Short Tone Bursts Research Articles

Effects of monaural sound stimulation on subjective visual vertical.

Sound stimulation can influence electrophysiological vestibular reflexes. However, the effects of sound stimulation on space perception remain unknown. To know the effects of monaural sound stimulation on subjective visual vertical (SVV). We measured SVV with and without monaural sound stimulation (105 dB, 500 Hz short tone burst presented at 4.7 Hz) in 50 healthy volunteers (aged 20-77 [mean = 42.7] years). The mean SVV was deviated 0.139° to the left by right monaural sound stimulation and 0.123° to the right by left monaural sound stimulation. SVV changes due to right and left ear stimulations were significantly different (p = 0.019). Sound stimulation resulted in a significant change in SVV on the left side (p = 0.014) in participants aged 50 or younger (mean = 35.6 years) (n = 37). This study is the first to show the possibility that the monaural sound input deviates the SVV toward the opposite side and is more pronounced for left-ear input. The vestibular-evoked myogenic potential responses may be involved in the mechanism of the contralateral SVV deviation due to sound input.

Functional neuroanatomy of the vestibular cortex and vestibular stimulation methods for neuroimaging studies

The vestibular cortex is a distributed network of multisensory areas that plays a crucial role in balance, posture, and spatial orientation. The core region of the vestibular cortex is the parietoinsular vestibular cortex (PIVC), which is located at the junction between the posterior insula, parietal operculum, and retroinsular region. The PIVC is connected to other vestibular areas, the primary and secondary somatosensory cortices, and the premotor and posterior parietal cortices. It also sends projections to the vestibular nuclei in the brainstem. The PIVC is a multisensory region that integrates vestibular, visual, and somatosensory information to create a representation of head-in-space motion, which is used to control eye movements, posture, and balance. Other regions of the vestibular cortex include the primary somatosensory, posterior parietal, and frontal cortices. The primary somatosensory cortex is involved in processing information about touch and body position. The posterior parietal cortex is involved in integrating vestibular, visual, and somatosensory information to create a representation of spatial orientation. The frontal cortex is involved in controlling posture, and eye movements. The various methods used to stimulate the vestibular receptors in neuroimaging studies include caloric vestibular stimulation (CVS), galvanic vestibular stimulation (GVS), and auditory vestibular stimulation (AVS). CVS uses warm or cold water or air to stimulate the semicircular canals, GVS uses a weak electrical current to stimulate the vestibular nerve, and AVS uses high-intensity clicks or short tone bursts to stimulate the otolithic receptors.

Saccular functions differ for Meniere's disease with and without coexisting headaches.

To elucidate the differences between the cases of Meniere's disease (MD) with and without coexisting headaches, especially migraine. The clinical characteristics and vestibular functions are compared. Fifteen patients with definite unilateral MD without headaches (MD/H-; 10 males and 5 females; mean age of 55.8 years), and 20 patients with definite unilateral MD with headaches (MD/H+; 3 males and 17 females; mean age of 54.4 years; 15 cases of migraine without aura and 5 cases of suspected migraine or tension-type headache) were enrolled. The medical records, caloric test results, and cervical vestibular evoked myogenic potential (cVEMP) of the patients were reviewed. A monothermal caloric test by injection of cold water was performed, and canal paresis was assessed. cVEMP was recorded using 500 Hz short tone bursts, and the asymmetry ratio using the corrected amplitude of p13-n23 was determined. The patients in the MD/H- group were predominantly male, whereas more female patients were seen in MD/H+ group (p = 0.004). In the MD/H+ group, the frequency of vertigo and the dizziness handicap inventory (DHI) values were significantly higher than those in the MD/H- group (p = 0.045, <0.001, respectively). There was no statistical difference in the ages, duration of illness, or the hearing levels between both groups. The caloric testing results were abnormal for 10 of the 13 MD/H- cases, and 14 of the 16 MD/H+ cases, which revealed no significant difference between both groups. The cVEMP results revealed positive saccular dysfunction based on the asymmetry ratio of 4 of the 15 MD/H- cases, and 14 of the 20 MD/H+ cases; it was significantly more prevalent in the MD/H+ group than in the MD/H- group (p = 0.018). Multivariate analysis of sex, frequency of vertigo, DHI, and cVEMP results showed significant differences only in the cVEMP results (p = 0.049). The present study revealed differences in patients with MD depending on the presence or absence of headaches. MD without headaches showed a significant male preponderance. MD with coexisting headaches was more associated with severe saccular dysfunctions than MD without headaches. Concomitant headache may affect the manifestations of the vestibular function, especially in the sacculus, in MD cases.

