Measurements of human middle ear forward and reverse acoustics: Implications for otoacoustic emissions

Abstract

Middle and inner ears from human cadaver temporal bones were stimulated in the forward direction by an ear-canal sound source, and in the reverse direction by an inner-ear sound source. For each stimulus type, three variables were measured: (a) Pec--ear-canal pressure with a probe-tube microphone within 3 mm of the eardrum, (b) Vst--stapes velocity with a laser interferometer, and (c) Pv--vestibule pressure with a hydrophone. From these variables, the forward middle-ear pressure gain (M1), the cochlear input impedance (Zc), the reverse middle-ear pressure gain (M2), and the reverse middle-ear impedance (M3) are directly obtained for the first time from the same preparation. These measurements can be used to fully characterize the middle ear as a two-port system. Presently, the effect of the middle ear on otoacoustic emissions (OAEs) is quantified by calculating the roundtrip middle-ear pressure gain Gme(RT) as the product of M1 and M2. In the 2-6.8 kHz region, absolute value(Gme(RT)) decreases with a slope of -22 dB/oct, while OAEs (both click evoked and distortion products) tend to be independent of frequency; this suggests a steep slope in vestibule pressure from 2 kHz to at least 4 kHz for click evoked OAEs and to at least 6.8 kHz for distortion product OAEs. Contrary to common assumptions, measurements indicate that the emission generator mechanism is frequency dependent. Measurements are also used to estimate the reflectance of basally traveling waves at the stapes, and apically generated nonlinear reflections within the vestibule.

Estimation of Round-Trip Outer-Middle Ear Gain Using DPOAEs

“…As explained in the previous paragraph and as can be seen in Figure 10, the levels of the gain estimates are higher in Puria and Rosowski (1996) and Puria (2003) in comparison with our estimates at frequencies lower than 2 kHz. It has to be noted that the reverse stimulus by Puria and Rosowski (1996) and Puria (2003) was introduced at a location closer to the base than the site of DPOAE generation in our estimates. Therefore, at these lower frequencies, the cumulative cochlea gain effect on the OMEG estimates could be larger.…”

“…The OMEGs estimated for our participants ranged between −39 and −17 dB. The gain estimates range was smaller in our estimates than those of Puria and Rosowski (1996) and Puria (2003) but was similar to the range of the gain estimated by Keefe (2015). It should be noted that the OMEG estimates were not available for all frequencies between 1 and 3.3 kHz in our participants so the gain range might be larger than found here.…”

“…The probe-microphone that the ear canal was terminated with in our study was a three-port ER-10A, which was different than the probe-microphone used by Puria and Rosowski (1996) (i.e., ER-10C, Etymotic Research Inc., with a foam earplug) and Puria (2003) and Nakajima et al (2009) (i.e., ER7C, Etymotic Research Inc.). The extent to which the gain estimates could be affected by the probe-microphone should be investigated further by comparing the impedances of the aforementioned probe-microphones paired with the eartips that were used.…”

“…The round-trip middle ear pressure gain, ranged between −27 and −5 dB with one global minimum between 1 and 3.3 kHz (Puria and Rosowski 1996). The round-trip middle ear gain was estimated in five temporal bones in a later study by Puria (2003), which ranged between −34 and 0 dB. It should be noted that Puria (2003) Figure 10.…”

“…Investigating how the outer and middle ear shape the transmitted sound would benefit OAEs as a research and diagnostic tool. Efforts to determine sound transmission characteristics of the middle ear invasively were made on living human ears (Huber et al 2001;Chien et al 2009), human cadaveric temporal bones (Puria and Rosowski 1996;Puria et al 1997;Voss et al 2000;Aibara et al 2001;Puria 2003;Nakajima et al 2009), gerbils (Dong and Olson 2006;Ravicz et al 2008;Dong et al 2012), cats (Voss and Shera 2004), chinchillas (Songer and Rosowski 2007;Ravicz et al 2010;Ravicz and Rosowski 2013), and guinea pigs (Nuttall 1974;Magnan et al 1997). Huber et al (2001) measured stapes displacement during surgery in patients who were going under cochlear implantation.…”