bluuebunny/crossref_metadata_2025 huggingface dataset:
An algorithm for automatic needle localization in ultrasound‐guided breast biopsies
Authors: Draper Katharine J. , Blake Christopher C. , Gowman Linda , Downey Donal B. , Fenster Aaron
Published: July 2002

An algorithm was developed in order to reduce operator dependence in ultrasound‐guided breast biopsy, by automatically locating the needle in the ultrasound image, and displaying its location on the image for the user. Ultrasound images of a typical breast biopsy needle inserted in a tissue‐mimicking agar were obtained to test the algorithm. The resulting images were examined by a group of observers who recorded the values of the angle, intercept and tip coordinates of the needle in the image, and inter‐ and intra‐observer variability studies were performed on the results. The results of the algorithm segmentation were compared to the values recorded by the observers, and physical measurements recorded at the time the images were acquired. The algorithm segmentation was precise enough to successfully (when considering angle and tip segmentation) target 90% of tumors of 4.5 mm in diameter situated at the center of the image.
Improvement of dose distributions in abutment regions of intensity modulated radiation therapy and electron fields
Authors: Dogan Nesrin , Leybovich Leonid B. , Sethi Anil , Emami Bahman
Published: July 2002

In recent years, intensity modulated radiation therapy (IMRT) is used to radiate tumors that are in close proximity to vital organs. Targets consisting of a deep‐seated region followed by a superficial one may be treated with abutting photon and electron fields. However, no systematic study regarding matching of IMRT and electron beams was reported. In this work, a study of dose distributions in the abutment region between tomographic and step‐and‐shoot IMRT and electron fields was carried out. A method that significantly improves dose homogeneity between abutting tomographic IMRT and electron fields was developed and tested. In this method, a target region that is covered by IMRT was extended into the superficial target area by ∼2.0 cm. The length and shape of IMRT target extension was chosen such that high isodose lines bent away from the region treated by the electrons. This reduced the magnitude of hot spots caused by the “bulging effect” of electron field penumbra. To account for the uncertainties in positioning of the IMRT and electron fields, electron field penumbra was modified using conventional (photon) multileaf collimator (MLC). The electron beam was delivered in two steps: half of the dose delivered with MLCs in retracted position and another half with MLCs extended to the edge of electron field that abuts tomographic IMRT field. The experimental testing of this method using film dosimetry has demonstrated that the magnitude of the hot spots was reduced from ∼45% to ∼5% of the prescription dose. When an error of ±1.5 mm in field positioning was introduced, the dose inhomogeneity in the abutment region did not exceed ±15% of the prescription dose. With step‐and‐shoot IMRT, the most homogeneous dose distribution was achieved when there was a 3 mm gap between the IMRT and electron fields.
Efficiency of low‐contrast detail detectability in fluoroscopic imaging
Authors: Tapiovaara Markku J.
Published: July 2002

The detectability of a static low‐contrast detail in the dynamic fluoroscopic image of a homogeneous phantom was assessed by physical measurement of the signal‐to‐noise ratio (SNR) and by psychophysical measurement of the human observer detectability index The two‐alternative forced‐choice method was used for human observer tests. The image data consisted of digitally recorded fluoroscopic image sequences which were displayed in a continuous loop of varying length (1–50 frames) at a rate of 25 frames/s. Human detection performance was seen to improve with the SNR in all cases studied: when the signal was made stronger, the image noise lower, or when the SNR in the image sequence was made higher by increasing the length of the image sequence. The results imply that the statistical efficiency of humans decreases slowly when the number of frames in the displayed loop is increased. This decrease of efficiency with loop length was not seen in all test series, however, and it is possible that the phenomenon is partly related to the high values found at the greatest loop lengths studied. When the display contrast was high, the statistical efficiency of the human observer was 30%–40% for both static and dynamic images. The efficiency was somewhat lower, 15%–25%, for images that were displayed with a display contrast gain setting more typical of fluoroscopy. The accumulation rate of is a suitable quantity for the measurement of fluoroscopic image quality as related to a given static signal detection task. In contrast to this, visibility measurement by determination of the threshold contrast was seen to be unacceptably imprecise if the test is based on only one observer's opinion, as is often the case in practical quality assurance testing. The precision of the threshold contrast measurement could, however, be improved by using several observers and test objects with a smaller step between details than is usual.
The physical basis for empirical rules used to determine equivalent fields for phantom scatter
Authors: McDermott Patrick N.
Published: July 2002

