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On the influence of the middle ear muscles upon changes in sound transmission


Archives of Oto Rhino Laryngology 221(1): 47-60
On the influence of the middle ear muscles upon changes in sound transmission
The influence of artificially induced impedance changes on the frequency response of the middle ear was investigated in 3 experienced listeners. The tensor reflex was simulated by application of positive and negative air pressure to the outer ear canal. In this test-situation, the threshold shift (.DELTA.L) was greatest around the 1st resonance of the middle ear (.DELTA.L = 8 dB at 500 Hz). For bone-conduction, the effect was weaker by about 2 dB than for air conduction. The change in sound transmission was constant for all SPL [sound pressure level] and was mainly due to the impedance change of the middle ear. The influence of the stapedial reflex was strongly dependent on SPL. In the range between hearing threshold and 70 dB (HL [hearing level]) the attenuation was only 2 dB below 1 kHz. At higher levels the attenuation might amount to 30 dB. The excitation of the cochlea remained nearly constant. Apparently the intensity dependent influence of the stapedius reflex on sound transmission is due to a change of the stapes motion. The regulating device worked without considerable distortion but with an attack time of about 100 ms. The phenomenon of conductive recruitment in otosclerosis is probably due to the lack of this regulating effect by the fixed stapes. One function of the stapedial reflex could be the protection of the ear from high amplitudes during phonation and shouting. Because frequencies above 1 kHz are also attenuated, a protective function of the stapedial reflex in industrial noise exposure can also be assumed.

Accession: 006027936

PMID: 697648

DOI: 10.1007/bf00456383

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