Monaural and dichotic forward masking in the dolphin's auditory system.

Short-latency auditory-evoked potentials (AEPs) were recorded non-invasively in the bottlenose dolphin Tursiops truncatus. The stimuli were two sound clicks that were played either monaurally (both clicks to one and the same acoustic window) or dichotically (the leading stimulus (masker) to one acoustic window and the delayed stimulus (test) to the other window). The ratio of the levels of the two stimuli was 0, 10, or 20 dB (at 10 and 20 dB, the leading stimulus was of a higher level).

Forward masking in a bottlenose dolphin Tursiops truncatus: dependence on azimuthal positions of the masker and test sources.

Forward masking was investigated by the auditory evoked potentials (AEP) method in a bottlenose dolphin Tursiops truncatus using stimulation by two successive acoustic pulses (the masker and test) projected from spatially separated sources. The positions of the two sound sources either coincided with or were symmetrical relative to the head axis at azimuths from 0 to ± 90°. AEPs were recorded either from the vertex or from the lateral head surface next to the auditory meatus.

Ripple density resolution dependence on ripple width.

The goal of the study was to investigate how variations in ripple width influence the ripple density resolution. The influence of the ripple width was investigated with two experimental paradigms: (i) discrimination between a rippled test signal and a rippled reference signal with opposite ripple phases and (ii) discrimination between a rippled test signal and a flat reference signal. The ripple density resolution depended on the ripple width: the narrower the width, the higher the resolution.

Auditory evoked potential in stranded melon-headed whales (Peponocephala electra): With severe hearing loss and possibly caused by anthropogenic noise pollution.

Highly concentrated live mass stranding events of dolphins and whales happened in the eastern coast of China between June and October 2021. The current study adopted the non-invasive auditory evoked-potential technique to investigate the hearing threshold of a stranded melon headed whale (Peponocephala electra) at a frequency range of between 9.5 and 181 kHz.

The rate of cochlear compression in a dolphin: a forward-masking evoked-potential study.

The "active" cochlear mechanism of hearing manifests in the cochlear compression. Investigations of compression in odontocetes help to determine the frequency limit of the active mechanism. The compression may be evaluated by comparison of low- and on-frequency masking.

Evoked-potential audiogram variability in a group of wild Yangtze finless porpoises (Neophocaena asiaeorientalis asiaeorientalis).

Hearing is considered the primary sensory modality of cetaceans and enables their vital life functions. Information on the hearing sensitivity variability within a species obtained in a biologically relevant wild context is fundamental to evaluating potential noise impact and population-relevant management. Here, non-invasive auditory evoked-potential methods were adopted to describe the audiograms (11.

Rippled-spectrum resolution dependence on frequency: Estimates obtained by discrimination from rippled and nonrippled reference signals.

The resolution of spectral ripples is a useful test for the spectral resolution of hearing. However, the use of different measurement paradigms might yield diverging results because of a paradigm-dependent contribution of excitation-pattern and temporal-processing mechanisms. In the present study, ripple-density resolution was measured in normal-hearing listeners for several frequency bands (centered at 0.

Level-dependent masking of the auditory evoked responses in a dolphin: manifestation of the compressive nonlinearity.

At suprathreshold sound levels, interactions between masking noise and sound signals are liable to compressive nonlinearity in the auditory system. The compressive nonlinearity is a property of the "active" cochlear mechanism. It is not known whether this mechanism is capable to function at frequencies close to or above 100 kHz that are available to odontocetes (toothed whales, dolphins, and porpoises).

Adaptation in the auditory system of a beluga whale: effect of adapting sound parameters.

The effects of adapting sounds (pip trains or pure tones) on auditory evoked potentials (the rate following response, RFR) were investigated in a beluga whale. During RFR acquisition, adapting signals lasting 128 ms each were alternated with test signals lasting 16 ms each; the test signal levels varied randomly. Adapting signals were trains of cosine-enveloped tone pips or pure tones.

Eye Optics in Semiaquatic Mammals for Aerial and Aquatic Vision.

Based on anatomical measurements of refractive structures in the eye, the positions of focused images were computed for several groups of semiaquatic mammals: rodents, a nonpinniped semiaquatic carnivore (the sea otter), and pinniped carnivores (seals, sea lions, and the walrus). In semiaquatic rodents, eye optics enable emmetropia in the air but cause substantial hypermetropia in the water. In semiaquatic carnivores, there are several mechanisms for amphibious vision that focus images on the retina in both air and water.

Adaptation processes in the auditory system of a beluga whale Delphinapterus leucas.

