Michael D. Gray

Local acoustic particle motion guides sound-source localization behavior in the plainfin midshipman fish, Porichthys notatus

SUMMARY Sound-source localization behavior was studied in the plainfin midshipman fish (Porichthys notatus) by making use of the naturally occurring phonotaxis response of gravid females to playback of the males advertisement call. The observations took place outdoors in a circular concrete tank. A dipole sound projector was placed at the center of the tank and an 80–90 Hz tone (the approximate fundamental frequency to the males advertisement call) was broadcast to gravid females that were released from alternative sites approximately 100 cm from the source. The phonotaxic responses of females to the source were recorded, analyzed and compared with the sound field. One release site was approximately along the vibratory axis of the dipole source, and the other was approximately orthogonal to the vibratory axis. The sound field in the tank was fully characterized through measurements of the sound pressure field using hydrophones and acoustic particle motion using an accelerometer. These measurements confirmed that the sound field was a nearly ideal dipole. When released along the dipole vibratory axis, the responding female fish took essentially straight paths to the source. However, when released approximately 90 deg to the sources vibratory axis, the responding females took highly curved paths to the source that were approximately in line with the local particle motion axes. These results indicate that the acoustic cues used by fish during sound-source localization include the axes of particle motion of the local sound field.

Use of the swim bladder and lateral line in near-field sound source localization by fish

We investigated the roles of the swim bladder and the lateral line system in sound localization behavior by the plainfin midshipman fish (Porichthys notatus). Reproductive female midshipman underwent either surgical deflation of the swim bladder or cryoablation of the lateral line and were then tested in a monopolar sound source localization task. Fish with nominally ‘deflated’ swim bladders performed similar to sham-deflated controls; however, post-experiment evaluation of swim bladder deflation revealed that a majority of ‘deflated’ fish (88%, seven of the eight fish) that exhibited positive phonotaxis had partially inflated swim bladders. In total, 95% (21/22) of fish that localized the source had at least partially inflated swim bladders, indicating that pressure reception is likely required for sound source localization. In lateral line experiments, no difference was observed in the proportion of females exhibiting positive phonotaxis with ablated (37%) versus sham-ablated (47%) lateral line systems. These data suggest that the lateral line system is likely not required for sound source localization, although this system may be important for fine-tuning the approach to the sound source. We found that midshipman can solve the 180 deg ambiguity of source direction in the shallow water of our test tank, which is similar to their nesting environment. We also found that the potential directional cues (phase relationship between pressure and particle motion) in shallow water differs from a theoretical free-field. Therefore, the general question of how fish use acoustic pressure cues to solve the 180 deg ambiguity of source direction from the particle motion vector remains unresolved.

Threshold of hearing for swimming Bluefin tuna (Thunnus orientalis)

Hearing thresholds for three pairs of 1 m long Pacific bluefin tuna (Thunnus orientalis) were measured utilizing operant conditioning procedure with a food reward and a staircase psychophysical technique. Fish, swimming at 1–4 m/s, quickly learned to approach the feed when they heard a sound. Measurements were made at the Tuna Research and Conservation Center (Stanford University) in a 9.14 m diameter, 1.65 m deep indoor cylindrical tank. The acoustic stimulus was produced by radially oriented piezoelectric line sources centered at the bottom of the tank, which produced a circumferentially uniform sound field. The acoustics of the tank was thoroughly characterized for both acoustic pressure and particle motion using hydrophones and two neutrally buoyant accelerometers with response axes oriented in the radial and vertical directions. Thresholds, expressed in terms of pressure and particle acceleration, were obtained at six sinusoidal frequencies between 325 Hz and 800 Hz, a range that was limited by sourc...

Range discrimination in ultrasonic vibrometry: Theory and experiment

A technique has been developed to demodulate periodic broadband ultrasonic interrogation signals that are returned from multiple scattering sites to simultaneously determine the low-frequency displacement time histories of each individual site. The technique employs a broadband periodic transmit signal. The motions of scattering sites are separately determined from the echoed receive signal by an algorithm involving comb filtering and pulse synthesis. This algorithm permits spatial resolution comparable to pulse-echo techniques and displacement sensitivities comparable to pure-tone techniques. A system based on this technique was used to image transient audio-frequency displacements on the order of 1-10 μm peak (≥ 50 nm/√Hz) that were produced by propagating shear waves in a tissue phantom. The system used concentric transmitting and receiving transducers and a carrier signal centered at 2.5 MHz with an 800 kHz bandwidth. The system was self-noise-limited and capable of detecting motions of strongly reflecting regions on the order of 1 nm/√Hz. System performance is limited by several factors including signal selection, component hardware, and ultrasonic propagation within the media of interest.

