bone conduction (Christian Kaernbach )

Subject: bone conduction
From:    Christian Kaernbach  <chris(at)PSYCHOLOGIE.UNI-LEIPZIG.DE>
Date:    Tue, 28 Nov 2000 09:32:55 +0100

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 speculates that the waves enter through the vestibular or cochlear aqueduct. 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. These findings would be even more intriguing if it could be shown that no bone vibration took place. Maybe this could then be seen as a proof of aqueduct transmission. In order to prove that no extra fluid movement took place (more than the minimal movement needed to generate a pressure 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? Christian Kaernbach Institut fuer Allgemeine Psychologie Universitaet Leipzig Germany

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