Simple empirical rules are widely employed to determine the size of the square radiation field which is equivalent to either a rectangular field or a circular field with respect to phantom scatter. For a rectangular field, the area divided by the perimeter of the rectangle is equated to the area divided by the perimeter of the equivalent square. For circular fields, the area of the circle is sometimes equated to the area of the equivalent square. These empirical rules are very simple and remarkably accurate. They have been in daily use for 30 years, yet there is little discussion in the literature of their fundamental physical basis. An equation is derived for the equivalence of rectangular fields which has the form of the area over perimeter result multiplied by a “correction” factor. This equation is based on fundamental physical principles and it agrees better, within its domain of applicability, with published data than the area over perimeter rule. It is also shown that what appear to be different arbitrary rules for circles and rectangles both emerge from the same underlying physical analysis.
Validation of K x‐ray fluorescence bone lead measurements by inductively coupled plasma mass spectrometry in cadaver legs
Authors: Aro Antonio , Amarasiriwardena Chitra , Lee Mei‐Ling , Kim Rokho , Hu Howard
Published: July 2002

K x‐ray fluorescence (KXRF) systems are being used in a growing number of epidemiologic studies to measure bone lead levels as a biological marker of accumulated lead exposure. Although validation of the KXRF technique in lead‐doped phantoms and bare bone specimens has been repeatedly demonstrated, few studies have compared KXRF to chemical measurements of actual intact cadaver limbs (with skin and soft tissues). In this study, lead levels in eight amputated human legs were measured by KXRF; after dissection, levels in the bare bones were again measured by KXRF and then by inductively coupled plasma mass spectrometry (ICP‐MS). We observed close agreement between the KXRF and ICP‐MS measurements with correlation coefficients for both the tibia and patella greater than 0.9. In this study we provide further support for the validity of KXRF measurements, particularly with respect to the patella.
Demonstration of surface plasmons in metal island films and the effect of the surrounding medium—An undergraduate experiment
Authors: Orfanides P. , Buckner T. F. , Buncick M. C. , Meriaudeau F. , Ferrell T. L.
Published: July 2002

We present a demonstration of the surface plasmon phenomenon as it occurs in thin metal island films. The metal films are deposited on glass microscope slides. The effect of the surface plasmon resonance may be observed visually on the slide without further apparatus. Heating the film changes the shape of the islands and therefore the resonant frequency of the surface plasmon and changes the color of the film. Placing the film in a dielectric medium changes the resonance condition for the surface plasmon again and changes the color again. We show this by coating the slides with commercially available liquids with different indices of refraction. We present a theoretical model that assumes the islands are oblate spheroids. There are enough details given so that the equations can be programed and the theoretical optical absorbance can be reproduced. We also present a modification to the theory so that the shift in resonant frequency can be calculated when the spheroids are immersed in the index fluids. We describe our apparatus for making thin films and our optical spectrometer system. We then present optical absorbance measurements of thin films of both Ag and Au in air and in two liquids with different indices of refraction.
Carnot cycle for photon gas?
Authors: Lee M. Howard
Published: July 2002

The Carnot cycle for a photon gas provides a useful means to illustrate the thermodynamic laws. It is particularly useful in showing the path dependence of thermodynamic functions. Thermodynamic relationships to a neutrino gas are also drawn.
Matter waves in a gravitational field: An index of refraction for massive particles in general relativity
Authors: Evans James , Alsing Paul M. , Giorgetti Stefano , Nandi Kamal Kanti
Published: July 2002

We consider the propagation of massive-particle de Broglie waves in a static, isotropic metric in general relativity. We demonstrate the existence of an index of refraction that governs the waves and that has all the properties of a classical index of refraction. We confirm our interpretation with a Wentzel–Kramers–Brillouin solution of the general-relativistic Klein–Gordon equation. Finally, we make some observations on the significance of the optical action.
Getting more from pushing less: Negative specific heat and conductivity in nonequilibrium steady states
Authors: Zia R. K. P. , Praestgaard E. L. , Mouritsen O. G.
Published: July 2002

For students familiar with equilibrium statistical mechanics, the notion of a positive specific heat, being intimately related to the idea of stability, is both intuitively reasonable and mathematically provable. However, for systems in nonequilibrium stationary states, coupled to more than one energy reservoir, a negative specific heat is entirely possible. We present a minimal system that displays this phenomenon. For a system in contact with two thermal baths at different temperatures, the (internal) energy may increase when a thermostat is turned down. In another context, a similar phenomenon is negative conductivity, where a current may increase by decreasing the drive (for example, an external electric field). The counter-intuitive behavior in both processes may be described as getting more from pushing less. The crucial ingredients for this phenomenon and the elements needed for a minimal system are also presented.
Promoting conceptual change using collaborative groups in quantitative gateway courses
Authors: Kalman Calvin S. , Morris Stanley , Cottin Christopher , Gordon Robert
Published: July 2002

