Aleks Zosuls

A hydromechanical biomimetic cochlea: Experiments and models

The construction, measurement, and modeling of an artificial cochlea (ACochlea) are presented in this paper. An artificial basilar membrane (ABM) was made by depositing discrete Cu beams on a piezomembrane substrate. Rather than two fluid channels, as in the mammalian cochlea, a single fluid channel was implemented on one side of the ABM, facilitating the use of a laser to detect the ABM vibration on the other side. Measurements were performed on both the ABM and the ACochlea. The measurement results on the ABM show that the longitudinal coupling on the ABM is very strong. Reduced longitudinal coupling was achieved by cutting the membrane between adjacent beams using a laser. The measured results from the ACochlea with a laser-cut ABM demonstrate cochlear-like features, including traveling waves, sharp high-frequency rolloffs, and place-specific frequency selectivity. Companion computational models of the mechanical devices were formulated and implemented using a circuit simulator. Experimental data were compared with simulation results. The simulation results from the computational models of the ABM and the ACochlea are similar to their experimental counterparts.

A prediction of the minke whale (Balaenoptera acutorostrata)middle-ear transfer function

The lack of baleen whale (Cetacea Mysticeti) audiograms impedes the assessment of the impacts of anthropogenic noise on these animals. Estimates of audiograms, which are difficult to obtain behaviorally or electrophysiologically for baleen whales, can be made by simulating the audiogram as a series of components representing the outer, middle, and inner ear (Rosowski, 1991; Ruggero and Temchin, 2002). The middle-ear portion of the system can be represented by the middle-ear transfer function (METF), a measure of the transmission of acoustic energy from the external ear to the cochlea. An anatomically accurate finite element model of the minke whale (Balaenoptera acutorostrata) middle ear was developed to predict the METF for a mysticete species. The elastic moduli of the auditory ossicles were measured by using nanoindentation. Other mechanical properties were estimated from experimental stiffness measurements or from published values. The METF predicted a best frequency range between approximately 30 Hz and 7.5 kHz or between 100 Hz and 25 kHz depending on stimulation location. Parametric analysis found that the most sensitive parameters are the elastic moduli of the glove finger and joints and the Rayleigh damping stiffness coefficient β. The predicted hearing range matches well with the vocalization range.

Middle-ear stiffness of the bottlenose dolphin tursiops truncatus

Previous research on the cetacean auditory system has consisted mostly of behavioral studies on a limited number of species. Little quantitative physiologic data exists on cetacean hearing. The frequency range of hearing varies greatly across different mammalian species. Differences among species correlate with differences in the middle-ear transfer function. Middle-ear transfer functions depend on the mechanical stiffness of the middle ear and the cochlear input impedance. The purpose of this study was to measure the middle-ear stiffness for the bottlenose dolphin (Tursiops truncatus), a species specialized for underwater high-frequency hearing and echolocation. Middle-ear stiffness was measured with a force probe that applied a known displacement to the stapes and measured the restoring force. The average middle-ear stiffness in ten dolphin ears was 1.37 N/mum, which is considerably higher than that reported for most terrestrial mammals. The relationship between middle-ear stiffness and low-frequency hearing cutoff in Tursiops was shown to be comparable to that of terrestrial mammals

Prediction of a Mysticete Audiogram via Finite Element Analysis of the Middle Ear

The impact of anthropogenic sound on marine mammals is difficult to assess, especially for species without available audiograms. There are currently no audiograms for any species of mysticete because of their size and, in many cases, their endangerment status. Consequently, insight into the hearing range of all mysticete species comes from indirect sources such as vocalization recordings. In contrast to mysticetes, several odontocete species have published audiograms.

Elastic Modulus of Cetacean Auditory Ossicles

In order to model the hearing capabilities of marine mammals (cetaceans), it is necessary to understand the mechanical properties, such as elastic modulus, of the middle ear bones in these species. Biologically realistic models can be used to investigate the biomechanics of hearing in cetaceans, much of which is currently unknown. In the present study, the elastic moduli of the auditory ossicles (malleus, incus, and stapes) of eight species of cetacean, two baleen whales (mysticete) and six toothed whales (odontocete), were measured using nanoindentation. The two groups of mysticete ossicles overall had lower average elastic moduli (35.2 ± 13.3 GPa and 31.6 ± 6.5 GPa) than the groups of odontocete ossicles (53.3 ± 7.2 GPa to 62.3 ± 4.7 GPa). Interior bone generally had a higher modulus than cortical bone by up to 36%. The effects of freezing and formalin‐fixation on elastic modulus were also investigated, although samples were few and no clear trend could be discerned. The high elastic modulus of the ossicles and the differences in the elastic moduli between mysticetes and odontocetes are likely specializations in the bone for underwater hearing. Anat Rec, 297:892–900, 2014.

