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At least 955 records · Page 53Linked to original sources
PubMed2004

Event-related potentials associated with sound discrimination versus novelty detection in children.

In children, deviant sounds in an oddball paradigm elicit a mismatch negativity (MMN) indexing discrimination of sound change and late difference negativity (LDN) with unknown functional significance. Salient sounds elicit an ERP index if orienting, P3a, and a late negative component, Nc. We compared children's responses elicited by moderate sound changes and novel sounds to examine the relationships between MMN and LDN, and LDN and Nc. Two components of the Nc, the Nc1 and Nc2, were identified. The scalp topography of LDN differed from those of the MMN and Nc1. Children's early P3a appeared mature but late P3a lacked frontal predominance. The findings suggested that LDN is not linked with either the sensory or attentional processing. It might reflect cognitive, albeit preattentive, processing of sound change. The Nc1 appears to reflect cognitive attentive processing of salient stimuli and the Nc2 might reflect reorienting after distraction.

Adolescent↗
PubMed1998

Phono-Doppler Timing Relationships in Patients with a Fourth Heart Sound.

Controversies exist about the timing relationship between the fourth heart sound and the ventricular inflow Doppler events. Besides, there has been no data about the timing relationship between the fourth heart sound and the ventricular outflow Doppler events. This study was designed to measure these phono-Doppler timing relationships and to evaluate the influence of different Doppler modes on the timing relationship of the onset of the A wave. Twenty patients (61 +/- 9 years, 18 males and 2 females) with an audible and recordable fourth heart sound were included. No matter on the pulsed Doppler wave trace or on the continuous-wave trace, both the interval from the onset of the mitral A wave to the first vibration of the fourth heart sound and the interval from the peak velocity of the mitral A wave to the first vibration of the fourth heart sound differed significantly from zero (P < 0.001 for all). Nevertheless, the interval from the onset of the transmitted transmitral A wave to the first vibration of the fourth heart sound (0.4 +/- 1.7 ms) was not significantly different from zero (P = 0.314). The pulsed wave data and the continuous wave data were significantly correlated. Differences in the Doppler modes do not seem to lead to obvious changes in the Doppler-phono timing relationships.

Journal Article↗
PubMed2001

Vortex sound generation due to a flow impedance discontinuity on a flat surface.

The sound generated by the unsteady motion of a vortex filament moving over a flat boundary with a sharp flow impedance discontinuity is studied theoretically. Theoretical results show that the vortex filament undergoes significant accelerating or decelerating motions and radiates sound at the instant when it moves across the plane of impedance discontinuity. The accelerations and decelerations of the vortex filament are shown to be the major mechanisms of sound generation. The sound so produced has a large low-frequency content such that the change in the flow impedance affects only the sound generation process but not the subsequent sound propagation to the far field.

Journal Article↗
PubMed2001

On the sound sources of screech tones radiated from choked circular jets.

The generation mechanism of the screech tone in the helical oscillation mode is mainly investigated using a series of instantaneous schlieren photographs. From the photographs, five evanescent sound sources are observed as prominent points along the jet axis. The sound source for the dominant helical oscillation mode is found to be the second prominent point which moves along a circular orbit in a plane perpendicular to the jet axis and just downstream of the rear edge of the third shock cell. It is shown that the speed of a moving sound source is supersonic and that the Mach cone generated by the moving sound source forms the helical-shaped wave front of the screech tone for the helical oscillation mode of the jet. This idea of the moving sound source is well supported by a measured directionality of the screech tone. Sound sources of the other oscillation modes appearing in the other pressure ratio ranges are also described.

Journal Article↗
PubMed2002

The propagation of sound in narrow street canyons.

