Em. Burns et al., VOLUNTARY CONTRACTION OF MIDDLE-EAR MUSCLES - EFFECTS ON INPUT IMPEDANCE, ENERGY REFLECTANCE AND SPONTANEOUS OTOACOUSTIC EMISSIONS, Hearing research, 67(1-2), 1993, pp. 117-127
Two types of measurements were performed on a subject able to voluntar
ily contract her middle ear muscles (MEM). First, wideband measurement
s (0-11 kHz) of middle ear input impedance and energy reflectance were
obtained when the subject was relaxed and when she contracted her MEM
. The changes in impedance observed with voluntary MEM contraction wer
e similar to those reported in the literature for acoustically-elicite
d MEM contractions. The energy reflectance increased for frequencies b
elow about 4 kHz. Second, the effects of voluntary MEM contraction on
the frequencies and levels of spontaneous otoacoustic emissions (SOAEs
) were measured and compared to effects evoked by contralateral acoust
ic stimulation. Effects on SOAEs appear to be a more sensitive indicat
or of MEM activity than changes in impedance, and the effects due to v
oluntary MEM contraction were qualitatively similar to those evoked by
contralateral acoustic stimulation. These results suggest that in sub
jects with normally-functioning middle ears, only some effects on otoa
coustic emissions caused by contralateral stimuli whose levels are bel
ow the contralateral acoustic reflex threshold can be unequivocally at
tributed to the action of cochlear efferents. The temporal aspects of
SOAE frequency shifts caused by voluntary contraction of MEM show that
voluntary contraction fatigues rapidly over a time period of tens of
seconds.