Dynamic-range compression affects the lateral position of sounds

Dynamic-range compression acting independently at each ear in a bilateral hearing-aid or cochlear-implant fitting can alter interaural level differences (ILDs) potentially affecting spatial perception. The influence of compression on the lateral position of sounds was studied in normal-hearing listeners using virtual acoustic stimuli. In a lateralization task, listeners indicated the leftmost and rightmost extents of the auditory event and reported whether they heard (1) a single, stationary image, (2) a moving/gradually broadening image, or (3) a split image. Fast-acting compression significantly affected the perceived position of high-pass sounds. For sounds with abrupt onsets and offsets, compression shifted the entire image to a more central position. For sounds containing gradual onsets and offsets, including speech, compression increased the occurrence of moving and split images by up to 57 percentage points and increased the perceived lateral extent of the auditory event. The severity of the effects was reduced when undisturbed low-frequency binaural cues were made available. At high frequencies, listeners gave increased weight to ILDs relative to interaural time differences carried in the envelope when compression caused ILDs to change dynamically at low rates, although individual differences were apparent. Specific conditions are identified in which compression is likely to affect spatial perception.     

光源位置偏差对光斑的影响分析

以目前国内研制的多光源太阳模拟器光学系统为研究对象,采用数值计算和软件模拟相结合的的方法对太阳模拟器光学系统光源存在不同空间角度偏差时光斑汇聚形式和汇聚效果进行了分析,确定光源允许产生的最大位置偏差,并依据研究结果指导光斑的调节。结果表明,太阳模拟器光源的空间位置是影响复合光斑形状和能量分布的关键因素,可为太阳模拟器光源调节系统的设计、光斑数据分析和关键零部件加工精度的确定提供参考。     

The ability of listeners to use recovered envelope cues from speech fine structure

Recent work has demonstrated that auditory filters recover temporal-envelope cues from speech fine structure when the former were removed by filtering or distortion. This study extended this work by assessing the contribution of recovered envelope cues to consonant perception as a function of the analysis bandwidth, when vowel-consonant-vowel (VCV) stimuli were processed in order to keep their fine structure only. The envelopes of these stimuli were extracted at the output of a bank of auditory filters and applied to pure tones whose frequency corresponded to the original filters' center frequencies. The resulting stimuli were found to be intelligible when the envelope was extracted from a single, wide analysis band. However, intelligibility decreases from one to eight bands with no further decrease beyond this value, indicating that the recovered envelope cues did not play a major role in consonant perception when the analysis bandwidth was narrower than four times the bandwidth of a normal auditory filter (i.e., number of analysis bands > or =8 for frequencies spanning 80 to 8020 Hz).     

The influence of signal parameters on the sound source localization ability of a harbor porpoise (Phocoena phocoena)

It is unclear how well harbor porpoises can locate sound sources, and thus can locate acoustic alarms on gillnets. Therefore the ability of a porpoise to determine the location of a sound source was determined. The animal was trained to indicate the active one of 16 transducers in a 16-m-diam circle around a central listening station. The duration and received level of the narrowband frequency-modulated signals (center frequencies 16, 64 and 100 kHz) were varied. The animal's localization performance increased when the signal duration increased from 600 to 1000 ms. The lower the received sound pressure level (SPL) of the signal, the harder the animal found it to localize the sound source. When pulse duration was long enough (approximately 1 s) and the received SPLs of the sounds were high (34-50 dB above basic hearing thresholds or 3-15 dB above the theoretical masked detection threshold in the ambient noise condition of the present study), the animal could locate sounds of the three frequencies almost equally well. The porpoise was able to locate sound sources up to 124 degrees to its left or right more easily than sounds from behind it.     

The ability of the parasitoid fly Ormia ochracea to distinguish sounds in the vertical plane

The parasitic fly Ormia ochracea localizes its host, field crickets, by homing in on their calling song. Previous phonotactic studies indicate that their sound localization ability in azimuth is extraordinarily acute, but the fly's ability to localize the elevation of sound sources has not been tested to date. Here we show that in a freely-walking closed-loop Y-maze task elevational performance is well above chance, but slightly below the fly's performance in azimuth. Immobilizing the head or the halteres (sensory organs of balance) slightly lowered elevational discrimination, but performance was still well above chance. Because ormiine ears are thought to be symmetric and the pure-tone models of a cricket's call used in these experiments contained little to no spectral bandwidth, additional studies will be needed to elucidate the underlying cues. Nonetheless, it is clear that while walking, Ormia flies are capable of distinguishing sound sources that differ only in elevation.     

Individual differences in the processing of speech and nonspeech sounds by normal-hearing listeners.

