On the temporary effect of industrial noise on the hearing at 4,000 c/s of stapedectomized ears

The effects of middle ear muscle contraction on auditory and overload thresholds

The present investigation examined psychophysically the frequency-specific and nonlinear attenuation of sound energy provided by middle ear muscle contraction in normal hearers. Aural overload and absolute auditory thresholds were measured at 500, 1 000 and 2 000 Hz prior to and during acoustic stapedial reflex contraction. Reflex contraction was elicited with contralateral broad-band noise. Results revealed that overload thresholds were elevated at 500 and 1 000 Hz and a slight decrease in overload threshold was apparent at 2 000 Hz during reflex contraction while absolute thresholds remained essentially unchanged. These data are consistent with previous psychophysical and physiological findings. The aural overload test having been derived directly from observations of cochlear microphonic saturation, moreover, affords direct comparison to results of electrophysiological experimentation.

The role of the stapedius reflex in poststimulatory auditory fatigue

The human ear is very resistant against noise-induced damage in the low frequency range. The aim of the present study was to investigate whether or not the stapedium reflex is of any importance for this resistance. Subjects with peripheral facial palsy (Bell's palsy) including unilateral stapedius muscle paralysis were exposed to several different levels of narrow band noise centered at 0.5 and 2.0 kHz. Temporary threshold shift (TTS) at 0.75 kHz was significantly higher in the affected than in the nonaffected ear after 0.5 kHz noise at and above 110 dB SPL. After the exposure with 2.0 kHz narrow band noise there was no difference in TTS at 3.0 kHz between the affected and nonaffected ear. It is concluded that the attenuation provided by the stapedius reflex reduces TTS after low frequency noise exposure. An implication is that the stapedius reflex also may have the function of protecting the ear from hearing damage caused by low frequency noise exposure.