PubMed · 5852857
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H Martin, M Gignoux, H Cajgfinger. 1965. [Bone conduction and cochlear reserve].. https://pubmed.ncbi.nlm.nih.gov/5852857/
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A miniaturized artificial mastoid of size and weight that allow calibration and measurement of bone conduction hearing aids in a conventional audiometric soundproof box has been developed. Its level of mechanical impedance corresponds to the standard IEC 373 (1990) within the frequency range 250 Hz to 8 kHz. The miniaturized artificial mastoid consists of three parts: coupler, skull simulator (TU-1000), and an external electrical correction filter. The coupler is a highly damped mass-spring system designed to give the miniaturized artificial mastoid mechanical impedance in accordance with the standard IEC 373 (1990). It was found that the miniaturized artificial mastoid yielded results that are in correspondence with results obtained with the Brüel & Kjaer type 4930 artificial mastoid for frequencies above 450 Hz. Thus, at these frequencies, the miniaturized artificial mastoid can be used for audiometer calibration as well as measurement of bone conduction hearing aids.
A hearing aid patented by C. R. Schafer and supposedly based on detection of an amplitude-modulated carrier wave in the auditory cortex was re-examined. It is shown here that the hearing aid actually works by bone conduction of sound. It is concluded that detection of the modulation signal occurs by electrical nonlinearities and electrostriction in the bones of the face and skull.
BACKGROUND: Since the 17th centrury it was known that sounds could be perceived via air conduction and bone conduction and that this provided a means of differentiating between hearing disorders located in the middle ear and those located in the acoustic nerve. For a long time to come, however, there was no need for such a differential diagnosis. After the invention of the tuning fork in 1711 this instrument had soon become widely used in music, but it took well over 100 years until it was introduced into physiology and otology. FROM DIRECTIONAL HEARING TO WEBER'S TEST: J. B. Venturi, a physicist in Modena, Italy, in 1802 had shown that the perception of the direction from which a sound is coming is governed by the fact that one ear is hit by the sound more intensely than the other ear. C. T. Tourtual, a physician in Münster, Germany, demonstrated in 1827 that this also holds true for sound conducted via the skull bones. He used a watch as sound source. He found that occlusion of both ear canals would increase the sensation in both ears equally, but that occlusion of only one ear would increase the sensation only in the occluded ear, thus giving the impression that the sound were coming from that side. He was interested in a comparison between vision and audition, and he concluded that with regard to recognizing the direction of a sensory signal vision was superior to audition. In the same year 1827 C. Wheatstone, a physicist in London, investigating the mode of vibration of the tympanic membrane and using a tuning fork found the same phenomena as Tourtual and some more effects. E. H. Weber, an anatomist and physiologist in Leipzig, Germany, described the very same phenomena as Tourtual and Wheatstone once more in 1834. He wanted to prove that airborne sound is perceived by the vestibulum and the semicircular canals, bone conducted sound by the cochlea. None of these investigators was thinking of a clinical use of their findings and made no such suggestion. E. Schmalz, an otologist in Dresden, Germany, in 1845 introduced the tuning fork and the test later named after Weber into otology and explained in great detail all possibilities of a diagnostic evaluation of the test. His grand achievement, however, passed unnoticed at his time. THE RINNE TEST: A. Rinne, a physician in Göttingen, Germany. In 1855 described the test which later was named after him, in an elaborate treatise on the physiology of the ear. He wanted to demonstrate that in man and animals living in the air, as opposed to those living in water, the conduction of sound via the bones of the skull is just an unavoidable side effect of sound perception. He mentioned a clinical application of his test only in a footnote and obviously never used it himself in a systematic way. His test was made generally known by Lucae in Berlin only after 1880. The value of Weber's and Rinne's tuning fork tests was much disputed even at the turn of the century and only gradually became generally accepted.