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Author Topic: Why does the sound of nails on a blackboard elicit a physical response?  (Read 9366 times)

Lars Einar Jensen

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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?


 

Offline Chemistry4me

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I have heard that it is a resonance effect stimulating sensory nerves.
It occurs when the frequency of the sound vibrations is the same as the inherent frequency of impulses in the nerves.

http://en.wikipedia.org/wiki/Resonance

 

Offline Chemistry4me

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It seems likely that the response would be a result of preventing physical damage. If it was a response in the nerves of the fingertips, it would affect only the person making the noise, but as most everyone has experienced, the sound of fingernails scraping a chalkboard is painful to everyone within earshot. The response probably comes because the frequency of the sound is similar to the sound created by damage to the human body. Perhaps the chalkboard sound is like the sound of bones breaking, specifically the type of break that would come from jumping off of something too high to safely jump off of. Moreover, the slip and stick motion is similar to the feeling of teeth scraping together, or teeth being scraped by something too hard to chew. Perhaps the reaction comes from the need to preserve one's teeth for eating meat.

http://www.science.ca/askascientist/viewquestion.php?qID=303
 

Offline thedoc

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Offline RD

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

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So why do sounds with frequencies between 1-2 kHz cause the effect? My guess is that the effect is produced by activation of various myogenic reflex responses including the stapedius response, the post-auricular response and responses of other muscles innervated by the facial nerve (and possibly the trigeminal nerve). It so happens that the tuning curves of stapedius motorneurons have their best frequencies between 1-2 kHz with a threshold of about 75 dB in the cat (see Kobler et al. (1992), J. Neurophysiol. 68, 807-817).
http://www.citizenarcane.com/index.php/archives/2005/05/25/

* Analogous to photosensitive epilepsy: simulation at a particular frequency causing overload.
« Last Edit: 19/02/2010 11:36:49 by RD »
 

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