bluuebunny/crossref_metadata_2025 huggingface dataset:
Use of Monte-Carlo solutions of the PWE to test theoretical predictions
Authors: Ewart Terry E. , Maeaskill Charles
Published: October 2005

Recent theoretical solutions of the parabolic fourth moment equations for a field propagating in a medium with random inhomogeneities are available. These provide predictions of the spectral, cross spectral, covariance, and cross-covariance distributions of the intensity as a function of range, acoustic frequency, vertical wavenumber, and temporal frequency. The MATE results have been tested against theoretical predictions for the temporal frequency case, but only limited data are available for the vertical wavenumber case. Results will be presented on comparisons of Monte-Carlo solutions of the PWE for the case of media with Gaussian and power law autocorrelation functions. The Monte-Carlo simulations produce realizations of the complex field as a function of range scaled by the Fresnel length and the statistics of these fields are compared with theoretical predictions. The scattering regimes studied span a very wide range of the moment equation parameters Ϝ and χ. Results on the probability distributions of intensity will also be presented. Predictions of the complex field by Monte-Carlo simulation for the three-dimensional case of propagation in depth, range, and time will also be discussed. The computations were carried out on an IBM 3081 and a DEC VAX 750.
A three-dimensional model for computing the energy scattered from rough ocean bathymetry
Authors: Baer R. N. , Berman D. H. , Perkins J. S. , Wright E. B.
Published: October 2005

We discuss a computer model which predicts the directional distribution of bottom-scattered energy that is received by a linear acoustic array. An earlier version was presented last year [R. N. Baer, D. H. Berman, J. S. Perkins, and E. B. Wright, J. Acoust. Soc. Am. Suppl. 1 73, S10 (1983)]. The model is stochastic, incorporating statistics of the bathymetry and predicting statistics of the acoustic field. It has the advantage over deterministic approaches of not needing precise, usually unobtainable, environmental input. The model includes both the effects of bathymetric scattering and of refraction caused by a varying sound speed structure in the water column. It is a three-dimensional model in that it incorporates scattering out of a vertical plane. It utilizes the split-step solution for the parabolic equation approximation to the Helmholtz equation in regions away from the boundary. In the vicinity of the boundary, the coherence function is propagated along characteristic curves. Scattering is incorporated via a modified Kirchhoff formulation. In a sample calculation with a bathymetric height correlation length of 1600 m and an rms roughness of 32 m, array signal gains were degraded by 2 to 4 dB for frequencies ranging from 100 to 1000 Hz. In order to lessen the large computational load imposed by the many evaluations of the scattering integral, an exponential substitution approximation is employed. This approximation reduces the computation time of the scattering component by two orders of magnitude with minimal loss of accuracy. [Work supported by ONR.]
Numerical treatment of scattering from submerged objects
Authors: Werby M. F.
Published: October 2005

Acoustical scattering from submerged objects of arbitrary shape must, in general, be treated by numerical methods. It has proven very difficult to describe scattering from general objects without resorting to frequency limiting approximations. In this talk we describe extensions and improvements to a general numerical scheme originated by Waterman. This method is often referred to as the T-matrix method, the null-field method, or the extended integral equation by incorporating the interior solution (extinction theorem) as a constraint, and using an expansion procedure to obtain general solutions for a broad class of submerged targets without theoretical limitations on frequency. The formalism will be outlined for scattering from targets which are (1) rigid, (2) sound soft, (3) acoustic, (4) elastic solids, (5) elastic shells, and (6) elastic layered objects. Numerical difficulties encountered when using these methods in their conventional forms will be discussed, as well as procedures appropriate to overcome them. The discussion will describe: how to incorporate symmetry and conservation of energy; the coupled higher-order method; basis state optimization; eigen-expansion approaches; and efficient numerical strategies. The talk will be concluded by illustrating a number of numerical examples, emphasizing specific features peculiar to a variety of targets.
Computer modeling of mode interaction in a waveguide with a rough surface
Authors: Novarini Jorge C. , Medwin Herman
Published: October 2005

Acoustic scattering from surfaces with high slope elements is modeled numerically by describing the surface as a conjoint assemblage of wedges. The impulse response of the surface is then obtained by adding the single wedge responses which are calculated from the Biot and Tolstoy solution [J. Acoust. Soc. Am. 29, 381–391 (1957)]. By use of the FFT the spectral description of the scattered field is obtained. This method is then applied to the study of mode interaction due to wall roughness in waveguide propagation [Research supported by ONR.]
Computation of ocean reverberation scattering function
Authors: Princehouse D. W. , Goddard R. P.
Published: October 2005

