Chalkboard is mildly chilling. Silverware scraping together is higher on the scale. But the ultimate has to be the chewing on aluminum foil…I agree with handy on that. shudder
jayjay
Okay, to synopsize experiences with “the shudders”:
- Low frequencies cause the effect, not high frequencies.
- The low frequencies may be transmitted by touch or by sound. E.g., people with sensitivity to chewed aluminum, ice cubes, or graphite or the tearing of loose cotton or paper napkins.
- People are generally affected by a set of similar sensations, but not by all such sensations.
- People who are affected by touch are not affected by sound, and vice versa. (Is this true?)
- We haven’t talked much about the effect, other than to say it’s unpleasant, and causes shudders, but it seems to affect people the same way: it’s intolerable to the extent that it stops other thinking.
- Even the memory (or the anticipation) of the sensation can cause a mild reaction.
Observations. The sensation can’t be common in nature, or people would be constantly distressed. It must be related to some frequency that has–or use to have–a critical importance to the body, specifically the nervous system. Part of the range of sensitivities people have is close to the low end of audibility, because some people are not affected by sounds but by touch. So the range is somewhere near 20 Hz.
Question: Is this frequency somehow related to the natural resonance frequency of the nervous system (is there such a thing?)
Yes, there is a resonant frequency of the nervous system. It’s a property of the neruonal membrane – specifically, the propogation rate of a potential inversion wavefront along it.
And coincidentally, it works out to approximately 50 or 60 Hz, very near the frequency of our residential power systems. That’s part of the reason why they are so dangerous.
(They’d still be dangerous at 1000 Hz or higher, but for different reasons, and with different results. High frequencies are harder to keep “inside” wires, and they tend to create surface burns rather than deep tissue burns like 60 Hz power.)
Legend has it that the promethean of AC, Nikola Tesla - a man who enjoyed putting himself within many an AC circuit - chose 60 Hz as the standard. Originally, Edison’s engineers used 577 Hz [iirc] which is a tad bit safer and a LOT easier number to work with in the manual Fourier transform calculations involving (2*pi)^-1 that are ubiquitous in electrical engineering.
Others accuse Edison of changing the standard to 60 Hz to maximize the hazard of AC, during the big AC/DC wars between Edison Electric (DC) and Westinghouse (AC).
What does all this have to do with chalkboard heebie jeebies? Nothing, probably… but it’s one of my favorite geek history stories.
two pieces of glass scraping together drives me up the wall…
The above posts which attempt to explain this phenomenon do nothing but cause me to request that Cecil address this issue and deliver the straight dope on it.
This is a mystery of life as profound as sperm trees, IMO.
One guess I have is that it might have something to do with
our experience as fetuses. The low frequencies discussed
above seem likely to create vibrations in a mother’s body
that to the fetus would be quite distressing. So
distressing, that after birth we still cringe at them.