Hearing and cochlear microphonic potentials in the bat Eptesicus fuscus.

Abstract

Cochlear A. C. [alternating current] potentials recorded from the round window membrane of the bat Eptesicus fuscus were typified by relatively great peak outputs in response to auditory stimuli between 50 kHz and 90 kHz. A dynamic hearing range exceeding 70 db was measured to 90 kHz in one bat. The high frequency specialization of Eptesicus'' auditory system appeared present at the cochlear level. This unusual high frequency auditory capacity is theoretically suited for the detection of very small objects by echolocation. For one bat the magnitude of cochlear microphonic potentials elicited by puretone stimuli of threshold SPL [sound pressure level] was ascertained. There was no single magnitude of cochlear potential which was uniquely associated with absolute hearing thresholds. Thus, it is unlikely that density of cochlear stimulation (e.g. [mu]v/mm. of basilar membrane length) bears any simple relation to the initiation of "threshold level" impulses in the auditory nerve. Data from other animals agree with the above.