We report results on an experiment to promote conceptual change in the introductory calculus-based mechanics course using an approach based on collaborative learning. The approach is based on the notion of conceptual conflict developed by Hewson and Hewson [Instruct. Sci. 13, 1–13 (1984)]. Four basic concepts for which many students enter the class with alternative conceptions were treated in fall 1995 and fall 1996 in two sections taught by the same instructor. In fall 1995, in one section all four concepts were taught using the collaborative group approach and the other by standard professor-centered methods. In fall 1996, two sections were taught in section A using the collaborative group approach and in section B by standard methods. The other two concepts were taught in section B using the collaborative group approach and in section A by the standard professor-centered technique. (Subject matter in the traditional section was delivered using lectures, but delivery of concepts in both sections was supplemented with interactive computer programs, video disks, and VCR based materials.) Statistically significant greater conceptual change occurred in the treated groups compared to the control groups.
The rate of deflection of light in an accelerated frame and a gravitational field
Authors: Moreau William , Purdie Craig , Wood Joshua
Published: July 2002

We present calculations of the rate of deflection of light per unit central angle φ in a set of stationary frames along the light path in the gravitational field of the sun and in an equivalent (except for curvature) set of accelerated frames in flat spacetime in a study designed to further understanding of the equivalence principle in general relativity. The rate of deflection is emphasized in keeping with the local restriction of the equivalence principle in a metric theory of gravitation. In the sequence of stationary frames it is possible to distinguish the contribution from acceleration with respect to local inertial frames (the equivalence principle) from the total rate of deflection which includes the effect of spacetime curvature. Our results indicate that the deflection rate as a function of central angle can be expressed as dα/dφ=−(m/R)(1+2q)cos3 φ, where m is the geometric mass of the sun, R is the minimum radius at φ=0, and q is a curvature tagging parameter such that with q=0 we have only the effect of acceleration and with q=1 we have the full Schwarzschild curvature.
Strong field pair production
Authors: Holstein Barry R.
Published: July 2002

The subject of strong field pair creation, which has important cosmological implications associated with black hole decay, is studied in the simpler context of strong electric fields. The pair creation rate is calculated by formal methods first given by Schwinger as well as via less forbidding wave function techniques.
Time-varying spectral change in the vowels of children and adults
Authors: Assmann Peter F. , Katz William F.
Published: July 2002

Recent studies have shown that time-varying changes in formant pattern contribute to the phonetic specification of vowels. This variation could be especially important in children’s vowels, because children have higher fundamental frequencies (f0’s) than adults, and formant-frequency estimation is generally less reliable when f0 is high. To investigate the contribution of time-varying changes in formant pattern to the identification of children’s vowels, three experiments were carried out with natural and synthesized versions of 12 American English vowels spoken by children (ages 7, 5, and 3 years) as well as adult males and females. Experiment 1 showed that (i) vowels generated with a cascade formant synthesizer (with hand-tracked formants) were less accurately identified than natural versions; and (ii) vowels synthesized with steady-state formant frequencies were harder to identify than those which preserved the natural variation in formant pattern over time. The decline in intelligibility was similar across talker groups, and there was no evidence that formant movement plays a greater role in children’s vowels compared to adults. Experiment 2 replicated these findings using a semi-automatic formant-tracking algorithm. Experiment 3 showed that the effects of formant movement were the same for vowels synthesized with noise excitation (as in whispered speech) and pulsed excitation (as in voiced speech), although, on average, the whispered vowels were less accurately identified than their voiced counterparts. Taken together, the results indicate that the cues provided by changes in the formant frequencies over time contribute materially to the intelligibility of vowels produced by children and adults, but these time-varying formant frequency cues do not interact with properties of the voicing source.
The meaning of the Kelly–Lochbaum acoustic-tube model
Authors: Strube Hans Werner
Published: July 2002

The scattering equations of the Kelly–Lochbaum segmented tube, including the time-varying extension by Strube, are originally based on the assumption of uniform spatial segments and stepwise time update of the acoustic impedances. Here, it is shown that the same equations can be derived without these assumptions for a nonuniform time-varying tube from the discretization of space and time derivatives by the bilinear z transform or by centered differences along the rotated coordinates ct±x. Moreover, the same equations also hold for a chain of lattice circuits (or equivalents) with appropriate parameters, if time derivatives are discretized by the bilinear z transform. These circuits can also be extended to simulate uniform segments of varying length.
Effects of the salience of pitch and periodicity information on the intelligibility of four-channel vocoded speech: Implications for cochlear implants
Authors: Faulkner Andrew , Rosen Stuart , Smith Clare
Published: July 2002

Recent simulations of continuous interleaved sampling (CIS) cochlear implant speech processors have used acoustic stimulation that provides only weak cues to pitch, periodicity, and aperiodicity, although these are regarded as important perceptual factors of speech. Four-channel vocoders simulating CIS processors have been constructed, in which the salience of speech-derived periodicity and pitch information was manipulated. The highest salience of pitch and periodicity was provided by an explicit encoding, using a pulse carrier following fundamental frequency for voiced speech, and a noise carrier during voiceless speech. Other processors included noise-excited vocoders with envelope cutoff frequencies of 32 and 400 Hz. The use of a pulse carrier following fundamental frequency gave substantially higher performance in identification of frequency glides than did vocoders using envelope-modulated noise carriers. The perception of consonant voicing information was improved by processors that preserved periodicity, and connected discourse tracking rates were slightly faster with noise carriers modulated by envelopes with a cutoff frequency of 400 Hz compared to 32 Hz. However, consonant and vowel identification, sentence intelligibility, and connected discourse tracking rates were generally similar through all of the processors. For these speech tasks, pitch and periodicity beyond the weak information available from 400 Hz envelope-modulated noise did not contribute substantially to performance.
Beamforming for a circular microphone array mounted on spherically shaped objects
Authors: Meyer Jens
Published: July 2002

