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Re: finger nails on blackboard

Dear Bob and List

Having recently done some work on the pleasantness/unpleasantness of sounds
(JASA 110(1), 380-390, 2001) I was somewhat curious to read that it was the
low frequencies that produced the effect, since most of the literature I am
aware of (e.g. see review in Vitz (1973) P&P, 11, 84-88) suggests the
opposite. However, having got hold of a copy of the Halpern et al. paper I
note that sound in question has a fairly strong harmonic structure with a
fundamental at about 1.4 kHz. The fundamental is very weak and most of the
energy is in harmonics 2,3,4 and 5, starting at 2.8 kHz. By most standards
this sound would be considered to be quite high. So the term "low" should be
considered in relative terms.  Nevertheless, application of a high-pass
filter to this sound suggested that it was frequencies less than 2-3 kHz
which were predominant in the effect, and by implication the fundamental and
possibly the 2nd harmonic, i.e. sounds between about 1 - 2 kHz. In the
previous literature and my own work, sounds less than 1 kHz were considered
to be least annoying or most pleasant.

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).  (These should be distinguished from myogenic vestibular responses
mediated by the accessory nerve, which responds to frequencies less than 1
kHz.) In order for this to work then the scraping sound would have to be
above about 75 dB, but it's not clear from Halpern et al. what intensity
they presented the sounds to the subjects.  However, the proposed mechanism
would account for why the effect appears to be reflexive. It can't be very
pleasant having all those muscles twitching away!



> From: "Bob Carlyon" <bob.carlyon@MRC-CBU.CAM.AC.UK>
> Sent: 18 July 2001 10:06
> Subject: Re: finger nails on blackboard
> dunno exactly, but surprisingly it's the LOW frequencies thatare important
> for the effect.
> see D.L. HAlpern et al (1986) "Psychophysics of a chilling sound", Percept
> Psychophys, 39, 77-80
> bob
> At 01:02 17/07/2001 +0800, you wrote:
>>Dear list,
>>A question that has reoccurred over the last year in my philosophising
> about
>>sound is:
>>Why do we feel so uncomfortable when hearing the sound of finger nails
>>scraping on a blackboard?
>>I'm working on my PhD in ecological sound design and this question seems to
>>turn up every now and then...
>>Mikael Fernström, M.Sc.
>>Interaction Design Centre,
>>Department of Computer Science and Information Systems
>>University of Limerick, IRELAND
>>Phone: +353-61-202606 Mobile: +353-86-8188079
>>Web: www.idc.ul.ie www.softday.ie
> Dr. Bob Carlyon
> MRC Cognition and Brain Sciences Unit
> 15 Chaucer Rd.
> Cambridge CB2 2EF
> England
> Phone: (44) 1223 355294 ext 831
> Fax:   (44) 1223 359062
> email: bob.carlyon@mrc-cbu.cam.ac.uk