For many purposes, acoustic reverberation can be modeled as a zero-mean Gaussian process. The scattering environment can be abstracted as the “master Doppler-density matrix” (MDDM). Each element contains the beam-to-beam covariance of reverberation due to all of the scatterers in the ocean that fall into that particular range-Doppler cell. The size of a range-Doppler cell depends on the resolution of the sonar. We describe a computation of the MDDM that incorporates sonar motion, beam patterns, and a comprehensive description of the acoustic environment. Boundary backscattering strengths and forward reflection losses are functions of the grazing angles. Volume reverberation is a function of depth. A range-independent propagation model is used, and the full multipath structure of the ocean is modeled. Scatterer motion and transmit pulse spectrum are added by convolution. The MDDM is useful itself as a measure of expected scattering properties. It may also be used to generate simulated reverberation signals via a correlated random number generation/signal processing step.
Use of spectra of hydroacoustic recordings of large underwater explosions to calculate iterative estimates of the bubble oscillation sequence
Authors: Griffin James N. , Pound Galen W. , Cunfer Ronald S.
Published: October 2005

When an explosive charge is detonated under water, the explosion produces a shock wave and an oscillating gaseous bubble whose behavior is intimately related to the physical properties of the explosive itself and of its environment. Many of these properties can be calculated from detailed measurements of the shock wave and of the bubble and its oscillations, but such measurements are seldom available for large explosions. We show an iterative inversion procedure for making band-limited estimates of the shock wave and bubble oscillation pressure waveforms from power spectra of farfield hydroacoustic recordings of large underwater explosions. We also show the ensemble averaging procedure that is needed to produce spectral estimates of sufficient stability and resolution to support the inversion procedure.
Essential elements for the evaluation of whole-body vibration
Authors: Barton J.C.
Published: October 2005

In most practical situations, the subject of human response to whole-body vibration (WBV) cannot realistically be separated from the subject of measuring and evaluating WBV in a given environment. Thus it is necessary to consider the several essential elements which tie together the current knowledge about human response to WBV and methods of measuring and evaluating WBV data. The objective of the measurement and evaluation must be clearly defined. The criteria for evaluating the WBV data must be meaningful with respect to the objective of the evaluation. The strong psychological elements and confounding factors associated with the environment of interest must be taken into consideration. It must be understood that the WBV data are only a means of predicting human response in a WBV environment, and that the real end result is the way that people actually respond in that environment. The nature of random vibration must be well understood and the mathematical concepts for quantifying random data must be rigorously applied throughout the evaluation process.
Passenger discomfort response to combined noise and vibration
Authors: Leatherwood Jack D.
Published: October 2005

A comprehensive research program has been conducted by NASA Langley Research Center to develop a fundamental understanding of human discomfort response to combined noise and vibration typical of that experienced within air and surface transportation systems. Results of this research program produced an empirical model of passenger ride comfort for use in the prediction and/or assessment of passenger ride comfort. The model is based on subjective ratings from more than 3000 persons who were exposed to controlled combinations of noise and vibration in the passenger ride quality apparatus at Langley Research Center. This model has the unique capability of transforming individual elements of a vehicle's noise and vibration environment into subjective units and then combining the subjective units to produce a single discomfort index typifying passenger acceptance of the environment. This paper discusses the approach and basic elements of the NASA ride comfort research program, describes the resultant model and its applications to real vehicles, and discusses a portable ride quality meter that is a direct hardware/software implementation of the NASA ride comfort model.
Detection of low-frequency wind turbine noise and noise-induced building vibration
Authors: Shepherd Kevin P.
Published: October 2005

Horizontal axis wind turbines for which the rotor is mounted downwind of the supporting tower generate low-frequency impulsive noise due to the passage of the blades through the tower wake. The design and siting of wind turbines which are acoustically acceptable require an understanding of the human perception of wind turbine noise and any noise-induced building vibrations resulting from their operation. This paper will describe a series of laboratory experiments performed to determine the detection thresholds of real and synthesized wind turbine noise with and without the presence of background noise. The results will be compared with predictions based on assumed auditory filter bandwidths and pure tone threshold levels. In addition, the prediction of noise-induced building vibration and its detection will be discussed. [Work supported by NASA Langley Research Center.]
Assessing the severity of the hand-arm vibration syndrome by vibrotactile perception
Authors: Brammer A. J. , Taylor W. , Piercy J. E.
Published: October 2005

Recent epidemiological studies of workers exposed to vibration suggest that the neurological, vascular, and musculo-skeletal disturbances in the hand-arm system develop independently, with the neurological symptoms reported first. A conservative measure of the severity of the syndrome may thus be derived from the degree of numbness and loss of fine touch, which present evidence suggests is due to mechano-receptor dysfunction. Recent electrophysiological studies on primates, including man, reveal that not all receptor groups are involved in fine touch (i.e., Pacinian corpuscles). However, current medical practice for assessing the severity of the syndrome: (1) does not attempt to separate the response of different mechano-receptor groups in vibro-tactile measurements, and usually records the threshold of Pacinian corpuscles, and (2) is largely based on an evaluation of the vascular component. In view of the new evidence, it is hardly surprising that clinical tests of vibro-tactile perception as a diagnostic tool have produced contradictory results. An improved method of measurement coupled with a revised medical scheme for diagnosing the neurological component will be discussed.
Effect of inlet flow conditions on discrete-tone noise generated by axial flow devices
Authors: Washburn K. B. , Lauchle G. C.
Published: October 2005

