Why is the sound of fingernails scraping a blackboard so annoying?

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Dear Cecil: Why is it that the sound of fingernails scraping a chalkboard is so godawful annoying? Andy L., Syracuse, New York


Illustration by Slug Signorino

Cecil replies:

In these days when so many scientists are panting after research grants from Star Wars, Andy, it’s good to know there are still a few people around who know what’s really important. People like Lynn Halpern, Randy Blake, and Jim Hillenbrand of Northwestern University, for example. These daring pioneers of science recently conducted an investigation into the “psychoacoustics of a chilling sound” — in laymen’s terms, why the sound of fingernails scraping a chalkboard is so godawful annoying. What’s more, according to their scientific paper on the subject, the work was “supported” by the National Science Foundation. Cecil immediately jumped to the conclusion that not only were Halpern et al studying blackboard scraping, they had gotten the government to pay for it, which would put them in the running for research scam of the year. Unfortunately, further inquiry reveals that this was not exactly what happened. The National Science Foundation grant actually paid for some equipment Blake was using for more, ahem, “serious” research, which he was then able to put to disreputable ends. This does not make as good a story, I suppose, but it shows spunk all the same. Good work, gang.

In the aforementioned scientific paper (which appeared in a publication sternly entitled Perception & Psychophysics, and is not to be confused with a vulgar and sensationalized, if entertaining, article that appeared subsequently in Psychology Today), the authors note the antiquity of human curiosity on this subject. No less an authority than Aristotle acknowledged the “aversive quality” of scraping sounds. Our heroes even dug up the archaic English verb gride, which means to make godawful noises by means of scraping or cutting.

Getting down to business, Halpern and friends subjected 24 adult volunteers to various noises with a view to determining whether blackboard scraping was really as excruciating as it was made out to be. Generally speaking, they found, it was. (For purposes of reproducibility, the scraping was conducted not with fingernails but with a three-pronged garden tool, solemnly described as a “True Value Pacemaker model.”) Interestingly, “rubbing two pieces of styrofoam together,” the sound that results when you pry two styrofoam cups apart, came in second.

Next, by means of the magic of high tech, the researchers filtered out the most high-pitched portion of the scraping sound. To their great surprise, what remained was as unpleasant as ever. However, when they filtered out just the lower frequencies (particularly 3.0 to 6.0 kilohertz, for you weens), they found that what was left was relatively bearable — “quaint” or “tinkly,” in Blake’s description. In other words, it was the low-to-middle frequencies, not the high ones, that really set people’s nerves on edge.

So much for science; now for the woolgathering. Knowing that the preceding research by itself would not get them on many talk shows, Halpern and her associates set about considering just why, in the philosophical, Big Picture sense, humankind was so susceptible to scraping noises. (Actually, Blake says, they did not do this to get on talk shows. They hate talk shows. Sure.) Guessing that the whole thing may have had something to do with our monkey ancestors — looked at in the proper light, just about everything has something to do with our monkey ancestors — the researchers compared the waveforms of the scraping noise with those of the warning cries of macaque monkeys. The two sounds, they decided, closely resembled one another. Ergo, Blake writes in Psychology Today, “we speculate that our spine-tingling aversion to sounds like fingernails scraped over a surface may be a vestigial reflex” inherited from our primate forebears.

Well, maybe. But by a similar application of logic, it seems to me, we might just as plausibly conclude that the reason our hair is brown (most people, anyway) is that it enabled our monkey ancestors to hide amongst the coconuts. But hey, I didn’t get a research grant.

Cecil Adams

Send questions to Cecil via cecil@straightdope.com.