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Abstract: Comparisons between click-evoked auditory brainstem responses (ABR) and auditory steady-state responses (ASSR) were performed to determine if the click-evoked ABR could be used to predict hearing loss in the bottlenose dolphin (Tursiops truncatus). The ASSR was evoked using sinusoidal amplitude modulated tones at half octave frequency intervals from 20 to 160 kHz and utilized to determine the upper-frequency limit of hearing in each dolphin (i.e., the frequency at which threshold was equal to 120 dB re 1 μPa). The click-evoked ABR was then recorded following exposure to a moderate-amplitude click (peak-peak equivalent sound pressure level of 122 dB re 1 μPa, 5 to 100 μs duration) and examined to determine if relationships existed among the upper-frequency limit of hearing and the amplitude/latency characteristics of the click-evoked ABR. The ASSR and click-evoked ABR were measured in six dolphins (4 males and 2 females, from 13 to 49 y of age) with varying hearing sensitivity and frequency range of hearing. A significant relationship existed between click-evoked ABR wave amplitudes and the upper-frequency limit of hearing, although the number of waves showing the relationship varied with the duration of the click. Test times for assessment using frequency-specific ASSR and click-evoked ABR were ~45 min and 1 min, respectively. With further definition of normative data, measurement of click-evoked ABRs could form the basis of an expedited electrophysiologic method for hearing screening in delphinids.
Key Words: odontocete, bottlenose dolphin, Tursiops truncatus, hearing assessment, auditory steady-state response, auditory brainstem response, presbycusis
Document Type: Research Article
Page Numbers: 339-349