bluuebunny/crossref_metadata_2025 huggingface dataset:
Auditory representation of changes in vocal dynamic level.
Authors: Campbell Shari L.
Published: October 2005

It is well known that changes in vocal dynamic level do not result in a simple loudness increase. Rather, because the level of the higher harmonics tends to increase more rapidly than that of lower harmonics, distinct changes in timbre typically accompany the obvious changes in loudness. However, without reference to auditory transformations, it is difficult to determine which of the observed spectral changes are preserved in the ‘‘auditory spectrum,’’ or to estimate their perceptual effects. In order to address these issues, sung vowels were recorded from several classical singers. Data represent six voice classifications, three vowels, three dynamic levels, and three points within each singer’s fundamental frequency range. Various unidimensional metrics based on models of auditory processes such as frequency selectivity, masking, loudness perception, and timbre perception [Glasberg and Moore, Hear. Res. 47, 103–138 (1990); Aures, Acustica 59, 130–141 (1985)] were obtained. Results to date indicate that the weighted first moments of the specific loudness and sharpness distributions serve as promising means of quantifying changes associated with changes in vocal dynamic level, and that these metrics are most effective when derived from excitation patterns based on auditory filter shapes rather than masking patterns. [Work supported by UGACOE Faculty Research Grant.]
First formant spectral properties and initial stop–consonant [voice] judgments.
Authors: Molis Michelle R. , Diehl Randy L.
Published: October 2005

A low first formant (F1) onset frequency is an acoustic correlate of [+voice] consonants. This is predicted by the ‘‘low-frequency hypothesis’’ (LFH)—any increase in low-frequency energy near the consonantal closure will enhance the perception of [+voice] stop consonants. In contrast, Kluender, Lotto, and Jenison [J. Acoust. Soc. Am. 97, 2552–2567 (1995)] proposed that F1 onset frequency acts as a cue via an indirect effect on the temporal firing pattern of auditory-nerve fibers. Following voice onset, the synchronous firing of some mid- and high-CF fibers may become captured by energy in the region of F1. The degree of capture grows with decreased F1/F2 distance. It can also be enhanced by increasing the relative intensity of F1. In cases where F1 is more intense, the LFH predicts more [+voice] responses because the absolute amount of low-frequency energy is greater; the ‘‘synchrony capture hypothesis’’ predicts fewer [+voice] responses because synchrony capture is more likely as F1 intensity grows. In fact, manipulation of F1 intensity produced no change in subjects’ responses indicating that neither hypothesis is adequate in its present formulation. Evidence for changes in synchrony capture is provided by two computer models of auditory-nerve function. [Work supported by NIH.]
Preschool children’s use of dynamic acoustic information for word recognition.
Authors: Munson Benjamin , Edwards Jan , Fox Robert Allen
Published: October 2005

While young children’s ability to use dynamic acoustic information to categorize speech sounds has been studied in some detail [Nittrouer, J. Phon. 20, 1–32 (1992)], relatively little is known about their ability to use dynamic information for word recognition. This study investigates whether preschool children could use dynamic acoustic information to identify familiar words with missing consonants or vowels. A gated series [Elliot et al., Percept. Psychophys. 42, 150–157 (1987)] was used to examine young children’s identification of familiar CVC words with missing final consonants; similarly, a silent center series [Fox et al., J. Speech Hear. Res. 35, 892–902 (1992)] was used to examine identification of CVC words with missing vowels. Eighteen typically developing children aged three to five were tested. It was found that even the youngest children did remarkably well at recognizing words with missing final consonants, even at the longest gate when the consonant was deleted 40 ms before stop closure. By contrast, the children had more difficulty with the silent center series, with some children being unable to perform the task. Results will be presented also for a second set of gating and silent center tasks, in which a picture-pointing response, rather than a spoken response, was used.
A reconsideration of intensity-based duplex perception for speech.
Authors: Hall Michael D. , Kuhl Patricia K.
Published: October 2005

Duplex perception (DP) occurs when one stimulus component simultaneously contributes to two distinct percepts. In one potential demonstration, a sinusoidal glide is substituted for an F3 transition in a /da/ or /ga/ syllable, and the glide is claimed to distinguish the consonant while simultaneously being separately perceived as a nonspeech chirp. Recent concerns regarding the validity of evidence for this variant of DP were addressed using theoretically bias-free psychophysical methods. Individual thresholds for consonant, and chirp, perception were compared as a function of glide intensity. Consistent with DP, consonant identification and discrimination were maintained at glide intensities well below chirp detection threshold. Listeners also could not reliably match isolated glides to glides in speech context, indicating that consonants were not simply inferred from the perception of isolated glides. Methodological implications of the results are discussed, including the need to insure that the nature of consonant perception depends upon the mixture of a given glide with the remainder of the syllable. An alternative, and potentially more reliable method for evaluating chirp detection threshold also is provided. [Work supported by NIH.]
Stop consonant perception in 3- and 4-year-old children.
Authors: Ohde Ralph N. , Haley Katarina L.
Published: October 2005

