title: Changes in amplitude and phase of distortion-product otoacoustic emission fine-structure and separated components during efferent activation.
abstract: Medial olivocochlear (MOC) efferent fibers synapse directly on the outer hair cells (OHCs). Efferent activation evoked by contralateral acoustic stimulation (CAS) will affect OHC amplification and subsequent measures of distortion-product otoacoustic emissions (DPOAEs). The aim of this study was to investigate measures of total and separated DPOAEs during efferent activation. Efferent activation produces both suppression and enhancement of the total DPOAE level. Level enhancements occurred near fine-structure minima and were associated with consistent MOC evoked upward shifts in DPOAE fine-structure frequency. Examination of the phase of the separated components revealed that frequency shifts stemmed from increasing phase leads of the reflection component during CAS, while the generator component phase was nearly invariant. Separation of the two DPOAE components responsible for the fine-structure revealed more consistent reduction of the levels of both components. Using vector subtraction (which takes into account both level and phase) to estimate the changes in the unseparated DPOAE provided consistent evidence of DPOAE suppression. Including phase information provided a more sensitive, valid and consistent estimate of CAS function even if one does not know the position of the DPOAE in the fine-structure.
authors.affiliation: Graduate Center of the City University of New York, 365 Fifth Avenue, New York, New York 10016, USA. shenin@gc.cuny.edu
authors.forename: Simon
authors.initials: S
authors.lastname: Henin
authors.forename: Suzanne
authors.initials: S
authors.lastname: Thompson
authors.forename: Shukrallah
authors.initials: S
authors.lastname: Abdelrazeq
authors.forename: Glenis R
authors.initials: GR
authors.lastname: Long
mesh_terms: D000161:Acoustic Stimulation; D000162:Acoustics; D000328:Adult; D001298:Audiology / Q000379:methods*; D001307:Auditory Perception / Q000502:physiology*; D001309:Auditory Threshold / Q000502:physiology; D017626:Cochlear Nucleus / Q000502:physiology; D004424:Ear Canal / Q000502:physiology; D018072:Hair Cells, Auditory, Outer / Q000502:physiology*; D006801:Humans; D009847:Olivary Nucleus / Q000502:physiology; D017084:Otoacoustic Emissions, Spontaneous / Q000502:physiology*; D055815:Young Adult