Frequency tuning and acoustic enhancement of electrically evoked otoacoustic emissions in the guinea pig cochlea.

Electrically evoked otoacoustic emissions (EEOAEs) were generated by ac stimulation in scala media of turns 1, 2, and 3 in the guinea pig cochlea. In each turn EEOAEs were recorded at frequencies up to and slightly above the estimated characteristic frequency (CF) of the stimulation site. Acoustic enhancement of EEOAEs was present at all emission frequencies in turns 2 and 3 but could be demonstrated in turn 1 only at emission frequencies that fell within a notch in the EEOAE tuning function. There was no evidence, in any turn, of a transition from enhancement to suppression as the emission frequency approached the CF of the stimulation site. The results were not consistent with the hypothesis [D. C. Mountain and A. E. Hubbard, Hear, Res. 42, 195-202 (1989)] that acoustic enhancement results from a reduction in the effectiveness of forward transduction in a negative feedback loop.