The effect of upstream obstructions on the discrete-frequency noise generation of small, axial-flow fans is investigated. These cooling fans, which operate at very low Mach numbers, generate discrete tones through fluctuating blade-lift forces. These dipolelike acoustic sources are a direct consequence of nonuniformities in the velocity inflow field interacting with the rotor blades. In typical applications, several types of protuberances act to disrupt the inflow. Three basic types of obstructions are modeled. These include cylindrical, rectangular, and periodic structures. The fans operate in an otherwise free, anechoic environment. On-axis, farfield sound pressure level data are obtained through narrow-band spectral analysis. Levels at the blades passage frequency and several prominent harmonics are presented as functions of the nondimensionalized distance of the various obstructions from the rotor hub. Regions critical to noise reduction are determined as aids to the designer. [Work supported by IBM Corporation.]
Wind noise reduction using a two microphone array
Authors: Marshall Daniel F.
Published: October 2005

The effectiveness of a method for wind noise reduction by cross correlation of the outputs of two vertically spaced microphones was studied. Average wind noise reduction was calculated for several microphone spacings and sample lengths; improvement in noise level on the order of 8 dB was achieved for 1-s samples with microphones spaced 31 cm apart, with better performance for longer samples and greater spacings. Correlation of acoustic signals was also investigated.
On the technical application of loudness meters
Authors: Zwicker Eberhard
Published: October 2005

Very precise loudness meters based on ISO 532 but incorporating temporal effects in loudness provide measures of loudness meaningful for noise reduction. Two kinds of devices are available: One, hand driven, processes a larger dynamic range; the smaller, more convenient device is battery driven and uses some approximations. Three examples are discussed: (a) It is shown why a motorcycle, although producing less Aweighted SPL, is louder than another motorcycle which produces 3 dB(A) more level. (b) Instead of using the physical transmission loss to characterize the noise reduction achieved by different types of windows, it is much more significant to compare the loudness reduction attained by them. A comparison of these factors enables direct analysis of the meaningful improvement versus cost. (c) The loudness of speech, a sound with strong spectral and temporal variations, is often of importance in communication systems. The perceived loudness can be determined easily using the peaks in the running loudness-time function of speech. These peaks may be processed further in controlling or regulating acoustic environments, broadcasting, and reproduction systems.
Annoyance reactions caused by intermittent noise
Authors: Gjestland Truls
Published: October 2005

Annoyance reactions caused by exposure to noise consisting of clearly defined noise events in a steady background have been studied. The noise resembled that of heavy vehicles passing at a short distance or aircraft flyover near an airport. With all other parameters kept constant, the annoyance experienced by the test subjects seems to be highly dependent on the time between each single noise event. Interevent intervals of the order of 2 to 5 rain seem to be the least annoying. The results from this experiment have been combined with a previously published threshold theory to make a new model for assessing the annoyance caused by typical community noise.
Noise exposure assessment in Ontario Hydro
Authors: Behar A.
Published: October 2005

At Ontario Hydro, noise exposure assessments of groups of workers from the same trade are performed using noise dosimeters on statistically significant samples. The size of each sample is determined following the NIOSH procedure. Workers are tested during the whole shift for five consecutive days. From the measured doses, daily noise exposure levels, L̄OSHA, are calculated in dBA. Subsequently, each individual weekly noise exposure level L̄OSHA is obtained by averaging exposure levels over the whole week. Finally, with the values of L̄OSHA from the entire sample, the mean noise exposure level for the trade, L̄TRADE and the standard deviation are calculated. Because noise exposure levels are normally distributed, percentages of workers at risk can be calculated (e.g., percent of workers with noise exposure levels in excess of 90 dBA). Finally, by using the total number of workers and the sample size, the confidence limits of the above magnitudes are calculated. The value of the group noise exposure assessment as opposed to that of individuals is that the decision maker (e.g., a manager) can have an accurate picture of the situation of the whole trade in a short time without testing every employee.
A comparison of the acoustical and electrically induced auditory brainstem response in the guinea pig
Authors: Brown D. D. , Miyamoto R. T.
Published: October 2005

Electrical and Acoustical Auditory Brainstem Responses (ABRs) in a guinea pig model are compared in order to better define the characteristics of electrical stimulation. Also, the effects of the stimulating electrode location are being investigated because of its implications for cochlear implant design. The active electrodes are positioned in the basal and apical turns, while the return electrodes are placed in the eustachian tube and temporalis muscle. ABR morphology, wave latencies, and central conduction time are among the parameters studied. Electrode placement appears to have little effect on wave latencies or amplitudes. The acoustical and electrical wave morphologies differ. Latencies and central conduction time are shorter for electrical than for acoustical stimulation.
Age-related hearing loss in C57B1/6 mice and the auditory brainstem response
Authors: Paris-Hunter Kelly , Willott James F.
Published: October 2005