This paper will discuss the concept of phase modes to generate a desired beam pattern for a circular microphone array mounted around a rigid sphere. The method will be described for arrays consisting of omnidirectional and dipole sensors. The sound diffraction caused by the sphere is taken into account. It will be seen that the method allows, with some restrictions, the design of a wide variety of broadband beam patterns for a given elevation which usually will be the plane of the array. The directivity index is used to characterize the three-dimensional behavior of the array. Simulations show the realization of different beam patterns, based on a 16-element circular array located at the equator of a sphere with radius 0.085 m. The frequency range of this array is from 300 Hz to 5 kHz. Especially at low frequencies, a very good combination of the directivity index and the white noise gain is achieved which cannot be realized with “conventional” beamforming for an array of similar dimensions. The simulations are verified by means of a measurement.
Relationship between low-frequency aircraft noise and annoyance due to rattle and vibration
Authors: Fidell Sanford , Pearsons Karl , Silvati Laura , Sneddon Matthew
Published: July 2002

A near-replication of a study of the annoyance of rattle and vibration attributable to aircraft noise [Fidell et al., J. Acoust. Soc. Am. 106, 1408–1415 (1999)] was conducted in the vicinity of Minneapolis-St. Paul International Airport (MSP). The findings of the current study were similar to those reported earlier with respect to the types of objects cited as sources of rattle in homes, frequencies of notice of rattle, and the prevalence of annoyance due to aircraft noise-induced rattle. A reliably lower prevalence rate of annoyance (but not of complaints) with rattle and vibration was noted among respondents living in homes that had been treated to achieve a 5-dB improvement in A-weighted noise reduction than among respondents living in untreated homes. This difference is not due to any substantive increase in low-frequency noise reduction of acoustically treated homes, but may be associated with installation of nonrattling windows. Common interpretations of the prevalence of a consequential degree of annoyance attributable to low-frequency aircraft noise may be developed from the combined results of the present and prior studies.
Acoustic propagation through an internal wave field in a shallow water waveguide
Authors: Tielbürger Dirk , Finette Steven , Wolf Stephen
Published: July 2002

This paper addresses the problem of predicting and interpreting acoustic wave field properties in a stochastic ocean waveguide, for which the sound-speed variability within the water column is treated explicitly as a random process. It is assumed that the sound-speed distribution is composed of three components: a deterministic, time-independent profile and two stochastic components induced by internal wave activity. One random contribution represents a spatially diffuse Garrett–Munk field whose spectrum is constrained by the shallow water waveguide, while the second corresponds to spatially localized soliton packets. A high-angle elastic parabolic equation method is applied to compute single frequency realizations of the pressure field using this three-component representation of the sound-speed distribution. Ensemble-averaged transmission loss and scintillation index measures for the full pressure field and its modal components are estimated for different source depths and for both flat and sloping bottoms. Probability distributions of the mode amplitudes for different ranges are also presented. These statistical measures are incorporated into the analysis of range-dependent mode coupling between the internal wave and acoustic fields, and evidence is presented which supports a recent prediction that the scintillation index grows exponentially with range due to the competition between mode coupling and mode stripping found in shallow water waveguides. Full-field estimates of the scintillation index are also presented for a shallow water region on the continental slope off the New Jersey coast.
Classical and non-classical models of the cochlea
Authors: de Boer Egbert
Published: July 2002

In a “classical” model of the cochlea the response is controlled by a local parameter function, for instance, the BM impedance. In a non-classical model, the response is controlled by parameters that are distributed over space. In this note it is shown to which extent classical and non-classical models are equivalent. To each non-classical model there exists one classical model that yields the same response. However, the BM impedance of that classical model does not necessarily obey the requirements of a driving-point impedance.
A psychoacoustic annoyance concept for application in sound quality
Authors: Widmann U.
Published: July 2002

Industry engineers have to deal with the customer raising demands for acoustic comfort. At present, in the case of the judgment of sounds, manufacturers and customers go different ways. In the development labs noise is analyzed mainly by means of physical parameters. However, the customer judges a noise by means of human sense of hearing. These views can result in different assessments for the same sound. Therefore, objective quantities describing the different attributes of a sound in line with the human hearing system are necessary. In this study a psychoacoustic attempt is introduced aiming at a procedure for an objectively measurable psychoacoustic annoyance. The first results of a pilot study with synthetic noises with different loudness, sharpness, fluctuation strength, and roughness are presented, showing which psychoacoustic hearing sensations are related to the psychoacoustic annoyance evaluation of subjects. It is shown how the psychoacoustic annoyance evaluation changes if variations of more than one hearing sensation occur at the same time. A model summarizing the results for psychoacoustic annoyance is presented. General guidelines for application of the results for the development of consumer product sound is also presented. [See NOISE-CON Proceedings for full paper.]
The generation of psychoacoustic combination tones in relation to two-tone suppression effects in a computational model
Authors: Giguère Christian , Smoorenburg Guido F. , Kunov Hans
Published: July 2002

