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Abstract: Auditory evoked potentials (AEPs) were investigated in northern elephant seals (Mirounga angustirostris) to characterize the responses elicited by different acoustic stimulus types, examine temporal resolving capabilities, and evaluate the potential for using evoked responses to estimate hearing sensitivity. Clicks and tone pips were presented to individual seals to characterize evoked responses to broad- and narrowband stimuli. Tone pip trains and sinusoidally amplitude-modulated (SAM) tones were used to determine modulation rate transfer functions (MRTF) of the auditory system and to determine if the magnitude of the envelope-following response (EFR) relative to the stimulus level can be used to estimate hearing thresholds. Click evoked responses were characterized by three early positive peaks (~2.6, 4.4, and 6.1 ms) and a dominant negative peak at 7.2 ms and had average amplitudes of 264 nV (peak-to-peak [pk-pk]) for a corresponding stimulus level of 126 dB re 20 μPa (pk-pk). The use of dissociative drugs for the immobilization of the seals showed no demonstrable effect on the latencies or amplitudes of the click evoked response. Both the rate following response (RFR) and EFR amplitudes were maximal when the stimulus repetition rate or the amplitude modulation rate, respectively, were < 100 Hz. EFR amplitudes at the rate of amplitude modulation tracked near linearly with stimulus level. Thresholds for a 4-kHz SAM tone were estimated to be 45 dB re 20 μPa. Thus, the recording of AEPs is a viable means of studying auditory processes in the northern elephant seal.
Key Words: elephant seal, audiometry, evoked potential, hearing
Document Type: research article
Page Numbers: 110-121