In vivo ultrasonic attenuation in cetacean extracranial soft tissues

In vivo ultrasonic attenuation was estimated for extracranial soft tissues of two Tursiops truncatus and one Delphinapterus leucas. Backscatter data were non-invasively collected as part of routine health-based ultrasound examinations using a transducer operating in the 2.0–3.5 MHz frequency range. Data sets collected over the proximal mandible and temporal regions were processed to yield estimates of attenuation using a reference tissue phantom whose properties had been independently determined. The estimated attenuations were at the low end of the range of reported values for in vitro mammalian fatty and connective tissues.

Ultrasonic vibrometer for tissue characterization

Ultrasonic vibrometers are well suited to a variety of tissue‐characterization tasks because they exploit the lateral resolution and depth of field available with diagnostic ultrasound systems for measurements at lower frequencies. In the past, ultrasonic vibrometers have been used to measure the motion of surfaces with high impedance contrast to their surroundings (otoliths, swim bladders, and lung tissue). New ultrasonic vibrometry techniques have been developed and tested that permit calibrated real‐time (amplitude and phase) transduction of sub‐nanometer‐amplitude vibrations at audio frequencies. These can be configured using either analog or digital demodulation for carrier signals up to 10 MHz. In the fully digital configuration, the vibrometer offers better displacement resolution than has been previously reported for analog systems. It also has the capability to simultaneously distinguish between the displacements of multiple discrete vibrating scatterers or regions within a continuum of scatterer...

Dual confocal ultrasound system for shear wave elastography

A dual confocal transducer system for ultrasound‐based elastography is presented. The system is intended to noninvasively measure the complex shear speed in cetacean head tissues, including brain, jaw fat, and melon. The system instrumentation features a pair of dual‐element confocal ultrasound transducers, one of which is used to remotely generate low frequency (100‐1000 Hz) shear waves in soft tissues via radiation force, and the other is used to measure the resulting shear wave displacements using Doppler techniques. One transducer is configured as an open ring into which the other transducer can be placed and translated. The relative positions of the transducers are mechanically manipulated in order to measure short‐path propagation and estimate shear wave speed and loss. Work supported by ONR.

Nondestructive inspection system for corrosion detection in fuel tank liners

An ultrasonic, nondestructive inspection system for the early detection of corrosion in fuel tank aluminum liners was developed and tested. A Labview‐controlled scanner, which rode on the tank’s resident rib braces, housed a 10‐MHz transducer and a miniature video camera. The bi‐directional (axial, azimuthal) scan resolution was controlled by adjusting the surface standoff distance of the focused transducer to produce variable‐area interrogation sites. The phenomenon of increased backscatter from corrosion‐roughened surfaces was exploited to detect the presence of corrosion in its early stages. The transducer acted as both transmitter and receiver, capturing the echoes from the subject surface while the video camera captured an image of the surface under acoustic inspection. The acoustic and visual data were overlayed to form a composite image of the entire inspection surface. The system was field‐tested using two tanks pulled from active duty at the Marine Corps maintenance facility in Cherry Point, NC. ...

Startle reflex in fish

Directional hearing in fish is a poorly understood phenomenon, whose complexity makes it difficult to analyze. The directional, Mauthner cell mediated, startle response, which does not involve the CNS, is considerably simpler and more amenable to analysis but may still provide insight into the algorithms and mechanisms for more general directional hearing tasks. The startle reflex is modeled and studied experimentally in goldfish. The basic model posits that the initial polarity of both the incident acoustic pressure and particle acceleration measured by the fish’s auditory system determines the direction of a threat, and initiates an escape reflex in the appropriate direction. The startle reflex of goldfish is observed experimentally in a large acoustic test tank at Georgia Tech. The subject is placed in the center of the tank, and its behavior is observed using a video camera. The acoustic stimulus is generated using simple spherical sources driven to provide independent control of pressure and velocity...

Passive acoustic mapping and B-mode ultrasound imaging utilizing compressed sensing for real-time monitoring of cavitation-enhanced drug delivery

Ultrasound imaging presents a high-speed, low-cost approach for monitoring of focused ultrasound (FUS) therapy, and includes both conventional (B-mode) sonography and passive acoustic mapping (PAM) of acoustic emissions (Gyongy et al., 2010, Salgaonkar et al., 2009). Incorporation of novel algorithms and other signal processing techniques have improved the resolution and processing speed of PAM. However, while hardware developments such as increasing channel counts provide unprecedented data capture ability, real-time processing of the growing data stream presents an evolving challenge. Previous work has employed sparse array processing techniques for PAM including matching and basis pursuit (Gyongy & Coviello, 2011) and co-array processing (Coviello et al, 2012). Here we propose to extend PAM utilizing compressed sensing (CS). Acoustic emissions from FUS may be sparse in several domains, e.g. due to limited regions of space and time in which cavitation is likely from a focused transducer, and correlation...