London: Ever wondered why scraping your nails down a blackboard sounds so awful? It's because human ears are designed in such a way that it amplifies the screeching sound to make it intolerable, scientists say.
Researchers from Germany and Austria found that the noise of fingernails on a chalkboard is similar to human speech and human ears are "built" to hear sounds at that frequency.
The researchers, led by Michael Oehler of the Macromedia University for Media and Communication in Cologne, used a test where some listeners thought they were hearing to "difficult" experimental music, and others were told they were listening to various horrible sounds. Nails on a blackboard ranked above sounds such as a fork scraping on a plate and squeaking polystyrene.
It was found that the listeners who'd been told they were listening to fingernails were more disgusted and appalled than those who hadn't, the Daily Mail reported. But the psychological effect didn't account for how unpleasant we found the sound. Even listeners who were told they were listening to music still had a measurable "disgust" response, the researchers said.
The researchers measured heart rate, blood pressure and skin conductivity to work out which sounds were the worst. The researchers used recordings of fingernails and chalk, removing frequencies to work out which had the worst effect.
Removing the "scrappiest" parts of the nail-on-blackboard sound made no difference to how unpleasant people found it. They found that there is a physical response to sounds such as nails on a blackboard, and surprisingly, the "worst" sounds were those in the range of human speech, which varies between 2,000Hz and 4,000Hz.
The sound of nails down blackboards is disturbing to us because it lurks within the range that we are programmed to hear most intensely -- the frequency range of the human voice.
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