Science Questions

Why does the sound of nails on a blackboard elicit a physical response?

Sun, 8th Feb 2009

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Lahrs asked:

Why does the sound of nails on a blackboard elicit a physical response?


Chris - Itís making me cringe just thinking about it.  This is quite a commonly asked question.  The answer is psychologists and scientists donít know for sure.  One very plausible theory is that when you run fingers down blackboards the frequencies you hear are very high-pitched and the high-pitched frequencies are very similar to the frequencies that animals produce when theyíre in distress.  On argument is that we are genetically programmed and tuned-in to be sensitive to those frequencies.  That may alert us that an animal of our own species, perhaps, is in distress.  Perhaps itís being attacked or eaten or is in danger.  Therefore, by galvanising your attention and waking up and paying attention to that noise youíre therefore on high alert and you can make plans to run away or fight.  Thatís probably the best explanation there is for that at the moment.

Helen - I like the idea of experimentation on other animals to see which ones are sensitive to nails on blackboards.  We can put them in rooms perhaps and see which ones jump the most when we scratch our nails.


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Lars Einar Jensen asked the Naked Scientists: Can you tell me what happens when somebody either scratches glass with nails or cuts through cardboard with a knife that makes one get "chills down the spine"? Are there some medical or biological explanations for this unpleasant feeling that make the hair on your skin stand up. Even just thinking about the sound of cutting through cardboard can be enough for me to feel the chill. Love your show, keep it up. Lars Einar Jensen, Norway. What do you think? Lars Einar Jensen, Sat, 7th Feb 2009

Chemistry4me, Sun, 8th Feb 2009 Chemistry4me, Sun, 8th Feb 2009

Forget all that "it sounds like a distressed monkey" stuff, it's a resonance effect* ...

* Analogous to photosensitive epilepsy: simulation at a particular frequency causing overload. RD, Mon, 23rd Mar 2009

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