Interaction of spontaneous oto-acoustic emissions and external sounds

Abstract

Spontaneous oto-acoustic emissions (SOAE) were detected in 8 of 19 ears from 12 persons with normal hearing. On a subset of these individuals, additional characteristics of SOAE were studied including the suppression of SOAE level caused by an external tone. For suppressor tones below and slightly above the frequency of an SOAE, suppression is quite abrupt (about 5 dB of SOAE level reduction per dB increase in suppressor level); as suppressor frequency increases above the SOAE, the rate of suppression decreases. A release from suppression was demonstrated by the interaction of an SOAE with 2 external tones. When a tone above the SOAE frequency causes suppression, a 2nd tone above the suppressor frequency can cause the SOAE to increase nearly to its ambient level. Apparently, the 2nd tone suppressed some aspect of the intracochlear influence of the 1st tone. The growth rate of this secondary suppression appears to be near 1 dB/dB, a value similar to rates derived from existing measures of 2-tone suppression observed in auditory-nerve-fiber recordings in laboratory mammals.