The purpose of this study was to examine the importance of different acoustic properties for the perception of place of articulation in young children and adults. Ten adults and ten children in both of the age groups, 3 and 4 years, listened to synthesized consonant–vowel syllables comprised of all combinations of [b d g] and [i]. The synthesis parameters included manipulations of the following stimulus variables: formant transition (moving or straight), noise burst (present or absent), and voicing duration (10 or 46 ms). In a recent study [R. N. Ohde et al., J. Acoust. Soc. Am. 97, 3800–3812 (1995)] of children between 5 and 11 years of age, there was no difference between children and adults in terms of the perceptual weight placed on the dynamic formant transition cue. However, in the current study, preliminary findings indicate that young children’s identification of stop consonants was higher for moving transitions than straight transitions. In addition, the children’s identification of stops was frequently poor in the [i] context. Overall, these results suggest that children pay particular attention to dynamic cues in the early period of sound acquisition, and that they have reduced auditory sensitivity for acoustic correlates of place of articulation in the [i] context. [Work supported by NIDCD.]
Unusual elastic properties of pure and doped La2CuO4 as probed by resonant ultrasound spectroscopy.
Authors: Sarrao John L. , Fisk Z. , Darling T. , Migliori A.
Published: October 2005

La2CuO4 undergoes a structural phase transition from tetragonal to orthorhombic crystal symmetry as it is cooled below 525 K. Hole-doping the material (for example, by substituting Sr for La or Li for Cu) rapidly suppresses the structural transition temperature. Additionally, the in-plane lattice constant of La2−xSrxCu1−yLiyO4 is a function only of the combined hole count (i.e., x+y) and not of the individual Sr and Li concentrations. RUS measurements for stoichiometric, Sr-doped, and Li-doped La2CuO4 have been used not only to map out the phase diagram of this system but also to reveal the unconventional nature of the transition. These results suggest a strong coupling between hole concentration and structural properties as well as a large in-plane/out-of-plane anisotropy.
Cracks in steel rollers: Detection using resonant ultrasound spectroscopy.
Authors: Lei Ming
Published: October 2005

A resonant ultrasound technique has been applied to detect cracks in steel spherical rollers. Combining theoretical calculations with RUS measurements, steel rollers provided by a commercial source with various dimensions and aspect ratios were studied. As a result, correlations between aspect ratio and deformation type for some resonant modes were established. Empirical relationships between some specific modes and dimensions were also obtained, with which resonant frequencies of torsional, disk bending, and cylinder bending modes can be predicted from dimensions of the rollers for various aspect ratios. Hence, the testing frequency ranges for a given roller can be determined depending on the type of defects that need to be detected.
Scattering pole resonances: Relation to external and internal surface waves.
Authors: Überall H. , Duclos J. , El Hocine Khelil M. , Maze G. , Ripoche J. , Gérard A. , Bao X. L. , Raju P. K. , Sessarego J. P. , Sageloli J.
Published: October 2005

The resonance scattering theory and the singularity expansion method are based on the complex-frequency poles of the scattering amplitude; these are located off the real-frequency axis and lead to prominent resonances. Their physical origin lies in a phase matching of surface waves generated on the scattering object; hence a study of the resonances will lead to information on these surface waves. This will be demonstrated here for immersed elastic objects of plane, spherical, and cylindrical geometry where even the physical nature (fluidborne or elastic type) of the surface waves can be identified along portions of their dispersion curves, and where for multilayered structures individual-layer resonances can be distinguished, leading to solutions of the corresponding inverse problem.
Free vibrations of LiNbO3 piezoelectric crystals.
Authors: Dunn Martin L. , Ledbetter Hassel , Heyliger Paul
Published: October 2005

The first steps toward measuring the elastic and piezoelectric constants of piezoelectric solids using resonant ultrasound spectroscopy (RUS) have been undertaken. Specifically, free-vibration frequencies of a piezoelectric LiNbO3 crystal were measured up to 1 MHz. The vibration frequencies of the piezoelectric parallelepiped were also predicted using the finite element method with published values of the elastic, piezoelectric, and dielectric constants of LiNbO3. Published values of these constants from different sources using different methods are in reasonably good agreement. They also agree well with measurements of some of the constants performed in this study using a pulse-echo technique. Predicted piezoelectric vibration frequencies agree well with measured frequencies. Predictions from an elastic vibration analysis underestimate those from a piezoelectric vibration analysis by up to 12%. The results presented here suggest the feasibility of developing an inversion method to extract both the elastic and piezoelectric constants. This would extend the study of Ohno [I. Ohno, Phys. Chem. Minerals 17, 371–378 (1990)] who used RUS to determine the elastic constants of alpha quartz. The piezoelectric effect was considered, but no attempt was made to determine the piezoelectric constants as they were held fixed during the inversion to obtain the elastic constants.
The inherent background in acoustic wave scattering by a submerged target.
Authors: Choi Myoung Seon , Joo Young Sang , Lee Jong Po
Published: October 2005

