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Group Delay of Acoustic Emissions in the Ear

¹Oregon Hearing Research Center, Department of Otolaryngology and Head and Neck Surgery, and ²Department of Biomedical Engineering, Oregon Health and Science University, Oregon; ³Department of Physiology and ⁴Department of Otolaryngology and Head and Neck Surgery of School of Medicine, Xi'an Jiaotong University, Xi'an, China; and ⁵Kresge Hearing Research Institute, University of Michigan, Ann Arbor, Michigan; ⁶Shanghai Jiaotong University, Shanghai, China

Submitted 9 April 2006; accepted in final form 30 July 2006

It is commonly accepted that the cochlea emits sound by a backward traveling wave along the cochlear partition. This belief is mainly based on an observation that the group delay of the otoacoustic emission measured in the ear canal is twice as long as the forward delay. In this study, the otoacoustic emission was measured in the gerbil under anesthesia not only in the ear canal but also at the stapes, eliminating measurement errors arising from unknown external- and middle-ear delays. The emission group delay measured at the stapes was compared with the group delay of basilar membrane vibration at the putative emission-generation site, the forward delay. The results show that the total intracochlear delay of the emission is equal to or smaller than the forward delay. For emissions with an f2/f1 ratio <1.2, the data indicate that the reverse propagation of the emission from its generation site to the stapes is much faster than a forward traveling wave to the f2 location. In addition, that the round-trip delays are smaller than the forward delay implies a basal shift of the emission generation site, likely explained by the basal shift of primary-tone response peaks with increasing intensity. However, for emissions with an f1 << f2, the data cannot distinguish backward traveling waves from compression waves because of a very small f1 delay at the f2 site.

This article has been cited by other articles:

				W. He, A. Fridberger, E. Porsov, K. Grosh, and T. Ren Reverse wave propagation in the cochlea PNAS, February 19, 2008; 105(7): 2729 - 2733. [Abstract] [Full Text] [PDF]