Minimum audible movement angle in the horizontal plane as a function of stimulus frequency and bandwidth, source azimuth, and velocity.

Minimum audible movement angles (MAMAs) were measured in the horizontal plane for four normal-hearing adult subjects in a darkened anechoic chamber. On each trial, a single stimulus was presented, and the subject had to say whether it came from a stationary loudspeaker or from a loudspeaker that was moving at a constant angular velocity around him. Thresholds were established by adaptively varying stimulus duration. In experiment 1, MAMAs were measured as a function of center frequency (500-5000 Hz), velocity (10 degrees-180 degrees/s), and direction of motion (left versus right). There was no effect of direction of motion. MAMAs increased with velocity, from an average of 8.8 degrees of arc for a target moving at 10 degrees/s to an average of 20.2 degrees of arc for a target moving at 180 degrees/s. MAMAs were higher for a 3000-Hz tone than for tones of lower or higher frequencies, as has been previously reported [D. R. Perrott and J. Tucker, J. Acoust. Soc. Am. 83, 1522-1527 (1988)]. In experiment 2, minimum audible angles (MAAs) were measured with sequentially presented stationary tone pulses (500-5000 Hz), and were shown to exhibit the same dependence on signal frequency that the MAMAs showed (average MAA at 3000 Hz: 8.4 degrees; average MAA at the other frequencies: 3.4 degrees). In experiment 3, MAMAs and MAAs were measured as a function of stimulus bandwidth (centered at 3000 Hz) and listening azimuth (0 degrees vs 60 degrees). Average MAAs decreased monotonically as stimulus bandwidth increased from 0 Hz to wideband (from 8.4 degrees to 1.2 degrees at 0 degrees azimuth; from 11.3 degrees to 1.5 degrees at 60 degrees azimuth). As in experiment 1, MAMAs increased with stimulus velocity, from values comparable to the MAAs for the slowest-velocity (10 degrees/s) targets to 70 degrees of arc or more in the poorest condition (third-octave band of noise presented at a velocity of 180 degrees/s and an azimuth of 60 degrees). MAMAs obtained in the slower-velocity conditions depended in the same way on stimulus bandwidth and listening azimuth that MAAs depended on these variables. In no case was the MAMA ever smaller than the MAA. It is hypothesized that a minimum integration time is required to achieve optimal performance in a dynamic spatial resolution task. Average estimates of this minimum time based on the current data vary from 336 ms (for targets presented at midline) to 1116 ms (for narrow-band targets presented at 60 degrees azimuth).(ABSTRACT TRUNCATED AT 400 WORDS)     

Minimum auditory movement angle: binaural localization of moving sound sources

In the first experiment, subjects were asked to discriminate whether a sound was emanating from a moving or stationary source. The minimum audible movement angle (MAMA) thus defined was observed to increase as the source velocity increased. MAMA ranged from a low of 8.3 degrees with the slowest velocity employed (90 degrees/s) to a high of 21.2 degrees with the fastest velocity (360 degrees/s). In the second experiment, subjects were asked to localize where the moving source was, at signal on and offset. The results indicate that the apparent onset is displaced in the direction of motion and the amount of this displacement is directly related to source velocity. Less consistent results were observed with signal offset. The present results suggest that the binaural system is relatively insensitive to motion.     

Detection and discrimination of simulated motion of auditory targets in the horizontal plane