A new concept for the background in resonance scattering of acoustic waves by a submerged target is proposed. The idea is that the remainder after removing only the resonances from the target response must be used as the background. The complex wave numbers whose imaginary parts are the attenuation coefficients of elastic bulk waves in target are introduced to damp out the resonances. From the assumption that the structural damping coefficient, the product of the attenuation coefficients of elastic bulk waves, and the outer radius of target, is a large constant compared with the radiation damping coefficients of resonances, a simple mathematical expression is derived for elastic cylindrical shells and named the inherent background. It is shown that the inherent background leads to the impenetrable (i.e., rigid or soft) background in some limiting cases and also describes exactly the background of elastic shell over entire frequencies regardless of shell thickness.
The masking-level difference in low-noise noise.
Authors: Hall Joseph W. , Grose John H. , Hartmann William M.
Published: October 2005

The masking-level difference for a 500-Hz pure tone signal was examined for an interaurally in-phase noise having different degrees of power fluctuations. MLDs were reliably smaller in noise having relatively low power fluctuations. This effect was due to the following trends in the threshold data. (1) For all subjects, the So threshold improved as the degree of noise fluctuation decreased. (2) For some subjects, the Sπ threshold worsened as the degree of noise fluctuation decreased. (3) For some subjects, the Sπ threshold stayed constant as the degree of noise fluctuation decreased. These results are discussed in terms of comodulation masking release and the relevance of envelope cues for the MLD. [Work supported by AFOSR.]
The masking level difference in children: Effects of signal and masker bandwidths.
Authors: Grose John H. , Hall Joseph W. , Dev Madhu
Published: October 2005

The age at which the magnitude of the masking level difference (MLD) reaches adult levels depends partly upon masker bandwidth (BW). For wider BWs, children perform like adults by 5–6 years of age. For narrow BWs, adult-like performance is not reached until an older age. To examine this age dependence further, this study measured the MLD for a 500-Hz tone as a function of masker BW in a group of 20 children aged 5–10 years, and in a group of 10 adults. Masker BWs were 20, 40, 80, 160, 320, and 1000 Hz, centered at 500 Hz. The MLDs of the children were generally smaller than those of the adults for BW = 20 Hz. Children over 7 years of age had adult-like MLDs for all BWs ≥ 40 Hz. The youngest children did not reach adult levels until BWs ≥ 320 Hz. To determine whether the smaller MLDs at narrow BWs were due to the perceptual similarity between the masker and the signal, MLDs were also measured in conditions where both masker and signal had BWs = 20 or 320 Hz. Children under 8 years of age showed the same MLDs for both BWs. Older children and adults had larger MLDs for the narrow BW. [This work supported by NIH NIDCD.]
Benefit of binaural hearing in a multi-source environment. II. Speech intelligibility.
Authors: Hawley Monica L. , Litovsky Ruth Y. , Dunton Leah B. , Jones Jennifer K. , Colburn H. Steven
Published: October 2005

A multi-source listening environment was simulated under headphones by recording signals through KEMAR in a sound-deadened room. Seven loudspeakers were each positioned in the frontal plane 5 ft from KEMAR at 30-deg increments, ranging from +90 (right) to −90 (left). The recorded signals (IEEE Harvard sentences) were digitally mixed and played back under headphones in a sound-proof booth using a Digital Audio Tape (DAT) player. Speech intelligibility was measured for a ‘‘target’’ sentence in the presence of various ‘‘jammers.’’ Three variables were manipulated. First, the number of ‘‘jammers’’ was either none, one, two, or three. Second, the relative location of the targets and jammers was varied, such that they were either in close proximity, widely separated, or some of each. Third, the jammer content comprised of either other sentences, speech-shaped noise, babble or time-reversed sentences. Normal-hearing listeners were tested under binaural and monaural conditions. On each trial the location of the target sentence was known, and the percentage of key words correctly identified is reported. Speech intelligibility was degraded as the number of jammers and as the target proximity to the jammers was increased. [Work supported by NIH DC02696, DC00100-21.]
Correlational analysis of acoustic cues for the discrimination of auditory motion.
Authors: Wang Wen , Lutfi Robert A.
Published: October 2005

Previously, it was reported that differential auditory thresholds for velocity and acceleration do not appear simply related to thresholds for displacement using synthesized sound sources [Wang and Lutfi, J. Acoust. Soc. Am. 95, 2897(A) (1994)]. The present study was undertaken to de- termine if the failure to find a simple relation might be due to differences in the types of cues mediating these thresholds. The sound of a source moving in a straight path on the azimuthal plane was synthesized over headphones to include three dynamic cues for motion: Doppler shift, intensity, and interaural delay. The three cues were perturbed slightly from trial to trial so that correlations with listener responses could be used to estimate the relative weight given to each cue. A 2IFC procedure was used to measure differential thresholds for displacement, velocity, and acceleration of four listeners. For the discrimination of displacement, responses were most highly correlated with intensity or interaural delay, but for the discrimination of velocity and acceleration, responses were most highly correlated with Doppler shift. The results provide a means of accounting for differences in sensitivity to motion that cannot be inferred from sensitivity to displacement alone. [Research supported by NIDCD R01 DC01262-04.]
Effect of the number of distracting streams on the focusing of attention on one auditory stream.
Authors: Brochard Renaud , Drake Carolyn , McAdams Steve , Botte Marie-Claire
Published: October 2005

