bluuebunny/crossref_metadata_2025 huggingface dataset:
Modal analysis of the vocal tract
Authors: Firth Ian M.
Published: October 2005

The modes of oscillation of the vocal tract (the formants) have been investigated for the first time using the method of modal analysis. While this technique is generally used to study the modal properties of mechanical structures, preliminary studies have shown that this powerful method can be applied to the structure of the air column of the vocal tract. The analysis was carried out by applying an impulse above the larynx on the outside of the throat with closed glottis, and measuring the transfer response at an array of points inside the mouth. Modal analysis presents speech modes in animated form, which allows a comprehensive understanding of their detail to be obtained which has not been available in speech research before. For one subject, details of the modes of the first eight formants to 6.4 kHz will be presented. The first five formants are standing waves propagating in one dimension along the tract, but the sixth to the eighth formants show distinct propagation in two dimensions. Formant frequencies and bandwidths are available from the modal properties. The method has the capability of providing data on the three-dimensional vibration of the tract which has not been available before. The application of this technique to other associated investigations in speech will be mentioned.
Remote sensing of the upper ocean with sound: A design study
Authors: Chotiros Nicholas P.
Published: October 2005

In order to obtain a better understanding of ocean dynamics, it is desirable to be able to observe the mechanical coupling between the kinetic processes of the ocean, such as surface motion, turbulence, and internal waves. The important issues in designing a sonar for this purpose are presented. The objective is not only to measure the statistics of the processes, such as mean velocity or rate of kinetic energy dissipation, but also to track the movement of discrete water masses in three dimensions. The critical design issues and signal processing requirements will be discussed. [Work supported by ONR.]
Waveguide characterizing and source localization in a shallow water waveguide using Prony's method
Authors: Shang E. C. , Haung Z. Y. , Wang H. P.
Published: October 2005

Horizontal samplings of a point source in a shallow water waveguide are processed by Prony's method. First, when the source position is known, a high resolution estimation of the normal mode parameter km—the horizontal component of mode wavenumber, can be obtained. Owing to the weak damping process, βm, the modal attenuation coefficient can be obtained by using a modified Prony's method. In this paper, an “interval average and iterative” approach is proposed. A numerical example illustrates that, a 10−4 resolution of km (150-Hz frequency) is provided by a 500-m data length, roughly an order of magnitude smaller than the data length required by the Hankel transformation technique. Second, when the source position is unknown but the waveguide characters (km, βm) are known, the same procedure can be used for source position estimation. Some numerical examples in typical shallow water waveguide will be presented.
Estimation of seafloor geoacoustic parameters from cross correlation of measured and simulated broadband signals
Authors: Vidmar Paul J. , Oakley David W.
Published: October 2005

The ratio R of the compressional (P) wave velocity to water sound speed, and g, the gradient of P wave velocity, have been measured for an abyssal plains environment by maximizing the similarity between measured and simulated low-frequency broadband acoustic signals from a single shot (explosive source) at long range. Simulated time series were produced by a computational model that predicts low-frequency bottom interacting waveforms that agree well with small grazing angle acoustic data from this environment [D. P. Knobles and P. J. Vidmar, J. Acoust. Soc. Am. 79, 1760–1766 (1986)]. Our measure similarity is Cmax, the maximum of the absolute value of the cross-correlation function of two time series, and Cmax has a strong dependence on R, g, and the experimental geometry; it has a weak dependence on the sediment density and P wave attenuation. Estimates of R and g agree with reported values. [Work supported by the NORDA Bottom Interaction Program.]
The frequency and depth dependence of geoacoustic parameters in a stratified sea bottom, remote-sensed from shallow water acoustic propagation
Authors: Zhou Ji-xun , Rogers Peter H. , Jarzynski Jacek
Published: October 2005

Due to the difficulty of direct measurement, inverse techniques need to be developed for determining the bottom geoacoustic parameters in low- and middle-frequency ranges. In this paper, dispersion analysis and normal mode measurements in shallow water are extended to extract acoustic attenuation and speed in a horizontally stratified bottom versus frequency and depth. The uncertainty is discussed. The computational and experimental results show that for a given frequency band, we can find an equivalent depth profile of sea-bottom acoustic attenuation with a linear frequency dependence (without depth structure) on some field characteristics, such as the attenuation rate of individual mode, the frequency response of long-range sound propagation, and the amplitude ratio of mode 2 to mode 1, etc. But the resultant equivalent negative gradient for sea-bottom attenuation is too strong to be accepted in comparison with previously available data. The conclusion is that nonlinear frequency dependence of the acoustic attenuation in the upper sedimentary layer is required to explain many aspects of shallow water sound propagation.
Results from remote sensing experiments of bottom shear modulus profile using a passive BSMP system
Authors: Yamamoto Tokuo , Conner Craig , Badiey Mohsen , Turgut Altan
Published: October 2005

