Stimulated acoustic emissions in the ear canal of the gerbil

Ear-canal sound pressure and cochlear potentials were monitored inthe anesthetized gerbil to study the origins of acoustic emissions produced by transient and continuous stimuli. No evidence was found of any delayed emissions (echoes) originating within the cochlea in the acoustic or cochlear microphonic (CM) waveforms. However, strong acoustic and CM distortion products occurred when two primary tones of moderate levels were presented to the ear; the site of origin of these products was traced to the cochlea. Further, the levels of distortion followed a complex time course after anoxia, often becoming stronger after animal death for up to one hour, then decaying to the noise floor of the system. The disappearance of the distortion products was coincident with elimination of both the negative endocochlear potential and the CM response to a fundamental tone.