Jeffrey L. Pawloski

Echolocation signals and transmission beam pattern of a false killer whale (Pseudorca crassidens)

The echolocation transmission beam pattern of a false killer whale (Pseudorca crassidens) was measured in the vertical and horizontal planes. A vertical array of seven broadband miniature hydrophones was used to measure the beam pattern in the vertical plane and a horizontal array of the same hydrophones was used in the horizontal plane. The measurements were performed in the open waters of Kaneohe Bay, Oahu, Hawaii, while the whale performed a target discrimination task. Four types of signals, characterized by their frequency spectra, were measured. Type-1 signals had a single low-frequency peak at 40 +/- 9 kHz and a low-amplitude shoulder at high frequencies. Type-2 signals had a bimodal frequency characteristic with a primary peak at 46 +/- 7 kHz and a secondary peak at 88 +/- 13 kHz. Type-3 signals were also bimodal but with a primary peak at 100 +/- 7 kHz and a secondary peak at 49 +/- 9 kHz. Type-4 signals had a single high-frequency peak at 104 +/- 7 kHz. The center frequency of the signals were found to be linearly correlated to the peak-to-peak source level, increasing with increasing source level. The major axis of the vertical beam was directed slightly downward between 0 and -5 degrees, in contrast to the +5 to 10 degrees for Tursiops and Delphinapterus. The beam in the horizontal plane was directed forward between 0 degrees and -5 degrees.(ABSTRACT TRUNCATED AT 250 WORDS)

Temporary threshold shifts and recovery following noise exposure in the Atlantic bottlenosed dolphin (Tursiops truncatus)

Behaviorally determined hearing thresholds for a 7.5-kHz tone for an Atlantic bottlenosed dolphin (Tursiops truncatus) were obtained following exposure to fatiguing low-frequency octave band noise. The fatiguing stimulus ranged from 4 to 11 kHz and was gradually increased in intensity to 179 dB re 1 microPa and in duration to 55 min. Exposures occurred no more frequently than once per week. Measured temporary threshold shifts averaged 11 dB. Threshold determination took at least 20 min. Recovery was examined 360, 180, 90, and 45 min following exposure and was essentially complete within 45 min.

Dolphin hearing: Relative sensitivity as a function of point of application of a contact sound source in the jaw and head region

The auditory input area of the dolphin head was investigated in an unrestrained animal trained to beach itself and to accept noninvasive electroencephalograph (EEG) electrodes for the recording of the auditory brain-stem response (ABR). The stimulus was a synthetic dolphin click, transmitted from a piezo-electric transducer and coupled to the skin via a small volume of water. The results conform with earlier experiments on acute preparations that show best auditory sensitivity at the middle of the lower jaw. Minimum latency was found at the rear of the lower jaw. A shaded receiver configuration for the dolphin ear is proposed.

Modulation rate transfer functions to low-frequency carriers in three species of cetaceans

A temporal modulation rate transfer function (MRTF) is a quantitative description of the ability of a system to follow the temporal envelope of a stimulating waveform. In this study MRTFs were obtained from three cetacean species: the false killer whale Pseudorca crassidens; the beluga whale Delphinapterus leucas; and the bottlenosed dolphin Tursiops truncatus, using auditory-evoked potentials. Steady-state electrophysiological responses were recorded noninvasively from behaving, alert animals using suction cup electrodes placed on the scalp surface. Responses were elicited using continuous two-tone (TT) and sinusoidally amplitude-modulated (SAM) stimuli. MRTFs were obtained for modulation frequencies ranging from 18–4019 Hz using carrier and primary frequencies of 500, 1000, 4000, and 10000 Hz. Scalp potentials followed the low-frequency temporal envelope of the stimulating waveform; this envelope following response (EFR) was the dependent variable in all experiments. MRTFs were generally low-pass in shape with corner frequencies between approximately 1–2 kHz.

Evoked potential recording during echolocation in a false killer whale Pseudorca crassidens (L)

Auditory brainstem responses (ABRs) were recorded in a false killer whale while the animal echolocated a target. The ABR collection was triggered by echolocation clicks of the animal. In these conditions, the recorded ABR pattern contained a duplicate set of waves. A comparison of ABR wave delays recorded during echolocation with those recorded during regular external stimulation with experimenter generated clicks showed that the first set of waves may be a response to the emitted click whereas the second one may be a response to the echo. Both responses, to the emitted click and to the echo, were of comparable amplitude in spite of the intensity difference of these two sounds that may differ by more than 40 dB near the animal’s head. This finding indicates the presence of some mechanism of releasing responses to echoes from masking by loud emitted clicks. The evoked-potential method may be productive to investigate these mechanisms.