Recently, an entirely new method of a passive remote system BSMP to extract the bottom shear modulus profile from the measured bottom motion induced by surface gravity waves [T. Yamamoto and T. Torii, Geophys. J. R. Astron. Soc. 85, 413–432 (1986)] was developed. The BSMP inversion has been proven to ‘be unique and consistent. Pilot systems of BSMP have been built and tested at the Great Bahama Bank, the Ohi River Delta, and the New Jersey Shelf. The shear modulus profiles of a wide range of bottom sediments and rocks and of complex layered structures have been extracted by the BSMP systems and have been supported by direct measurements. In this paper, experimental procedures and results from these BSMP experiments are discussed. [Work supported by ONR.]
Exploratory study of the potential effects of exposure to sonic boom on human health
Authors: Sutherland Louis C. , Plotkin Kenneth J.
Published: October 2005

A study has been carried out to investigate possible human health effects caused by exposure of residents of the State of Nevada to sonic boom during the period from 1969–1983. The sonic boom environments were estimated from an analysis of historical Air Force records of supersonic fighter aircraft operations and on available DUD-maintained computerized records of supersonic operations of military aircraft. The estimates of sonic boom environments were considered sufficiently reliable to use in searching for a possible link to health effects. The epidemiological study on the health effects, carried out by the Department of Community and Environmental Medicine of the University of California, Irvine, involved an extensive statistical analysis of any possible correlation between sonic boom exposure and all available mortality and morbidity health data for Nevada residents for the same geographic areas and time periods. From the data collected, no convincing evidence was found to prove or disprove the existence of adverse health effects due to exposure to sonic boom. If such evidence exists, it is most likely to be found only in a prospective study of a substantial sample of individuals over time. [Work supported by U.S. Air Force AAMRL under contract with Systems Research Laboratory, Dayton, OH.]
Theoretical and experimental investigation of the insertion loss of a dissipative muffler
Authors: Pommer Christian , Tarnow Viggo
Published: October 2005

By using a global theory of sound propagation in a circular duct with a dissipative material, the equivalent acoustical impedance of the cross section of the duct was calculated at low frequencies. Plane wave theory was then used to calculate the four-pole parameters of the duct using empirical formulas of the propagation constant and specific impedance of a dissipative porous material. The insertion loss of a single chamber dissipative muffler was calculated for different geometries and dissipative materials, and the insertion loss was measured using two microphone probes and white noise. The measurements were performed with different geometries and with different porous materials. The acoustical properties of the porous materials were calculated on the basis of the measured flow resistance and the calculated acoustical properties were compared with results obtained by using a standing wave tube method. A good agreement was found between the calculated and measured insertion loss of the single chamber dissipative muffler in the frequency range below the cutoff frequency of the muffler.
Acoustic radiation from a plate with sinusoidally varying properties
Authors: Pierucci Mauro
Published: October 2005

The acoustic radiation produced by an infinite flat plate with sinusoidally varying properties and driven by a distributed load is presented. The plate is assumed to be thin with constant thickness, but with stiffness varying sinusoidally along the axis. The analysis is an extension of the work previously reported [M. Pierucci, J. Acoust. Soc. Am. Suppl. 1 79, S35 (1986)]. The analysis consists of solving the coupled fluid-structure equations with the added difficulty of having nonconstant coefficients. The system reduces to a convoluted equation, which has been solved analytically. The results indicate the presence of acoustic pressure components radiating in directions that are related to the difference between the forcing function wavenumber and the wavenumber of the stiffness variation. Acoustic radiation patterns will be presented.
Time domain propagation studies with the NPE: Two short movies
Authors: McDonald B. Edward , Plante Dan , Ambrosiano John , Kuperman William A.
Published: October 2005

The nonlinear progressive wave equation (NPE) model has been used to investigate the propagation of linear and nonlinear broadband signals in a range-dependent shallow water waveguide. The NPE is the nonlinear time domain equivalent of the frequency domain parabolic wave equation (PE). Results from each of the studies are given in short computer-generated movies illustrating a four-cycle sine-wave pulse propagating a total of 20 km in isovelocity water (c = 1500 m/s) over a bottom (c = 1600 m/s) whose depth profile contains a shelf of slope 0.15 connecting regions of constant depth 225 and 150 m. Effects evident in the movies are: radiation into the bottom resulting in head waves that re-radiate back into the water column; energy dumping following reflection from the sloping bottom and surface; and mode separation at late times. Early time results suggest that bottom penetration is greater when nonlinearity is included.
Comparing effects of different starting fields for parabolic equation models
Authors: Robinson E. Richard , Wood David H.
Published: October 2005