During the first 7 months of life, C57BL/6 mice demonstrate progressive sensorineural hearing loss for high frequencies (> 12 kHz), with little loss of sensitivity for lower frequencies. Auditory brainstem responses (ABRs) were obtained from C57 mice of both sexes aged 1 to 7 months. Stimuli (1 ms duration, 0.1 ms rise-fall, 10/s rate) of two types were used: For “low-pass” (LP), stimuli frequencies above 12 kHz were filtered from white noise; for “high-pass” (HP) stimuli frequencies below 12 kHz were filtered. A wound clip over the vertex served as the active electrode and a bite bar was the reference. Thresholds of ABR wave I progressively increased by about 20 dB (re: 20 μPa) by 7 months for the HP stimulus but increased by only 5 dB for the LP stimulus. Ratios of amplitudes of later ABR waves to early waves increased with age for high intensity stimuli. Amplitude-intensity function slopes of waves IV and V (but not I-III) increased with age. Both effects were more pronounced for HP stimuli. Sex differences were not observed in any of these findings. In summary, early and late ABR waves of hearing-impaired C57 mice change in different ways with age, and the changes depend on the frequency spectrum of the stimulus. [Supported by a Research Career Development Award and a grant from NIH.]
An experimental study of acoustic signature in peach-faced lovebirds (Agapornis roseicollis)
Authors: Wheeler Leslie A. , Busnel Rene-Guy
Published: October 2005

Contact calls from various emitters were modified and played back to isolated individuals in a two-choice situation (mate versus another bird of the same sex). Response selectivity was compared with that observed for unmodified calls. Modifications included low-pass filtering, elimination or recombination of call segments, temporal inversion, transposition or inversion of frequencies by ring modulator, and call synthesis by icophone. Those which least perturbed the acoustic signature were filtering and elimination of call segments. These were interpreted as limited to reduction or elimination of energy at particular temporal or frequency addresses with consequent reduction in number of information bits transmitted. Modifications which most perturbed the signature were frequency inversion or transposition and temporal inversion. These were interpreted as both the elimination of energy at particular temporal or frequency addresses and its redistribution to other addresses. Each intact parameter seemed to contribute to the creation of an acoustic signature but none was sufficient in itself when other parameters were modified. The acoustic signature does not appear to be based on any particular cue or set of independent cues, but rather on the relationships among the set of parameter values. Results are compared with those from other bird and mammal species, including man.
Changes in call rate of Woodhouse's toad in response to synthetic calls
Authors: Leek M. R. , Sullivan B. K.
Published: October 2005

Woodhouse's toad (Bufo woodhousei), in contrast to many other anurans, has one all-purpose call used by the male to attract females as well as to announce his presence to competing males. The call has a pulse rate of about 160 per second and a dominant frequency of about 1500 Hz. The rate of calling is specific to an individual and may range from one to eight calls per minute. Although male call rate is correlated with mating success, males reduce their call rate in response to playbacks of conspecific calls [B. K. Sullivan, J. Herpetol. (in press)]. By observing the alteration of call rates of males in response to a series of synthesized calls, we hoped to identify some important acoustic characteristics of the natural call. The synthetic calls were either complex tones or bandpassed noise, with systematic variation of the dominant frequency or the pulse rate. The calls were presented over a small speaker to individual male toads in their natural environment. The toads responded equally well to synthetic calls with different pulse rates if the dominant frequency was preserved. Maintaining the typical pulse rate while changing the dominant frequency, however, was less effective in eliciting changes in calling rate. Changes in call rate in response to a wide range of synthetic calls may reflect the male's attempts to avoid acoustic interference from other species in his environment, not only his own conspecific rivals.
Transition from simultaneous to forward masking II
Authors: Weber Daniel L. , Kudlacz Judy M. , Langer Theresa
Published: October 2005

A stimulus condition in which the signal presentation partially overlaps the end of the masker presentation is intermediate between a simultaneous masking condition (complete overlap) and a forward-masking condition (no overlap). In two experiments, we sought to determine what underlies signal detection in such conditions. In the first experiment, the masked threshold for a 20-ms, 1-kHz sinusoidal signal (20-ms cosine-squared ramps with no steady state) was measured as a function of its temporal position with respect to a 400-ms, 1-kHz, 70-dB SPL sinusoidal masker (quadrature phase, 0-ms ramps). These “transition curves” are compared to those obtained for the “simultaneous-” and “forward-masked’ portions of each signal. These signals were generated with 1-ms ramps during the final 1 ms of the masker such that the portion of the 20-ms signal which followed the masker was eliminated for the “simultaneous” signal, and the portion which overlapped the masker was eliminated for the “forward” signal, Comparison of these curves for three masker levels shows good agreement with the results from the second experiment in which transition curves were obtained for on- and off-frequency maskers. Both experiments point to a transition region which occurs when 90% to 10% of the signal energy occurs during the masker presentation.
A computer-controlled psychoacoustic laboratory for under $10 000
Authors: Ayers Thomas J.
Published: October 2005