The amplitude of the psychoacoustic distortion product 2 f1−f2 elicited by primaries f1 and f2 depends on the method of measurement. The cancellation-tone procedure gives consistently higher estimates of the distortion product than nonsimultaneous procedures. It was suggested that the difference could be attributed to suppression effects by the lower primary f1 [Smoorenburg, J. Acoust. Soc. Am. 52, 615–632 (1972)]. Simulations carried out with a computational model of the auditory periphery including a single, but distributed, compressive nonlinearity confirm the hypothesis; the amount of suppression produced at 2 f1−f2 by f1 equals the difference between simultaneous and nonsimultaneous methods of measuring the amplitude of the distortion product. This is in agreement with psychoacoustical data [Shannon and Houtgast, J. Acoust. Soc. Am. 68, 825–829 (1980)]. The model also reveals the importance of suppression effects by f1 to bring the phase of the traveling wave associated with the cancellation tone 2 f1−f2 in exact opposition with that of the distortion product 2 f1−f2 generated by the primaries. There is also evidence of suppression effects by the higher primary f2 when L2≫L1. In the model, cancellation occurs over a substantial portion of the basilar membrane near the characteristic place for 2 f1−f2.
A comparison of perceptual word similarity metrics
Authors: Iverson Paul , Auer Edward T. , Bernstein Lynne E.
Published: July 2002

Contemporary theories of spoken-word recognition rely on the notion that the stimulus word is mapped against, or selected from, words in long-term memory in terms of its phonetic (form-based) attributes. A few metrics have been proposed to model the form-based similarity of words, including an abstract phonemic metric computed directly on the lexicon (i.e., Coltheart-n), and perceptual metrics derived from the results of phoneme identification experiments. The results of applying several different metrics to phoneme and word identification data (open-set and forced-choice tasks) will be discussed, and these metrics across stimulus conditions with a range of intelligibility levels and similarity structures (visual-only lipreading, audio-only conditions processed by a vocoder, and audiovisual conditions pairing vocoded audio with lipreading) will be compared. The our results suggest that graded perceptual metrics may be most useful for understanding the results of word identification experiments across a wide range of stimulus conditions. [Work supported by NIH DC00695.]
Bistatic bottom scattering: Model, experiments, and model/ data comparison
Authors: Williams Kevin L. , Jackson Darrell R.
Published: July 2002

A model is presented for bistatic scattering from ocean sediments. It treats scattering due to both roughness of the seabed and volume inhomogeneities within the sediment. Accordingly, the scattered intensity is assumed to be a sum of two terms, one proportional to the roughness-scattering cross section and the other proportional to the volume-scattering cross section. The model is tested against data acquired as part of the Coastal Benthic Boundary Layer (CBBL) research program. As part of that program, an autonomous, circularly scanning sonar system was deployed in well-characterized regions. This sonar operated at 40 kHz, had a 5° horizontal beam, and acquired backscattering data over a 50-m radius. During part of the deployment, it operated in conjunction with a mobile receiving array so as to acquire bistatic data. The experimental apparatus and procedures are presented, and results are compared with model predictions.
Control of vocal intensity in budgerigars (Melopsittacus undulatus): Differential reinforcement of vocal intensity and the Lombard effect
Authors: Manabe Kazuchika , Sadr Ehsanee I. , Dooling Robert J.
Published: July 2002

Call production in budgerigars was studied using operant conditioning. In several experiments, budgerigars were reinforced with food for producing calls that were above or below a criterion level of intensity. This differential reinforcement procedure was successful in controlling vocal intensity in both directions showing that the intensity with which budgerigars produce vocalizations is under voluntary control. In additional experiments, call intensity maintained by food reinforcement was measured both in the quiet and in the presence of various levels of broadband noise. Call intensity in budgerigars increased significantly in noise, paralleling the well-known Lombard effect in humans which is the reflexive increase in speech intensity during communication in noise. Call intensity was measured in broadband noise and in a notched noise (no energy between 1.5 and 4.5 kHz) with the same overall level. Results show that noise in the spectral region of contact calls is most effective in causing an increase in vocal intensity. In aggregate, these experiments show that budgerigars have voluntary control over the intensive aspect of their vocalizations, that they normally monitor their vocal output though external auditory feedback, and, like humans, they exhibit the Lombard effect.
A task-dynamic approach to gestural anticipation in speech: A hybrid recurrent network
Authors: Saltzman Elliot , Mitra Suvobrata
Published: July 2002

