Biomedical subjects

C W Turl

Publications and source records attributed to C W Turl.

4 recordsLinked to original sources

PubMed1987

Comparison of target detection capabilities of the beluga and bottlenose dolphin.

The echolocation detection capabilities of a beluga (Delphinapterus leucas) and an Atlantic bottlenose dolphin (Tursiops truncatus) were directly compared in a target detection experiment. Both animals were trained to detect targets in the presence of masking noise. Targets were stainless-steel, water-filled spheres 7.62 and 22.86 cm in diameter. Target ranges of 16.5 and 40 m were used with the 7.62-cm sphere and 80 m with the 22.86-cm sphere. Masking noise with a flat spectrum from 40-160 kHz was projected from a spherical transducer placed 4 or 5 m, depending on the target distance, from the animal hoop station in line with the target. Target detection performance was determined as a function of masking noise level at each target range. The echo-to-noise ratio (Ee/No)max for the beluga at the 75% correct response threshold was approximately 1.0 dB compared to about 10 dB for the dolphin. The differences of each animal's detection performance across the three ranges were consistent with target strength and transmission loss differences. It is speculated that the difference in performance between the two species may be due to differences in critical bandwidth, signal processing capability, or echolocation strategy.

Acoustic Stimulation↗

PubMed1987

Propagation of beluga echolocation signals.

The propagation characteristics of high-frequency echolocation signals (peak energies above 100 kHz) of the beluga (Delphinapterus leucas) were measured while the animal performed a target detection task. The whale was trained to station on a bite plate so that its transmission beam could be measured in the vertical and horizontal planes using hydrophone arrays. The transitional region between the acoustic near- and farfields was also located using an array of hydrophones that extended directly in front of the animal in the horizontal plane. Three distinct modes of signals were observed. Mode 1 signals had click intervals greater than the time required for the signals to travel to the target and back (two-way transit time). Mode 2 signals had click intervals shorter than the two-way transit time, and mode 3 signals had high repetition rates with an average click interval of 1.7 ms, approximately 2% of the two-way transit time. The average click intervals for the modes 1 and 2 signals were 193 and 44 ms, respectively. The vertical and horizontal beam patterns of the mode 1 signals had similar 3-dB beamwidths of approximately 6.5 degrees. The major axis of the vertical beam was directed approximately 5 degrees above the plane defined by the animal's teeth. The near- to farfield transition region was approximately 0.64-0.75 m from the tip of the animal's mouth.

Animals↗

PubMed1986

Target detection by the beluga using a surface-reflected path.

During an echolocation-in-noise experiment we suspected that a beluga (Delphinapterus leucas) was using a surface-reflected path to maximize detection performance. We tested and confirmed this suspicion by acoustically and mechanically denying access to surface path information. The whale's performance varied as the surface-reflected path was denied.

Animals↗

PubMed1983

Target detection in reverberation by an echolocating Atlantic bottlenose dolphin (Tursiops truncatus).

An experiment was conducted to determine the ability of an echolocating Atlantic bottlenose dolphin (Tursiops truncatus) to detect targets in the presence of reverberation. Reverberation was induced by a clutter screen consisting of forty-eight 5.1-cm-diam cork spheres spaced 15.2 cm apart and arranged in a rectangular array, located behind the targets. Hollow aluminum cylinders having the same outer diameter and wall thickness and three different lengths were used as targets. The dolphin was trained to station in a hoop, 6 m from the targets, and to echolocate the target upon the reception of an audio cue. Only one of the targets would be presented in a target-present trial. Data were collected on the animal's detection performance as a function of the separation distance between the clutter screen and the targets. The animal's performance for the smallest cylinder varied from 91% to 55% correct as the separation distance decreased from 10.2 to 0 cm. The target strength of the clutter screen and the cylinders were measured both in terms of the energies and the maximum peak-to-peak amplitudes of the incident and reflected echoes. These measurements indicated that when the target-clutter screen separation distance was 0 cm, the dolphin's 50% correct detection occurred at an energy echo-to-reverberation ratio of approximately 0.25 dB and at peak-to-peak echo-to-reverberation ratio of 2.6 dB. The results also indicated that the dolphin's performance varied almost linearly with the echo-to-reverberation ratio. The animal's pulse emissions were monitored by a microprocessor system and the results are presented in terms of the average number of clicks and the average response latency, as a function of the separation distance.

Animals↗