The effects of prolonged sound stimuli (tone pip trains) on evoked potentials (the rate following response, RFR) were investigated in a beluga whale. The stimuli (rhythmic tone pips) were of 64 kHz frequency at levels from 80 to 140 dB re 1 μPa. During stimulation, every 1000 ms stimulus level either was kept constant (the steady-state stimulation) or changed up/down by 20 or 40 dB.

Contribution of Cochlear Compression to Discrimination of Rippled Spectra in On- and Low-frequency Noise.

The goal of the study was to assess cochlear compression when rippled-spectrum signals are perceived in noise assuming that the noise might produce both masking and confounding effects. In normal listeners, discrimination between rippled signals with and without ripple phase reversals was assessed in background noise. The signals were band-limited (0.

Hearing sensitivity to gliding rippled spectrum patterns.

The sensitivity of human hearing to gliding rippled spectrum patterns of sound was investigated. The test signal was 2-oct wide rippled noise with the ripples gliding along the frequency scale. Both ripple density and gliding velocity were frequency-proportional across the signal band; i.

Four odontocete species change hearing levels when warned of impending loud sound.

Hearing sensitivity change was investigated when a warning sound preceded a loud sound in the false killer whale (Pseudorca crassidens), the bottlenose dolphin (Tursiops truncatus), the beluga whale (Delphinaperus leucas) and the harbor porpoise (Phocoena phocoena). Hearing sensitivity was measured using pip-train test stimuli and auditory evoked potential recording. When the test/warning stimuli preceded a loud sound, hearing thresholds before the loud sound increased relative to the baseline by 13 to 17 dB.

Discrimination of rippled-spectrum patterns in noise: A manifestation of compressive nonlinearity.

In normal-hearing listeners, rippled-spectrum discrimination was psychophysically investigated in both silence and with a simultaneous masker background using the following two paradigms: measuring the ripple density resolution with the phase-reversal test and measuring the ripple-shift threshold with the ripple-shift test. The 0.5-oct wide signal was centered on 2 kHz, the signal levels were 50 and 80 dB SPL, and the masker levels varied from 30 to 100 dB SPL.

Auditory sensitivity to local stimulation of the head surface in a beluga whale (Delphinapterus leucas).

Using the auditory evoked response technique, sensitivity to local acoustic stimulation of the ventro-lateral head surface was investigated in a beluga whale (Delphinapterus leucas). The stimuli were tone pip trains of carrier frequencies ranging from 16 to 128 kHz with a pip rate of 1 kHz. For higher frequencies (90-128 kHz), the low-threshold point was located next to the medial side of the middle portion of the lower jaw.

Conditioned hearing sensitivity change in the harbor porpoise (Phocoena phocoena).

Hearing sensitivity, during trials in which a warning sound preceding a loud sound, was investigated in two harbor porpoises (Phocoena phocoena). Sensitivity was measured using pip-train test stimuli and auditory evoked potential recording. When a hearing test/warning stimulus, with a frequency of either 45 or 32 kHz, preceded a loud 32 kHz tone with a sound pressure level of 152 dB re 1 μPa root mean square, lasting 2 s yielding an sound exposure level (SEL) of 155 dB re 1 μPa(2)s, pooled hearing thresholds measured just before the loud sound increased relative to baseline thresholds.

Retinal Ganglion Cell Topography and Retinal Resolution in the Baikal Seal (Pusa sibirica).

The total number, size, topographic distribution, and cell density of ganglion cells were studied in retinal wholemounts of Baikal seals (Pusa sibirica). The ganglion cell size varied from 10 to 38 μm. A distinct cell group consisted of large ganglion cells of more than 30 μm in diameter.

Auditory evoked potentials in the auditory system of a beluga whale Delphinapterus leucas to prolonged sound stimuli.

The effects of prolonged (up to 1500 s) sound stimuli (tone pip trains) on evoked potentials (the rate following response, RFR) were investigated in a beluga whale. The stimuli (rhythmic tone pips) were of frequencies of 45, 64, and 90 kHz at levels from 20 to 60 dB above threshold. Two experimental protocols were used: short- and long-duration.

Expectancy and conditioned hearing levels in the bottlenose dolphin (Tursiops truncatus).

The hearing sensitivity of a bottlenose dolphin for a warning sound, when the exact time of the arrival of a loud sound could or could not be predicted, was measured. Sensitivity was measured when the time of onset of the loud sound was randomly varied (random-variation sessions) and when the time of onset of the loud sound and the pattern of stimulus levels was constant (fixed-stimulus sessions). The loud sound was kept the same in both of the series.