Three experiments investigated subjects' ability to detect and discriminate the simulated horizontal motion of auditory targets in an anechoic environment. "Moving" stimuli were produced by dynamic application of stereophonic balancing algorithms to a two-loudspeaker system with a 30 degree separation. All stimuli were 500-Hz tones. In experiment 1, subjects had to discriminate a left-to-right moving stimulus from a stationary stimulus pulsed for the same duration (300 or 600 ms). For both durations, minimum audible "movement" angles ("MAMA's") were on the order of 5 degrees for stimuli presented at 0 degrees azimuth (straight ahead), and increased to greater than 30 degrees for stimuli presented at +/- 90 degrees azimuth. Experiment 2 further investigated MAMA's at 0 degrees azimuth, employing two different procedures to track threshold: holding stimulus duration constant (at 100-600 ms) while varying velocity; or holding the velocity constant (at 22 degrees-360 degrees/s) while varying duration. Results from the two procedures agreed with each other and with the MAMA's determined by Perrott and Musicant for actually moving sound sources [J. Acoust. Soc. Am. 62, 1463-1466 (1977b)]: As stimulus duration decreased below 100-150 ms, the MAMA's increased sharply from 5 degrees-20 degrees or more, indicating that there is some minimum integration time required for subjects to perform optimally in an auditory spatial resolution task. Experiment 3 determined differential "velocity" thresholds employing simulated reference velocities of 0 degrees-150 degrees/s and stimulus durations of 150-600 ms. As with experiments 1 and 2, the data are more easily summarized by considering angular distance than velocity: For a given "extent of movement" of a reference target, about 4 degrees-10 degrees additional extent is required for threshold discrimination between two "moving" targets, more or less independently of stimulus duration or reference velocity. These data suggest that for the range of simulated velocities employed in these experiments, subjects respond to spatial changes--not velocity per se--when presented with a "motion" detection or discrimination task.     

Minimum audible angle thresholds for sources varying in both elevation and azimuth

Minimum audible angle (MAA) thresholds were obtained for four subjects in a two-alternative, forced-choice, three up/one down, adaptive paradigm as a function of the orientation of the array of sources. With sources distributed on the horizontal plane, the mean MAA threshold was 0.97 degrees. With the sources distributed on the vertical plane (array rotated 90 degrees), the mean MAA threshold was 3.65 degrees. Performance in both conditions was well in line with previous experiments of this type. Tests were also conducted with sources distributed on oblique planes. As the array was rotated from 10 degrees-60 degrees from the horizontal plane, relatively little change in the MAA threshold was observed; the mean MAA thresholds ranged from 0.78 degrees to 1.06 degrees. Only when the array was nearly vertical (80 degrees) was there any appreciable loss in spatial resolution; the MAA threshold had increased to 1.8 degrees. The relevance of these results to research on auditory localization under natural listening conditions, especially in the presence of head movements, is also discussed.     

Underwater auditory localization by a swimming harbor seal (Phoca vitulina)

The underwater sound localization acuity of a swimming harbor seal (Phoca vitulina) was measured in the horizontal plane at 13 different positions. The stimulus was either a double sound (two 6-kHz pure tones lasting 0.5 s separated by an interval of 0.2 s) or a single continuous sound of 1.2 s. Testing was conducted in a 10-m-diam underwater half circle arena with hidden loudspeakers installed at the exterior perimeter. The animal was trained to swim along the diameter of the half circle and to change its course towards the sound source as soon as the signal was given. The seal indicated the sound source by touching its assumed position at the board of the half circle. The deviation of the seals choice from the actual sound source was measured by means of video analysis. In trials with the double sound the seal localized the sound sources with a mean deviation of 2.8 degrees and in trials with the single sound with a mean deviation of 4.5 degrees. In a second experiment minimum audible angles of the stationary animal were found to be 9.8 degrees in front and 9.7 degrees in the back of the seal's head.     

Two-dimensional sound localization by human listeners

This study measured the ability of subjects to localize broadband sound sources that varied in both horizontal and vertical location. Brief (150 ms) sounds were presented in a free field, and subjects reported the apparent stimulus location by turning to face the sound source; head orientation was measured electromagnetically. Localization of continuous sounds also was tested to estimate errors in the motor act of orienting with the head. Localization performance was excellent for brief sounds presented in front of the subject. The smallest errors, averaged across subjects, were about 2 degrees and 3.5 degrees in the horizontal and vertical dimensions, respectively. The sizes of errors increased, for more peripheral stimulus locations, to maxima of about 20 degrees. Localization performance was better in the horizontal than in the vertical dimension for stimuli located on or near the frontal midline, but the opposite was true for most stimuli located further peripheral. Front/back confusions occurred in 6% of trials; the characteristics of those responses suggest that subjects derived horizontal localization information principally from interaural difference cues. The generally high level of performance obtained with the head orientation technique argues for its utility in continuing studies of sound localization.     