The experiment reported here deals with the conditions under which listeners are able to focus their attention on one particular auditory stream within multi-stream sequences. Such sequences were composed of two to four isochronous pulses each with a different tempo (ISI=300, 400, 500 or 700 ms) and frequency (from 234 Hz). The effective focusing of attention on one stream was obtained by asking subjects to detect a local temporal irregularity in a target stream in the presence of one, two, or three other streams. To help subjects focus their attention, the multi-streams sequences were preceded by a cue composed of the regular target sequence. Temporal irregularity detection thresholds in the target stream were measured using a 2AFC paradigm (4 up/1 down). The results showed, contrary to expectations, that the ability to focus on one stream was independent of the number of streams (no difference in thresholds when more than two streams were added). So, listeners seem to create two perceptual spaces: one composed of the focused stream, and one composed of the nonfocused streams, irrespective of their physical characteristics. It is also easier to focus on outer streams (the highest or the lowest frequency) than on inner streams.
The effect of a free-field auditory target’s horizontal motion on its detectability.
Authors: Xiao Xin , Grantham D. Wesley
Published: October 2005

Previous work has shown that the motion of an auditory signal, when simulated over earphones by presenting a binaural stimulus with a changing interaural temporal difference, does not enhance its detectability relative to that of a stationary signal [Grantham and Luethke, J. Acoust. Soc. Am. 83, 1117–1123 (1988)]. The present study will compare the detectability of stationary and moving auditory targets presented in free-field, where all cues for location, including interaural level differences and spectral information, will be available. Six normal-hearing subjects will be tested individually in a darkened anechoic chamber. Masked threshold will be determined in an adaptive, single-interval 2AFC procedure for targets that are either stationary or moving at various velocities. Three different signals will be employed: a 500-Hz tone, an 8000-Hz tone, and a broadband noise. Preliminary results from one subject indicate that motion may enhance the detectability of broadband noise targets, but not of the pure-tone targets. [Work supported by NIDCD.]
Effects of musician’s earplugs and protective headgear on localization ability in the horizontal plane.
Authors: Vause Nancy L. , Grantham D. Wesley
Published: October 2005

The purpose of this study is to determine how well normal-hearing humans can localize sound sources while wearing protective headgear with and without hearing protection. Six subjects will participate in a source identification task to be conducted in an anechoic chamber. On each trial the stimulus (a 100-ms broadband source) will be presented from one of 20 loudspeakers arrayed in a semicircular arc, and the subject must state which loudspeaker emitted the sound. The arc spans 160° in the horizontal plane at ear level and is about 1.8 m distant from the subject. Each subject will be tested in eight conditions, involving various combinations of wearing protective headgear and three types of earplugs: the EAR plug and the Etymotic ER15 and ER25 ‘‘musician’s’’ earplugs. In addition, testing will be conducted at each of two orientations: frontal (center of the array at subject’s midline) and lateral (center of the array at 90° azimuth). Results are expected (a) to reveal whether the Etymotic earplugs (which are designed to attenuate equally across a broad frequency range) preserve localization accuracy, and (b) to quantify the interactive effects on localization performance of protective headgear and earplugs. [Work supported by NIDCD and NOHR.]
Lateralization of nonspeech audio-visual stimulus combinations.
Authors: Holt N. J.
Published: October 2005

Ability to lateralize stimuli was measured in eight normally hearing subjects. In experiment 1 auditory or visual stimuli were presented. Subjects responded with an auditory or visual pointer in conditions where stimulus and response modalities were the same (uni-modal) or different (cross-modal). A linear relationship was found between the position of the target stimuli and the perceived lateral position, establishing the correspondence between auditorily and visually presented positions, consistent with Yost [J. Acoust. Soc. Am. 70, 397–409 (1981)]. Mean judgments of linear position were independent of stimulus or response modality. In experiment 2 subjects were presented with bi-modal audio-visual stimuli with spatially and temporally correspondent modal components and subjects responded with an auditory pointer. Mean judgments of position were similar to those in experiment 1 but standard deviations were significantly smaller for the bi-modal stimuli relative to uni-modal stimuli. Experiments 3 and 4 involved manipulations of the spatial or temporal relationship between modal components of bi-modal stimuli. Whereas the relative importance of the visual modality was confirmed [Colavita, Percept. Psychophys. 15(2), 409–412 (1974)] the results of both experiments indicated that perception of the location of an audio-visual stimulus is influenced by information conveyed in both modalities. [Work supported by UKBBSRC.]
Detection of timing deviations in simple and complex rhythms.
Authors: Barnes Ralph , Reiss Jones Mari , Klein James
Published: October 2005

