Subject: Fwd: Re: finger nails on blackboard From: Bob Carlyon <bob.carlyon(at)MRC-CBU.CAM.AC.UK> Date: Tue, 31 Jul 2001 09:46:00 +0100>To: Michael Norris <michaeln(at)csee.uq.edu.au> >From: Bob Carlyon <bob.carlyon(at)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! > > >bob > >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 >> 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! >> > >> > 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? >> >>-m. >> >>----------------------- /\/\/\/- ------------------------------------- >> The graph data may not convey the true nature of the screech - the >> reader may add a visceral sense to the consideration of this report >> by chewing on a piece of aluminium foil while viewing the data. >> -- Barry McKinnon, `Fork Screech Analysis' >>---------------------------------------------------------------------- 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(at)mrc-cbu.cam.ac.uk !!!!!NOTE NEW PHONE EXTENSION NUMBER!!!!