Underwater localization of pure tones by harbor seals (Phoca vitulina)

The underwater sound localization acuity of harbor seals (Phoca vitulina) was measured in the horizontal plane. Minimum audible angles (MAAs) of pure tones were determined as a function of frequency from 0.2 to 16 kHz for two seals. Testing was conducted in a 10-m-diam underwater half circle using a right/left psychophysical procedure. The results indicate that for both harbor seals, MAAs were large at high frequencies (13.5 degrees and 17.4 degrees at 16 kHz), transitional at intermediate frequencies (9.6 degrees and 10.1 degrees at 4 kHz), and particularly small at low frequencies (3.2 degrees and 3.1 degrees at 0.2 kHz). Harbor seals seem to be able to utilize both binaural cues, interaural time differences (ITDs) and interaural intensity differences (IIDs), but a significant decrease in the sound localization acuity with increasing frequency suggests that IID cues may not be as robust as ITD cues under water. These results suggest that the harbor seal can be regarded as a low-frequency specialist. Additionally, to obtain a MAA more representative of the species, the horizontal underwater MAA of six adult harbor seals was measured at 2 kHz under identical conditions. The MAAs of the six animals ranged from 8.8 degrees to 11.7 degrees , resulting in a mean MAA of 10.3 degrees .     

Minimum audible movement angle: marking the end points of the path traveled by a moving sound source

Four experienced subjects were tested on their ability to discriminate the direction of motion or the order of events in a single-interval, two-alternative, forced-choice adaptive paradigm. Two conditions, employing a broadband "pink" noise (500-8000 Hz), were examined: (1) A continuous noise was available from the moving sound source during the entire period of travel; and (2) 10-ms noise pulses were presented from the moving source at the beginning and end of the arc traveled (during the interpulse interval the source was inactive). Minimum audible movement angle (MAMA) thresholds were significantly lower when the moving source was active throughout the period of travel (0.914 degrees) than when only the end points of the arc of travel were "marked" (1.604 degrees). These results do not support the notion that the discrimination of motion can be reduced to a simple comparison of the location of the source at signal onset and the position of the source at signal offset. The MAMA thresholds obtained with broadband noise in the current experiment are considerably lower than the thresholds previously observed with tonal targets.     

Low-frequency horizontal acoustic refraction caused by internal wave solitons in a shallow sea

The effect of internal wave solitons on the sound field generated by a point source in a shallow sea is considered. In the framework of the theory of “horizontal rays and vertical modes,” the sound field pattern governed by the aforementioned hydrodynamic effect is investigated. It is shown that solitons can induce time-periodic focusing and defocusing of horizontal rays propagating at shallow angles to the internal wave front. This may result in the formation of “dynamical” horizontal sound channels, which, in its turn, results in considerable temporal fluctuations of the field along the acoustic track oriented along the internal wave front. For the sound field calculations, an approach is developed on the basis of the parabolic approximation in the horizontal plane and the mode representation in the vertical direction. The results obtained can be used for remote monitoring of internal wave packets in a shallow sea.     

Discrimination of sound source velocity in human listeners

The ability of six human subjects to discriminate the velocity of moving sound sources was examined using broadband stimuli presented in virtual auditory space. Subjects were presented with two successive stimuli moving in the frontal horizontal plane level with the ears, and were required to judge which moved the fastest. Discrimination thresholds were calculated for reference velocities of 15, 30, and 60 degrees/s under three stimulus conditions. In one condition, stimuli were centered on 0 degrees azimuth and their duration varied randomly to prevent subjects from using displacement as an indicator of velocity. Performance varied between subjects giving median thresholds of 5.5, 9.1, and 14.8 degrees/s for the three reference velocities, respectively. In a second condition, pairs of stimuli were presented for a constant duration and subjects would have been able to use displacement to assist their judgment as faster stimuli traveled further. It was found that thresholds decreased significantly for all velocities (3.8, 7.1, and 9.8 degrees/s), suggesting that the subjects were using the additional displacement cue. The third condition differed from the second in that the stimuli were "anchored" on the same starting location rather than centered on the midline, thus doubling the spatial offset between stimulus endpoints. Subjects showed the lowest thresholds in this condition (2.9, 4.0, and 7.0 degrees/s). The results suggested that the auditory system is sensitive to velocity per se, but velocity comparisons are greatly aided if displacement cues are present.     