This experiment was designed to determine whether or not polyrhythmic structure and attentional set influence auditory stream segregation. In sequences where streaming does not occur listeners are often quite accurate in detecting small time changes, but this is not true when sequences stream. Here a two-alternative forced-choice task was used to examine time discrimination within polyrhythmic patterns involving two different tone frequencies (high, low). Polyrhythms with narrow, medium, and wide frequency separations between high and low tones were presented to each subject; single frequency control patterns were also used. Listeners determined whether a small time change in the rhythm occurred early or late in a recurrent presentation of each pattern. In addition to manipulation of frequency separation, rhythmic structure (simple, complex) and attentional set (selective, divided) were varied. Results indicated that both frequency separation (narrow, medium, wide) and rhythm (simple, complex) affected time-change detection. These findings have implications for theories of attention and stream segregation. [Work supported by NSF.]
The design of a satellite boom with enhanced vibration performance using genetic algorithm techniques.
Authors: Keane A. J.
Published: October 2005

This paper examines the application of passive vibration control methods to a simplified satellite boom. It is suggested that such methods may allow an efficient means by which to control structural vibrations. In this research, an initial structure is designed having a regular, repeating geometric pattern. This design is then modified using a genetic algorithm (GA), which is one of a number of recently developed evolutionary computing methods. Here the GA changes the geometry of the design by altering the three-dimensional coordinates of its joints. The aim is to minimize the band-averaged noise transmission along the boom. This paper shows that by altering the geometry in this way, significant improvements in the structure’s noise performance can be achieved. While this research is far from complete, the work outlined demonstrates the potential usefulness of this approach for controlling structural vibrations.
Active control of sound transmission through a structure into a coupled enclosure of arbitrary shape.
Authors: Cazzolato Ben S. , Hansen Colin H.
Published: October 2005

A numerical procedure for assessing the performance of an active noise and vibration control system for a harmonically excited weakly coupled multimodal vibroacoustic system is presented. The structure and the contiguous acoustic space have been modeled separately with a commercially available finite element analysis package (ANSYS) and then combined using a modal coupling theory for weakly coupled systems. Numerical results are compared against experimental measurements for a finite longitudinally stiffened cylinder with an integral floor. Experimental based response matrices were measured and used to predict the system response. Modal analysis was applied in order to reduce the required effort in determining the response matrix. A design methodology for optimizing the physical control system is reviewed and several trends presented.
Investigation of the dynamic response and stability of a Stirling cycle cryocooler.
Authors: Hausle F. W. , Gully W. G. , Bond Leonard J.
Published: October 2005

Existing analytical models for acoustic cryocooler vibration analysis assume 1-D axisymmetric behavior. A multiple scales perturbation analysis is used to describe the lateral dynamic response and stability of an axially oscillating Stirling cycle cryocooler core. The model of the oscillating core mass is assumed to possess two degrees of lateral motion freedom and the forcing function is multiple harmonic axial motion. A pair of mechanical springs which support the core mass is assumed to have axial-displacement-dependent lateral stiffness characteristics which results in parametric excitation of the lateral degrees of freedom. The effect of perturbing gas–fluid forces acting on the piston, which disturb the otherwise axisymmetric motion, is investigated. The perturbation analysis predicts the dynamic response in closed form and identifies regions of operation for unstable/chaotic motion. The results of the closed-form dynamic response predictions are compared with a numerical time-step Runga–Kutta method [F. Hausle, J. Acoust. Soc. Am. 94, 1853 (1993)]. Model results are also compared with experimental displacement-time-frequency data obtained with a new design of cryocooler. The insight given by this analysis is expected to lead to improved cryocooler design based on better understanding of the domain of configurational and operational parameters.
Explicit solution to the Kirchhoff integral formulation.
Authors: Wu Sean F. , Hu Qiang
Published: October 2005

An explicit solution to the Kirchhoff integral formulation for predicting acoustic radiation from a vibrating object is derived. The radiated acoustic pressure is shown to be expressible in terms of integrations of the normal and tangential components of the particle velocity over a surface that encloses the object. If this surface coincides with that of the vibrating object, then the normal component of the particle velocity is equal to that of the surface velocity, which is normally assumed given. The tangential component of the particle velocity, however, is different from that of the surface velocity, but is determinable experimentally by using an intensity probe. For a class of special cases in which the object dilates uniformly, the tangential component of the particle velocity is identically zero. Under this condition, the radiated acoustic pressure can be obtained by directly integrating the normal component of the surface velocity over the vibrating surface, rather than solving the surface acoustic pressure first, and then the radiated acoustic pressure, as it is traditionally done in the numerical solutions to the Kirchhoff integral formulation.
Stimulus variability and spoken word recognition: The effects of age and hearing impairment.
Authors: Sommers Mitchell S.
Published: October 2005