This paper addresses an important problem of predicting sound propagation in narrow street canyons with width less than 10 m, which are commonly found in a built-up urban district. Major noise sources are, for example, air conditioners installed on building facades and powered mechanical equipment for repair and construction work. Interference effects due to multiple reflections from building facades and ground surfaces are important contributions in these complex environments. Although the studies of sound transmission in urban areas can be traced back to as early as the 1960s, the resulting mathematical and numerical models are still unable to predict sound fields accurately in city streets. This is understandable because sound propagation in city streets involves many intriguing phenomena such as reflections and scattering at the building facades, diffusion effects due to recessions and protrusions of building surfaces, geometric spreading, and atmospheric absorption. This paper describes the development of a numerical model for the prediction of sound fields in city streets. To simplify the problem, a typical city street is represented by two parallel reflecting walls and a flat impedance ground. The numerical model is based on a simple ray theory that takes account of multiple reflections from the building facades. The sound fields due to the point source and its images are summed coherently such that mutual interference effects between contributing rays can be included in the analysis. Indoor experiments are conducted in an anechoic chamber. Experimental data are compared with theoretical predictions to establish the validity and usefulness of this simple model. Outdoor experimental measurements have also been conducted to further validate the model.

Journal Article↗
PubMed2003

The sound-speed gradient and refraction in the near-ground atmosphere.

A systematic description of sound refraction in the near-ground atmosphere is developed by modeling the effective sound-speed gradient with Monin-Obukhov similarity theory. The resulting gradient equation can be recast in a form involving just three nondimensional variables. The first is the ratio of a sound-speed scale (representing the strength of the turbulent fluctuations in the sound speed) to the friction velocity. The second is the ratio of the actual height to a transitional height where contributions from the near-ground wind-speed gradients and the adiabatic lapse rate are roughly balanced. The third is simply the cosine of the angle between the propagation direction and mean wind direction. When the magnitude of the sound-speed scale/friction velocity ratio is large, refraction is unconditionally upward or downward, depending on sign of the ratio. A small value for this ratio indicates nearly neutral atmospheric stratification, for which refraction is determined by the wind direction for small values of the nondimensional height and is upward for larger values. The contribution to refraction from air humidity is determined as a function of the Bowen ratio and found to be significant over wet surfaces. Weather conditions appropriate for measurement of sound pressure levels are also discussed.

Journal Article↗
PubMed2003

Time-domain simulation of sound production of the sho.

A physical model based on the sound production mechanism of the sho is proposed with intention of applying it to sound synthesis. Time-domain simulation was done using this model, and effects of the tube length and blowing pressure on the sounding frequency and sounds spectra were investigated. The reed vibration, pressure variation inside the tube, and threshold blowing pressure for oscillation were measured by artificially blowing air into the sho. The experimental results are in acceptable agreement with simulation results in terms of the relationships between tube length and threshold pressure and between tube length and the sounding frequency. In addition, recorded sound waveforms and simulated ones have a common feature in the sense that high-frequency components of their spectra increase with increasing blowing pressure. Further, it is concluded that a sho reed acts as an "outward-striking valve."

Journal Article↗
PubMed2003

Gas-phase generation of photoacoustic sound in an open environment.

The photoacoustic effect is commonly exploited for molecular spectroscopy, nondestructive evaluation, and trace gas detection. Photoacoustic sound is produced when a photoactive material absorbs electromagnetic radiation and converts it to acoustic waves. This article focuses on the generation of photoacoustic sound from thermal expansion of photoactive gases due to unsteady heating from a laser light source, and extends the work of prior studies on photoacoustic sound generation in an open environment. Starting with the forced free-space wave equation, a simple model is constructed for photoacoustic sounds produced by both acoustically distributed and compact gas clouds. The model accounts for laser absorption through the Lambert-Beer law and includes the effects of photoactive gas cloud characteristics (shape, size, and concentration distribution), but does not include molecular diffusion, thermal conduction, convection, or the effects of acoustic propagation through sound-absorbing inhomogeneous media. This model is compared to experimentally measured photoacoustic sounds generated by scanning a 10.6-micron carbon dioxide (CO2) laser beam through small clouds of a photoactive gas, sulfur hexafluoride (SF6). For the current investigation, the photoactive gas clouds are formed either by low flow-rate calibrated leak sources or by a laminar jet emerging from a 1.6-mm-diam tube. Model-measurement comparisons are presented over a 3- to 160-kHz bandwidth. Signal pulse shapes from simple gas cloud geometries are found to match calculated results when unmeasured gas cloud characteristics within the model are adjusted.

Journal Article↗
PubMed2004

Sound generation by steady flow through glottis-shaped orifices.

