Re: bone conduction (Martin Braun )

Subject: Re: bone conduction
From:    Martin Braun  <nombraun(at)POST.NETLINK.SE>
Date:    Tue, 28 Nov 2000 11:54:24 +0100

----- Original Message ----- From: Christian Kaernbach <chris(at)PSYCHOLOGIE.UNI-LEIPZIG.DE> To: <AUDITORY(at)LISTS.MCGILL.CA> Sent: Tuesday, November 28, 2000 9:32 AM Subject: bone conduction > The results by Freeman et al. (2000) and Sohmer et al. (2000) cited by > Martin Braun constitute intriguing evidence that bone conduction occurs > when a bone vibrator is applied to the brain of animals with parts of > the skull removed, to the fontanels of neonates, or to the eye. These > findings are about the start of the transmission pathway: it needs not > be bone. How about the end of the transmission pathway? Braun speculate= s > that the waves enter through the vestibular or cochlear aqueduct. No, it was suggested by the authors themselves. See the final sentences i= n each of the two abstracts. The details are in the full papers, of course. > It could, however, be bone. Were there made measurements with bone > microphones close to the receiving ear to prove that no bone vibration > took place? The abstracts don't tell. The full paper does. Freeman et al. (2000) carried out just this experime= nt with one rat and with one guinea pig using a Bruel and Kjaer acceleromete= r (Type 4393). Results: no bone vibration, when the vibrator was applied to the brain. [Reversing the instruments, however, showed the propagation of vibration from bone to brain.] > These findings would be even more intriguing if it could be shown that > no bone vibration took place. Exactly this was shown. > Maybe this could then be seen as a proof > of aqueduct transmission. In order to prove that no extra fluid movemen= t > took place (more than the minimal movement needed to generate a pressur= e > wave) it could be a good idea to monitor what happens to the round > window (and/or the tympanic membrane). > > And why not block the round window? No extra displacement of the fluid > would take place (as a control, the oval window impedance should change > dramatically). If hearing thresholds (and frequency separation) would > remain unaltered after round window blocking, this would constitute a > proof of pressure waves being perfectly sufficient and the traveling > wave being an epiphenomenon. If thresholds would rise or the frequency > tuning would go down, this would show the improving effect of traveling > waves. Are there any data on that? Yes, there are. Freeman et al. (2000) carried out just these experiments.= In six fat sand rats, which are particularly suited for such a preparation, they completely immobilized the stapes (confirmed postmortem). In three of the= se animals also the round window was immobilized. In the former case hearing thresholds even improved (5-10 dB), in the latter case they worsened (25-= 30 dB), when the vibrator was applied to the brain. Thus it was demonstrated that "bulk flow" of cochlear fluids is not necessary for hair cell stimulation. [By the way, reading the full papers should be recommended. They are well written throughout.] > Christian Kaernbach > Institut fuer Allgemeine Psychologie > Universitaet Leipzig > Germany Martin Braun Neuroscience of Music Gansbyn 14 S-671 95 Kl=E4ssbol Sweden nombraun(at)

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