Auditory evoked potential measurement methodology for odontocetes and a comparison of measured thresholds with those obtained using psychophysical techniques

Abstract

Most measurements of the hearing capabilities of toothed whales and dolphins have been taken using traditional psychophysical procedures in which the animals have been maintained in laboratory environments and trained to behaviorally report the sensation or difference of acoustic stimuli. Because of the advantage of rapid data collection, increased opportunities, and new methods, Auditory Evoked Potentials (AEPs) have become increasingly used to measure audition. The use of this new procedure calls to question the comparability of the established literature and the new results collected with AEPs. The results of behavioral and AEP methods have been directly compared with basic audiogram measurements and have been shown to produce similar (but not exactly the same) values when the envelope following response procedure has been used and the length of the stimulus is taken into account. The AEP methods allow possible audiometric opportunities beyond those available with conventional psychophysics including: (1) the measurement of stranded dolphins and whales that may never be kept in laboratories, (2) the testing of stranded animals for hearing deficits perhaps caused by overexposure to noise, and (3) passive testing of hearing mechanisms while animals actively echolocate. [Work supported by the Office of Naval Research and NOAA-NMFS.]