While a large portion of the variance among listeners in speech recognition is associated with the audibility of components of the speech waveform, it is not possible to predict individual differences in the accuracy of speech processing strictly from the audiogram. This has suggested that some of the variance may be associated with individual differences in spectral or temporal resolving power, or acuity. Psychoacoustic measures of spectral-temporal acuity with nonspeech stimuli have been shown, however, to correlate only weakly (or not at all) with speech processing. In a replication and extension of an earlier study [Watson et al., J. Acoust. Soc. Am. Suppl. 1 71. S73 (1982)] 93 normal-hearing college students were tested on speech perception tasks (nonsense syllables, words, and sentences in a noise background) and on six spectral-temporal discrimination tasks using simple and complex nonspeech sounds. Factor analysis showed that the abilities that explain performance on the nonspeech tasks are quite distinct from those that account for performance on the speech tasks. Performance was significantly correlated among speech tasks and among nonspeech tasks. Either, (a) auditory spectral-temporal acuity for nonspeech sounds is orthogonal to speech processing abilities, or (b) the appropriate tasks or types of nonspeech stimuli that challenge the abilities required for speech recognition have yet to be identified.     

碘喷孔位置的变化对激光性能的影响

在主、副气流流量不变的情况下,仅改变氧碘化学激光器中碘喷孔的位置,数值模拟了其混合气体流场特性和小信号增益分布等的变化.计算结果表明,碘喷孔在喷管叶片上的位置沿气流方向往下游移动,混合状况变差,光腔中小信号增益降低,输出功率减小,饱和光强沿气流方向的衰减变得平缓.     

碘喷孔位置的变化对激光性能的影响

 在主、副气流流量不变的情况下,仅改变氧碘化学激光器中碘喷孔的位置,数值模拟了其混合气体流场特性和小信号增益分布等的变化。计算结果表明,碘喷孔在喷管叶片上的位置沿气流方向往下游移动,混合状况变差,光腔中小信号增益降低,输出功率减小,饱和光强沿气流方向的衰减变得平缓。     

碘喷孔位置的变化对激光性能的影响

在主、副气流流量不变的情况下,仅改变氧碘化学激光器中碘喷孔的位置,数值模拟了其混合气体流场特性和小信号增益分布等的变化。计算结果表明,碘喷孔在喷管叶片上的位置沿气流方向往下游移动,混合状况变差,光腔中小信号增益降低,输出功率减小,饱和光强沿气流方向的衰减变得平缓。     

The influence of Ga source and substrate position on the growth of low dimensional GaN wires by chemical vapour deposition

This paper presents the investigation of low dimensional GaN structures synthesized from Ni-catalyzed chemical vapour deposition (CVD) method under two different conditions, i.e. Ga source and substrate position. Comparative studies based on the morphological, structural and optical characteristics of synthesized GaN wires were carried out in this work. The variations of morphological and dimensional aspects of the GaN wires were attributed to the position of Ga precursor and substrates. These factors were found to be able to influence the degree of supersaturation of gaseous reactants, which is essential in the growth of GaN wires by vapour-liquid-solid (VLS) mechanism. The synthesized GaN wires typically were found to have diameters ranging 35-80 nm (nanowires) and 0.4-1.3 μm (microwires), respectively, with length up to several ten of microns. X-ray diffraction (XRD) results indicated that the grown GaN wires were hexagonal wurzite phase. Ultraviolet (UV) and blue emissions were observed from photoluminescence (PL) measurements. Raman spectra displayed asymmetrical and broadened bands which could be ascribed to the size effect, surface disorder and internal strain of the synthesized GaN wires.     

Effects of pulsing of a target tone on the ability to hear it out in different types of complex sounds

Judgments of whether a sinusoidal probe is higher or lower in frequency than the closest partial ("target") in a multi-partial complex are improved when the target is pulsed on and off. These experiments explored the contribution of reduction in perceptual confusion and recovery from adaptation to this effect. In experiment 1, all partials except the target were replaced by noise to reduce perceptual confusion. Performance was much better than when the background was composed of multiple partials. When the level of the target was reduced to avoid ceiling effects, no effect of pulsing the target occurred. In experiment 2, the target and background partials were irregularly and independently amplitude modulated. This gave a large effect of pulsing the target, suggesting that if recovery from adaptation contributes to the effect, amplitude fluctuations do not prevent this. In experiment 3, the background was composed of multiple steady partials, but the target was irregularly amplitude modulated. This gave better performance than when the target was unmodulated and a moderate effect of pulsing the target. It is argued that when the target and background are steady tones, pulsing the target may result both in reduction of perceptual confusion and recovery from adaptation.     

