perceive a possibly dangerous change/threat in the pattern of our environment if there is no pattern there in the first place? Noise is disorderly sound. Any kind of organized sound creates a comprehensible pattern: music, speech, birdsong, waterfall, even the white noise of a freeway. Fingernails on a blackboard? It's the soundtrack for a movie set in hell.
Reply | Report Abuse | Link to thisThe answer is simple,some years ago I ran some tests and surprise, surprise,the sound nails on a chalkboard almost perfectly matched the sound of lions knawing on bones,that I recorded at a zoo.I find it odd that somebody alot smarter than myself hasn't figured this out,it was on a hunch that I thought that the sound of predetors doing nasty things might be scary,and smart animals would turn and run away.
Reply | Report Abuse | Link to thisThe history of the US Intellligence divisions includes using sound as harassment and torture. The Branch Davidians were subjected to irritating sound, as was Noriego. Other less known cases include using sound as a directed energy weapon breaching the parameters of torture. Sound and ultrasound are covert weapons today. Also, there is a device which merchants have been using around the industrialized world that is high frequency that only teenagers can hear, and it is so irritating that it makes then leave a location, which is it's intended purpose. Lastly, microwave radio waves create what is perceived as sound, often high pitched and irritating. Timely to read an article discussing this subject.
Reply | Report Abuse | Link to thisAm I the only person who has doubts about the claim of a reader that s/he recorded the sound of lions chewing on bones at the zoo? Which zoo? I've never been able to get close enough to lion in a zoo to even take a great photo. And are lions normally fed food with bones? If the reader is a zoo keeper, can s/he please give us more information on this?
Reply | Report Abuse | Link to thisI suspect, at least for me, it's not the sound, per se, that bothers me but more of a sympathetic reaction as if it's my own fingernails doing the screeching on the board. Like hearing someone else do it makes me feel as if I'm doing it. If that makes sense. Also, a similar feeling that gets me to cringe far more badly than the chalkboard is the noise/vibration of pulling the paper off of a really frozen popsicle.
Reply | Report Abuse | Link to thisI feel a pain when I hear the chalkboard screeching sound. Other sounds induce feelings of discomfort or pain, for example the rubbing of styrofoam against another surface. I have often wondered if my response (and others like me) is due to a mild form of synesthesia.
Reply | Report Abuse | Link to thisyes lions are sometimes fed bones...at one zoo i worked in we gave horse hind quarters to our big cats on a fairly regular basis...and thier are many zoos where u could hear the lions chewing and knawing thier foods
Reply | Report Abuse | Link to thisAn evolutionary response to disorder, "roughness aversion" in sound, how we interpret music, and a match with the sound of lions chewing on bones....I think all of these answers are wrong. People dislike the sound of nails scratching against a chalkboard because when they hear the sound, they imagine themselves dragging their nails against the chalkboard. A simple test for this would be to play the sound and see if people touch their nails or move their fingers more than they do when they hear other similar high frequency sounds.
Reply | Report Abuse | Link to thisOne point to make though, is that primates often hear and communicate with higher pitches normally. It sounds like a poor test, as it seems primates would likely not react to high-pitched noises regardless. In fact, I think NPR had a story recently about how music affects primates. Not until they greatly rose the pitch the they even respond somewhat like humans.
Reply | Report Abuse | Link to this2 stricklandbrent:
Reply | Report Abuse | Link to thisWell, I never performed that scratching myself or at least I can't remember doing. Maybe that is why this sound never triggers any bad feelings in me? This is PRO your theory.
But by and large i don't believe i would feel any sort of aversion/pain/any other uncomfortable feeling if I would try to scratch the chalkboard. I mean it's not painful to your fingernails after all. And that was CONTRA.
Does the reaction have anything to do with the fequency of a baby's cry (1.6 to 3.1 Khz)?
Reply | Report Abuse | Link to thisI 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.
Reply | Report Abuse | Link to thisAlternatively, scratching the blackboard may cause uncomfortable vibrations in the fingernails, and this association is enough to cause discomfort when hearing the sound.
I was thinking. For my self, I think the sound may bother me because I am aware of how it feels. The abrading sensation of moving my fingers across a chalkboard is unpleasant to me. It may be that the negative sensation of have my finger nails tugged at and chalk dust ground under my nails, is easily associated with the usual sound.
Reply | Report Abuse | Link to thisI should have read your post first! ... not trying to steal your thunder ;).
Reply | Report Abuse | Link to thisIt's exactly the same thing as mirror neurons - the act of processing the scraping sound evokes some of the sensation which you would feel if you were doing it. We use a lot of sound feedback to enhance the sense of touch - if you block your ears, it is harder to judge how rough a surface is when you rub your hand over it.
Reply | Report Abuse | Link to thisI know a person who runs from the room when someone handles or uses paper towels, because he cannot stand the sound. It takes him a little while to compose herself afterwards. Generally he does not react strangely to any other sounds. Paper towels, for me, make hardly any sound and are not disturbing. What is going on?
Reply | Report Abuse | Link to thisI know a person who runs from the room when someone handles or uses paper towels, because he cannot stand the sound. It takes him a little while to compose herself afterwards. Generally he does not react strangely to any other sounds. Paper towels, for me, make hardly any sound and are not disturbing. What is going on?
Reply | Report Abuse | Link to thisTo 513755 “Inexplicably though, I can't stand the sound of digging a hole in the earth with a wooden stick. Like kids do sometimes in a sandbox.”
Reply | Report Abuse | Link to thisI think you are sensitive to low frequency sound. Just test it on the low pitch section of a piano.
One of my college classmate felt very unpleasant at the sound of stirring a metal spoon in an enamelware, which is a very usual sound in your daily life. I just wonder how he manage to live on with all these enamel bowls, plate, mugs and so on. Amazingly, the spoon stirring in an enamel bowl sound very pleasant to me. We can even choose various enamelware to make a simple musical instrument （with the aid of water).
I think the more interesting question is...why does the sound of nails moving along a chalkboard elicit a -tactile- sensation? People often get a shiver along their spine or even get goosebumps when they hear this sound. It's probably the most common synesthetic experience (and is a good example to use when explaining synesthesia to someone), so I was hoping this article would have shed a little insight in that direction.
Reply | Report Abuse | Link to thisAgreed, I don't think this article was very informative at all.
Reply | Report Abuse | Link to thisThis is a very sensible theory (regarding the sound of the teeth grinding against the bones).
Reply | Report Abuse | Link to thisAnd I can add something interesting to what FelixWatts said about the discomfort in his teeth when he hears this high-frequency sound:
About a week ago I started a dental bleaching process, and on the third day I felt the dental sensitivity started rising like crazy and at the same time I noticed that I started overreacting to some sounds that I had never reacted in such a way to before.
I started cringing when I took something out of a paper bag/plastic bag, and when I simply moved the frying pan on a gas-stove. I practically felt my teeth reacting to this sound.
So if you put all this together - the bones, the teeth - an interesting theory starts arising. Looks like there is a defense mechanism that protects our teeth from destruction. Like when our ancestors were eating mammoth meat, for example, and their teeth touched the bones this grinding sound signaled 'Hey, be attentive or you're going to ruin your teeth!'.
This can also be applied to eating fruits, like when you take a bite of a peach and you accidentally get your teeth into its stone.
This reaction could be a universal signal of danger, too. Like jack.123 said, our ancestors could hear this sound and they became aware that there was a predator somewhere around in the bushes.
Also there's evidence that men are more susceptible to hating these noises. Why? Because they were the hunters and had to deal with the predators more often than women, thus this reaction is manifested more explicitly.
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