Abstract: Auditory brainstem responses (ABRs) of a Pacific white-sided dolphin (Lagenorhynchus obliquidens) in the presence of masking noise were measured at John G. Shedd Aquarium in Chicago. The dolphin was trained to wear suction cups with 1-cm diameter, gold-plated metallic electrodes typically used for human EEG measurements embedded in the cups. The animal was trained to station in a hoop, facing a sound projector 5 m away. ABR thresholds were obtained by progressively reducing the level of click stimuli, having peak frequencies of 8, 16, 32, 64, 80, and 100 kHz. The thresholds were obtained in the presence of broadband masking noise. The ABR waveforms were slightly different than for other odontocetes, having 7 to 8 waves present—the most for any odontocetes measured so far. The response latency of 1.3 to 1.5 ms is similar to those of other dolphins of approximately the same size. The peaks in the Fourier transform of the ABR waveform occurred at 650 and 1,200 Hz, very similar to the 600 to 650 and 1,100 to 1,200 Hz for Tursiops truncatus. The deepest null in the spectrum, which occurred at about 950 Hz, was much deeper than for the bottlenose dolphin. Masked ABR thresholds expressed in peak-to-peak values were between 38 and 56 dB above the rms values of the masking noise.

Key Words: auditory brainstem response, masked threshold, click evoked potentials, ABR masked threshold, Pacific white-sided dolphin, Lagenorhynchus obliquidens 

Document Type: research article

DOI: 10.1578/AM.33.1.2007.76

Page Numbers: 76 – 84