Comparison of the directional characteristics of swift ion excitation for two small biomolecules: glycine and alanine

The characteristics of ions that enter the plasma sheath with an oblique incident angle have been investigated in the presence of an external magnetic field. The ion dynamics in a collisional and collisionless magnetized plasma sheath have been numerically calculated by using a fluid model. Several values for the ion velocity at the sheath edge, orientation and strength of the magnetic field and the ion-neutral collision frequency have been considered. The results show that in a collisionless magnetized plasma sheath, the behaviour of ions that obliquely enter the sheath with some specific velocities at the sheath edge and at some specific orientations and strengths of magnetic field, is more complicated than that of ions with normal entrance angles. For the oblique entrance of ions, the weak magnetic fields cause some fluctuations in ion velocity around its boundary value, i.e. the ion velocity does not accelerate. However, the numerical calculations show that the ion dynamics in a collisional magnetized plasma sheath are the same for both normal and inclined entrance of ions into the sheath.     

Nonmonotonic effects of perpendicular magnetic anisotropy on current-driven vortex wall motions in magnetic nanostripes

In a magnetic nanostripe, the effects of perpendicular magnetic anisotropy(PMA) on the current-driven horizontal motion of vortex wall along the stripe and the vertical motion of the vortex core are studied by micromagnetic simulations.The results show that the horizontal and vertical motion can generally be monotonously enhanced by PMA. However, when the current is small, a nonmonotonic phenomenon for the horizontal motion is found. Namely, the velocity of the horizontal motion firstly decreases and then increases with the increase of the PMA. We find that the reason for this is that the PMA can firstly increase and then decrease the confining force induced by the confining potential energy. In addition, the PMA always enhances the driving force induced by the current.     

Ocular aberrations in the peripheral visual field

We modified a commercial Hartmann-Shack aberrometer and used it to measure ocular aberrations twice at each of 38 points across the central 42 degrees horizontal x 32 degrees vertical visual fields of five young emmetropic subjects. Some Zernike aberration coefficients show coefficient field distributions that were similar to the field dependence predicted by Seidel theory (astigmatism, oblique astigmatism, horizontal coma, vertical coma), but defocus did not demonstrate such similarity.     

基于矢量水听器的深海直达波区域声传播特性及其应用

对于深海近水面声源产生的声场, 处于较大深度处的接收器在一定水平距离范围内能接收到直达波. 2014年在某深海海域进行的水声考察实验中, 应用深度为140 m的拖曳声源发射实验信号, 布放在水下3146 m深处的矢量水听器成功地接收到了直达波信号. 本文应用射线理论, 分析了深海直达波区域声场的传播特性, 得出了水平振速与垂直振速的传播损失与声线到达接收点处的掠射角以及收发水平距离之间的关系. 在以上分析的基础上, 提出了一种利用水平振速与垂直振速的能量差估计声源距离的方法, 并结合2014年实验数据对实验中两条航线上8 km范围内的目标声源进行了测距, 测距结果与目标的GPS数据符合得较好.     

On the possibility of applying the reciprocity principle in the vector-scalar fields of mutipole sources in a waveguide

We study the applicability of the reciprocity principles in an underwater waveguide for the vector-scalar fields of multipole sources. We show analytically and numerically that multipole sources are divided into two groups according to this principle: in the first group, the sound pressure field and the horizontal projections of the vibration velocity vectors satisfy the reciprocity principle, while the vertical projections of these vectors do not. In the second group, the pressure and the horizontal projections of the vibration velocity vector do not satisfy the reciprocity principle, while their vertical projections do. We establish that the phase gradients and angles of arrival of signals in the vertical plane do not satisfy the reciprocity principle for the vector-scalar fields of volumetric sources with arbitrary directivity in the vertical plane.     

次声波在非均匀运动大气中非线性传播特性的研究

基于有限时域差分方法将大气中近似到二阶的非线性波动方程进行离散化,得到了数值模拟所采用的差分方程. 在此基础上,对线阵列辐射的脉冲声波在非均匀运动大气中的垂直和斜向传播进行了二维数值模拟,模拟了武汉地区(114:20°E, 30:37°N)在夏季和冬季UT=29000 s时开始传播的脉冲声波在不同时刻的声压分布. 模拟时通过采用Msise00和HWM93 两个大气模型,考虑了由于大气温度和密度变化以及大气风场存在所引起的大气不均匀性和运动性. 通过研究上述两季有风与无风条件下的声压差值p_r,可以发现:风场对次声波在传播中声压分布的影响较大;由于不同季节和不同传播距离上"有效声速"的不同,导致了两季p_r分布波形存在差异;风场对声波非线性传播的影响要远大于其对线性传播的影响. 关键词： 次声波传播 非均匀运动大气 有效声速     

