Nails on a Chalkboard

by Mary Ellen Eagan

I had an “NPR moment” the other day, but it was not the kind they advertise on pledge drives.  This story about Why Nails on a Chalkboard Drive Us Crazy had me sticking my fingers in my ears in a way I hadn’t since high school.  Not good when you’re driving (so I’ll caution you, too, before you click through to be sure you have hands free).

Nails on a Chalkboard

The team of German and Austrian researchers, Michael Öhler of the Macromedia University for Media and Communication in Cologne and Christoph Reuter from the University of Vienna, first picked out two sounds they determined were the most annoying to people: scratching fingernails on a chalkboard and squealing chalk on a slate.  They then played the sounds to a group of volunteers, half of whom were told their real origin and the other half who believed they came from contemporary music.  The researchers found that people who believed the sounds were art rated them as less grating than those who knew where they really came from, suggesting a psychological component to people’s annoyance.

But they also found that the research subjects had clear physiological reactions to the noises, such as increased heart rate, sweating and blood pressure regardless of their beliefs of the sounds’ origin.  This is apparently the consequence of the frequency of the sounds, between 2,000 and 4,000 hertz, which hits the frequency range over which the human ear is considered to be most sensitive because of the anatomy of the ear canal, the scientists said.

I’m blogging about it because it makes two points that are relevant to human reaction to transportation noise:  frequency and attitude.

- First, transportation noise also happens to have most of its acoustic energy in the same mid-frequency range (also babies crying – see my previous post on that issue).

- Second, attitude plays a significant role in our response (annoyance) to sound (noise).  The chalkboard research showed that when subjects were told before listening to it that the recording was “modern music”, they were much more tolerant than when they were told they’d be hearing nails on a chalkboard.  We often joke about people being much more tolerant of “the sound of Freedom” near military bases, but there is good reason.   Sandy Fidell has written extensively that a significant portion of the variance in annoyance dose-response curves (comparing aircraft noise exposure doses to levels of high annoyance) can be attributed to attitude toward the noise source.  Airports that take this to heart, and make concerted efforts at public outreach, can attest to the difference that attitude makes.

Fortunately, in the case of both chalkboards and aircraft noise, technology has evolved significantly in the last 30 years, so that the need to stick our fingers in our ears is much less.

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