Three experiments were conducted to investigate the effects of age and hearing loss on the ability to maintain perceptual constancy in spoken word recognition. Specifically, the studies examined how variations in talker characteristics, speaking rate, and overall amplitude affected perceptual identification in normal-hearing young (NHY), normal-hearing elderly (NHE), and hearing-impaired elderly (HIE) listeners. The three dimensions were selected because variations in voice characteristics and speaking rate affect features of speech signals that are important for word recognition while overall amplitude changes do not have direct effects on phonetic identification. Thus, both phonetically-relevant and irrelevant sources of variability were investigated. Age differences, as indicated by greater effects of variability for the NHE compared with the NHY listeners, were observed for conditions with trial-to-trial variations in talker characteristics and overall amplitude. Effects of hearing impairment, as indicated by reduced scores for the HIE compared with the NHE group, were observed for conditions with variations in either speaking rate or talker characteristics. Considered together, the findings suggest that age-related changes in perceptual normalization, selective attention, and absolute sensitivity may all contribute to the reduced speech understanding often reported for older adults. Several possible mechanisms for the age- and hearing-related deficits are discussed.
F0 discrimination and concurrent vowel identification by hearing-impaired listeners.
Authors: Summers Van , Leek Marjorie R.
Published: October 2005

Labeling of concurrently presented vowels generally improves with the F0 difference between vowels (up to a limit of 2 to 4 semitones difference). One interpretation of this finding is that the processing of F0 differences between vowels allows listeners to group spectral components according to a common fundamental and thereby improve identification. However, the benefit of F0 differences may be reduced for hearing-impaired listeners to the extent that accuracy in processing F0 is compromised by the sensory impairment. In this study, normal-hearing and hearing-impaired listeners were tested to determine F0 difference limens for synthetic tokens of five steady-state vowels. The same stimuli were then used in a concurrent-vowel labeling task. Preliminary results indicate accurate processing of F0 differences between vowels, with thresholds generally below 2.0 Hz across vowels and listeners. On concurrent-vowel data collected thus far, hearing-impaired listeners showed an overall reduction in labeling accuracy relative to normal-hearing listeners. However, the benefit to labeling associated with F0 differences between vowels was of similar magnitude across groups. Additional subjects are being tested and analyses correlating performance on the F0 task with F0-benefit on the labeling task will be reported. [Work supported by NIH.]
Hearing impairment and same–different reaction time.
Authors: Seitz Philip F. , Rakerd Brad
Published: October 2005

Reaction time (RT) studies provide information about perceptual and post-perceptual information processing. A prior investigation found only small differences between the mean RTs of hearing-impaired (HI) and normal-hearing (NH) subjects performing a simple RT task with subjectively loud and soft tonal stimuli. The present study extended that group comparison to a choice RT task. Subjects with early-onset, moderate-to-severe sensorineural hearing impairments (N=8) and NH controls (N=14) made same–different judgments about digit pairs. In an auditory condition spoken digits were presented at two levels of loudness, representing the endpoints of a subject’s dynamic range. In a visual condition digits were shown at the dimmest and brightest settings of a computer monitor. All subjects performed accurately in both modalities (≳90% correct). Notable findings regarding RT were as follows: (1) The intensity variations had no significant effect for either group; (2) the two groups had comparable RTs in the visual condition; (3) the HI group was significantly slower in the auditory condition; and (4) subjects’ auditory and visual performance were strongly correlated for the NH group but not for the HI group. Factors affecting group and individual differences will be discussed. [Work supported by NIH-NIDCD.]
Assimilation of non-native vowel contrasts to the American English vowel system.
Authors: Best Catherine T. , Faber Alice , Levitt Andrea
Published: October 2005

The perceptual assimilation model (PAM) [Best et al., JEP:HPP 14, 345–360 (1988)] predicts that two non-native sounds that are assimilated to the same nature category will be harder for listeners to discriminate between than sounds that are assimilated to two different native categories (TC contrasts); how difficult will depend on whether they are equally good (or bad) exemplars of the single native category (SC contrasts) or not (CG contrasts). PAM was based on studies of consonant perception, as were subsequent tests of the model. This study extends the model to non-native vowels. American listeners performed keyword identification [W. Strange and T. L. Gottfried, J. Acoust. Soc. Am. 68, 1622–1625 (1979)] and categorical AXB discrimination tasks using six non-native vowel contrasts, Norwegian /i–y/, /i–■/, French /o–õ/, /œ–y/, /œ–■/, and Thai /■–■/. Assimilation patterns for a particular vowel contrast, inferred from keyword results, were more variable than in consonant studies but nonetheless strongly related to discrimination performance: TC contrasts were better discriminated than CG contrasts, which in turn were better discriminated than SC contrasts. Moreover, listeners who assimilated a particular contrast in TC fashion were better able to discriminate it than listeners who assimilated it in CG or SC fashion. [Work supported by NIH.]
Acquisition of non-native vowel categories.
Authors: Kingston John , Bartels Christine , Benki Jose , Moore Deanna , Rice Jeremy , Thorburn Rachel , Macmillan Neil
Published: October 2005

