Experimental Study of Bone Conduction in Ears with Mechanical Impairment of the Ossicles

Abstract

The cochlear-microphonic potential of guinea pigs was recorded during stimulation by bone-conducted sounds. The amplitude and the phase of the response were measured while the ossicles were altered in various ways. At low and middle frequencies, fixation of the ossicular chain produces a decrease of amplitude and a phase advance of about 70°, while an increase of the mass yields an increase of amplitude and a phase lag greater than 180°. A progressive increase of the mass, produced by introducing paraffin oil in the middle-ear cavity, yields a progressive variation of amplitude and phase and, at a particular moment, a complete disappearance of the response. Symmetrical results were obtained by altering the intrabullar pressure. All these results are interpreted as showing the participation of several mechanisms contributing to the whole response. At low frequencies a translational mechanism involves two components: one related to the motion of the ossicular chain and the other related to the motion of the perilymphatic fluid. These two components contribute to the whole response according to their amplitude and phase. At higher frequencies a compressional mode of bone conduction, independent of the motion of the ossicles, is responsible for the stimulation. These findings agree with the alteration of bone conduction observed in clinical cases and provide an explanation for the lateralization of the sound source in an ear affected by conductive deafness, as shown in the Weber test. This lateralization may be accounted for by the observed phase shifts.

The use of acoustical test fixtures for the measurement of hearing protector attenuation. Part II: Modeling the external ear, simulating bone conduction, and comparing test fixture and real-ear data

“…this is true up to 4000 Hz for humans (up to 2500 Hz for guinea pigs;Legouix and Tarab, 1959). Reference measurements of the subjective occlusion effect and the threshold SPL of air and bone conduction in the occluded ear canal were done monaurally on five subjects, using a modified BBE-Untone earplug with a built-in electret microphone(Sennheiser KE4/211 with a 0.71-mm probe).…”

A Qualitative Explanation of the Weber Test

“…Several authors support this theory. [4][5][6] Naunton and Elpern reviewed the hypothesis and decided that the phase difference could account for only 5 dB of perceived loudness at most. They agreed with others 2,7 that intensity differences account for the perceived loudness.…”

Air pressure changes in the external auditory meatus

“…Overall, the studies of Legouix and Tarab (1959), Tonndorf (1966), and Kaufmann etal. (1968) on animals, and of Barany (1938), Kirikae (1959), Bekesy (1960), Huizing (1960) and Humes (1979) on humans, indicate that there is an external, middle and inner ear component involved in bone conduction hearing in both animals and man.…”