[The application of otoacoustic emissions measurement in the assessment of the function of cochlear efferent fibers: the study of normal hearing subjects].

It has been shown by L. Collet in 1990 that the contralateral noise stimulation causes the decrease in the amplitude of otoacoustic emissions in the ipsilateral (tested) ear. This effect is linked to the activation of crossed efferent fibres in the cochlea. This non-invasive method is becoming a useful tool in assessing the function of efferent system in human. In this study the effect of contralateral noise stimulation was assessed in 10 young subjects with normal hearing. The contralateral stimulation caused the decrease in the amplitude of both transient evoked otoacoustic emission (TEOAE) and distortion-product otoacoustic emission (DPOAE) in the majority of tested ears. The statistically significant effect was observed already at the intensity of noise of 40 dB (A). At the lower level of noise (30 dB-A) the small increase in the amplitude of otoacoustic emissions in some ears was observed. The suppressive effect of contralateral stimulation depended clearly on the intensity of noise; the higher intensity of noise, the greater suppressive effect was seen. However, the decrease in the otoacoustic emissions was very small (usually in the range from 1 to 2 dB), which may limit practical application of this method in the assessment of the function of efferent system.