The sources of electrically evoked otoacoustic emissions

It has been hypothesized that electrically evoked otoacoustic emissions (EEOAEs) are generated at a site on the basilar membrane near the stimulating electrode. From this original site, the energy propagates towards the oval window, giving rise to the short time delay component (SDC) of EEOAEs. The energy also propagates towards its characteristic frequency (CF) location, and the emission reflected from the CF location forms a long time delay component (LDC). This hypothesis is directly tested in this study by using an acoustical swept tone to modulate the EEOAEs generated by alternating electric current delivered to the round window niche in gerbils. An acoustical tone with a high sound pressure level or a small frequency separation from the EEOAE frequency induced a strong suppression of the EEOAE LDC, but no obvious suppression of the SDC. When the electrical current frequency was fixed, the swept acoustic tone induced a slight suppression, an enhanced peak, and a strong suppression of EEOAEs as the acoustic frequency was swept from the low to high frequency. These data indicate that the electrical current induced cochlear partition vibration near the stimulating electrode. One part of this energy propagates directly to the ear canal, forming the SDC, and the other part propagates to its CF place and is reflected from there to the ear canal, forming the LDC.