A parabolic equation model requires a starting field; that is, the values of the field must be given as a function of depth at a fixed range. A desirable starting field must satisfy two requirements: (1) It should excite the propagating modes with the proper amplitudes; and (2) it should excite nonpropagating modes only to the extent that their effects can be filtered out with increasing range by the false bottom usually added under the ocean floor, which can more than double the depths involved. In practice, the usual approach is to use an easily computed result such as a Gaussian, filtered Gaussian, sine, or uniform ocean starting field. The false bottom is then increased to meet the second criterion. The advantage of the normal mode starting field is that it does not excite unwanted nonpropagating modes, which minimizes the need for the false bottom, which in turn reduces the running time of the model proportionally—once the starting field is computed.
A comparison of parabolic equation models with stepwise coupled modes in a shallow-water range-dependent environment
Authors: Syck James M. , Monti Joseph M.
Published: October 2005

Parabolic equation calculations are compared with stepwise coupled mode COUPLE calculations for a set of runs for which the two models have overlapping capability. The PE calculations were then extended to consider the additional case of refracting sediment. Normal mode start-up fields were used in the calculations. PE models have capabilities differing in the areas of wide angle capability, treatment of the bottom, and numerical methods. The intent of this paper is to discuss which of these differences make a difference. The environment chosen was that presented in the previous paper. Calculations were performed at 50 and 300 Hz. Water depths varied somewhat, but averaged about 150 m, corresponding to 3 wavelengths and 15 wavelengths at 50 and 300 Hz, respectively. The dependence of depth with range took two forms. The first consisted of smoothly varying linear segments, the second was the same as the first with a number of spikelike irregularities added in. Differences are discussed in terms of numerical issues and the physics incorporated in the models.
HYPER: A hybrid parabolic equation-ray model for underwater sound propagation in the vicinity of smooth caustics
Authors: Tappert Frederic , Weinberg Henry
Published: October 2005

The hybrid parabolic equation-ray model (HYPER) uses modified ray tracing of geometrical acoustics to locate important propagation paths. Then HYPER solves a modified parabolic equation in a small region near the rays to compute the pressure field. This paper applies the HYPER model to investigate acoustic propagation in the vicinity of smooth caustics. Results are compared with ordinary ray theory, modified ray theory, and the wave solution for a range-independent case. Some range-dependent examples are also presented. [Funding for this work was provided by the AEAS Program Office, ONR Detachment, Code 132.]
Fast field computations using transmutation
Authors: Gilbert Robert P. , Wood Daivd H.
Published: October 2005

Fast field computations without range dependence are based on computing the Hankel transform of the Green's function of the separated depth-dependent ordinary differential equation. As usual, the required Green's function is expressed in terms of two solutions of the homogeneous differential equation, the first satisfying the boundary condition at the surface of the ocean, the second satisfying the boundary condition at the bottom of the ocean, and the Wronskian of these two functions. In our approach, one solution is given in terms of one transmutation that preserves the surface boundary condition, and the other is given in terms of a different transmutation that preserves the bottom boundary condition. Once the two different transmutation kernels are found, they are applied to trigometric functions that satisfy the respective boundary conditions, and the Green's function is numerically computed. A fast Hankel transform (the usual fast Fourier transform approximation was used) completes the calculation of the field versus range.
Numerical solution for the diffraction of internal sound sources by a free-flooded cylindrical shroud
Authors: Martinez Rudolph
Published: October 2005

The problem of determining virtual source distributions for an insonified free-flooded pipe of finite length is posed as a pair of coupled integral equations. The geometry is assumed to have a rigid outer surface and a locally reacting inner surface. Predictions are made of directivity patterns of diffracted sound, with particular interest in the effect of lining characteristics on levels of on-axis noise. At each chosen frequency the solution to the boundary-value problem is checked by confirming the power balance between that injected at the incident source, and the sum of corresponding radiated and lining-dissipated values. The effect of finite length on input energy is established upon comparison to that for the similarly lined infinite waveguide.
The airborne noise path for an acoustic source inside a fluid-loaded cylindrical shell
Authors: Lo Edmond Y.
Published: October 2005

The radiation of noise from machinery located inside a submerged elastic structure involves both a direct structure-borne and flanking airborne path. Calculations were performed to assess the importance of the latter for a cylindrical shell excited by an interior monopole source. An analytic solution for the interior pressure field is derived for a prescribed wall impedance using the Helmholtz integral equation approach, Farfield pressures are evaluated for a baffled section of the shell. Transfer functions of farfield to interior pressures are presented over a frequency range encompassing the ring frequency. The excess insertion loss arising from the interior application of various absorptive blankets is evaluated.
Resolution of low-frequency attenuation anomalies in the Southern Hemisphere
Authors: Denham R. N. , Bannister R. W. , Guthrie K. M. , Mellen R. H. , Browning D. G.
Published: October 2005

During Project KIWI ONE [D. G. Browning et al., Nature 282, 820–822 (1979)] anomalously high values of low-frequency attenuation were observed in the central South Pacific Ocean. Similar results were obtained along a track from New Zealand into the Southern Ocean during Project TASMAN TWO [R. W. Bannister et al., J. Acoust. Soc. Am. 62, 847–859 (1977)]. A recent analysis of oceanographic data by Mellen shows that both regions are included in a relatively high pH contour at the sound channel axis. The corresponding predicted values of attenuation are in reasonable agreement with the measured data.
Sound transmission loss single number ratings
Authors: Walker Keith W.
Published: October 2005

