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A Straight Dope Classic from Cecil's storehouse of human knowledge
12-Dec-1986
Dear Cecil:
Why is it that the sound of fingernails scraping a chalkboard is so godawful annoying?
--Andy L., Syracuse, New York
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
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