After years of research scientists may have finally discovered why we hate the noise fingernails make when they scrape a chalkboard.
According to newswise, the reason why the scraping is so gut wrenchingly abhorrent to most people is because of the shape of human ears – or at least that’s what a group of researchers from the University of Cologne and the University of Austria believe.
More specifically, it’s because human ears have evolved to amplify sounds within a certain range of frequencies.
In order to conduct this study, the scientists involved had to play a lot of fingernail-scraping clips to the poor souls who volunteered for the experiment.
Half the study subjects were told what the sounds were while the other half thought that they were listening to selections from contemporary music.
Scientists asked the participants to rate each sound’s unpleasantness, and also gauged the subjects’ stress responses to the noises by measuring their blood pressure, heart rate, and skin conductivity (a measure of sweating).
They discovered that the human ear is particularly sensitive to pitches in the mid-to-low-level range of frequencies, which is the peak of human hearing.
Interestingly, when the scientists removed all the pitch information in this range from the audio recordings, the study participants rated the noises as more pleasant than other versions of the sounds.
It’s thought that people are sensitive to this band of frequencies because the sounds in this range are amplified, due to the anatomy of the ear canal; they are literally louder to us than other sounds are.
So scraping a chalkboard may set your teeth on edge because the sound sits right in the sweet spot of human hearing.