Several single number ratings, including STC, for rating the sound insulation properties of walls were correlated with the A-weighted sound reductions of a group of gypsum board partitions for several types of sound source. None of the ratings fared well for the broad range of sound types. It is shown that a single rating method cannot deal with all sound sources. Two new ratings are proposed to supplement STC for coverage of indoor and outdoor noise reduction.
A source spectrum for simplified sound isolation tests specifically for results correlated to NIC ratings
Authors: Breitz Nigel D. , Leventhall H. G.
Published: October 2005

Using one-third octave-band sound transmission and reverberation time data of 54 party walls (ISO717, ISO140), the differences in dBA values between rooms were simulated as a function of wideband (90 Hz–3.5 kHz) source room spectra. An optimal source room spectrum was obtained by minimizing the standard deviation of (ΔdBAi − NICi) (i = 1.54) from the mean value. The rank correlation coefficient was seen to increase for decreasing standard deviation. The absorption data of the rooms were used to extend the results to the sound power spectrum of the source. Results, examples, statistical data, and comparison with other workers will be given.
On corner positioning of the sound source for sound isolation tests
Authors: Breitz Nigel D. , Leventhall H. G.
Published: October 2005

For reproducibility of simplified sound isolation tests [when a large (∼ 12 m) approximately spherical, omnidirectional sound source is not used], it is appropriate to specify requirements for source placement. A scale model of a building with an exaggerated lopsided but reasonable quantity of absorption in one room (panel absorbers on wall surfaces around one corner) was used to investigate deviation of radiated power for the corner position from rigid wall conditions, the objective being to excite modes to an extent depending on their frequency and not mode number. The model and experiment will be discussed, and the results for this model as well as those for a full-sized baffled loudspeaker will be given. The placement is of more importance in countries where the 100-Hz, one-third octave band is included. In light of annoyance from hi-fi bass, the European range would seem more appropriate.
A rigid background analysis of the acoustic scattering from solid elastic targets
Authors: Trivett D. H. , Sammelmann Gary S. , Hackman Roger H.
Published: October 2005

At previous meetings of the Acoustical Society of America [L. H. Green, D. H. Trivett, and L. Flax, J. Acoust. Soc. Am. Suppl. 1 77, S79 (1985)], it was demonstrated that, for the analysis of the elastic excitations in the acoustic scattering from elastic targets, the proper background to subtract is a rigid background. This choice was utilized to analyze the low-frequency scattering from spherical and infinite cylindrical shells over a broad range of frequencies and shell thicknesses. However, in a recent paper on the acoustic scattering from elastic spheroidal solids [M. F. Werby and G. J. Tango, J. Acoust. Soc. Am. 79, 1260–1268 (1986)], it is concluded that a rigid background is inappropriate for elastic targets that have either low shear speeds or low densities. A complete reexamination of the scattering from elastic solids is presented to demonstrate that the rigid background is the appropriate choice in this case, too. In the course of this analysis, it is also demonstrated that Werby and Tungo have misinterpreted the nature of the elastic response of the scatterer.
Time-frequency analysis of acoustic reflection waves from elastic spheres
Authors: Yen N. , Dragonette Louis R. , Sarkissian Angie
Published: October 2005

A processing algorithm based on the Wigner distribution function is used to analyze the acoustic reflection from a solid sphere in a joint time and frequency representation. Test cases for spheres constructed from various elastic materials were computed from the theoretical form functions in the frequency range for ka from 0.3 to 20. It is observed from such time-frequency displays that the behavior of the scattered wave from those penetrable scatterers can be expressed in several related wave groups with certain frequency component concentrations and distinct time delays. Such features were exploited to reveal their relationship with the shape of the sphere and the velocity of sound wave propagation through the structure. The time separation among different delayed wave groups provides the characteristic parameters of the scatterer as their destructive interference will form strong nulls corresponding to the sharp spectrum lines predicted from the resonance scattering theory. Utilization of time-frequency analysis as a practical approach to describe a reflective elastic sphere is discussed.
Classification of resonances and remote aspect-ratio determination of submerged spheroidal elastic shells
Authors: Gaunaurd G. C. , Werby M. F.
Published: October 2005

