Class nuisances and exasperated teachers have been using the old nails-on-a-chalkboard trick for ages. For the longest time, no one could really explain why the sound evoked such a negative response in humans. Most people assumed it was the high-pitch part of the sound that caused discomfort. But a 1986 study by Vanderbilt psychologist Randolph Blake and two colleagues found that the sound annoyed people even when the high-pitch frequencies were removed. And when the medium-pitch frequencies were taken out, they found that the sound was actually tolerable. The study earned Blake a 2006 Ig Nobel Prize, given to those who produce "improbable research" that "[makes] people laugh and then [makes] them think."
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