01996nas a2200181 4500008004100000022001400041245016200055210006900217260001600286300001600302490000800318520134700326100001801673700002401691700002401715700002401739856005101763 2018 eng d a0001-496600aForward masking recovery in bottlenose dolphins ( Tursiops truncatus): Auditory brainstem responses to paired-click stimuli in high-pass masking noise0 aForward masking recovery in bottlenose dolphins iTursiops trunca cJan-09-2018 a1740 - 17400 v1443 a

Adaptation is a fundamental process in the auditory system and underlies the automatic gain control system of echolocating bottlenose dolphins. As pulse-echo delay increases, auditory brainstem response (ABR) amplitudes to the echoes progressively increase. This study examined adaptation across cochlear frequency regions using a paired-click (i.e., forward masking) paradigm and high-pass masking noise. Bottlenose dolphins passively listened to paired click stimuli (20–160 kHz “pink” spectra). A “conditioning” click was followed by a “probe” click with equal amplitude and a time delay ranging from 125 to 750 μs. ABRs to click pairs were obtained with and without high-pass masking noise that precluded the basal turn of the cochlea from responding to the click stimuli. The ABR evoked by a single click (temporally aligned with the first click of the paired-click condition) was subtracted from the click-pair ABR to visualize the response evoked by the probe click. Probe ABR amplitudes recovered linearly with increasing delay relative to the conditioning click, and were approximately 70% of full response amplitude at 750-μs delay. Paired-click interval ABR amplitude recovery functions were similar for the unmasked and high-pass masked conditions. [Work sponsored by ONR.]

1 aMulsow, Jason1 aCoffinger, Sean, P.1 aFinneran, James, J.1 aBurkard, Robert, F. uhttp://asa.scitation.org/doi/10.1121/1.506771802022nas a2200193 4500008004100000022001400041245012000055210006900175260001600244300001600260490000800276520139100284100001901675700001801694700002601712700002401738700001501762856005101777 2018 eng d a0001-496600aBottlenose dolphin ( Tursiops truncatus) vocal modifications in response to spectrally pink background noise0 aBottlenose dolphin iTursiops truncatusi vocal modifications in r cJan-09-2018 a1742 - 17420 v1443 a

The increase of oceanic shipping is a global predicament. The resulting proliferation of underwater noise levels is a serious concern for marine mammal welfare, as it has the potential to interfere with the communicative signals of bottlenose dolphins (Tursiops truncatus). The Lombard effect and other noise-induced vocal modifications may be employed to compensate for reduced signal-to-noise ratios. This study aimed to determine which vocal modifications dolphins use during experimentally controlled background noise conditions. Three dolphins (ages 30–52) participated in behavioral hearing tests using an adaptive up-down staircase, go/no-go procedure with 15 or 40 kHz tones. Tones decreased by 3 dB increments if a dolphin responded to the tone with a conditioned whistle, and increased by 3 dB if they did not. Dolphins performed this task during ambient noise (control) conditions, as well as three elevated bandpass noise (experimental) conditions: 0.6–5 kHz (115 dB re 1 μPa) and 0.6–10 kHz (115 and 125 dB re 1 μPa). The acoustic parameters of the dolphins’ response whistles and victory squeals, such as duration, frequency, amplitude, and response latency, were analyzed and compared between control and noise conditions. These data provide a complement to field studies of odontocete noise-induced vocal modifications in the wild.

1 aZapetis, Maria1 aMulsow, Jason1 aSchlundt, Carolyn, E.1 aFinneran, James, J.1 aLyn, Heidi uhttp://asa.scitation.org/doi/10.1121/1.506772401960nas a2200181 4500008004100000022001400041245015000055210006900205260001600274300001600290490000800306520132700314100002001641700002401661700001801685700002401703856005101727 2018 eng d a0001-496600aDependence of bottlenose dolphin (Tursiops truncatus) auditory brainstem responses on noise burst rise time, amplitude, and envelope shape0 aDependence of bottlenose dolphin iTursiops truncatusi auditory b cJan-09-2018 a1741 - 17410 v1443 a