A Single Short 'Tone Burst' Results in Optimal Drug Delivery to Tumours Using Ultrasound-Triggered Therapeutic Microbubbles.

Advanced drug delivery systems, such as ultrasound-mediated drug delivery, show great promise for increasing the therapeutic index. Improvements in delivery by altering the ultrasound parameters have been studied heavily in vitro but relatively little in vivo. Here, the same therapeutic microbubble and tumour type are used to determine whether altering ultrasound parameters can improve drug delivery. Liposomes were loaded with SN38 and attached via avidin: biotin linkages to microbubbles. The whole structure was targeted to the tumour vasculature by the addition of anti-vascular endothelial growth factor receptor 2 antibodies. Tumour drug delivery and metabolism were quantified in SW480 xenografts after application of an ultrasound trigger to the tumour region. Increasing the trigger duration from 5 s to 2 min or increasing the number of 5 s triggers did not improve drug delivery, nor did changing to a chirp trigger designed to stimulate a greater proportion of the microbubble population, although this did show that the short tone trigger resulted in greater release of free SN38. Examination of ultrasound triggers in vivo to improve drug delivery is justified as there are multiple mechanisms at play that may not allow direct translation from in vitro findings. In this setting, a short tone burst gives the best ultrasound parameters for tumoural drug delivery.

Asymmetry and tuning shift of the cervical vestibular evoked myogenic potential indicate saccular dysfunction in idiopathic normal pressure hydrocephalus

ObjectiveThe purpose of this study was to investigate the effects of excessive cerebrospinal fluid (CSF) retention on the peripheral vestibular function and the inner ear fluid in patients with idiopathic normal pressure hydrocephalus (iNPH). MethodsIn 25 patients with iNPH (14 females, age 65–88 years), cervical vestibular evoked myogenic potential (cVEMP) was measured before the spinal tap test. The asymmetry ratios (ARs) and tuning properties in 500 Hz and 1,000 Hz short-tone burst stimuli of cVEMP were evaluated. Furthermore, cVEMP was measured in an age-matched control group of 12 non-iNPH patients. ResultsSeven (28%) iNPH patients exhibited a cVEMP asymmetry (AR > 33%). cVEMP tuning was significantly shifted to a higher frequency in the iNPH group than in the age-matched control group. ConclusionsOne-fourth of patients with iNPH had obvious saccular dysfunction. A high rate of a shift in cVEMP tuning in the iNPH group indicated that excessive CSF accumulation propagated to the endolymph and perilymph. SignificanceSaccular dysfunction might be one of the possible causes of imbalance in iNPH, and the shift in cVEMP tuning may be a determining factor in the diagnosis and treatment strategy.

Similarities and Differences Between Vestibular and Cochlear Systems - A Review of Clinical and Physiological Evidence.