Free-field release from masking

Free-field release from masking was studied as a function of the spatial separation of a signal and masker in a two-interval, forced-choice (2IFC) adaptive paradigm. The signal was a 250-ms train of clicks (100/s) generated by filtering 50-microseconds pulses with a TDH-49 speaker (0.9 to 9.0 kHz). The masker was continuous broadband (0.7 to 11 kHz) white noise presented at a level of 44 dBA measured at the position of the subject's head. In experiment I, masked and absolute thresholds were measured for 36 signal source locations (10 degree increments) along the horizontal plane as a function of seven masking source locations (30 degree increments). In experiment II, both absolute and masked thresholds were measured for seven signal locations along three vertical planes located at azimuthal rotations of 0 degrees (median vertical plane), 45 degrees, and 90 degrees. In experiment III, monaural absolute and masked thresholds were measured for various signal-masker configurations. Masking-level differences (MLDs) were computed relative to the condition where the signal and mask were in front of the subjects after using absolute thresholds to account for differences in the signal's sound-pressure level (SPL) due to direction. Maximum MLDs were 15 dB along the horizontal plane, 8 dB along the vertical, and 9 dB under monaural conditions.     

EPR and HYSCORE investigation of the electronic structure of the model complex Mn(imidazole)6: exploring Mn(II)-imidazole binding using single crystals

The electronic structure of the Mn(II)-imidazole binding was studied by EPR spectroscopy using the model complex Mn(Im)(6) diluted in a single crystal of Zn(Im)(6)Cl(2).4(H(2)O). The second rank zero-field splitting (ZFS) tensor (D tensor) of the two sites, a and b, present in the crystal was determined by measuring the orientation patterns of the echo-detected EPR spectra in three different planes at 10K (D(a)=-106, D(b)=-118, E(a)=-17, E(b)=-22x10(-4)cm(-1). Euler angles with respect to the crystal habitus: alpha(a)=13 degrees , beta(a)=76 degrees , gamma(a)=108.5 degrees , alpha(b)=14 degrees , beta(b)=73.5 degrees , gamma(b)=103.5 degrees ). The contribution of cubic ZFS terms to the spectrum allowed us to determine the orientation of the N-Mn-N directions of the complex as well (Euler angles in the D tensor reference frame alpha=100 degrees , beta=23 degrees , gamma=0 degrees , both centers having the same orientation). The hyperfine interactions with (14)N were explored by HYSCORE spectroscopy. The correlation patterns and modulation amplitudes in the 2D experiments were studied for different electron spin transitions and orientations of the crystal. Signals of three different pairs of nitrogens were found. The results were analyzed considering that the N-Mn binding directions are principal directions of the hyperfine and nuclear quadrupole tensor of (14)N. All three pairs of nitrogens were found to be almost equivalent with an isotropic contribution of A(iso) approximately 3.2MHz and an almost axial anisotropic coupling of 2T approximately 1.1MHz along the N-Mn bonding direction. The nuclear quadrupole principal values are 1.5MHz along the bonding direction, -0.6MHz in the direction perpendicular to the imidazole plane, and -0.9MHz in the direction perpendicular to both.     

Directional UV photoemission from clean and sulphur saturated (100), (110) and (111) nickel surfaces

Angle resolved photoemission energy distribution curves (EDC's) were obtained on clean and sulphur saturated (100), (110) and (111) nickel surfaces for excitation energies equal to 10.2, 13.5, 16.8 and 21.2 eV. The EDC's of clean surfaces are weakly structured at θ = 0° and become more rich in features for oblique angles. In the explored energy range, adsorption of sulphur produces two extra-structures at initial energies depending on surface orientation. One of which situated at about ?4.5 eV below the Fermi level is in good agreement with Hagstrum ion neutralization spectroscopy results, the other at around ?1.8 cV has never been observed before. A remarkable similarity of adsorption effects on the three surfaces is found. These results are compared with experimental data obtained previously on equivalent sulphur saturated surfaces by INS and discussed in relation to recent theoretical calculations on chalcogen adsorption on nickel.