A series of experiments examined the dependence of dolphin auditory brainstem response (ABR) peak amplitudes and latencies by stimulus level, rise times, and envelope shape. Stimuli were spectrally “pink” noise bursts with frequency content from 10 to 160 kHz, rise times that varied from 32 μs to 4 ms, and plateau sound pressure levels from 102 to 138 dB re 1 μPa. Cosine and cosine-cubed rise (and fall) envelopes were tested, and results were compared to those obtained for dolphins using noise bursts with linear rise envelopes [Finneran et al., J. Acoust. Soc. Am. 143, 2914–2921 (2018)]. Results for the cosine and cosine-cubed envelopes showed that ABR peak amplitudes were a function of envelope sound pressure at the end of a fixed integration window of approximately 260 μs. This is congruent with the previous findings for linear envelopes. The ABR peak latencies for the cosine and cosine-cubed envelopes were dependent on the second derivative of the envelope pressure function, as opposed to the first derivative of the pressure function for linear envelopes. These data are consistent with single-unit and nearfield response data for terrestrial mammals. [Work supported by Navy Living Marine Resources and SSC Pacific Naval Innovative Science and Engineering Programs.]

1 aJones, Ryan, A.1 aFinneran, James, J.1 aMulsow, Jason1 aBurkard, Robert, F. uhttp://asa.scitation.org/doi/10.1121/1.506772202099nas a2200181 4500008004100000022001400041245006900055210006900124260001600193300001600209490000800225520154400233100002401777700002301801700002401824700001801848856005101866 2018 eng d a0001-496600aPassive echo detection and discrimination in bottlenose dolphins0 aPassive echo detection and discrimination in bottlenose dolphins cJan-09-2018 a1741 - 17410 v1443 a

Echolocation in bottlenose dolphins (Tursiops truncatus) is an active process involving outgoing signal transmission and echo reception. Transmitted echolocation “clicks” interact with a target to produce echoes that contain representative information about the target. Echolocation allows dolphins to detect, discriminate, and identify complex targets using only their hearing. However, it is unclear whether dolphins capitalize on an internal representation of echolocation clicks for matched filter processing or whether the same information (and performance) can be obtained through passive echo reception (i.e., without a corresponding ensonifying click). Here, we investigate the passive echo discrimination ability of a bottlenose dolphin by embedding a target echo in a stream of distractor echoes with similar spectral and time-domain characteristics. Initial testing has demonstrated excellent echo-discrimination ability in the light of multiple distractor echoes of similar amplitude. Additional testing is underway with expanded distractor sets and echo-ordering complexity. The paradigm specifically investigates the plausibility of perceptual identification without the potential for matched filter processing. If representational identity is attainable via a passive process and not degraded relative to active echolocation, then the function of the echolocation click might not serve in matched filter processing, though it would remain important for ensonification and in determining target location.

1 aCoffinger, Sean, P.1 aHouser, Dorian, S.1 aFinneran, James, J.1 aMulsow, Jason uhttp://asa.scitation.org/doi/10.1121/1.506772101622nas a2200193 4500008004100000022001400041245011200055210007100167260001600238300001600254490000800270520098500278100002601263700001801289700002701307700002401334700001901358856005101377 2018 eng d a0001-496600aDirectional hearing sensitivity for 2–30 kHz sounds in the bottlenose dolphin (Tursiops truncatus)0 aDirectional hearing sensitivity for 2–30 kHz sounds in the bottl cJan-09-2018 a1741 - 17410 v1443 a

Bottlenose dolphins (Tursiops truncatus) depend on sounds with frequencies <30 kHz for social communication and foraging, but little information on the directional dependence of hearing thresholds for these sounds exists. This study measured behavioral hearing thresholds for 2, 10, 20, and 30-kHz tones projected from eight different angular positions around the dolphin in both the horizontal and vertical planes to determine whether the receiving beam at these frequencies was directional. Omni-directional hearing was hypothesized for sounds below 30 kHz, but this hypothesis was rejected. Results from two bottlenose dolphins demonstrated a positive relationship between directivity and the frequency of the test tone, with asymmetric beam patterns. Directional hearing sensitivity declined most dramatically between 10 kHz and 2 kHz. The results suggest that dolphins’ directional hearing is more pronounced for lower frequencies than previously predicted.

1 aAccomando, Alyssa, W.1 aMulsow, Jason1 aBranstetter, Brian, K.1 aFinneran, James, J.1 aJenkins, Keith uhttp://asa.scitation.org/doi/10.1121/1.5067720