Contraction of the stapedius muscle affects sound transmission by air conduction and bone conduction differently.
A contraction of the stapedius muscle decreases the sound transmission through the middle ear in the order of 10 dB for frequencies below approximately 1.5 kHz. It is not very clear how a stapedius muscle contraction affect sound transmission to the inner ear by bone conduction, but it is generally assumed that it affect the sound transmission by bone conduction less than it does by air conduction.
Materials and Methods
Growth functions of Auditory Steady State Responses (ASSR) in the frequency range 0.5 to 4 kHz was measured in ten subjects. The ASSR stimuli were either supplied by air conduction or bone conduction. Simultaneously, a noise stimuli designed not to interfere with the ASSR stimuli was presented to elicit the stapedius reflex. By comparing ASSR growth functions at different eliciting levels, the influence from the stapedius reflex could be estimated.
It was found that the stapedius reflex decreases sound transmission by air conduction by 5 to 20 dB at frequencies below 2 kHz and 0 to 5 dB when the stimulation is by bone conduction.
The stapedius reflex attenuate air conducted sound at low frequencies more than it does bone conducted sound
Elsevier Science B.V., Amsterdam. , 2010. Vol. 263, no 01-Feb, 243-243 p.