The evoked response to repeated brief stimuli, such as clicks or short tone bursts, is used for clinical evaluation of the function of both the auditory and vestibular systems. One auditory response is a neural potential — the Auditory Brainstem Response (ABR) — recorded by surface electrodes on the head. The clinical analogue for testing the otolithic response to abrupt sounds and vibration is the myogenic potential recorded from tensed muscles — the vestibular evoked myogenic potential (VEMP). VEMPs have provided clinicians with a long sought-after tool — a simple, clinically realistic indicator of the function of each of the 4 otolithic sensory regions. We review the basic neural evidence for VEMPs and discuss the similarities and differences between otolithic and cochlear receptors and afferents. VEMPs are probably initiated by sound or vibration selectively activating afferent neurons with irregular resting discharge originating from the unique type I receptors at a specialized region of the otolithic maculae (the striola). We review how changes in VEMP responses indicate the functional state of peripheral vestibular function and the likely transduction mechanisms allowing otolithic receptors and afferents to trigger such very short latency responses. In section “ELECTROPHYSIOLOGY” we show how cochlear and vestibular receptors and afferents have many similar electrophysiological characteristics [e.g., both generate microphonics, summating potentials, and compound action potentials (the vestibular evoked potential, VsEP)]. Recent electrophysiological evidence shows that the hydrodynamic changes in the labyrinth caused by increased fluid volume (endolymphatic hydrops), change the responses of utricular receptors and afferents in a way which mimics the changes in vestibular function attributed to endolymphatic hydrops in human patients. In section “MECHANICS OF OTOLITHS IN VEMPS TESTING” we show how the major VEMP results (latency and frequency response) follow from modeling the physical characteristics of the macula (dimensions, stiffness etc.). In particular, the structure and mechanical operation of the utricular macula explains the very fast response of the type I receptors and irregular afferents which is the very basis of VEMPs and these structural changes of the macula in Menière’s Disease (MD) predict the upward shift of VEMP tuning in these patients.

Experimental and numerical analysis of Lamb wave transmission through the coronal suture of a dry human skull

Cranial Lamb waves have recently gained attention as potential means for ultrasound imaging and diagnostics of the skull. The inherent capability of these waves to travel for long distances across the cranial vault requires the understanding of transmission mechanisms across cranial sutures, which remain mostly unexplored. This work investigates such mechanism in the coronal suture of a dry human skull. The transmission analysis is performed experimentally by recording velocity arrays induced by short tone-bursts along curvilinear paths that intercept the suture at different locations. For each path, the experimental frequency-wavenumber spectrum of the incident wave indicates the presence of fundamental and higher order Lamb modes, with transmission being mainly associated with the fundamental antisymmetric Lamb mode. By calculating the corresponding transmission coefficients and comparing them with those obtained from a semi-analytical multilayered model of the cranial bone, we demonstrate that the coronal suture can be described by a simplified constitutive law defined by distributed shear and compressional stiffness coefficients. The experimental results and the estimated suture constitutive parameters provide the basis for a comparative analysis of the suture mechanical properties at different spatial locations, which may be employed for suture characterization and imaging.

Cervical Vestibular Evoked Myogenic Potentials That Are Absent at 500 Hz But Present at 1000 Hz Are Characteristic of Endolymphatic Hydrops-Related Disease.

It remains unclear whether the dominance of 1000 Hz responses over responses at 500 Hz in cervical vestibular evoked myogenic potentials (cVEMPs) are characteristic of endolymphatic hydrops (EH), due to the presence of patients with absent responses at both frequencies. The purpose of the present study is to examine whether the dominant cVEMP responses at 1000 Hz over 500 Hz are characteristic findings of EH-related diseases among patients who show various cVEMP findings. We retrospectively reviewed the medical records of 470 consecutive patients who underwent cVEMP testing with short-tone bursts at both 500 Hz and 1000 Hz. We categorized the cVEMP responses of these 470 patients into the following five groups: (group 1) present responses at both frequencies bilaterally, (group 2) present responses at 500 Hz but absent at 1000 Hz on at least one side, (group 3) absent responses at 500 Hz but present at 1000 Hz on at least one side, (group 4) absent responses at both frequencies on one side and present at both frequencies on the other side, and (group 5) absent responses at both frequencies bilaterally. We compared the proportion of EH-related diseases between each group and the other four groups and then investigated any increased or decreased disease incidence in each group. In group 3, the proportion of EH-related disease was significantly higher (p < 0.01), and the incidence of an EH-related disease was greatly increased (standard residual value > 3). cVEMPs that are absent at 500 Hz and present at 1000 Hz may be characteristic of EH-related disease.