Given a setup time of only a few months and a budget of only $10K, a researcher with very little background in electronics or computing can assemble an amazingly versatile system. Our configuration uses a popular microcomputer and commercially available A-D-A and parallel digital port and add-on boards for control functions. Analog voltage outputs control frequency and amplitude of two phase-lockable signal generators. After bandpass filtering, the signals are shaped and gated by electronic switches, and fine level adjustments are made by programmable attenuators (all under software control); signals are then mixed and delivered to headphones. Simple programs can be written in BASIC lot other languages) for a wide variety of psychophysical procedures and experiments, such as psychophysical tuning curves, automatic up-down tracked fixed-frequency audiograms, and 2AFC PEST masked thresholds; data and summary statistics are printed on paper. The only difficulty facing the would be researcher is finding (or finding funds for) an adequately sound-isolated test chamber. [Work supported by the Deafness Research Foundation.]
Classification of timing and loudness of second heart sound components by expert and novice physicians
Authors: Johnson Thomas L.
Published: October 2005

Consistent and accurate assessment of the relative timing and loudness of second heart sound (S2) components is essential to skilled performance of cardiac auscultation. Classification of S2 “splitting” and loudness of P2 (the pulmonic component of S2) by expert and novice physicians were examined in experiments designed to minimize the influence of higher order cognitive factors on auscultation performance. Stimuli were recorded heart sounds in which the temporal separation and relative intensity of S2 components were controlled by digital wave form editing. The task was to classify S2 splitting and P2 loudness using categories commonly employed in making chart notation. Experts' responses were more consistent and accurate with respect to detection of underlying pathology than the responses of novices. Perceptual category boundaries for novices varied when the heart rate changed and when a systolic murmur was introduced, while expert boundaries remained stable. Most experts were able to detect asynchrony in S2 components of less than 20 ms. [Work supported by the Graduate School and the Dwan Chair for Education in Pediatric Cardiology at the University of Minnesota.]
Ototoxicity and the role of high-frequency audiometry
Authors: Dreschler W. A. , Hulst R.J.A.M. v.d. , Tange R. A.
Published: October 2005

Ototoxicity is one of the unwanted side effects of a number of medical drugs. Within this category of drugs, aminoglycocides antibiotics and platinum derivates are the most well known. Cis-platinum and carboxy platinum are often used as anticancer drugs, for example, in cases of testicular and ovarian malignancy. Auditory damage may be reduced by changes in dose, way of administration, and composition of the medical drug treatment. In these cases, early detection of ototoxicity is vital. As ototoxicity appears to be most pronounced in the higher frequencies, it can be assessed at an earlier stage by using high-frequency audiometry from 8 to 20 kHz. The reference curves in this frequency region are strongly age related. In addition, we have investigated the precision of the measurement. In spite of inaccuracies of headphone positioning, which may influence high-frequency thresholds above all, standard deviations were obtained as for audiometry in the normal-frequency range. Finally, some case studies will illustrate the importance of high-frequency audiometry.
Recovery from acute siren noise exposure: A case study
Authors: Johnson David W. , Gawtry Randall
Published: October 2005

A 41-year-old male firefighter arrived at a hospital emergency room 43 h post acute noise exposure (mechanical siren, 2.5 min total exposure time in an enclosed space) with complaints of tinnitus, decreased hearing, and vague balance problems. He was subsequently evaluated in an otolaryngology clinic and an audiology clinic. The presented complaints resolved during the next month. The subject did return for follow-up. ENT findings were unremarkable at both visits. OSHA baseline audiometrics, audiometry at 47 h post noise insult, and audiometry at 30 days post noise exposure were reviewed. Extended high-frequency audiometry (8 to 20 kHz) was obtained during the initial hospital audiometry (47 h post noise insult) and at the time of the follow-up audiometry. Conventional audiometry and extended high-frequency threshold data were explored and changes in threshold hearing acuity were examined for potential correlation with subjective complaints. Extended high-tone andiometry did suggest a tenuous correlation with the presented complaints. Formal sound pressure readings during mechanical siren operation were taken at the site of noise exposure to delineate noise dosage. Implications of siren noise exposure on long-term hearing sensitivity change were explored.
On the temporal course of simultaneous tone-on-tone masking
Authors: Bacon Sid P. , Viemeister Neal F.
Published: October 2005

We measured the simultaneous masking of a 20-ms, 1-kHz signal by an 80-dB-SPL variable-frequency masker that either was gated on for 50 ms (signal temporally centered) or was presented continuously. For masker frequencies above the signal frequency, the gated masker produced 5 to 20 dB more masking, depending on masker frequency, than did the continuous masker. This difference does not appear to result from the spread of energy produced by gating either the masker or the signal. Signal threshold also was measured as a function of the signal's temporal position in an 800-ms, 80-dB-SPL, 1250-Hz masker. Threshold decreased rapidly as the onset delay of the signal was increased from 0 ms (simultaneous onset); “continuous-masked threshold” generally was reached within 140 ms. Threshold increased, however, as the onset delay increased from approximately 640 to 780 ms (simultaneous offset). Since the size of these temporal effects depends upon masker frequency, these data indicate that the high-frequency side of simultaneous-masked psychophysical tuning curves may depend, at least for short-duration signals, on whether the masker is gated or continuous and, for gated maskers, on the temporal location of the signal within the masker. [Work supported by NINCDS NS12125.]
Reaction time to tones presented in simple backgrounds
Authors: Emmerich David S. , Fantini Deborah A. , Ellermeier Wolfgang
Published: October 2005