Acoustic scattering was studied from submerged, steel, spheroidal shells in their resonance region. Arbitrary angular incidences were considered to analyze the possible aspect-angle dependence of the resonances. The shells are sufficiently thin so that the “proper backgrounds” of the RST [G. C. Gaunaurd and M. F. Werby, Int. J. Solids Structures 22, 1149–1159 (1986)] can be suitably suppressed, and the resonances can be adequately isolated. It is shown that the shell resonances are caused by surface standing waves propagating at discrete frequencies with an almost constant phase velocity. From this (surface) standing-wave interpretation (viz., geodesics) accurate resonance locations have been derived. Only two basic vibrational modes seem to exist, one along and the other normal to the axis of symmetry. Thus, only resonances corresponding to these two directions are possible. Furthermore, the fixed resonance locations seem to have amplitudes that change with incidence angle. Hence, this procedure permits the classification of resonances, and it can he exploited to extract the aspect ratio of the spheroidal shell from its returned echo. These points are illustrated with numerous computational examples. [Work supported by NAVELEX and ONR.]
Acoustic resonance scattering by large aspect-ratio solid targets
Authors: Green L. H. , Ku C. George , Werby M. F.
Published: October 2005

Previously, Werby and Tango [J. Acoust. Soc. Am. 79, 1260–1268 (1986)] examined the resonance response of solid spheroidal targets as a function of material properties. Results were presented for several different materials for targets with an aspect ratio ⩽2. Here the previous analysis is extended to high aspect-ratio targets. The transition matrix approach to acoustic scattering utilizing spherical basis states is used. Results for several different materials are presented over a KL/2 range of 0.5–16.0 for targets with aspect ratios from 1–10. It is demonstrated that the phase velocity of the Rayleigh resonances on solid spheriods is closely related to the shear speed of the material. In addition, high Q resonant peaks are shown to dominate the backscattered response for many high aspect-ratio targets.
Scattering of acoustic waves by a finite cylindrical shell containing a mixture of wax and colophony immersed in water
Authors: Bao X. , Varadan V. V. , Varadan V. K. , Xu Q. , Wang T.
Published: October 2005

A method employing boundary and finite element approaches as well as model analysis is used to study the scattering of acoustic waves by a finite cylindrical shell immersed in water. The cylindrical shell contains a mixture of wax and colophony and thus the elastic wave propagation in this mixture is also considered. The computed frequency response and direction pattern of the backscattering target strength show excellent agreement with measurements.
Coupling coefficient G for the Fabry-Perot representation of backscattering from spheres and cylinders: Quantitative GTD for elastic objects in water
Authors: Marston Philip L.
Published: October 2005

For each class of elastic surface wave, the contribution fsw to the total form function may be written in a Fabry-Perot representation [K. L. Williams and P. L. Marston, J. Acoust. Soc. Am. 79, 1702–1708 (1986)]. For backscattering |fsw| = |G exp[− 2β(π − θsw)]/[j + exp(− 2πβ + i2πxc/csw)]|, where x = ka and for spheres j = + 1. The surface wave's phase velocity and angular attenuation coefficients are csw and β while sin θsw = c/csw. The exact form function was synthesized by summing various fsw with a specular term. An expression for G, which had to be evaluated by numerical differentiation, was derived for solid spheres via a Sommerfeld-Watson transformation. In the present research, a simple approximation for |G| is derived by matching fsw with the RST result near a resonance when β is small. This gives |G| ≈ 8πβc/csw for spheres while for circular cylinders j = − 1 and |G| ≈ 8πβ/(πx)1/2. Comparison with the exact |G(x)| for Rayleigh waves on solid tungsten carbide and aluminum spheres gives agreement even when 2πβ is not ≪ 1. These approximations of |G| should also apply to the scattering of short tone bursts and to the fsw for hollow elastic shells. [Work supported by ONR.]
Acoustical holography based on Bojarski's exact inverse scattering theory
Authors: Gan Woon S.
Published: October 2005

This paper investigated the use of Bojarski's exact inverse scattering theory (BEIST) as the basis of acoustical holography (AH). The purpose is to improve generalized holography although generalized holography originates from BEIST. Generalized holography is not the complete solution of BEIST and some information is missing. Generalized holography (GH) has to be recast as an inverse scattering problem and not as an inverse source problem. By interpreting GH as inverse scattering, one takes account of sound diffraction and refraction within an inhomogeneous object, giving detailed information on the object that is not available in GH. In the present AH setup, more than one scattering experiment has to be performed using different insonifying waves of different frequencies to determine the object's properties. This is the same as what is done in diffraction tomography experiment. The holographic field equation was obtained using the BEIST. It included the scattering amplitude. A set of simultaneous equations was obtained relating the object (or scatterer) to the recorded scattering amplitudes as specified for some discrete sets of frequencies. These simultaneous equations were solved for the scatterer in terms of the measured scattering amplitudes. A new type of exact inverse scattering algorithm for AH is proposed.
Static, dynamic, and relational factors in vowel perception
Authors: Nearey Terrance M.
Published: October 2005

