Date of Graduation

Spring 2011


Doctor of Audiology


Communication Sciences and Disorders

Committee Chair

Wafaa Kaf


outer hair cells, cochlear microphonics, electrocochleography, distortion-product otoacoustic emission, efferent system, medial olivocochlear bundle, suppression

Subject Categories

Communication Sciences and Disorders


The present study examined and compared the effect of the contralateral stimulation of the auditory efferent system on the cochlear microphonics (CM) versus the distortion product otoacoustic emissions (DPOAEs). The DPOAEs and the CM were recorded from the right ear of 16 normal-hearing young female adults with and without 60 dB sound-pressure-level (SPL) broad band noise (BBN) in the left ear. DPOAEs were obtained at 0.5, 2, and 4 kHz, with L1 = 65 dB SPL and L2 = 50 dB SPL, and f2/f1 ratio = 1.2. The CM was recorded from the right tympanic membrane at 90 dB SPL using three stimuli (click and 0.5 and 2 kHz tone bursts) and two polarities (condensation and rarefaction). Results showed both suppression and enhancement of the DPOAE and the CM responses in the presence of BBN, but the effect was not statistically significant at any of the tested conditions. When the ratio of the suppression or enhancement was used, the effect was marginal for the 2 kHz TB stimulus of the CM. Results also showed a possible relation between the stimulus polarity and the type of effect on the CM. In conclusion, there is some evidence that the efferent system is involved in the suppression and enhancement of the CM, mainly at 2 kHz TB. This might be due to the nature of the CM recording from the basal turn of the cochlea. This study provided the first descriptions of the contralateral suppression of CM in humans. More research is needed to enhance the sensitivity of the CM test methodology to examine the function of the efferent system clinically.


© Fadi Jamil Najem

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