Recent simulations of the anticipatory timing of speech gestures within the task-dynamic model of gestural patterning are described. To accomplish this, a sequential neural network architecture is used in a simplified dynamical system in which the network’s outputs define the activations of gestures within a set of vocal tract constrictions (‘‘tract variables’’) whose dynamics are second order. These activations act only to insert target values into the tract-variable dynamics; the stiffness and damping coefficients are fixed. The forward dynamics, from current tract-variable state and target inputs to the next tract-variable state, are then modeled by a second recurrent network whose outputs are fed back to the sequential network. In this manner the simulated articulatory timing patterns are sensitive both to the intended linguistic sequence and to the articulatory dynamics themselves. Simulations will be described suggesting that anticipatory gestural timing is defined along a simple implemented continuum between rigid time-locking and unrestricted lookahead behavior. Temporally elastic anticipatory behavior such as that reported for French lip protrusion falls naturally within this continuum. These results provide an elegant account of interspeaker and interlanguage differences in anticipatory gestural timing. [Work supported by NIH.]
The relation between identification and discrimination of vowels in young and elderly listeners
Authors: Coughlin Maureen , Kewley-Port Diane , Humes Larry E.
Published: July 2002

This study examined both the identification and discrimination of vowels by three listener groups: elderly hearing-impaired, elderly normal-hearing, and young normal-hearing. Each hearing-impaired listener had a longstanding symmetrical, sloping, mild-to-moderate sensorineural hearing loss. Two signal levels [70 and 95 dB sound-pressure level (SPL)] were selected to assess the effects of audibility on both tasks. The stimuli were four vowels, /ɪ,e,ɛ,æ/, synthesized for a female talker. Difference limens (DLs) were estimated for both F1 and F2 formants using adaptive tracking. Discrimination DLs for F1 formants were the same across groups and levels. Discrimination DLs for F2 showed that the best formant resolution was for the young normal-hearing group, the poorest was for the elderly normal-hearing group, and resolution for the elderly hearing-impaired group fell in between the other two at both signal levels. Only the elderly hearing-impaired group had DLs that were significantly poorer than those of the young listeners at the lower, 70 dB, level. In the identification task at both levels, young normal-hearing listeners demonstrated near-perfect performance (M=95%), while both elderly groups were similar to one another and demonstrated lower performance (M=71%). The results were examined using correlational analysis of the performance of the hearing-impaired subjects relative to that of the normal-hearing groups. The results suggest that both age and hearing impairment contribute to decreased vowel perception performance in elderly hearing-impaired persons.
Psychoacoustical evaluation of PSOLA. II. Double-formant stimuli and the role of vocal perturbation
Authors: Kortekaas Reinier W. L. , Kohlrausch Armin
Published: July 2002

This article presents the results of listening experiments and psychoacoustical modeling aimed at evaluating the pitch synchronous overlap-and-add (PSOLA) technique. This technique can be used for simultaneous modification of pitch and duration of natural speech, using simple and efficient time-domain operations on the speech waveform. The first set of experiments tested the ability of subjects to discriminate double-formant stimuli, modified in fundamental frequency using PSOLA, from unmodified stimuli. Of the potential auditory discrimination cues induced by PSOLA, cues from the first formant were found to generally dominate discrimination performance. In the second set of experiments the influence of vocal perturbation, i.e., jitter and shimmer, on discriminability of PSOLA-modified single-formant stimuli was determined. The data show that discriminability deteriorates at most modestly in the presence of jitter and shimmer. With the exception of a few conditions, the trends in these data could be replicated by either using a modulation-discrimination or an intensity-discrimination model, dependent on the formant frequency. As a baseline experiment detection thresholds for jitter and shimmer were measured. Thresholds for jitter could be replicated by using either the modulation-discrimination or the intensity-discrimination model, dependent on the (mean) fundamental frequency of stimuli. The thresholds for shimmer could be accurately predicted for stimuli with a 250-Hz fundamental, but less accurately in the case of a 100-Hz fundamental.
Parabolic equations for gravity and acousto-gravity waves
Authors: Lingevitch Joseph F. , Collins Michael D. , Siegmann William L.
Published: July 2002

Parabolic equations for gravity and acousto-gravity waves are derived and implemented. The wave equations for these problems contain singularities at depths at which the buoyancy frequency equals the forcing frequency. One of the advantages of the parabolic equation solution is that it is easy to avoid numerical problems associated with the singularities. Some problems involve an infinite number of propagating modes. This artifact of neglecting viscosity is handled by including stability constraints in the rational approximations used in the implementation of the parabolic equation. The parabolic equation is tested for idealized problems involving surface, internal, and interface gravity waves. Parabolic equation solutions are also presented for range-dependent problems involving internal waves in the ocean and acousto-gravity waves in the atmosphere.
Stochastic models for scattering by seafloor roughness
Authors: Jackson Darrell R.
Published: July 2002