Echolocation in the Risso's dolphin, Grampus griseus

The Risso’s dolphin (Grampus griseus) is an exclusively cephalopod-consuming delphinid with a distinctive vertical indentation along its forehead. To investigate whether or not the species echolocates, a female Risso’s dolphin was trained to discriminate an aluminum cylinder from a nylon sphere (experiment 1) or an aluminum sphere (experiment 2) while wearing eyecups and free swimming in an open-water pen in Kaneohe Bay, Hawaii. The dolphin completed the task with little difficulty despite being blindfolded. Clicks emitted by the dolphin were acquired at average amplitudes of 192.6 dB re 1 μPa, with estimated sources levels up to 216 dB re 1 μPa-1 m. Clicks were acquired with peak frequencies as high as 104.7 kHz (Mfp=47.9 kHz), center frequencies as high as 85.7 kHz (Mf0=56.5 kHz), 3-dB bandwidths up to 94.1 kHz (MBW=39.7 kHz), and root-mean-square bandwidths up to 32.8 kHz (MRMS=23.3 kHz). Click durations were between 40 and 70 μs. The data establish that the Risso’s dolphin echolocates, and that, aside...

Detection of noise with rippled spectra by the Atlantic bottlenose dolphin

A dolphin was required to discriminate between rippled and nonrippled noise projected by an underwater transducer. Random noise was summed with its delayed replica to produce noise having ripples separated by 1/T Hz in the frequency domain, where T is the delay time. Three different experiments were conducted in which a dolphin was required to discriminate rippled and nonrippled noise using both cos+ and cos− stimuli. In the first experiment, the dolphin detected the cos− rippled stimulus at a correct response level of at least 75% for delays between 15 and 500 μs, and the cos+ rippled stimulus for delays of 13 to 190 μs. In the second experiment, the dolphin’s sensitivity to rippled noise was measured by attenuating the delayed replica for different delays. The dolphin was most sensitive for a delay of 100 μs. Its sensitivity at 100 μs was 5 dB better for the cos+ than the cos− stimuli. In the third experiment, broadband cos+ noise was also filtered in different 1/3 octave bands to determine if the anima...

Measuring recovery from temporary threshold shifts with evoked auditory potentials in the bottlenosed dolphin Tursiops truncatus

Temporary threshold shifts can be short‐lived in the bottlenosed dolphin and therefore difficult to measure with conventional trained behavioral psychophysical techniques. The time course of recovery from temporary threshold shifts was measured using evoked auditory potentials collected from a bottlenosed dolphin trained to wear rubber suction cups containing human EEG skin surface electrodes. During each session, following an initial measure of hearing thresholds using the evoked auditory potential procedure, the animal voluntarily positioned within a hoop 1 m underwater while 160 dB re 1 micropascal noise between 4 and 11 kHz was presented for 30 min. Immediately following the noise exposure, evoked thresholds were again obtained. The dolphin swam down into a second hoop located one meter in front of a calibrated hydrophone. Evoked potential thresholds were obtained 5, 10, 15, 25, 45, and 105 min following the exposure for amplitude modulated pure tones of 8, 11.2, 16, 22.5, and 32 kHz. Maximum shifts o...

Transmission beam pattern of a false killer whale

The echolocation transmission beam pattern of a false killer whale (Pseudorca crassidens) was measured in the vertical and horizontal planes. A vertical array of seven broadband miniature hydrophones was used to measure the beam pattern in the vertical plane and a horizontal array of the same hydrophones was used in the horizontal plane. The measurements were performed in the open waters of Kaneohe Bay, Oahu, Hawaii, with the whale performing a discrimination task. The width of the beams in both planes were similar to those of the Atlantic bottlenose dolphin (Tursiops truncatus), and broader than those of the beluga whale (Delphinapterus leucas). The major axis of the vertical beam was directed slightly downwards between 0° and −5°, in contrast to the +5 to 10° for Tursiops and Delphinapterus. The beam in the horizontal plane was directed forward. Differences in the fatty structure of the melon of Pseudorca, Tursiops, and Delphinapterus could explain differences in the elevation angle of the vertical beam...

Animal echolocation and signal processing

The echolocation capabilities of dolphins and small whales exceed those of current man-made sonars. Dolphins, beluga whales and false killer whales can perceive small targets presented over 110 m away, can classify target shapes independent of internal target reverberation, can discriminate wall thickness differences in targets of less than .2 mm, and can operate in high noise environments. Recent natural observations indicate that several species may also detect and choose targets buried in sediment. These tasks are accomplished through the use of range-gated clicks that tend to be broad band with peak frequencies exceeding 100 kHz. The short (50 microsec) pulses can have amplitudes exceeding 220 db and bandwidths exceeding 60 kHz. This paper provides a short review of animal echolocation capabilities, methodologies used to examine them, and potential uses of neural networks and other signal processing techniques to understand and perhaps duplicate those animal capabilities.<<ETX>>