This paper reviews theories and empirical findings that bear on the perception of English vowels, with emphasis on the comparison of data-analytic pattern recognition studies with results from speech perception experiments. Methodological approaches and empirical results from research at the University of Alberta [e.g., T. M. Nearey and P. F. Assmann, J. Acoust. Soc. Am. 80, 1297–1308 (1986)] will be compared and contrasted to work in other laboratories. Issues to be considered include: (1) the role F1 and F2 and that of fundamental frequency and higher formants; (2) “vowel-space and speaking rate normalization” (global speaker context); (3) vowel-inherent spectral change (diphthongizatiun); and (4) local phonetic context (e.g., consonantal context). While all of the above factors have been shown to have reliable effects on vowel perception, the relative weight of such effects and the circumstances which may alter these weights remain far from clear. Analysis of these problems in current research and suggestions for future studies will be presented.
Judgments of coarticulated vowels are based on dynamic information
Authors: Williams David R.
Published: October 2005

Due to coarticulation, formant frequencies for vowels such as [u] and [ɪ] are lower between labial consonants than in isolated productions. When asked to categorize stimuli from three-formant or analogous three-tone [ᴜ]-[ɪ] and [WUW]-[WIW] continua matched on formant midpoint frequencies, listeners place their category boundaries closer to [ᴜ] for the [w w] stimuli. However, listeners asked to judge the relative pitch height of the same three-tone stimuli do not show a shift in category boundary locations [Williams et al., J. Acoust. Soc. Am. Suppl. 1 74, S66 (1983)]. To determine whether or not this lack of a shift resulted because midpoint frequencies of the [w_w] stimuli were isolated perceptually, subjects judged either vowel class or pitch height of the same stimuli with reference to isolated [ᴜ] and [ɪ]. While vowel categorization results were similar to those observed previously, pitch height boundaries now exhibited a shift opposite to that for the vowel judgments. Thus listeners apparently integrated across most (or all) of the duration of the [w w] stimuli when judging their pitch. These findings indicate that auditory mechanisms which isolate and interactively process successive time-varying and more stable regions of the speech signal cannot account for the perception of coarticulated vowels. [Work supported by NICHD Grant HD-01994.]
The perception of reduced vowel stimuli
Authors: Garrison Laurie F. , Sawusch James R.
Published: October 2005

Most theories of vowel recognition employ the first two spectral peaks (F1 and F2) or some transform of these as perceptual dimensions for the vowel space. This experiment was designed to investigate how humans categorize vowels that do not contain the usual F0, F1, and F2. Subjects were presented with single formant vowels (270–2938 Hz; F0 of 125 or 215 Hz) and asked to identify them using 12 vowel labels. The data show high-frequency stimuli were identified as front vowels and low frequencies were identified as back vowels. The [i] category was used for both extreme high and low frequencies. The tense vowel labels [u], [o], [a], and [i] predominated. A second set of stimuli consisting of tone analog to F1 and F2 (no F0) was presented to subjects for identification. These stimuli were also consistently categorized. As with the single formant stimuli, subjects used the tense vowel labels most often. Results will be discussed with reference to models and the nature of prototypes in vowel recognition. [Work supported by NINCDS.]
Why is the formant frequency difference limen asymmetric?
Authors: Hermansky Hynek
Published: October 2005

Flanagan [J. Acoust. Soc. Am. 27, 613–617 (1955)] observed asymmetries in formant frequency difference limen in the perception of some synthesized vowel-like sounds and attributed those asymmetries to the proximity of neighboring formants. This hypothesis about the origin of the asymmetries in the perception of differences in vowel formant position is tangible and is widely accepted. The perceptual experiments of Hermansky and Jaykin [J. Acoust. Soc. Am. Suppl. 1 80, S18 (1986)] showed that the asymmetries in formant frequency difference limen can be reversed by small changes in fundamental frequency in the experiment. This observation questions the contribution of neighboring formants as a factor in the perception of small differences in formant position. Results of experiments in the perception of synthetic vowel-like sounds will be presented. They suggest that the formant distribution was not a major factor contributing to perceptual asymmetries in Flanagan's experiment. The role of formant structure in vowel perception is discussed.
Perceptual learning of vowels in a neuromorphic system
Authors: Morin Todd M. , Nusbaum Howard C.
Published: October 2005

Linear neuromorphic systems assume that stimuli are perceived as linear combinations of a set of underlying features represented as the eigenvectors of the stimulus space. Learning in this type of system is an autoassociative process that induces prototypes for each perceptual category. Anderson et al. [Psychol. Rev. 84, 413–451 (1977)] proposed that human listeners learn vowel categories through just this type of computational mechanism. To investigate this claim, a linear autoassociating network was trained on a set of prototypical American-English vowels. Performance of this network was examined for learning and classifying vowels produced by an average male talker. In addition, the effects of different auditory coding representations were compared on recognition performance for the male vowels. Since it is necessary for the underlying feature space to be linearly independent, the perceptual representation of the vowels can affect learning. Furthermore, the extent to which the underlying feature space learned from a set of vowels is shared between talkers is investigated. For this type of network to be a plausible model of vowel perception, it must be capable of perceptual constancy across talkers. Finally, the effects of different learning algorithms on the development of vowel categories in perceptual space were compared. The results of these studies and their implications for simple, linear network models of speech perception are discussed.
Identification of “hybrid” vowels in sentence context
Authors: Jenkins James J. , Strange Winifred
Published: October 2005

