摘要:

This paper reports the results of a study that investigated localization performance of simulated externalized signals in sensorineural hearing loss (SNHL) listeners when signals were presented with either unbalanced [equal sensation level (EqSL)] or balanced [equal sound‐pressure level (EqSPL)]hearing aid gain at the two ears. In previous reports from this laboratory, it has been found that when equalizing by SL, the perceived lateral position was essentially linearly dependent on the degree and direction of asymmetry in normal‐hearing (NH) and SNHL listeners. Equalizing by SPL showed no such dependency. It was hypothesized that the current practice of fitting ‘‘binaural’’ hearing aids in asymmetric SNHL listeners using prescription formulas might result in SPL imbalance which would disrupt the previously adapted system and impair localization. The present study was designed to address this issue by measuring localization using a simulated externalized auditory image combined with head position control of IID and ITD to spatially fix the image. Absolute and signed error deviations from center were analyzed. Significant interactions of group (NH versus SNHL)*frequency and balance (EqSL or Eq SPL)*frequency were found. These data will be discussed in terms of auditory adaptation and strategies of fitting binaural hearing aids. [Work supported by NIDRR.]

ISSN:0001-4966    

DOI:10.1121/1.422651

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

An acute acoustic trauma (AAT) results when the unprotected ear is exposed to very high sound pressure levels, usually as the result of an industrial or military accident. There is no commonly accepted treatment in the U.S. for an AAT. A study was performed to evaluate the effects of a corticoid steroid (dexamethasone) on the hearing loss from a series of blast waves that would simulate an AAT. Dexamethasone is commonly used as an anti‐inflammatory agent in veterinary medicine. Groups of chinchillas were exposed individually to ten 160‐dB peak SPL reverberant blast waves from a conventional shock tube at a rate of one blast per minute. Immediately following the exposure, the animals were injected with dexamethasone alone (1.0–2.0 mg/kg IV) or in combination with dimethyl sulfoxide (DMSO), a free‐radical scavenger. Individual groups of animals showed the well‐known extreme variability in hearing losses as noted in earlier studies [e.g., R. P. Hamerniketal., J. Acoust. Soc. Am.90, 197–204 (1991)]. Examining the median permanent threshold shifts (PTS) of the groups of animals showed a distinct dose‐response effect with increasing dosages of dexamethasone associated with lower levels of PTS in the frequency region most affected by the noise exposure.

ISSN:0001-4966    

DOI:10.1121/1.422659

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

Magnesium (Mg) deficiency was found to increase noise‐induced hearing loss in laboratory animals. This paper reports both prophylactic and therapeutic effects of Mg on the acoustic trauma produced by a high‐level impulse noise series (Lpeak167 dB, 38 min, 1/s). Hearing loss was tested by auditory brainstem response audiometry at frequencies between 0.5 and 32 kHz. Permanent hearing threshold shifts (PTS) were measured 1 week after the exposure. For the prophylaxis experiments, anesthetized guinea pigs with either a physiologically high or low Mg status, produced by different diets, were used. For the therapy experiments, animals with the low Mg status received (immediately after exposure) either Mg injections combined with a Mg‐rich diet or saline as a placebo. Total Mg concentrations of perilymph, cerebrospinal fluid, and plasma were analyzed to test the Mg status of the animals. The PTS was found to be significantly lower in the high‐Mg group than in the low‐Mg group. This also applies to the PTS found between the therapy and the placebo groups. There was a good correlation between the PTS and the perilymphatic Mg. The intracochlear Mg level seems to play an important role in the acoustic trauma. [Supported by German Defence Ministry.]

ISSN:0001-4966    

DOI:10.1121/1.422660

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

The following problem is posed and solved: given an elastic structure vibrating under the action of a harmonic point force, find the time‐average potential and kinetic energy, loss factor, and other energy characteristics of the structure if known are only the complex amplitudes of the force and velocity response at the driving point,fandv. The structure is assumed to be linear, with viscous and hysteric damping not necessarily proportional. It is shown that the problem has a mathematically exact solution only for lossless systems. For structures with losses, there exist rather accurate estimates valid at low and middle frequencies. The main result is the equation relating the total vibration energy of the structure to the derivative of its input impedance,f/v, or mobility,v/f, with respect to frequency. Computer simulation examples with typical structures (rod, plate) illustrate the accuracy and the range of validity of the estimates. The results presented allow one to obtain the energy characteristics of a forced vibrating structure by the most economic way: without measuring or computing the response all over the structure and using only the data measured at one singular point.

ISSN:0001-4966    

DOI:10.1121/1.422669

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

An inventory of vocal tract area functions, acquired from magnetic resonance imaging experiments, is used as the basis for creating simulations of sentence‐level speech. A first approach is a ‘‘brute‐force’’ method in which a phonetic transcription of a sentence is time aligned with the recorded acoustic signal. Each element of the transcription is assigned one of the stored vocal tract area functions in the acquired inventory, thus serving as a ‘‘target’’ through which the time‐varying area function should pass. This method has produced intelligible speech but maintains a machinelike quality. A second approach uses a parametric representation of the MRI‐acquired area function inventory based on a principal components analysis to generate area functions not in the original inventory. The first three formants of each generated area function were computed and stored in a database, thus creating a mapping between formant frequencies and vocal tract parameters (area functions). Except for the edge of the formant space, the mapping between formants and area functions is one‐to‐one. This method produces connected speech with natural sounding vowels when only a microphone signal is used but requires additional signals to derive the consonantal contribution to the vocal tract shape. [Supported by NIH grant RO1 DC02532.]