Although the signature of human voice is mostly tonal, it also includes a significant broadband component. Quadrupolelike sources due to turbulence in the region downstream of the glottis, and dipolelike sources due to the force applied by the vocal folds onto the surrounding fluid are the two primary broadband sound generating mechanisms. In this study, experiments were conducted to characterize the broadband sound emissions of confined stationary jets through rubber orifices formed to imitate the approximate shape of the human glottis at different stages during one cycle of vocal fold vibrations. The radiated sound pressure spectra downstream of the orifices were measured for varying flow rates, orifice shapes, and gas mixtures. The nondimensional sound pressure spectra were decomposed into the product of three functions: a source function F, a radiation efficiency function M, and an acoustic response function G. The results show that, as for circular jets, the quadrupole source contributions dominated for straight and convergent orifices. For divergent jets, whistling tonal sounds were emitted at low flow rates. At high flow rates for the same geometry, dipole contributions dominated the sound radiated by free jets. However, possible source-load acoustic feedback may have hampered accurate source identification in confined flows.

Computer Simulation↗
PubMed2005

Equations for finite-difference, time-domain simulation of sound propagation in moving inhomogeneous media and numerical implementation.

Finite-difference, time-domain (FDTD) calculations are typically performed with partial differential equations that are first order in time. Equation sets appropriate for FDTD calculations in a moving inhomogeneous medium (with an emphasis on the atmosphere) are derived and discussed in this paper. Two candidate equation sets, both derived from linearized equations of fluid dynamics, are proposed. The first, which contains three coupled equations for the sound pressure, vector acoustic velocity, and acoustic density, is obtained without any approximations. The second, which contains two coupled equations for the sound pressure and vector acoustic velocity, is derived by ignoring terms proportional to the divergence of the medium velocity and the gradient of the ambient pressure. It is shown that the second set has the same or a wider range of applicability than equations for the sound pressure that have been previously used for analytical and numerical studies of sound propagation in a moving atmosphere. Practical FDTD implementation of the second set of equations is discussed. Results show good agreement with theoretical predictions of the sound pressure due to a point monochromatic source in a uniform, high Mach number flow and with Fast Field Program calculations of sound propagation in a stratified moving atmosphere.

Journal Article↗
PubMed2006

The near-ground structure of the nocturnal sound field.

The near-ground behavior of the low-frequency (100 Hz to 500 Hz) sound field in the nocturnal sound duct is studied theoretically and experimentally. In the first few meters of the atmosphere, narrow-band sound fields are found to have a characteristic vertical structure. The sound field is the superposition of a "surface mode," whose magnitude decreases monotonically with altitude, with a sum of "higher modes," each of whose magnitudes has a pronounced minimum a few meters from the ground at approximately the same height. The surface mode attenuates to negligible levels after a few hundred meters from the source. Consequently, more than a few hundred meters from a narrow-band source, there is a "quiet height" at which the sound level is reduced by 10 to 15 dB relative to its value on the ground. The narrow-band quiet height is shown to be a robust feature of nocturnal sound propagation.

Journal Article↗
PubMed2006

Mean field of a low-frequency sound wave propagating in a fluctuating ocean.

Statistical characteristics of low-frequency sound waves propagating over long distances in a fluctuating ocean are important for many practical problems. In this paper, using the theory of multiple scattering, the mean field of a low-frequency sound wave was analytically calculated. In these calculations, the ratio of the sound wavelength and the scale of random inhomogeneities can be arbitrary. Furthermore, the correlation function of inhomogeneities is expressed in terms of a modal spectrum (e.g., internal waves modes). The obtained mean sound field is expressed as a sum of normal modes that attenuate exponentially. It is shown that the extinction coefficients of the modes are linearly related to the spectrum of random inhomogeneities in the ocean. Measurements of the extinction coefficients can therefore be used for retrieving this spectrum. The mean sound field is calculated for both 3D and 2D geometries of sound propagation. The results obtained can be used to study the range of applicability of the 2D propagation model.

Journal Article↗
PubMed1977

Description of the measurement of an individual's continuous sound exposure during a 31-day period.