It has been demonstrated that listeners can identify the intended vowel in n CVC syllable even when the vowel nucleus has been attenuated to silence, leaving only onglides and offglides (Silent-Center syllables). Verbrugge and Rakerd [Lang. Speech 29, 39–57 (1986)] constructed “hybrid” Silent-Center syllables by cross-splicing onglides and offglides of citation-form CVC syllables spoken by a male and a female talker such that the formant trajectories were discontinuous. Identification of the intended vowel in hybrid syllables was no less accurate than vowel identification of the single-talker Silent-Center syllables. The present study replicates this research with syllables spoken in a earlier sentence “I say the word /dVd/ somemore,” using ten American-English vowels. Hybrid Silent-Center stimuli were prepared by crossing the stimulus sentences so that the sentence started with one talker and switched to the other talker after the silent portion of the test stimulus. Silent-Center Control stimuli were also prepared for each talker. The findings suggest that dynamic syllable structure provides talker-independent information about an articulatory/acoustic event. [Research supported by NINCDS.]
Explorations in speaker normalization
Authors: Ohala John J. , Hasegawa Yoko
Published: October 2005

Some preliminary efforts are reported at speaker normalization based on the assumption that listeners are tacitly aware (a) that they are listening to an instrument (the human vocal tract) which when uniform (unconstricted) should have resonances whose lowest frequencies are spaced according to the ratios 1:3:5:7, etc., (b) that the exact frequencies of these resonances depend on the length of the vocal tract, and (c) that what is relevant in resonances from a nonuniform tract is the ratio of these lowest resonances to their uniform value. There are probably several cues the listener could use to estimate the size of the speaker; for starters, we use the mean (long-term) F4. The reference resonances for F1r, F2r, F3r, i.e., those from the “uniform” tract, are 1/7, 3/7, and 5/7, respectively, of mean F4. The normalization consists in converting measured formant frequencies, F1m, etc., into the ratios of log F1m/log F1r. The results of applying this normalization to the entire voiced portion of vowels in a variety of CVC syllables is reported. [Work supported by a Sloan grant to Berkeley Cognitive Science Program.]
Evaluation of a spectrum target prediction model in speech perception
Authors: Akagi Masato
Published: October 2005

A mathematical model of the target prediction mechanism based on psychological experiments [Furui and Akagi, 12th ICA Toronto, A2-6 (July 1986)] is evaluated. In continuous speech, spectral undershoot is produced by coarticulation and the speech spectrum seldom meets its ideal target. It is assumed for the model that the undershoot is compensated by a prediction mechanism in the auditory system, realizing the target spectrum as an internal representation of speech spectrum. In this paper, three viewpoints are discussed comparing the results of the model with those of psychological experiments. (1) The model compensates for a transitional part of connected Japanese vowels and decreases the length of the transitional part that produces spurious vowel spectrum. (These spectra are actually unperceived under any speaking conditions.) (2) A perceptual critical point, where the following vowel in Japanese C-V syllable is initially perceived, corresponds well with its physically estimated point by the model. (3) The model is also applicable for compensating the transitional part of consonants in Japanese syllables and achieves the extraction of stable acoustic features for consonants. The results indicate that the model recovers phoneme characteristics neutralized by the coarticulation and corresponds well to the human hearing mechanism.
The problem of serial order in auditory word recognition
Authors: Nusbaum Howard C. , Greenspan Steven L. , Jensen Mathew
Published: October 2005

Recently, there has been a resurgence of interest in parallel distributed processing models of human perception. When speech perception is modeled in this type of spatially distributed network, a problem arises in coding the temporal order of perceptual units such as phonemes or words. In general, three solutions to this problem have been proposed: First, perceptual units may be context coded such as in context-sensitive allophones. The order of units presented at different points in time can be determined by matching the context “edges” of each activated unit. Second, different portions of the network may represent different time frames. By this approach, the recognition of each successive perceptual unit activates representations in successive segments of the network. Finally, temporal order may be represented in the computational dynamics of the network. In this case, expectations about serial order are used to shift the focus of processing attention within the network. Thus, while the first two approaches recode temporal order into a spatial or spatial-like representation, the third uses a temporal representation. Each of these approaches has positive and negative attributes, the implications of which will be discussed for a neuromorphic theory of speech perception. [Work supported, in part, by NIH.]
The neighborhood activation model of auditory word recognition
Authors: Lute Paul A.
Published: October 2005

