Why Nails On A Chalkboard Drives Us Crazy

Robert Siegel talks to Michael Oehler, a professor at the University of Media and Communication in Cologne, Germany, about why people find the sound of fingernails on a chalkboard so irritating. Oehler was one of the researchers who presented a paper on the subject at the recent Acoustical Society of America conference. He says the most obnoxious frequencies of the noise are amplified by the shape of the human ear canal — making people cringe when they hear it.

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ROBERT SIEGEL, HOST:

A warning now, the following conversation will contain no obscenities, no violent references, no graphic descriptions of unmentionable deeds, but it will contain an extremely irritating sound. A sound that, as new research tells us, human beings are predisposed to detest. It is the sound of a fingernail on an old-fashioned chalkboard. Brace yourself. Here it is.

(SOUNDBITE OF FINGERNAIL SCRATCHING ON CHALKBOARD)

SIEGEL: Ooh, just one more time.

(SOUNDBITE OF FINGERNAIL SCRATCHING ON CHALKBOARD)

SIEGEL: I promise we will not do that again. What we will do is ask an expert why many of you had that spine-tingling, hair-raising reaction just now. Michael Oehler of the University of Media and Communication in Cologne, Germany, joins us. Welcome to the program.

DR. MICHAEL OEHLER: Hello. I'm glad to be here.

SIEGEL: And tell us, what did you learn? What's so special about this particular sound that we hate it?

OEHLER: Well, the aim of the study was to detect specific features of the sounds responsible for the perceived unpleasantness, and we wanted to know if there was a correlation between perception and physiological reaction. And the most significant result was that the parts of the sounds in the frequency range between 2,000 and 4,000 hertz were particularly important for the perceived unpleasantness. And that is remarkable, because between about two and four kilohertz, the human ear is most sensitive. And many important acoustic features of pitch sounds can be found in this area.

SIEGEL: So are there other sounds that occupy the same range of - actually, there are two meanings of the word hertz here - the same range of hertz as the sound of fingernails on the chalkboard?

OEHLER: Yeah. We tested another sound that was just chalk on a board.

SIEGEL: Chalk on the blackboard?

OEHLER: Yes. Exactly.

SIEGEL: Yeah.

OEHLER: And we got about the same results with the chalk.

SIEGEL: And it's just the way our ears have evolved that this happens to be a particular range of sounds that we react to very badly.

OEHLER: Yeah. One explanation for the sensitivity of the ear in this area is the open ear gain. Some frequencies are amplified due to the anatomy of the ear canal. But we also found that pitch information is very important for the perceived unpleasantness. And if these two things go together, this makes a very unpleasant sound perception.

SIEGEL: This knowledge may be too late for the blackboard industry. I think the chalkboarders have died since you started the research. It's been replaced by the whiteboard and the Magic Marker or whatever we call - the felt-tipped pen.

(SOUNDBITE OF LAUGHTER)

OEHLER: Yeah. That's true. But we also have many other sounds, and the knowledge could be used to make them a bit more pleasant. If we think about sounds of a vacuum cleaner or whatever, but you could use this knowledge to operate in these frequency areas and make the sound a bit more pleasant.

SIEGEL: You're saying just to get that vacuum cleaner sound out of the 2,000 to 4,000 hertz range and people will not react so badly to it when they turn it on is what you're saying.

OEHLER: Oh, yeah. It's just one example. I don't know if it really works with a vacuum cleaner, but there are many sounds in our environment that are perceived as unpleasant, and perhaps it's a way to make it a bit more pleasant.

SIEGEL: Did you find in your research that if you just told people I'm now going to play you the sound of fingernails scraping on a blackboard that they had the reaction that we have from hearing the sound?

OEHLER: Yeah, yeah, exactly. If the subjects knew about the origin of the sounds, the judgments tended to be more negative and the correlation between the perception and the physiological reaction was even stronger. And conversely, if the subjects thought they were hearing parts of a contemporary composition, what we told them, they perceived the sounds as less unpleasant. So this was really striking.

(SOUNDBITE OF LAUGHTER)

SIEGEL: So the reaction would depend on how avant-garde the experiment subjects might be?

OEHLER: Yes. We should test this also with a (unintelligible), yes. It's true.

SIEGEL: Well, Professor Oehler, thank you very much for talking with us about your work.

OEHLER: You're welcome. I was glad to talk to you.

SIEGEL: OK. That's Michael Oehler, who's professor of media and music management at the University of Media and Communication in Cologne, in Germany. He's part of a team of researchers who just presented a paper at the Acoustical Society of America conference about why fingernails on chalkboards are so irritating to the human ear.

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