Abstract
Previous studies have demonstrated that increasing-frequency chirp (up-chirp) stimuli can enhance auditory brainstem response (ABR) amplitudes by compensating for temporal dispersion occurring along the cochlear partition. In this study, ABRs were measured in two bottlenose dolphins in response to 5-µs, spectrally “white” clicks, up-chirps, and decreasing-frequency chirps (down-chirps). For all stimuli, bandwidth was constant (10 to 180 kHz) and peak-equivalent sound pressure levels (peSPLs) were 115, 125, or 135 dB re 1 μPa. Chirp durations varied from 125 to 2000 μs. Up-chirps with durations less than ~1000 μs generally increased ABR peak amplitudes compared to clicks with the same peSPL or energy flux spectral density level, while down-chirps with durations above ~250 to 500 μs decreased ABR amplitudes relative to clicks. Increases in ABR amplitude occurred with up-chirps having a broad range of durations. The findings parallel those from human studies and suggest that the use of chirp stimuli may be an effective way to enhance broadband ABR amplitudes in larger marine mammals. [Work supported by US Navy Living Marine Resources Program.]
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