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What do you Expect Regarding the Cochlear Microphonic in ECochG Testing?

James W. Hall III, PhD

January 13, 2014

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Question

What do you expect to see in ECochG testing using rarefaction and condensation clicks in normal individuals?

Answer

Most normal hearing persons have very small cochlear microphonic (CM) waves on separate stimulation with rarefaction and condensation clicks. With a typical earlobe or mastoid electrode, even the ECochG AP component (wave I of the ABR) is only about 0.2 or 0.3 microvolts, so the CM is almost impossible to see unless there's no noise in the recording. Using a TM electrode, however, it's possible to see clear CM in a normal hearing subject and it's very easy to see the CM with the trans-tympanic approach (although it's hard to find normal hearing subjects who will participate in a study).

The CM in many ANSD patients is abnormally enlarged (maybe due to dysfunction of the efferent system) and often easy to detect even with an ABR recording technique.

This Ask the Expert was asked as a follow up question to Dr. Hall's course, Clinical Applications of Electrocochleography Today, which can be accessed in the AudiologyOnline Course Library.


james w hall iii

James W. Hall III, PhD

James W. Hall III, PhD is an internationally recognized audiologist with 40-years of clinical, teaching, research, and administrative experience. He received his Ph.D. in audiology from Baylor College of Medicine under the direction of James Jerger.  During his career, Dr. Hall has held clinical and academic audiology positions at major medical centers. Dr. Hall now holds appointments as Professor at Salus University and the University of Hawaii, and as Extraordinary Professor at the University of Pretoria South Africa. Dr. Hall is the author of over 160 peer-reviewed journal articles, monographs, or book chapters, and nine textbooks including the 2014 Introduction to Audiology Today and the 2015 eHandbook of Auditory Evoked Responses.

 


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