Rl. Goode et al., NEW KNOWLEDGE ABOUT THE FUNCTION OF THE HUMAN MIDDLE-EAR - DEVELOPMENT OF AN IMPROVED ANALOG MODEL, The American journal of otology, 15(2), 1994, pp. 145-154
Conventional teaching regarding the acoustic function of the human mid
dle ear is that it serves as an impedance matching system to offset th
e loss that occurs when sound passes from the low-impedance sound fiel
d to the high-impedance cochlear fluid. A transformer analogy is often
used with the pressure transformation produced by the eardrum; footpl
ate area ratio and the lever ratio considered to be approximately 27 d
B. Recent data on middle ear function has shown this to be only partia
lly correct. A transformer analogy is not appropriate since the pressu
re gain of the middle ear decreases above 1000 Hz and does not depend
on the cochlear load at all frequencies. Experiments are described of
umbo, malleus short process, and stapes displacement in human temporal
bones using a laser Doppler measuring system (LDS). The measurements
support previous studies that indicate that in addition to a roll-off
in tympanic membrane function above 1000 Hz, there is slippage in the
ossicular lever system that causes an increasing ''lever ratio' above
1000 Hz, thought to be caused by translational movement of the ossicul
ar rotation axis near the short process. An improved analog circuit mo
del of the external and middle ear has been developed that produces re
sults equivalent to those found in the temporal bones.