The influence of extraneous sounds on the perceptual estimation of first-formant frequency in vowels

The contribution of extraneous sounds to the perceptual estimation of the first-formant (F1) frequency of voiced vowels was investigated using a continuum of vowels perceived as changing from/I/to/epsilon/as F1 was increased. Any phonetic effects of adding extraneous sounds were measured as a change in the position of the phoneme boundary on the continuum. Experiments 1-5 demonstrated that a pair of extraneous tones, mistuned from harmonic values of the fundamental frequency of the vowel, could influence perceived vowel quality when added in the F1 region. Perceived F1 frequency was lowered when the tones were added on the lower skirt of F1, and raised when they were added on the upper skirt. Experiments 6 and 7 demonstrated that adding a narrow-band noise in the F1 region could produce a similar pattern of boundary shifts, despite the differences in temporal properties and timbre between a noise band and a voiced vowel. The data are interpreted using the concept of the harmonic sieve [Duifhuis et al., J. Acoust. Soc. Am. 71, 1568-1580 (1982)]. The results imply a partial failure of the harmonic sieve to exclude extraneous sounds from the perceptual estimation of F1 frequency. Implications for the nature of the hypothetical harmonic sieve are discussed.     

The influence of talker differences on vowel identification by normal-hearing and hearing-impaired listeners.

Vowel identification was tested in quiet, noise, and reverberation with 20 normal-hearing subjects and 20 hearing-impaired subjects. Stimuli were 15 English vowels spoken in a /b-t/context by six male talkers. Each talker produced five tokens of each vowel. In quiet, all stimuli were identified by two judges as the intended targets. The stimuli were degraded by reverberation or speech-spectrum noise. Vowel identification scores depended upon talker, listening condition, and subject type. The relationship between identification errors and spectral details of the vowels is discussed.     

The influence of the source on the resolution of a positron annihilation lifetime spectrometer

A detailed study of the prompt resolution curve of a positron annihilation lifetime spectrometer shows that the isotope used as source has great influence on its shape.     

Perception of the sound source position

This paper presents several experiments on sound source localization. They are based on monaural click presented at different interclick intervals (ICI), from 10 to 100 ms. Trains of clicks were presented to 10 healthy subjects. At short interclick intervals the clicks were perceived as a blur of clicks having a buzzy quality. Moreover, it was proven that the accurateness in the response improves with the increase of the length of ICI. The present results imply the usefulness of the interclick interval in estimating the perceptual accuracy. An important benefit of this task is that this enables a careful examination of the sound source perception threshold. This allows detecting, localizing and dividing with a high accuracy the sounds in the environment. The text was submitted by the authors in English.     

Acoustic source separation for the detection of coronary artery sounds

Coronary artery disease (CAD) is the leading cause of death in the United States, being responsible for more than 20% of all deaths in the country. This is in large part due to the difficulty of diagnostic screening for CAD. Phonoangiography seeks to detect CAD via the acoustic signature associated with turbulent flow near an abnormally constricted, or stenosed, region. However, the usefulness of the technique is severely hindered by the low strength of the CAD signal compared to the background noise within the chest. In this work, acoustic finite element analysis (FEA) was performed on physiologically accurate chest geometries to demonstrate the feasibility of an original acoustic source separation methodology for isolating coronary sounds. This approach is based upon pseudoinversion of mixing matrices determined through a combination of experiment and computation. This allows calculation of the sound emitted by the coronary arteries based upon measurements of the acoustic velocity on the chest surface. This work demonstrates the feasibility of such a technique computationally and examines the vulnerability of the proposed approach to measurement errors.     

The influence of substrate geometry on the emission properties of a liquid metal ion source

The effect of needle radius, cone angle and shaft diameter on the threshold voltage and angular intensity — total current relationships for a Ga liquid-metal ion source (LMIS) was investigated. The variation of threshold voltage with needle geometry could be described in terms of the Taylor theory of liquid cone formation by electrostatic fields. The beam energy spread was mainly a function of total source current and was not a sensitive function of emitter geometry. Source angular intensity at a constant total current increased linearly with threshold voltage when the latter was altered due to source geometry.     

The influence of lateral interactions on the vibrational spectrum of adsorbed CO

Vibrational spectroscopy of adsorbed CO often reveals strong shifts of the CO stretch absorption band to higher frequencies as a function of increasing coverage. It is shown that such shifts are due essentially to dipole-dipole interactions. The extent of the experimentally observed effect can, however, only be reproduced when screening by the substrate is taken into account properly.     

Range effects in the identification of lateral position

Experiments on the identification of interaural time and interaural amplitude differences were conducted to evaluate the effects of stimulus range on identification performance. Three stimulus sets, large range (LR), small-range center (SRC), and small-range side (SRS), were used in experiments on interaural time and amplitude identification. As expected, data for both sets of measurements show worse resolution for LR than SRC or SRS, demonstrating that the ability to distinguish between two fixed interaural differences can be strongly influenced by the total range of such differences in the stimulus set.