Date of Graduation

Spring 2012


Doctor of Audiology


Communication Sciences and Disorders

Committee Chair

Wafaa Kaf


medial olivocochlear bundle, suppression effect, outer hair cells, cochlear microphonic, contralateral stimulation, ipsilateral stimulation, electrocochleography, efferent system.

Subject Categories

Communication Sciences and Disorders


The current study was designed to investigate the effect of activating the crossed and uncrossed medial olivocochlear bundle (MOCB) in humans to better understand the function of the efferent system. Cochlear microphonic (CM) for 0.5 and 2.0 kHz tone burst (TB) was recorded in 17 female subjects (20-30 years old) while activating the crossed or uncrossed MOCB. Activation of the MOCB was completed at three levels of broadband noise (BBN) (40, 50, and 60 dBSPL). CM amplitude was recorded without presenting BBN as a baseline. Then, CM amplitude was recorded while presenting BBN ipsilaterally or contralaterally at the different BBN levels. The change in CM amplitude was measured by subtracting the without-BBN condition from the with-BBN condition. Enhancement/suppression of the CM amplitude was observed when the BBN was presented. Greater change in CM amplitude was observed when 0.5 kHz TB was used compared to 2.0 kHz. Greater change in CM amplitude was observed when the uncrossed fibers were activated (contralateral activation) compared to the crossed fibers (ipsilateral activation). For the BBN level, 50 dBSPL seemed to have the greatest effect on the CM amplitude. The current results support the theory that the MOCB modulates the outer hair cells, which could help explain the function of the efferent system.


© Abdullah M. Jamos

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