Models for acoustic scattering by seafloor roughness can be divided into numerical models that treat individual realizations of the random seafloor and stochastic models that provide statistical moments representing the scattered field. Such stochastic models require statistical submodels for seafloor roughness and incorporate acoustic submodels that connect statistics of the scattered field with statistics of the random interface. Thus, one must consider the compatibility of the interface and acoustic submodels. Recent work by various investigators has resulted in a number of improvements over classical perturbation and Kirchhoff results. A variety of seafloor types (e.g., fluid, elastic, layered) can now be treated, and improved acoustic approximations permit application over a wider range of roughness parameters. Questions remain, however, as to the accuracy of the newer models. [Work supported by ONR.]
Native-language phonetic and phonological constraints on perception of non-native speech contrasts
Authors: Best Catherine
Published: July 2002

Adults discriminate many non-native speech contrasts poorly, especially from an unfamiliar language that is not (yet) an L2. The Perceptual Assimilation Model (PAM) [Best et al., JEP: HPP 14, 34 560 (1988)] posits that this difficulty stems from knowledge of both the phonological functions and the phonetic details of native speech segments. Thus, discrimination of an unfamiliar contrast depends not only on whether it resembles a native phonological contrast, but also on perceived goodness of fit between the non-native segments and native phonetic category(s). Cross-language comparisons support PAMs prediction that perceptual assimilation of contrasting non-native segments to a single native category yields poorer discrimination than assimilation to two categories (TC contrasts). Discrimination is worst if both phones are equally similar to a single category (SC), substantially better if they differ in category goodness (CG), near ceiling for TC assimilations, and good to excellent for consonants that fail to be assimilated as speech, instead being perceived as nonspeech events (non-assimilable: NA). Recent findings indicate that, as predicted, SC, CG, and TC assimilations are associated with preferential activation of left hemisphere language regions, whereas NA stimuli yields bilateral brain activation. Other findings with fluent bilinguals indicate a persisting L1 effect on non-native consonant discrimination even if their L2 is acquired prior to 5 years. [Work supported by NICHHD and NIDCD.]
Dispersion of longitudinal waves propagating in liquid-filled cylindrical shells
Authors: Kwun Hegeon , Bartels Keith A. , Dynes Christopher
Published: July 2002

The dispersion of the first two longitudinal wave modes, L(0,1) and L(0,2), was experimentally investigated for a cylindrical shell (such as a pipe or tube) that was completely filled with a liquid. It was observed that the presence of a liquid inside the cylinder dramatically alters the dispersion curve for the L(0,2) mode by dividing (or branching) the curve into approximately equally spaced regions separated by cutoff-type behavior. This branching was attributed to coupling between the unperturbed L(0,2) mode in the shell and the unperturbed longitudinal modes in a liquid cylinder with rigid boundaries, LL(0,2N), where N is an integer. The physical mechanism for the mode coupling was determined to be radial resonances in the combined liquid/pipe system. In time domain, the liquid effects on the dispersion are manifested as a long-duration signal or a series of short-duration pulses, depending on the pulse length of the transmitted signal relative to the reciprocal of the frequency interval between branching.
Time-delay estimation techniques applied to the acoustic detection of jet aircraft transits
Authors: Ferguson Brian G.
Published: July 2002

Time-delay estimation techniques are used to observe the transits of jet aircraft. Noisy time-delay estimates are rejected by using a coincidence (or Boolean) detector. Cross correlating the beamformed outputs of two arrays of receivers leads to a significant improvement in detection performance when compared with the results of cross correlating the outputs of two single receivers. During the passage of a jet aircraft overhead, the differential time of arrival of the acoustic wave fronts at the receivers varies rapidly with time, and so the integration time for each time-delay estimate is required to be short. Also, the differential (Doppler) time scale compression between the received signals is required to be zero prior to cross correlation, otherwise the time-delay estimates will be in error. A digital time series interpolation technique, which is implemented using the discrete Fourier transform, enables the receiver waveform having the larger Doppler compression to be expanded (or time dilated) so that it has the same time base as the waveform from the other receiver. When the time scale factors of both receiver waveforms match, the cross-correlation function attains its global maximum value at a time displacement corresponding to the correct time delay.
A method to determine the speech transmission index from speech waveforms
Authors: Payton Karen L. , Braida Louis D.
Published: July 2002

A method for computing the speech transmission index (STI) using real speech stimuli is presented and evaluated. The method reduces the effects of some of the artifacts that can be encountered when speech waveforms are used as probe stimuli. Speech-based STIs are computed for conversational and clearly articulated speech in several noisy, reverberant, and noisy-reverberant environments and compared with speech intelligibility scores. The results indicate that, for each speaking style, the speech-based STI values are monotonically related to intelligibility scores for the degraded speech conditions tested. Therefore, the STI can be computed using speech probe waveforms and the values of the resulting indices are as good predictors of intelligibility scores as those derived from MTFs by theoretical methods.
Perceptual salience of individually distinctive features in the calls of adult king penguins
Authors: Lengagne Thierry , Aubin Thierry , Jouventin Pierre , Lauga Jacques
Published: July 2002