ISSN:0001-4966    

DOI:10.1121/1.422672

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

Simulation data are presented from a computer model that combines vocal fold tissue mechanics, laryngeal aerodynamics, and vocal tract acoustics. These simulations are based upon the laws of physics that govern airflow, vibration of the vocal folds, and wave propagation in the vocal tract. The tissue mechanics was modeled with the finite element method with 100 nodes and 166 elements in each layer of the 15‐layer model. The laryngeal aerodynamics was modeled by the solution of two‐dimensional unsteady Navier–Stokes equations with a finite volume method with a 64×82 nonuniform staggered grid. The model has been used to demonstrate self‐oscillatory characteristics of the vocal folds and the flow pattern in the larynx. In this study, simulations were performed for lung pressure ranging from 4 to 24 cm of water. Adduction control was simulated with activation of thyroarytenoid (TA) muscle that caused increased tension and bulging of the vocal folds. Results are reported for glottal waveform, nodal coordinates, and velocity distributions in the larynx. Preliminary data suggest that the relationship between mean pressure and mean flow is almost linear. Frequency and amplitude contours of the model as functions of the lung’s pressure and TA activation level reveal their increasing pattern with these parameters.

ISSN:0001-4966    

DOI:10.1121/1.422676

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

An important aspect that needs improvement in medical ultrasound systems is related to the 2‐D imaging of the prostate. 2‐D viewing of 3‐D anatomy limits our ability to quantify and visualize prostate disease and is partly responsible for the reported variabilities. This occurs because: (i) the diagnostician must integrate multiple 2‐D images in his mind during the procedure, leading to inefficiency and variability; (ii) The 2‐D ultrasound images represent a thin plane at some arbitrary angle in the body, making it difficult to localize the image plane. To overcome these difficulties, we have developed a 3‐D ultrasound system to image the prostate. Our 3‐D ultrasound imaging system consists of: a conventional ultrasound machine and transducer; a custom‐built assembly for rotating the probe under microcomputer control; a microcomputer with a video grabber; and software to reconstruct and display 3‐D images. A typical scan of 200 2‐D B‐mode images takes only 13 s, and the reconstruction less than 1 s. This paper will detail the 3‐D imaging approach and its use for imaging the prostate in 3‐D. Various applications will be discussed related to prostate cancer diagnosis, prostate volume measurements, and 3‐D ultrasound‐guided therapeutic procedures such as cryosurgery.

ISSN:0001-4966    

DOI:10.1121/1.422682

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

This paper presents an autonomous system for detecting lesions in the breast. The Wold decomposition algorithm described is used to decompose the RF echo of the breast into its diffuse and coherent components. The coherent component is modeled as a periodic sequence and the diffuse component is modeled as an autoregressive time series of low order. The parameters of the model are estimated from selected regions of the RF image and used as detection features. The database of images that was used contained 370 B‐scan images from 52 patients, obtained in the Radiology department of the Thomas Jefferson Hospital. The pathologies of interest are carcinoma fibrocystic and stromal fibrosis disease and fibroadenoma. Empirical ROC techniques were used to evaluate the detection rate on single parameters of the model, such as the residual error variance and the autoregressive parameters of the diffuse component of the RF echo. The area under the empirical ROC curve for detecting lesion regions versus normal RF regions is 0.901. The area under the ROC curve for detecting carcinoma versus normal regions is 0.904. The corresponding areas for normal regions versus stromal fibrosis/fibrocystic regions and fibroadenoma regions are 0.942 and 0.899, respectively.

ISSN:0001-4966    

DOI:10.1121/1.422684

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

At high frequencies, two mechanisms of seabed scattering are usually taken into account which are due to roughness of the seabed surface (sediment–water interface) and volume inhomogeneities of near‐surface sediment. The mean parameters of bottom medium are usually considered as independent from spatial coordinates. This corresponds to the assumption that sound penetration into the sediment is sufficiently small because of strong absorption. In this paper, more general models are considered where seabeds are assumed as statistically stratified (plane‐layered on the average) with the mean parameters taken as various functions of depth. In particular, they can be step functions corresponding to different types of sediments in different layers. Another type of stratification corresponds to continuous depth‐dependences and involve gradients of mean parameters. Effects of stratification are shown to be important at lower frequences due to scattering from internal interfaces and volume inhomogeneities of deep layers as well as the influence of regular refraction and reflection within seabed medium. As numerical examples, angular dependencies of the scattering strength in both monostatic and bistatic cases at different frequencies are calculated for seabeds of various types. Comparison with available data is presented and discussed. [Work supported by ONR.]

ISSN:0001-4966    

DOI:10.1121/1.422688

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

In most theoretical developments of sediment volume scattering, the medium is assumed to have weak fluctuations in sound speed and density and is assumed to be statistically homogeneous. An exact integral equation method has been developed and is used to test these assumptions. Small perturbation theory results for single frequency bistatic scattering from the seafloor are compared with Monte Carlo simulations. Half‐space and multiple scattering effects not included in most previous treatments are observed.

ISSN:0001-4966    

DOI:10.1121/1.422818

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP