Place specificity of the click-evoked auditory brainstem response in the bottlenose dolphin (Tursiops truncatus)

Abstract

Cochlear place specificity of the auditory brainstem response (ABR) was investigated in five bottlenose dolphins by measuring ABRs to broadband clicks presented simultaneously with masking noise having various high-pass cutoff frequencies. Click and noise stimuli were digitally compensated to account for the transmitting response of the piezoelectric transducers and any multipath propagation effects to achieve "white" or "pink" spectral characteristics. Narrowband evoked responses were derived by sequentially subtracting responses obtained with noise at lower high-pass cutoff frequencies from those obtained with noise having higher cutoff frequencies. The results revealed little contribution to the click-evoked brainstem response from frequency bands below 10 kHz and, in dolphins with full hearing bandwidth, the largest amplitude derived band evoked responses were obtained from the highest frequency bands. Narrowband latencies decreased with increasing frequency and were adequately fit with a power function exhibiting relatively large change in latency with frequency below ∼30 kHz and little change above ∼30 kHz. These data demonstrate that frequency bands below ∼10 kHz do not substantively contribute to the farfield ABR in the bottlenose dolphin when using place-specific approaches such as high-pass subtractive-masking techniques.

Dolphin echolocation behaviour during active long-range target approaches

“…Two trained bottlenose dolphins, T. truncatus (Montagu 1821) -SAY (36 year old female, ∼220 kg) and TRO (23 year old male, ∼180 kg)with previous long-range echolocation training experience (Finneran, 2013;Finneran et al, 2014) and normal high-frequency hearing (Finneran et al, 2016b) participated in the study. The dolphins belonged to the US Navy Marine Mammal Program (MMP) population and were regular participants in Navy MMP psychophysical research.…”

The effects of click rate on the auditory brainstem response of bottlenose dolphins

“…ABR peak latencies were on average $0.1 ms longer in the HI animals than the NH animals in the present study at low rates. In the Finneran et al (2016) high-pass masking study, the two NH animals showed mean latency differences (averaged across the various peaks) of 0.04 and 0.08 ms between the unmasked white click and the white click with 56 kHz high-pass noise. Again, considering all of the differences in the present study and the Finneran et al (2016) report, these results are in remarkably good agreement.…”

“…In the Finneran et al (2016) high-pass masking study, the two NH animals showed mean latency differences (averaged across the various peaks) of 0.04 and 0.08 ms between the unmasked white click and the white click with 56 kHz high-pass noise. Again, considering all of the differences in the present study and the Finneran et al (2016) report, these results are in remarkably good agreement. Simply put, in those animals with a high-frequency hearing loss, the latency increase relative to that of the NH dolphins likely reflects the traveling wave delay from the extreme base of the cochlea to the cochlear place where normal or near-normal hearing function is achieved.…”

“…It seems likely that this simply reflects the absence of a response from the basal regions of the cochlea in the HI dolphins. Finneran et al (2016) assessed the effects FIG. 8.…”

Neural representation of the self-heard biosonar click in bottlenose dolphins (Tursiops truncatus)

“…In the biosonar experiment, auditory brainstem responses (ABRs) to the self-heard biosonar click were measured in two dolphins during an echolocation task (e.g., see Supin et al, 2003). To isolate individual regions of the cochlea and obtain cochlear place-specific ABRs, masking noise was presented to the dolphins during the echolocation task, and the subtractive high-pass noise (HPN) technique (Teas et al, 1962;Don and Eggermont, 1978;Finneran et al, 2016b) was used to derive narrowband ABRs from ABRs to the broadband biosonar clicks. In this method, ABRs are measured in the presence of a broadband stimulus (e.g., the self-heard click) and high-pass masking noise, with the noise high-pass cutoff frequency adjusted to cover the frequency range of interest.…”