MECHANICAL RESPONSE OF THE BASILAR MEMBRANE TO LATERAL MICROMANIPULATION

The role of wave propagation in the cochlea can be founded on detailed knowledge of the mechanical properties of the basilar membrane. In this study, measurements of lateral point stiffness and longitudinal coupling were made on gerbil basilar membranes in vitro. We designed an integrated optical imaging system and basilar membrane manipulator, in which a calibrated glass micropipette is used to displace the basilar membrane laterally. Because the tissue deformations occur in the optical plane of the microscope objective, detailed images of the movement of the basilar membrane ultrastructure are obtained. The motion is measured by matching features in successive images. It was found that the lateral point stiffness in the arcuate zone is 0.2–0.5 N/m, in the pectinate zone is 2–3 N/m, and increases to over 10 N/m near the spiral ligament. To compute the longitudinal coupling, the displacement field was measured quantitatively using image registration. It was found that the tissue in compression has a space constant of 7.6 μm and the tissue in tension has a longer space constant of 10.5 μm. The correlation of mechanical properties to anatomically distinct regions of the basilar membrane supports the conclusion that these regions serve different functional roles.

PREDICTING CETACEAN AUDIOGRAMS

during playback of bottlenose dolphin sounds is similar to the observed behaviour of other species of fish such as Gulf toadfish (Remage-Healey et al. 2006) and silver perch (Luczkovich et al. 2000). Both of these species suppressed vocalizations in apparent response to low-frequency sounds made by bottlenose dolphin. Similarly, Mann et al. (1998) observed that American shad Alosa sapidissima are able to detect simulated dolphin echolocations, although at much higher frequencies (100-180 kHz) than we used here.

How is sound conducted to the cochlea in toothed whales

Toothed whales (Odontocetes) typically have small occluded ear canals and sea water has a characteristic impedance that is much more similar to the impedance of soft tissues of the head than is the case for the air-tissue interface in terrestrial mammals. This makes it plausible that significant acoustic energy is being transmitted to their middle ear by tissue conduction. In addition, some authors have proposed that sound reaches the cochlea via bone conduction rather than via the tympanic membrane. To address these issues, we have developed a method to measure stapes velocity in response to vibrational stimulation at arbitrary locations on heads and ears harvested from stranded animals. Stapes velocity was measured with a Laser Doppler Velocimeter at the footplate with the cochlea drained. In all species tested, the transfer function of stapes velocity referenced to actuator velocity showed a high-pass characteristic. The corner frequency varied with species and experiment between 4 kHz and 60 kHz. This...

Reverse Engineering the Cetacean Ear to Extract Audiograms

The cochlear frequency-place map is believed to be an important determinant of the frequencies that a species can hear as well as the bandwidth of cochlear filters. Both features impact an animal’s ability to detect biologically significant sounds in noise. The cochlear frequency-place map is created in part by a stiffness gradient in the basilar membrane (BM) in which stiff regions respond best to high frequencies and more compliant regions respond best to low frequencies.

Multi-species Baleen Whale audiogram modelling

In this research, we produced model audiograms for two Mysticetes (baleen whales) that are among the species most likely to be subject to impacts from common lower frequency anthropogenic sound sources deployed in the oceans. These models are needed for species-specific risk assessments for hearing impacts, for determining optimal signals for playback experiments, and for determining effective electrode and sound source placements for auditory brainstem response (ABR) measures in live stranded whales. We employed micro and UHRCT, dissection, and histology of minke (Balaenoptera acutorostrata) and humpback (Megaptera novaeangliae) heads and ears to calculate inner ear frequency maps for determining total hearing range, the frequency of peak sensitivity, and the probable frequency of NIHL liability (“notch”). The anatomically derived data were then combined with direct measures via nanoindentation of middle ear stiffness, Young’s modulus, frequency response, and inner ear stiffness to determine the middle e...