Subject: Re: finger nails on blackboard From: Michael Norris <michaeln(at)CSEE.UQ.EDU.AU> Date: Tue, 31 Jul 2001 09:33:20 +1000On 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' ----------------------------------------------------------------------