The neural representation of the dolphin broadband biosonar click was investigated by measuring auditory brainstem responses (ABRs) to “self-heard” clicks masked with noise bursts having various high-pass cutoff frequencies. Narrowband ABRs were obtained by sequentially subtracting responses obtained with noise having lower high-pass cutoff frequencies from those obtained with noise having higher cutoff frequencies. For comparison to the biosonar data, ABRs were also measured in a passive listening experiment, where external clicks and masking noise were presented to the dolphins and narrowband ABRs were again derived using the subtractive high-pass noise technique. The results showed little change in the peak latencies of the ABR to the self-heard click from 28 to 113 kHz; i.e., the high-frequency neural responses to the self-heard click were delayed relative to those of an external, spectrally “pink” click. The neural representation of the self-heard click is thus highly synchronous across the echolocation frequencies and does not strongly resemble that of a frequency modulated downsweep (i.e., decreasing-frequency chirp). Longer ABR latencies at higher frequencies are hypothesized to arise from spectral differences between self-heard clicks and external clicks, forward masking from previously emitted biosonar clicks, or neural inhibition accompanying the emission of clicks.
Neural representation of the self-heard biosonar click in bottlenose dolphins (Tursiops truncatus)
James J. Finneran, Jason Mulsow, Dorian S. Houser, Carolyn E. Schlundt; Neural representation of the self-heard biosonar click in bottlenose dolphins (Tursiops truncatus). J. Acoust. Soc. Am. 1 May 2017; 141 (5): 3379–3395. https://doi.org/10.1121/1.4983191
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