Idiopathic sudden sensorineural hearing loss: Labyrinthitis or ischemia? Consideration based on VHIT and CVEMP

Majority of patients presented with sudden sensorineural hearing loss (SSHL) are idiopathic. In other words, causes of their hearing losses are unknown. It is widely believed that viral infection (labyrinthitis) and vascular ischemia could be the most probable etiologies. However, it is not easy to determine the etiology in each case. It is also well-known that SSHL is frequently accompanied by vertigo. Recently, cervical vestibular evoked myogenic potential (cVEMP) and video head impulse test (vHIT) enabled us to assess functions of all the 5 parts of the vestibular labyrinth. Patients presented with sudden hearing loss with or without vertigo were enrolled. These subjects underwent vHIT of the 6 canals and cVEMP. When a decreased VOR gain and catch-up (corrective) saccades were observed, the relevant canal was regarded damaged. Five hundred Hz air-conducted short-tone bursts (rise/fall time = 1 msec, plateau time = 2 msec, 125 dB SPL) were used to evoke cVEMP. the asymmetry ratio of p13-n23 amplitude was assessed. Patients with high tone hearing loss showed tendency of isolated posterior semicircular canal dysfunction with preserved cVEMP responses. On the other hand, patients with profound flat hearing loss showed tendency of absent cVEMP and diversity of canal dysfunction. This study suggested that high tone loss could be caused by ischemia of the vestibulo-cochlear artery while flat profound loss might be caused by labyrinthitis. Saccule function shown by cVEMP might be an indicator of etiology of SSHL with vertigo.

Refined Auditory Brainstem Response Measurement Identified Potential Models of Congenital Deafness in Laboratory Mouse Strains.

Introduction: To detect congenital hearing loss in mice, an objective measure is needed other than mouse behavioral observation. This study aimed to refine the methodology of auditory brainstem response measurement and identify potential congenital hearing loss models in laboratory mouse strains. Methods: Mice were anesthetized and fitted with head electrodes. Each mouse underwent four ABR measurements according to four testing conditions: A - no chamber; conventional tone; B - chamber; conventional tone; C - no chamber; short tone; D - chamber; short tone. Potential congenital hearing loss models were identified using 10 mice from each strain (C57BL, BALB/c, CH3, ICR, and ddY) through sound-attenuated ABR measurements with short-tone bursts. Potential congenital hearing loss models exhibited hearing thresholds ≥30 dB in both ears. Data were analyzed for normal distribution and variance homogeneity using the D’Agostino-Pearson/Kolmogorov-Smirnov and F value tests, respectively. One-way analysis of variance (ANOVA), with the Tukey-Kramer test, was used to conduct parametric analysis, and the Kruskal-Wallis/Friedman test, with a Dunn’s test for post hoc analysis, was used to perform non-parametric analysis. Results: The simultaneous use of a sound-attenuating chamber and short-tone bursts provided clearly defined wave patterns, even at lower sound intensities. Inbred strains, especially C57BL/6 sub-strains, constitute suitable congenital hearing loss models. Conclusions: Our study shows that environmental factors should be addressed in animal studies of hearing function. Potential congenital hearing loss models may be found amongst commercially available inbred strains.

Evaluation of Saccule Function in Patients with Vitamin D Deficiency.

Background and ObjectivesConsidering important role of vitamin D in many physiological processes including vestibular system in the ear, aim of present study is to evaluate saccule function via cervical vestibular evoked myogenic potential (cVEMP), in patients with vitamin D deficiency.Subjects and MethodsAfter routine audiological tests, cVEMP were recorded in 15 patients with vitamin D deficiency and 16 normal subjects. The short tone burst (95 dB nHL, 500 Hz) was presented to ears. cVEMP was recorded with surface electromyography over the contracted ipsilateral sternocleidomastoid muscle.ResultsMean of p13, n13, interpeak latencies and amplitude ratios were measured in both groups. Statistical analysis did not show differences between two groups.ConclusionsMaybe serum 25-hydroxyvitamin D concentration was not low enough to have effect on saccule in the patients in present study or saccule have had low susceptibility to effects of vitamin D deficiency. For better judgment about effect of vitamin D deficiency on saccular function planning studies with high sample size is recommended.

Simultaneous Presentation of Definite Vestibular Migraine and Definite Ménière's Disease: Overlapping Syndrome of Two Diseases.