The neighborhood activation model (NAM) of auditory word recognition describes the processes by which a stimulus word is identified in the context of phonetically similar words activated in memory. Stimulus input activates a set of acoustic-phonetic patterns in memory that must be discriminated and chosen among. These acoustic-phonetic patterns receive activation levels proportional to their similarities to the stimulus input. The activation levels may then be adjusted by biases arising from higher-level information, such as word frequency. The interaction of the bottom-up sensory input and top-down biasing information is assumed to take place within individual processing units called word decision units. These units monitor the activation levels of their acoustic-phonetic patterns, any higher-level information that may optimize decisions among the competing patterns, and the activity of all other word decision units. The NAM states that increasing the number of acoustic-phonetic patterns activated in memory by the stimulus input will slow processing and reduce identification accuracy. It also states that effects of word frequency are directly tied to the number and nature of similar words activated in memory and that word frequency is not intrinsic to the activation levels of the acoustic-phonetic patterns. [Work supported by NIH Grant NS-12179.]
Quasidipole and quasiquadrupole scattering from Arctic leads
Authors: Medwin Herman , Reitzel Ken J.
Published: October 2005

The leading and trailing edges of a plane ice plate and the perimeter of a polynya represent arrangements of wedge scatterers that are mirrored in the adjacent, pressure-release, water-air interface. As a result, an edge that is exposed to low-frequency underwater sound will backscatter energy in a pattern that closely resembles radiation from an acoustic dipole. Likewise, the reradiation from a lead whose separation is small compared to a wavelength can resemble radiation from a quadrupole. The reason for this behavior, and its significance in the total low-frequency scatter from the Arctic canopy, is discussed in terms of wedge theory and the laboratory scale model experiments, which confirm this interpretation. [Work supported by ONR.]
Dependence of low-frequency backscatter on the size and orientation of lineal Arctic scatterers
Authors: Browne Michael J. , Medwin Herman
Published: October 2005

The backscatter of low-frequency underwater sound from the Arctic ice canopy is generally caused by leads and ridges of a vast variety of sizes, orientations. and spacings. Laboratory scale-model experiments, guided by the theory of sound diffraction from wedges, have been used to determine the dependence of low-frequency backscatter on the geometrical parameters. The specific variation with the orientation and length of the lineal scatterer is demonstrated, and it is shown that the predominant scatter occurs when there is a section of the lead or ridge that is azimuthally perpendicular to the sound path. [Work supported by ONR.]
The validity of the perturbation approximation for rough surface scattering
Authors: Thorsos Eric I. , Jackson Darrell R.
Published: October 2005

The accuracy of the first- and second-order perturbation theory approximations for randomly rough, pressure-release surfaces has been examined through comparison with exact numerical results based on solving an integral equation. A Gaussian roughness spectrum was chosen for the surfaces, and a Monte Carlo procedure was used to obtain the average bistatic scattering cross section. Results will be presented to show that the condition h/λ ≪ 1, where h is the rms waveheight and λ is the acoustic wavelength, is not sufficient to ensure the accuracy of first-order perturbation theory. An additional constraint must also be imposed on the surface correlation length. [Work supported by ONR.]
First-order three-dimensional scattering from rough interfaces and the effects of shadowing, local reflection coefficients, and surface gradient terms
Authors: Keiffer Richard , Werby M. F.
Published: October 2005

It is usual in the development of rough interface models to limit theory to two-dimensional models or to ignore shadowing and penetration into the surface as well as surface gradient terms that arise in the formal derivation of the equations. The secood-order term has recently been examined to determine its importance in scattering from rough interfaces. The purpose of this study is to examine the effects of (a) shadowing, (b) penetration, and (c) surface gradient terms on the overall calculation of some representative surfaces. Moreover, a full three-dimensional model can allow for out-of-plane scatter, and this effect will also be examined. The method of treatment of penetration into the surface is via a local reflection coefficient. Preliminary results show that the majority of these effects are most important in backscatter, where they tend to enhance the magnitude relative to the forward direction.
Extended time and space results from MATE
Authors: Ewart Terry E. , Reynolds S. A.
Published: October 2005

In the Mid-Ocean Acoustic Transmission Experiment (MATE) pulsed tones and Taylor-weighted FM slides at 2.083, 4.167, 8.333, and 12.5 kHz were received, after propagation over an 18.1-km wholly refracted Fermat path, at four tower-mounted transducers located at the corners of a 3-m vertical by 150-m horizontal rectangle oriented transverse to the raypath. Extensive oceanographic measurements are available to characterize the deterministic and stochastic sound velocity field of the scattering volume. The scattering parameters γ and X range over 145–31 500 and 0.094–0.016, respectively. Earlier publications focused on a 6-day intensity time series. The newly processed data extend the time series to 15 days and provide 8 days of data measured simultaneously at the horizontally separated receivers. These measurements of the complex field, together with the space/time sound velocity measurements, provide a unique data set with which to test predictions of the various acoustic field moments. Results will be presented for single receivers and vertically and horizontally spaced pairs. Theoretical predictions, where available, will be compared. Implications of the results to our understanding of WPRM will be discussed. [Work supported by ONR.]