A dosimeter based on the equal energy rule with range from 55 to 110 dB was used to monitor continuously the noise exposure of one subject. The subject, who is the second author of this report, works in a relatively quiet laboratory area. The daily A-weighted average sound level was measured for each 24-h period [L(eq(24))] beginning at approximately 8:00 a.m. During the day the noise exposure associated with specific activities was noted. The 31-day average sound level was 76 dB while the daily L(eq)(24)) values varied from a low of 59 dB to a high of 83 dB. The type of activity that contributed most of the subject's total sound dose was night-time parties at private homes or nightclubs. Five such parties accounted for 42% of his total sound dose. One exposure at an automobile hobby shop and three outings at a bowling alley contributed another 27% to the total sound dose. If these outside recreational activities had been avoided, the 31-day average sound level would have been reduced to 71 dB. The problems involved in monitoring a 24-h noise exposure as well as future plans for more elaborate studies are discussed.

Environmental Exposure↗
PubMed1996

Speech perception is hearing sounds, not tongues.

Three types of evidence are reviewed which cast doubt on claims that recovery of the speaker's articulations is an inherent part of speech perception: (a) Phonological data (e.g., universal tendencies of languages' segment inventories, phonotactic patterns, sound changes, etc.) show unmistakably that the acoustic-auditory properties of speech sounds, not their articulations, are the primary determinant of their behavior. (b) Infants and various nonhuman species can differentiate certain sound contrasts in human speech even though it is highly unlikely that they can deduce the vocal tract movements generating the sounds. (c) Humans can differentiate many nonspeech sounds almost as complex as speech, e.g., music, machine noises, as well as bird and monkey vocalizations, where there is little or no possibility of recovering the mechanisms producing the sounds.

Humans↗
PubMed1997

Annoyance caused by sounds of wheeled and tracked vehicles.

In a laboratory experiment, the relationship between the annoyance caused by sounds of tracked and wheeled vehicles was investigated. Sounds of various vehicles, ranging from a main battle tank (MBT) to a passenger car, were recorded at several distances. Subjects were presented with these sounds and were asked to judge the annoyance if they were exposed to them at home on a regular basis. Overall, sounds emanated from military tracked vehicles were judged to be less annoying than civil passenger cars, provided that the indoor A-weighted sound-exposure levels (ASELs) were the same. It should be noted that receiver distance and operating conditions were not specifically matched for military and civil vehicles but were chosen to represent typical ranges of values found in practice. For steady-speed conditions, the sounds were judged to be equally annoying if the (indoor) ASELs of the tracked armored personnel carrier (APC) and the MBT exceeded that of a passenger car by 5 and 10 dB, respectively. In specific driving conditions such as alternate accelerations and decelerations, however, these differences were smaller. For ASELs below 55 dB, passenger cars were found to be more annoying than heavier wheeled vehicles, such as a bus or a truck with a trailer. The data indicate that the difference between the high-frequency part and the low-frequency part of the spectrum might play a role in the annoyance. With respect to noise-zoning procedures it is highly interesting that the outdoor ASEL could predict the annoyance, as rated indoors, better than could any indoor noise measure. The 5- and 10-dB bonuses to the indoor level of the APC and the MBT, respectively, were reduced to 1 and 3 dB if the dose was measured outdoors.

Adolescent↗
PubMed1995

Spontaneous and sound-evoked discharge characteristics of complex-spiking neurons in the dorsal cochlear nucleus of the unanesthetized decerebrate cat.

1. We examined the spontaneous and sound-evoked discharge characteristics of 20 complex-spiking units recorded in the dorsal cochlear nucleus (DCN) of 15 unanesthetized, decerebrate cats. 2. The extracellularly recorded complex spikes consisted of bursts of two to five action potentials whose size gradually decreased during the burst. Complex spikes were observed both in the spontaneous and sound-evoked activity of the units in our sample. 3. The spontaneous rates (SRs) of DCN complex-spiking units ranged from 0 to 30 spikes/s. Spontaneous activity consisted of complex and simple (i.e., the common single neuronal action potential) spikes. Comparison of the SR distributions of the DCN complex-spiking units with that of a total sample of 194 DCN units (from 9 cats) suggests that the complex-spiking units tended to be in the lower half of the DCN SR distribution. 4. Sound-evoked discharges could consist of both complex and simple spikes. On the basis of their sound-driven responses, we divided the DCN complex-spiking units into two groups. The majority (15 of 20, 75%) were weakly driven by pure tones and inhibited by broadband noise. They tended to have broad response areas. Their response latencies to pure tone and noise stimuli were relatively long (10-20 ms). The recording depths of these units tended to be superficial (i.e., 10 of 15 units were located within 400 microns of the dorsal surface of the DCN). A minority (5 of 20, 25%) of the complex-spiking units were strongly driven by pure tone and broadband noise stimuli. These units had more clearly defined excitatory regions of response areas than the weakly driven units. Their response latencies to pure tone and noise stimuli were short (< 10 ms). The recording depths of these units tended to be deeper (i.e., 4 of 5 units were located at 400-700 microns) than those of the weakly driven units. 5. Intracellular recording and labeling studies of in vitro DCN slice preparations have correlated complex spikes with the superficially located cartwheel cells. Given the complex spikes of the units, many of which were located superficially, we suggest that our sample, particularly the weakly driven group of neurons, corresponds to the cartwheel cells. 6. Cartwheel cells are putative inhibitory interneurons whose axons primarily contact on the main projection neurons of DCN, the fusiform cells. The present finding of sound-evoked discharges by the superficially located complex-spiking units suggests that cartwheel cells should play a role in modifying the sound-evoked responses of the fusiform cells.