In an earlier study [Emmerich, Pitchford, and Becker, Percept. Psychophys. 20, 210–214 (1976)] designed to investigate the suppression effects of a tonal background on simple reaction time to suprathreshold signal tones, the authors obtained somewhat disconcerting results. For widely separated background and signal frequencies, the presence of a continuous tonal “masker” facilitated rather than impaired reaction time. The present research had two purposes: to investigate the influence of a background tone on reaction time for a variety of background frequencies and intensities, and to investigate one possible explanation of the facilitation of reaction time which was observed earlier. As in the earlier study, for moderate intensities the presence of a background tone in the stimulus profile facilitated reaction time over a wide range of background frequencies. Additional results are consistent with the notion that observers are able to monitor the ongoing neural activity in response to the continuously present background while listening for the presentation of the signal, and that modulation of this activity when the signal is presented is a useful cue in this situation.
Release from masking through ipsilateral and contralateral comodulation of a flanking band
Authors: Hall Joseph W. , Haggard Mark P. , D. Antony , Harvey G.
Published: October 2005

Part of the masking of a tone by noise accrues from the difficulty of evaluating the mean increment in power during the observation interval, in relation to the distribution of power fluctuations in random noise. This decision theory model of detection must now be developed to encompass an estimation and correction procedure for noise envelope fluctuations defined by critical bands other than those containing the signal. As shown by Hall et al. [J. Acoust. Soc. Am. 76, 50–56 (1984)], presence of common envelope fluctuations in two separate noise bands can permit the signal in one to be released from masking by 2 to 10 dB, depending on the stimulus parameters. The estimation and correction process seems to occur at more than one stage in the auditory system, as we find a release from masking with contralateral as well as ipsilateral presentation of the flanking band. The magnitude of the contralateral effect is not as large as the ipsilateral effect.
The listening band can be shifted by a pretrial adaptor tone
Authors: Divenyi Pierre L.
Published: October 2005

Discrimination of a gap between two brief sinusoids is very good (1–1.5 ms) as long as the frequency of the two tones is identical or, at least, very close. It deteriorates, however, when the frequencies of the two markers of the gap are 2 oct or more apart [Divenyi and Sachs, Percept. Psychophys. 24, 429–436 (1978)]. One possible explanation of this poorer performance is that the focus of listening is being continuously shifted by the changing frequency of the stimulus which makes monitoring of the temporal envelope at either of the two frequencies very difficult. In the present experiments trained listeners were asked to perform a gap discrimination test using a 2AFC adaptive procedure, with the frequency difference of the two markers being either 0 Hz or 2 oct (with 1 kHz as the geometric center frequency). In additional conditions one pretrial “adaptor” was added, 300 ms in duration and having a frequency either that of the first or the second tone of the stimulus (when the frequency difference of the markers was 2 oct). The interstimulus interval as well as the interval separating the offset of the adaptor and the onset of the stimulus were randomized, in order to eliminate any rhythmic cue. Results indicate that the performance in the 2-oct condition can be either improve or deteriorate, depending on the frequency of the adaptor tone. The results are thus consistent with a listening band hypothesis.
Generalization and maintenance of pitch-change effects
Authors: Peters Robert W. , Hall Joseph W.
Published: October 2005

In a previous study, we demonstrated that the pitch of a complex tone could be changed and maintained in the direction of another complex tone with which it had been associated. Questions in the present study were whether the pitch change would generalize to the nonconditioned ear and to other similar tones. Information was also desired on possible long-term characteristics of the pitch change. Experimental stimuli were pitch-shift tones of 1150-1350-1550-1750 and 1250,-1450-1650-1850 Hz. Each was used with different subjects to test both up and down pitch changes. These tones are normally judged to have pitches of about 190 and 210 Hz, respectively. The conditioning tone was the first five harmonics of fundamental 200 Hz. To establish the pitch change, this tone and one of the pitch-shift tones were heard together for 30 min each day for 5 nonconsecutive days. The results indicated that the average pitch change of about 8 Hz: (1) generalized to the nontest ear after being initially ear specific, (2) generalized more readily to higher rather than lower tones relative to the conditioned tone, and (3) was still maintained at approximately 3 mo after the conditioning sessions.
Pitch shift: Effect of paradigm
Authors: Richards V. M.
Published: October 2005

