Using auditory evoked potentials to measure marine mammal hearing.

Abstract

The use of auditory evoked potential (AEP) measurements for examining the hearing of marine mammals was accelerated by the need to rapidly test hearing following sound exposures during temporary threshold shift experiments. AEP measures have allowed quick measurements of hearing following intense noise exposures of sounds ranging from filtered white noise to 53‐C sonars. The refinement of AEP hearing measurements with envelope following response measures leads to comparisons between behavioral and AEP hearing thresholds. These comparisons have allowed an expansion of basic hearing measurements including measures of new species such as the white‐beaked dolphin and polar bear, measures of increased numbers of the same species in order to better examine population audiogram estimates and variability, and testing of hearing of animals in the field. AEP measures have also allowed the measurement of hearing during echolocation. A false killer whale has been shown to hear its own outgoing signal 40 dB down from the same sort of signal presented directly in front of it, actively control the level of its hearing of echolocation returns in an automatic gain control of hearing, and hear sounds other than echolocation sounds 20 dB differently when it is echolocating depending on target condition.