Acoustic Stimulation↗
PubMed2000

Neural measurement of sound duration: control by excitatory-inhibitory interactions in the inferior colliculus.

In the inferior colliculus (IC) of the big brown bat, a subpopulation of cells ( approximately 35%) are tuned to a narrow range of sound durations. Band-pass tuning for sound duration has not been seen at lower levels of the auditory pathway. Previous work suggests that it arises at the IC through the interaction of sound-evoked, temporally offset, excitatory and inhibitory inputs. To test this hypothesis, we recorded from duration-tuned neurons in the IC and examined duration tuning before and after iontophoretic infusion of antagonists to gamma-aminobutyric acid-A (GABA(A)) (bicuculline) or glycine (strychnine). The criterion for duration tuning was that the neuron's spike count as a function of duration had a peak value at one duration or a range of durations that was >/=2 times the lowest nonzero value at longer durations. Out of 21 units tested with bicuculline, duration tuning was eliminated in 15, broadened in two, and unaltered in four. Out of 10 units tested with strychnine, duration tuning was eliminated in four, broadened in one, and unaltered in five. For units tested with both bicuculline and strychnine, bicuculline had a greater effect on reducing or abolishing duration tuning than did strychnine. Bicuculline and strychnine both produced changes in discharge pattern. There was nearly always a shift from an offset response to an onset response, indicating that in the predrug condition, inhibition arrived simultaneously with excitation or preceded it. There was often an increase in the length of the spike train, indicating that in the predrug condition, inhibition also coincided with later parts of excitation. These findings support two hypotheses. First, duration tuning is created in the IC. Second, although the construction of duration tuning varies in some details among IC neurons, it follows three rules: 1) an excitatory and an inhibitory event are temporally linked to the onset of sound but temporally offset from one another; 2) the duration of some inhibitory event must be linked to the duration of the sound; 3) an excitatory event must be linked to the offset of sound.

Acoustic Stimulation↗
PubMedDate not supplied

Large vestibular evoked myogenic potentials in response to bone-conducted sounds in patients with superior canal dehiscence syndrome.

Dehiscence of the superior semicircular canal is a 'new' vestibular entity. Among these patients, the vestibular evoked myogenic potentials (VEMP) in response to air-conducted sounds are large. In the present study, VEMP in response to bone-conducted sounds were studied in 5 normal subjects, in 3 patients after (unilateral) labyrinthectomy and in 4 patients with (unilateral) superior canal dehiscence syndrome. The bone-conducted sound stimulus was a 250- and a 500- tone burst delivered monaurally on the mastoid using standard bone conductors. Among the normals, bone-conducted sounds delivered monaurally caused VEMP bilaterally. There was, however, a transcranial attenuation for the 500-Hz stimulus, but less so for the 250-Hz stimulus. Among the patients with labyrinthectomy there were VEMP on the healthy side, but not on the lesioned side, irrespective of whether the bone-conducted sounds were presented behind the healthy or the operated ear. Among the patients with superior canal dehiscence syndrome, the VEMP on the affected side were larger than on the healthy side. This suggests that there is also vestibular hypersensitivity for bone-conducted sounds in these patients.

Adult↗