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Fwd: Re: finger nails on blackboard

To: Michael Norris <michaeln@csee.uq.edu.au>
From: Bob Carlyon <bob.carlyon@mrc-cbu.cam.ac.uk>
Subject: Re: finger nails on blackboard

I'm not sure whether this is relevant, but the emails of Neal Todd and
Michael Norris reminded me of some aversive stimuli played to me by my
former colleague arnold wilkins, who is an expert on visually aversive
stimuli. He played a 2500-Hz tone frequency modulated by +/- 25% at 16 Hz,
over the loudspeaker of his macintosh computer. This was very unpleasant,
and sounded like something "drilling through one's head". When I made the
stimuli in the lab, and played them over headphones, they were not nearly
as aversive. It turned out that the mac loudspeaker had a sharp peak in
its frequency response just above the carrier frequency (at 2675 Hz), and
that this was inducing some AM into the sounds, at a rate of 16 Hz and a
modulation depth of 6 dB (the shape of the envelope was more like a square
wave than a sine wave). When we added this AM to the FM sounds generated
in the lab and played over headphones, they now sounded aversive. Further
investigations pointed towards the AM being more important than the FM for
this effect, at which point I decided to stick to anally retentive
psychoacoustics, and I never looked back!


At 09:33 31/07/2001 +1000, you wrote:
On Mon, 30 Jul 2001, Neil Todd wrote:

> So why do sounds with frequencies between 1-2 kHz cause the effect? My
> 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
> 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
> would account for why the effect appears to be reflexive. It can't be very
> pleasant having all those muscles twitching away!
> Neil

The next question is:  is the temporal structure of the sound important?
Halpern&al tried flattening the amplitude countour and found only a
small difference, but that may not have much affected the amplitude
contour in the 1-2KHz band. I'm thinking that if the effect is due to
something like this muscle twitching, maybe the stimulus needs to be
aperiodic to avoid adaptation.  ?  or is that a silly thing to say?


----------------------- /\/\/\/- -------------------------------------
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 reader may add a visceral sense to the consideration of this report
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Dr. Bob Carlyon
MRC Cognition and Brain Sciences Unit
15 Chaucer Rd.
Cambridge CB2 2EF
Phone: (44) 1223 355294 ext 831
Fax:   (44) 1223 359062
email: bob.carlyon@mrc-cbu.cam.ac.uk