This concerns the relation between pitch and repetition-rate discrimination of complex signals. First, subjects matched the pitch of a train of high-frequency Gaussian clicks to the pitch of a pure tone. Subjects set the frequency of the tone lower than the repetition rate of the complex signal, a discrepancy that increased with higher carrier frequencies. This agrees with Terhardt [Acustica 24, 126–136 (1971)]. Second, a two-interval force-choice paradigm was used to measure repetition-rate discrimination. On each trial, a signal's period was increased in one interval, and decreased in the other. Of interest were cases of discrimination between signals of equal period, but of different pitches (e.g., a tone and a complex signal). If pitch is used for rate discrimination, then it should be easier to detect differences when the period of the tone is decreased and that of the complex increased. Trial by trial analysis shows this to hold. Moreover, the extent of the pitch shift describes differences in detectability for all signals tested, suggesting that pitch alone can describe these rate discrimination data. [Supported by NIH Grant NS 07787.]
Auditory thresholds using varying attenuation rate (attenuation step) and suprathreshold starting intensity
Authors: Young I. M. , Lowry L. D.
Published: October 2005

Bekesy fixed-frequency thresholds for pulsed and continuous tones were compared for different starting intensities and attenuation rates (attenuation steps) in subjects with normal hearing. Starting intensities were 38, 58, 78, and 98 dB SPL. Attenuation rates were 1, 2, 4, and 8 dB/s with attenuation steps in 0.25, 0.5, 1.0, and 2.0 dB/s, respectively. For pulsed tones, the threshold was not significantly affected by varying starting intensities or attenuation rates (attenuation steps). Reducing the attenuation rate (attenuation step) produced an elevation of continuous tone thresholds for a given suprathreshold starting intensity. Increase in the suprathreshold starting intensity produced an elevation of continuous tone thresholds for a given attenuation rate (attenuation step). The slower the attenuation rate (the slower the attenuation step) and the higher the suprathreshold starting intensity, the higher the threshold. This is considered a manifestation of normal adaptation. Present findings were compared and discussed with our previous studies for the threshold differences measured by different attenuation rates with a fixed attenuation step in 0.2 dB starting at the same suprathreshold intensities.
High-resolution seismic profiling with a low-frequency parametric array
Authors: Muir T. G. , Wyber R. J.
Published: October 2005

The application of nonlinear acoustics to seismic profiling, exploration, and sedimentary geophysics has long been recognized as having great potential, due to the unique opportunities for high resolution measurements. These measurements, in turn, open new avenues for theoretical developments in areas of sediment characterization and acoustic modeling for scattering and propagation. The present paper reviews the utilization of a parametric research tool in sub-bottom profiling experiments conducted offshore southern California and Oahu, Hawaii. An instrument capable of parametric operation in the 1–5 kHz band with a nominal 3° beamwidth was used in a transient mode to generate a Ricker wavelet with a 0.8-ms duration. The results of normal incidence sub-bottom profiling are presented to demonstrate the precision mapping of bedrock stratigraphy, including tilted bedding, faulting, the presence of discrete inhomogeneities, etc. Results on the profiling of the unconsolidated sediment layers are also presented, demonstrating the existence and quantification of microlayering. The stochastic properties of the sedimentary microlaying are computed from the data for use in an acoustic scattering model. [Work supported by the U.S. Navy Office of Naval Research.]
Parametric sonar in an integrated target strength system and for determining the performance of acoustic materials
Authors: Cook James C. , House John R.
Published: October 2005

At high frequencies, it is perfectly possible to undertake target strength experiments in shallow and sheltered waters, but at low frequencies it is generally necessary because of reverberation problems to work in deep waters. To provide a target strength measurement system for restricted waters, an experimental sonar is under development based on the use of a nonlinear parametric sonar operating in association with high resolution electrically scanned equipment. By operating the latter at a harmonic of the parametric primary frequency, the low frequency (parametric) system can be directed accurately at the target. The system will allow the simultaneous measurement at a number of frequencies with some degree of target resolution in azimuth. A technique has also been developed to measure the acoustic transmission properties of small panels (30 × 40 cm2) at various angles of incidence over a wide frequency range. The technique employs a parametric source to minimize edge diffraction effects that would be present using more conventional techniques. Various designs of acoustic materials in tile or sheet form can be evaluated thereby offering an intermediate measurement between small sample impedance tube measurements and large panels.
Listeners' identification of brief segments of natural isolated vowels
Authors: Nearey Terrance M. , Assmann Peter F.
Published: October 2005

Results are reported indicating the importance of spectral change in the identification of isolated vowels in Canadian English, including vowels usually considered monopthongal. Brief (30-ms Hamming windowed) segments were extracted from the “steady-state” (INITIAL) and “offglide” (FINAL) portions of 40 isolated vowels (ten categories × four speakers). Pairs of sections, separated by 10 ms, were presented to listeners in three conditions: (1) INITIAL-FINAL (I-F), (2) INITIAL-INITIAL (I-I), and (3) FINAL-INITIAL (F-I). Listeners' error rates were comparable for the I-F condition (14%) and the original tokens (13%), but considerably higher for I-I (32%) and F-I (38%) conditions. The fundamental and the first two formant frequencies were measured in each of the “steady-state” and “offglide” sections. These measures were used to predict listeners' identification using a model of the type described in Assmann, Nearey, and Hogan [J. Acoust. Soc. Am. 71, 975–989 (1982)]. Observed patterns of confusion were generally similar to model predictions.
The poor man's five-mode whole-body shaker
Authors: Purdy Alan H. , Simic Dusan P. , Conner William L.
Published: October 2005