Objectives: To review the clinical records of patients that exhibited the clinical features of both vestibular migraine (VM) and Ménière's disease (MD) during each episodic vertigo attack and to discuss the possible pathophysiology of such combination of symptoms.Subjects: Ten patients that were selected according to criteria based on a combination of the diagnostic criteria for definite MD and VM (9 females and one male, age: 22–54 years) were enrolled. They were required to show features of both diseases in each vertigo attack.Methods: The patients' medical histories and pure-tone audiometry, cervical vestibular evoked myogenic potential (cVEMP), video head-impulse test (vHIT), and caloric test results were examined. cVEMP was recorded using 500 and 1,000 Hz short tone bursts (125dBSPL, air-conducted), 500 Hz-1,000 Hz cVEMP slope, an index of endolymphatic hydrops in the saccule was calculated using normalized amplitudes of p13-n23. For performing vHIT, each subject was seated 1.5 m in front of a target and asked to keep watching it as their head was passively rotated by the examiner. Their eye movements were evaluated using video-oculography while their head movements were recorded using inertial sensors.Results: The patients were predominantly female. On average, the onset of migrainous headaches occurred 9 years earlier than the onset of vertigo attacks. All of the patients but one had migraines with auras. Five of the 10 patients had a family history of vertigo attacks accompanied by both migrainous and auditory symptoms. The patients mainly displayed hearing loss at low frequencies. Nine patients exhibited 500–1,000 Hz cVEMP slope < −19.9, which was suggestive of endolymphatic hydrops. None of the patients who underwent vHIT showed abnormal canal function. One patient showed unilaterally decreased caloric responses.Conclusions: These patients presented with simultaneous MD and VM signs/symptoms might be referred to “VM/MD overlapping syndrome (VM/MD-OS)” as a new clinical syndrome.

Ageing-related changes in the cortical processing of otolith information in humans.

Acoustic short tone bursts (STB) trigger ocular and cervical vestibular-evoked myogenic potentials (oVEMPs/cVEMPs) by activating irregular otolith afferents. Simultaneously, STBs introduce an artificial net acceleration signal of otolith origin into the vestibular network. VEMP parameters as diagnostic otolith processing markers have been shown to decline after the age of thirty. To delineate the differential effects of healthy ageing on the cortical vestibular subnetwork processing otolith information, we measured cVEMPs and the differential effects of unilateral STB in three age groups (20-40, 40-60 and 60+; n=42) using functional neuroimaging. STB evoked responses in the main vestibular hubs in the parieto-opercular cortex. Whereas cVEMP amplitudes declined linearly with age, analysis of the BOLD response size depicted a u-shaped curve. Vestibular perception of the otolith stimulus on the other hand remained unchanged with age. Therefore, we propose that the comparably larger BOLD responses past the age of sixty could reflect a mechanism of central sensitisation for otolith perception to counterbalance the concurrent peripheral vestibular and somatosensory function decline.

Local Discontinuous Galerkin Methods for the Khokhlov–Zabolotskaya–Kuznetzov Equation

Khokhlov–Zabolotskaya–Kuznetzov (KZK) equation is a model that describes the propagation of the ultrasound beams in the thermoviscous fluid. It contains a nonlocal diffraction term, an absorption term and a nonlinear term. Accurate numerical methods to simulate the KZK equation are important to its broad applications in medical ultrasound simulations. In this paper, we propose a local discontinuous Galerkin method to solve the KZK equation. We prove the $$L^2$$ stability of our scheme and conduct a series of numerical experiments including the focused circular short tone burst excitation and the propagation of unfocused sound beams, which show that our scheme leads to accurate solutions and performs better than the benchmark solutions in the literature.

Focal areas of increased lipid concentration on the coating of microbubbles during short tone-burst ultrasound insonification.