Is the acquisition of foreign phoneme identification determined by native abstract categories [Best, Development of Speech Perception, pp. 167–224 (1994)] or by particular tokens [Pisoni et al., Development of Speech Perception, pp. 121–166 (1994)]? If Best is correct, members of all instances of the same phonological contrast should be equally easy to identify. If Pisoni et al. are correct, then listeners should not generalize to new speakers or contexts. The acquisition by American English listeners of the potentially four front rounded German vowels /y:,y,oe:,oe/ was examined. Speaker and consonantal context were manipulated. Listeners improved with training. Our listeners, in contrast to those of Pisoni et al. (1994), generalized to new speakers and contexts. Contrary to Best’s 1994 prediction that identification of the same contrast would be equally easy, it was found in this study that listeners who heard one set of speakers identified the mid tense:lax /oe:,oe/ pair more accurately than the high /y:,y/ pair, and identified the lax high:mid /y,oe/ pair more accurately than the tense /y:,oe:/ pair. Listeners who heard a second set of speakers reversed these inequalities. Thus assimilation makes generalization to novel stimuli possible but does not preclude sensitivity to phonetic differences. [Work supported by NIH Grant No. 5-R29-DC01708 and NSF Grant No. DBD92-12043.]
An exact absorbing boundary condition and its application to three-dimensional scattering from thin dispersive structures
Authors: Cao Jiasu , He Sailing
Published: October 2005

It is emphasized that the three-dimensional time-domain wave-splitting formalism provides an ‘‘absorbing ’’ (or ‘‘radiation’’) boundary condition which is exact. When the splitting operator is known in an explicit form which can be implemented numerically, this can be used to advantage in scattering computation. In the present paper this fact is exploited in a time-domain computation of three-dimensional scattering from a slab characterized by an inhomogeneous dispersion (i.e., memory function; in general this function depends, besides on the time variable, on all three Cartesian space coordinates). Numerical results based on the exact absorbing boundary condition are given, and compared with results using a local approximation of the exact condition.
A proof of the convergence of the segmentation approach used in analysis of one-dimensional linear systems
Authors: Gupta V. H.
Published: October 2005

A numerical approach that involves discretization of a linear system with spatially varying properties into a sequence of a large number of segments, has been in vogue for quite some time, in order to obtain the transfer matrix for a nonuniform cross section of general shapes. In this paper, a mathematical proof of the convergence of the method is presented. A method is also presented with which one can obtain the equivalent differential equation, to whose solution the segmentation approach converges. This can be useful in ascertaining the correctness of the approach in case the segment transfer matrices have been derived using some empirical principles. The techniques have been illustrated by suitable examples.
Guided antiplane shear wave propagation in layers reinforced by periodically spaced cylinders
Authors: Lu Yichi
Published: October 2005

When a guided wave is propagated in a layer containing elastic cylinders, the presence of the cylinders gives rise to both amplitude and phase changes of the wave, and thus the variations in the dispersion relation for guided wave propagation in the layer. Using the reflection and transmission coefficients of an antiplane shear wave propagating across an array of periodically spaced cylinders in a full space, the effects of periodically spaced cylinders on the dispersion relation for guided antiplane shear wave propagation in a layer and a layer resting on a half-space (Love waves) have been investigated. This study is aimed at ultrasonic testing of continuously reinforced laminae or reinforced concrete slabs. Although only SH waves are studied, the results obtained should be relevant for other wave modes and lay the foundation for solutions of localized ultrasonic sources as well. It is found that the volume fraction of cylinders determines the influence of the cylinders on the dispersion relation. Thus waves propagate faster at a given frequency when the volume fraction of the stiffer cylinders is greater. The phase velocity and the group velocity for the inhomogeneous layer are larger than those based on the equivalent effective homogeneous layer. Either the phase velocity measurement or the group velocity measurement may be used to determine the volume percentage of cylinders when it is unknown and is sought after.
Deformation and position of acoustically levitated liquid drops
Authors: Shi W. Tao , Apfel Robert E.
Published: October 2005

A new numerical method has been developed for studying the static deformation of an acoustically levitated liquid drop in air. After the Fourier transformation is applied to the original integral form of the Helmholtz formula for the scattering of an axisymmetric acoustic wave by an incompressible liquid drop, solutions which are valid for all degrees of axisymmetric deformation up to the point of drop break-up are obtained. Calculations are presented for drops in both gravity and gravity-free environments, and are found to be in good agreement with experimental measurements by others. A physical picture of the competing processes introduced by drop deformation in a sound field is also presented. The predictions for the 1g case can be applied to ground-based experiments in which surface properties of acoustically levitated drops are being measured.
High-resolution bubble sizing through detection of the subharmonic response with a two-frequency excitation technique
Authors: Phelps Andy D. , Leighton Timothy G.
Published: October 2005