The Institute is concerned (among other things) with the effects of whole-body vibration on the musculo-skeletal system as well as effects to psycho-motor performance on the operators of heavy vehicles. To study these effects in the laboratory setting requires a simulation of the actual road or field vibration conditions, i.e., three axes of translation and two of rotation. This paper describes the theory, design, and construction of a simple, relatively inexpensive shaker system driven by a single hydraulic cylinder. This system can produce all five modes simultaneously with a minimum of 0.4 g at 1 Hz. Frequency response is 1–30 Hz.
Scattering of ultrasound from flocs
Authors: Konwar Lohit , Gibbs Ronald J. , Jarzynski Jacek
Published: October 2005

In the oceans the primary particle size of the sediments in the water column and on the bottom is 1 to 2 μm in diameter. However, in the high salt concentration of the ocean these primary particles are attracted to each other to form flocs. The effect of these flocs on the scattering and transmission of sound in the ocean is unknown. This paper presents laboratory measurements of scattering of ultrasound from flocs at various stages of formation. These data are used to estimate the effect these flocs have on sound transmission and scattering, and to evaluate the possibility of using sound to study flocs in the oceans.
Perception of temporal versus spectral information in French vowels
Authors: Gottfried Terry L. , Beddor Patrice Speeter
Published: October 2005

Perceptual effects of orthogonal variations in temporal and spectral information differentiating French /o/ and /ɔ/were examined. Although both parameters contribute to acoustic differentiation of /o/ and /ɔ/, several phonetic and phonological characteristics of French lead us to expect that duration is a less important perceptual dimension in French than in languages like American English. Three 10-step /kot/-/kot/ continua were synthesized by systematically varying F1 and F2 of the vowel nuclei. The three continua differed in vowel duration: 200, 160, and 120 ms. Two perceptual tests, identification (labeling stimuli as /o/ or /ɔ/) and rating (judging vowel category goodness on a five-point scale), were presented to two groups of listeners: native French and native American English learning French. Preliminary results indicate language group differences. Native French listeners showed little effect of vowel duration in either perceptual task. Americans generally showed displacements of the /o/-/ɔ/ boundary and shifts in category goodness as a function of vowel duration (indicating a trading relation between temporal and spectral information). Further perceptual study investigates whether these French-speaking Americans also differ from Americans with no knowledge of French. [Supported by NIH Grants 5-F32-NS-07196-02 and RR-05596 and SUNY Research Foundation.]
Visual speech perception experiments using a video speech synthesizer
Authors: Brooke N. M. , McGrath M. , Summerfield A. Q.
Published: October 2005

A general-purpose computer-graphics package has been implemented for displaying animated simulations of a variable range of facial topographies, shapes, and articulatory gestures in realtime, at a rate of 50 frames per second. The topographies can now include features, like the teeth, which may be only intermittently visible. Animation is achieved by supplying streams of time-varying positional data, presently obtained from measurements of talkers speaking VCV or CVC utterances, but strategies for synthesis by interpolating between successive target configurations will also be discussed. The package can generate (a) spatially and temporally graded continua of stimuli, including stimuli in which the movements of normally related articulators are deliberately decoupled, (b) different subsets of articulators, and (c) different talkers. Experience gained from a prototypical identification experiment using /aCV/ utterances has been used to develop a refined facial model which is being applied to study the relative importance of lip and teeth movements in the perception of nondiphthongal vowels. The results will be reported. [Work supported by MRC.]
Spectral peaks and the perception of back vowels
Authors: Assmann Peter F.
Published: October 2005

Delattre et al. [Word 8, 195–210 (1952)] proposed that the ear effectively averages energy from two formants in close proximity. This position has been supported by Chistovich and Lublinskaya [Hear. Res. 1, 185–195 (1979)] who demonstrated integration effects for formant peaks separated by less than a critical distance of 3 to 3.5 Barks. In a previous report [Assmann and Nearey, J. Acoust. Soc. Am. Suppl. 1 74, S89-S90 (1983)] it was demonstrated that height differences in steady-state front vowels can be predicted fairly accurately by the center of gravity of the two most prominent harmonics in the F1 region. Similar results were obtained for both low and high fundamental frequencies (125 and 250 Hz) suggesting a variable (f0-dependent) integration range. Results will be presented from experiments examining the perceptual interaction of F1 and F2 in back vowels as a function of formant spacing, fundamental frequency and the levels of harmonics in the region of F1 and F2. [Work supported by SSHRC.]