Acoustic behavior of lipid-coated microbubbles has been widely studied, which has led to several numerical microbubble dynamics models that incorporate lipid coating behavior, such as buckling and rupture. In this study we investigated the relationship between microbubble acoustic and lipid coating behavior on a nanosecond scale by using fluorescently labeled lipids. It is hypothesized that a local increased concentration of lipids, appearing as a focal area of increased fluorescence intensity (hot spot) in the fluorescence image, is related to buckling and folding of the lipid layer thereby highly influencing the microbubble acoustic behavior. To test this hypothesis, the lipid microbubble coating was fluorescently labeled. The vibration of the microbubble (n = 177; 2.3–10.3 μm in diameter) upon insonification at an ultrasound frequency of 0.5 or 1 MHz at 25 or 50 kPa acoustic pressure was recorded with the UPMC Cam, an ultra-high-speed fluorescence camera, operated at ~4–5 million frames per second. During short tone-burst excitation, hot spots on the microbubble coating occurred at relative vibration amplitudes > 0.3 irrespective of frequency and acoustic pressure. Around resonance, the majority of the microbubbles formed hot spots. When the microbubble also deflated acoustically, hot spot formation was likely irreversible. Although compression-only behavior (defined as substantially more microbubble compression than expansion) and subharmonic responses were observed in those microbubbles that formed hot spots, both phenomena were also found in microbubbles that did not form hot spots during insonification. In conclusion, this study reveals hot spot formation of the lipid monolayer in the microbubble’s compression phase. However, our experimental results show that there is no direct relationship between hot spot formation of the lipid coating and microbubble acoustic behaviors such as compression-only and the generation of a subharmonic response. Hence, our hypothesis that hot spots are related to acoustic buckling could not be verified.

Is Alteration of Tuning Property in Cervical Vestibular-Evoked Myogenic Potential Specific for Ménière’s Disease?

The aim of this study is to show sensitivity and specificity of cervical vestibular-evoked myogenic potential (cVEMP) tuning property test to Ménière's disease (MD) in comparison with healthy controls (HC) and patients with other vestibular diseases. Totally 92 subjects (50 women and 42 men, 20-77 years of age) were enrolled in this study. Subjects were composed of 38 definite unilateral MD patients, 11 unilateral benign paroxysmal positional vertigo patients, 14 vestibular migraine patients, 19 unilateral vestibular neuritis patients, and 10 HC. The subjects underwent cVEMP testing to 500 and 1,000 Hz short tone bursts (125 dBSPL). The corrected amplitudes of the first biphasic responses (p13-n23) (cVEMP) were measured. Then, a tuning property index (the 500-1,000 Hz cVEMP slope) was calculated. The area of under the ROC curve (AUC) was 0.75 in comparison with other vestibular disease patients, while AUC was 0.77 in comparison with other vestibular disease patients plus HC. The best cutoff point of the 500-1,000 Hz cVEMP slope was -19.9. Sensitivity of the tuning property test to MD was 0.74, while specificity was 0.76 to other vestibular disease patients. The tuning property test of cVEMP is useful as a screening test of MD.

Pitch priming in sequences of two sounds.

Frequency discrimination limens (FDLs) were measured for pairs of stimuli differing from each other with respect to pitch salience. One of the two stimuli to be compared within a trial was a pure tone of at least 100 ms, evoking a salient pitch, while the other stimulus consisted of only eight sinusoidal cycles (experiment 1), or was a noise band with a Gaussian spectral envelope, evoking a weak pitch corresponding to the peak frequency (experiment 2). From trial to trial, frequency was varied randomly and widely. In both experiments, the FDLs were lower, by an average factor of about 3, when the stimulus with the more salient pitch preceded the other stimulus than vice versa. Evidence is presented against an interpretation of this temporal asymmetry in terms of memory limitations. It is suggested that the asymmetry reflects a pitch-priming effect. In two additional experiments, both of the stimuli to be compared within a trial were very short tone bursts or noise bands; perceptually, they differed only with respect to pitch height. Performance was markedly better than in experiments 1 and 2, and was not improved when the two stimuli were preceded by a 300-ms tone intended to produce pitch priming.

Detection of Saccular Endolymphatic Hydrops in Ménière's Disease Using a Modified Glycerol cVEMP Test in Combination With the Tuning Property Test.

