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The sound of fingernails on a chalkboard is universally irritating, possibly due to its similarity to animal warning sounds or the scraping of rocks on teeth. The action itself may also stimulate unpleasant nerve endings, and the disharmonious sound disrupts our senses.
There are few natural sounds more irritating than fingernails on a chalkboard, with the possible exceptions of foam cups rubbing together, a squeaking door hinge, or a dentist’s drill. What seems to distinguish nail chiming from other irritants is the apparent universality of it. Few people living on the planet can help but shudder in agony when the high-pitched scraping noise begins and everyone is relieved when the event is over. No one can say with scientific certainty why the sound is so incredibly irritating, but there are a number of interesting theories.
Some believe the sound is similar to the high-pitched screech of an animal indicating danger to the rest of its group. Macaques, for example, have been known to make a warning sound of relatively similar pitch and duration to the dreaded claws on a blackboard sound. It has been suggested that humans instinctively react to sound, creating a “fight or flight” response.
Another theory holds that the sound of fingernails on a chalkboard is similar to the scraping sound of rocks against teeth. Scraping noises are particularly irritating because they remind us of painful dental experiences or the uncomfortable sensation of biting into a piece of rock or metal. The scraping sound is created by fingernails alternately sliding and gripping the rough surface of the chalkboard. Experiments conducted by scraping a garden tool against a blackboard showed that the lower frequencies of the noise were particularly annoying.
Similarly, some have theorized that it’s not the sound, it’s the action itself. Anyone who has ever scratched their fingernails against a chalkboard is unlikely to forget the experience. As your fingertips drag across the rough surface of the chalkboard, numerous nerve endings are stimulated, and not necessarily in a positive way. When people hear the sound, they are most likely to have a sympathetic response and identify with the unpleasant sensations that accompany the sound.
Sometimes it’s a matter of harmony versus disharmony, aurally speaking. Many people are very sensitive to changes in pitch or frequency. For example, a guitar with an off-key string can disrupt an entire performance. The attention signals generated by local televisions are often irritating for a reason. The emergency signal has been tuned out of tune to distinguish it from normal background noise. The ultimate in irritating, out-of-tune harmonics is most likely the sound generated by fingernails on a chalkboard. There’s simply nothing remotely harmonious about that grating, abrasive sound, so we react strongly whenever we’re forced to hear it.
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