Sizing bubbles in fluid using a two-frequency excitation technique is not prone to the same drawbacks of some other sizing methods—it has a global maximum at the bubble resonance frequency and allows good spatial resolution. The bubble is insonated with a high fixed imaging signal and a variable pumping signal tuned to the resonant frequency of the bubble, which are coupled at resonance by the high-amplitude oscillation of the bubble wall, with the formation of sum-and-difference terms. This paper examines both the resonance and off-resonance behavior of such combination frequency signals. A coupling of the subharmonic bubble response with the imaging frequency is shown to be a much more accurate and unambiguous detector of the bubble resonance than couplings involving the fundamental resonance. The characteristics of this subharmonic signal are examined using an automated sizing method, and the dependence of the response on the pumping signal amplitude and the frequency step size between two successive pumping frequencies is examined. The location of a definite subharmonic threshold is reported and quantified both for single bubbles held on a wire and for free rising bubbles moving through the focus of the transducers. This amplitude is found to be orders of magnitude lower than that predicted by traditional volumetric pulsation models, but agrees very closely with the theoretical onset of surface waves.
Experiments on surface waves over a model impedance plane using acoustical pulses
Authors: Daigle Gilles A. , Stinson Michael R. , Havelock David I.
Published: October 2005

Experiments studying the propagation of acoustical pulses above a model surface are described. Under appropriate conditions, sound waves traveling in the horizontal direction above an impedance plane consist of a body wave and a surface wave. The body wave propagates at the speed of sound in air c while the surface wave is characterized by phase velocity ν<c and an amplitude that decreases exponentially with vertical height above the surface. Calculations of acoustical pulses propagating above an idealized impedance plane confirm these characteristics and show the surface wave as a distinct arrival from the body wave. Measurements have been made of pulses generated from a point source above a model surface consisting of a square lattice of cavities. The impedance of the surface was measured and theoretically modeled. The impedance values were used to compute predicted pulses. There is good agreement between the measured and predicted acoustical pulses.
Analysis of spatial reverberation statistics in the central Arctic
Authors: LePage Kevin , Schmidt Henrik
Published: October 2005

The horizontal covariance structure of long-range acoustic transmissions measured during the CEAREX 89 experiment is evaluated. Air-gun signatures received at a two-dimensional, horizontal array are processed for signal covariance at bubble pulse frequencies. The modal spectrum of the received signals is compact due to mode stripping, and the signals received on the array have low signal to noise ratio since the source level of the air gun is insufficient to overcome the spreading and scattering losses to the receiving camp. To increase SNR the received waveforms are stacked over 27 shots. The resulting waveforms exhibit the extremely high coherence characteristic of Arctic propagation. The average signal is removed from the stacked waveforms and the spatial covariance of the residual scattered field is estimated at the air-gun bubble pulse frequencies. The resulting statistics show the anisotropy characteristic of low grazing angle rough surface scattering. Based on these observations, an inversion for the spatial statistics of the ice canopy roughness is obtained using an elastic perturbation theory parametrization.
Geoacoustic databases for matched-field processing: Preliminary results in shallow water off San Diego, California
Authors: Bachman Richard T. , Schey Philip W. , Booth Newell O. , Ryan Frank J.
Published: October 2005

Detailed seafloor environmental modeling of a moderately complex shallow water area, coupled with multitone matched-field processing, produced reliable and unambiguous source detection and tracking. Frequency averaging of the matched-field output sufficiently reduced sidelobe ambiguities. The seabed geologic model is a gridded database containing water depth, sediment grain size, sediment thickness, and acoustic basement type. Grid cells are squares of side length equal to 2 arc s. Software, separate from the geologic model, computes a geoacoustic model for any desired grid square.
A boundary element solution for a mode conversion study on the edge reflection of Lamb waves
Authors: Cho Younho , Rose Joseph L.
Published: October 2005

The boundary element method, well known for bulk wave scattering, is extended to study the mode conversion phenomena of Lamb waves from a free edge. The elastodynamic interior boundary value problem is formulated as a hybrid boundary integral equation in conjunction with the normal mode expansion technique based on the Lamb wave dispersion equation. The present approach has the potential of easily handling the geometrical complexity of general guided wave scattering with improved computational efficiency due to the advantage of the boundary-type integral method. To check the accuracy of the boundary element program, vertical shear wave diffraction, due to a circular hole, is solved and compared with previous analytical solutions. Edge reflection factors for the multibackscattered modes in a steel plate are satisfied quite well with the principle of energy conservation. In the cases of A0, A1, and S0 incidence, the variations of the multireflection factors show similar tendencies to the existing results for glass. It is observed that the reflection of an incident wave becomes close to zero over a certain frequency range seen through energy interaction with other reflected modes, and increases again beyond this minimum point due to reverse mode conversion. The reflections of the higher symmetric incident modes, S1 and S2, are also investigated. It turns out that S1 mode is an unusual mode which is nearly unaffected by the mode conversion in the Lamb wave edge reflection.
Source influence parameters on elastic guided waves in an orthotropic plate
Authors: Pelts S. P. , Rose J. L.
Published: October 2005

An exact analytical solution for a three-dimensional case of the vibration of an infinite orthotropic plate loaded on its upper boundary is considered. The influence of source parameters on the characteristics of wave propagation in an orthotropic elastic infinite plate are analyzed. An asymptotic approximation for evaluating displacement in the far field is developed. Sample numerical calculation results are presented for various source parameters.