To determine the optimal method for detecting saccular endolymphatic hydrops (EH) in patients with Ménière's disease (MD) using a glycerol cervical vestibular evoked myogenic potential (cVEMP) test in combination with a tuning property test. Prospective patients series. Tertiary referral center. Twenty-three subjects (age: 36-77 years) were enrolled in this study. Seventeen subjects were diagnosed with definite MD. Six subjects were diagnosed with possible MD. Diagnostic. The corrected amplitudes of p13-n23 (cVEMP) were measured before and after the administration of 10% glycerol (500 ml, 2 h, intravenously). A tuning property index and the p13-n23 amplitude improvement ratio were calculated. The positivity rate (PR) during the tuning property test was 55% (definite MD-affected ears), 35% (definite MD-unaffected ears), and 25% (possible MD ears). The PR during the glycerol cVEMP amplitude test was 60, 8, and 0%, respectively. The use of modified criteria for the glycerol cVEMP test in combination with the tuning property test resulted in the PR increasing to 75, 57, and 25%, respectively. The pre-glycerol stage results obtained using the tuning property test almost (except in two ears) completely agreed with the glycerol cVEMP test results by the modified criteria. The tuning property test is an easy and useful way of detecting saccular EH. However, the glycerol cVEMP test is required in patients that do not respond to either 500 or 1000 Hz short tone bursts (STB).

Frequency response of proud and partially exposed spheres at flat interfaces

The backscattering spectrum of spheres at flat interfaces viewed at small grazing angles depends upon reflections from the sphere's surface and the interface, as well as the sphere's elastic response and Franz wave contributions. For partially exposed spheres, one approach to modeling the reflective contribution is to extend the Kirchhoff approximation [K. Baik and P. L. Marston, IEEE J. Ocean. Eng. 33, 386–396 (2008)] to spheres. Laboratory measurements were carried out using short tone bursts for solid spheres at air-water and sand-water interfaces in such a way that it was typically possible to distinguish between the reflective and delayed elastic contributions viewed in the time domain. For spheres at an air-water interface, the reflective contributions have strong similarities with the Kirchhoff approximation while the strength of the delayed elastic contributions depends strongly on the extent of exposure of elastic guided wave coupling regions. The spectra of proud targets have similarities with i...

Band limited chirp stimulation in vestibular evoked myogenic potentials.

Air conducted vestibular evoked myogenic potentials (VEMP) can be elicited by various low frequency and intense sound stimuli, mainly clicks or short tone bursts (STB). Chirp stimuli are increasingly used in diagnostic audiological evaluations as an effective means to obtain acoustically evoked responses in narrowed or extended frequency ranges. We hypothesized in this study that band limited chirp stimulation, which covers the main sensitivity range of sound sensitive otolithic afferents (around 500Hz), might be useful for application in cervical and ocular VEMP to air conduction. For this purpose we designed a chirp stimulus ranging 250-1000Hz (up chirp). The chirp stimulus was delivered with a stimulus intensity of 100dB nHL in normal subjects (n=10) and patients with otolith involvement (vestibular neuritis) (n=6). Amplitudes of the designed chirp ("CW-VEMP-chirp, 250-1000Hz") were compared with amplitudes of VEMPs evoked by click stimuli (0.1ms) and a short tone burst (STB, 1-2-1, 8ms, 500Hz). CVEMPs and oVEMPs were detectable in 9 of 10 normal individuals. Statistical evaluation in healthy patients revealed significantly larger cVEMP and oVEMP amplitudes for CW-VEMP-chirp (250-1000Hz) stimuli. CVEMP amplitudes evoked by CW-VEMP-chirp (250-1000Hz) showed a high stability in comparison with click and STB stimulation. CW-VEMP-chirp (250-1000Hz) showed abnormal cVEMP and oVEMP amplitudes in patients with vestibular neuritis, with the same properties as click and STB stimulated VEMPs. We conclude that the designed CW-VEMP-chirp (250-1000Hz) is an effective stimulus which can be further used in VEMP diagnostic. Since a chirp stimulus can be easily varied in its properties, in particular with regard to frequency, this might be a promising tool for further investigations.