In the king penguin, Aptenodytes patagonicus, incubation and brooding duties are undertaken alternately by both partners of a pair. Birds returning from foraging at sea find their mate in the crowded colony using acoustic signals. Acoustic recognition of the mate maintains and strengthens the mate’s fidelity and favors synchronization in the different stages of reproduction. In this study it was found that the king penguin vocalizes in response to the mate’s playback calls, but not to those of neighbors or unfamiliar conspecific individuals. To study individual features used by the birds for individual recognition of mates, various experimental signals consisting of synthesized modifications of the mate’s call were played back to the incubating bird. Results indicated that birds attend to the FM profile of the call, in particular its initial inflexion. The frequency modulation shape of the syllable can be assimilated to a vocal signature repeated though the different syllables of the call. King penguins pay little attention to the call’s AM envelope or its absolute frequency.
Perceptual adjustment to foreign-accented English
Authors: Clarke Constance M.
Published: July 2002

A central goal of speech research is to understand how the speech perception system handles variability. Previous work on variability due to differences in speakers’ voices has demonstrated that experience with a voice facilitates word intelligibility [L. C. Nygaard and D. B. Pisoni, Percept. Psychophys. 60, 355–376 (1998)]. The present study investigated whether a more abstract feature of voices, such as foreign accent, can also be perceptually learned and utilized in perception. The following question was tested: Does experience with an accent generalize to the perception of a new voice with the same accent? Two groups were trained with English sentences produced by either Spanish- or Chinese-accented voices. Both groups were then given a word intelligibility test in which sentences were presented in noise. Test sentences included both familiar and new Spanish- and Chinese-accented voices. Training improved intelligibility of familiar voices but did not affect perception of new voices with the trained accents. Results indicate that experience with an accent does not improve perception of a new voice with the same accent. Perceptual learning seems to be restricted to individual voices. Results are discussed with respect to current theories of speech perception. [Work supported by NSF.]
The role of duration in the perception of vowel quality
Authors: Hillenbrand James M. , Clark Michael J. , Houde Robert A.
Published: July 2002

Test signals consisted of formant synthesized versions of 300 utterances selected from a database of 1668 /hVd/ syllables spoken by 45 men, 48 women, and 46 children [Hillenbrand et al., J. Acoust. Soc. Am. 97, 3099–3111 (1995)]. Four versions of each utterance were synthesized: (1) an original duration set in which the duration of each vowel was matched as closely as possible to that of the original utterance, (2) a neutralized duration set in which the synthesis control parameters were linearly stretched or contracted to produce a fixed vowel duration of 272 ms (the mean of all 300 utterances), (3) a short duration set in which the contours were resampled to produce a fixed duration of 144 ms (two standard deviations below the mean), and (4) a long duration set in which the contours were resampled to produce a fixed duration of 400 ms (two standard deviations above the mean). The great majority of the signals were accurately identified under all four conditions, suggesting that the overall effect of duration on vowel identity is modest. Significant duration effects were observed, however, especially in the short-duration condition in which the majority of /æ/ tokens were heard as /ε/ and many tokens of /ɑ/ and /ɔ/ were heard as /ʌ/. [Work supported by NIH.]
Diffractive acoustic elements for laser ultrasonics
Authors: Clark M. , Sharples S. D. , Somekh Michael G.
Published: July 2002

Laser ultrasonics is an effective means of generating surface acoustic waves (SAWs). We have shown in previous publications how computer-generated holograms (CGHs) can be used to project optical distributions onto the sample surface. These can be used to control both the frequency content and the spatial distribution of the resulting ultrasound field. In this paper the concept is extended further to produce distributions which themselves act as diffractive acoustic elements (DAEs) for SAWs. It is demonstrated how frequency suppression, multiple foci, and frequency selective focusing of Rayleigh waves may be achieved with these elements. Agreement between the distributions predicted from the designs and those actually measured is excellent.
Typical Lubricating Greases as Linear Viscoelastic Materials
Authors: Criddle Dean W.
Published: July 2002

The results of an experimental study of rheological properties of typical lubricating greases are reported in this paper. Viscosity-shear rate relations are compared for steady-state shear and for transient shear conditions of stress relaxation and creep. In steady-state shear the systems are non-Newtonian, but under transient conditions of shear stress relaxation, they are linear viscoelastic for strains approaching their ultimate yield strain. The linear viscoelastic nature of two greases was confirmed by studies of the damping of a torsion pendulum for small strains. A sodium soap grease is shown to be linear viscoelastic by an analysis of creep data from the literature. Recognition of the wide range of strains for linear viscoelastic behavior simplifies the study of the flow and deformation of greases.