Visual perception of mean relative phase and phase variability.

Perception of relative phase and phase variability may play a fundamental role in interlimb coordination. This study was designed to investigate the perception of relative phase and of phase variability and the stability of perception in each case. Observers judged the relative phasing of two circles rhythmically moving on a computer display. The circles moved from side to side, simulating movement in the frontoparallel plane, or increased and decreased in size, simulating movement in depth. Under each viewing condition, participants observed the same displays but were to judge either mean relative phase or phase variability. Phase variability interfered with the mean-relative-phase judgments, in particular when the mean relative phase was 0°. Judgments of phase variability varied as a function of mean relative phase. Furthermore, the stability of the judgments followed an asymmetric inverted U-shaped relation with mean relative phase, as predicted by the Haken-Kelso-Bunz model. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Monocular unmasking of noise-embedded patterns.

Binocular disparity cues may help an observer "unmask" a target in a background, thereby enhancing its detectability. Here, we sought to determine whether similar effects could be produced by monocular displacement cues resulting from a two-frame sequential presentation of a Gabor pattern (a sinusoidal modulation of luminance combined with a Gaussian modulation of local contrast) embedded in an unvarying field of two-dimensional Gaussian noise. The Gabor in the second frame was spatially displaced relative to its location in the first frame; the horizontal displacement corresponded to a phase shift of the peak spatial frequency of the Gabor of 0°, 90°, 180°, 360°, or 540°. Monocular detection thresholds for the Gabor were appreciably lower for the 90°, 180°, and 540° shift, than for the 0° and 360° values. We explain these findings in terms of a model that constitutes the monocular analog of our summation model of binocular unmasking. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perceptual learning immediately yields new stable motor coordination.

Coordinated rhythmic movement is specifically structured in humans. Movement at 0° mean relative phase is maximally stable, 180° is less stable, and other coordinations can, but must, be learned. Variations in perceptual ability play a key role in determining the observed stabilities so we investigated whether stable movements can be acquired by improving perceptual ability. We assessed movement stability in Baseline, Post Training, and Retention sessions by having participants use a joystick to coordinate the movement of two dots on a screen at three relative phases. Perceptual ability was also assessed using a two-alternative forced choice task in which participants identified a target phase of 90° in a pair of displays. Participants then trained with progressively harder perceptual discriminations around 90° with feedback. Improved perceptual discrimination of 90° led to improved performance in the movement task at 90° with no training in the movement task. The improvement persisted until Retention without further exposure to either task. A control group's movement stability did not improve. Movement stability is a function of perceptual ability, and information is an integral part of the organization of this dynamical system. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Reducing maternal smoking and relapse: long-term evaluation of a pediatric intervention

Simultaneous recordings of action potentials (APs) of multiple single motor units (MUs) were obtained in brachialis and biceps (caput breve) muscles during sinusoidally modulated isometric contractions of elbow flexor muscles and during sinusoidal flexion/extension movements in the elbow against a preload in the extension direction. The results show that MUs typically fire in one short burst for each sinusoidal cycle. The mean phase lead of the bursts of APs relative to a sinusoidally modulated isometric torque in the elbow joint or relative to sinusoidal movements in the elbow increases gradually with frequency. The increase of the mean phase lead during isometric contractions was very similar for all MUs and could be explained well by modeling the force production of MUs with a second-order linear low-pass system. For sinusoidal flexion/extension movements each MU reveals a specific, reproducible phase lead as a function of frequency. However, there is a large variability in phase behavior between MUs. Also, the modulation of the firing rate for sinusoidal isometric contractions versus sinusoidal movements appeared to be different for various MUs. In simultaneous recordings some MUs clearly revealed a larger firing rate in each burst for movements relative to isometric contractions, whereas other MUs revealed a smaller firing rate. This suggests that some MUs are preferentially activated during movements whereas others are preferably activated during isometric contractions. The results demonstrate task-dependent changes in the relative activation of MUs within a single muscle for sinusoidal isometric contractions and movements.     

150t 钢包底吹氩喷嘴布置优化的水模型研究

针对钢厂150 t底吹氩钢包于0.2R圆周上成90°布置的双孔吹氩,钢水成分和温度均匀性较差的问题,进行了几何相似比1:4,双孔吹氩位置0.2~0.8 R,夹角45°~180°。吹气量54.6~491.4 L/h(相当于150 t钢包吹气量50~450 L/min)的水模型试验。试验结果表明,最优方案为双孔半径0.6 R圆周,夹角180°,每孔流量382.2 L/h(相当于150 t钢包350 L/min),混匀时间比原钢包的喷嘴布置减少28.6%。     

Learning a new bimanual coordination pattern: Reciprocal influences of intrinsic and to-be-learned patterns.

Examined the following questions: (1) How do previously learned coordination patterns affect new learning (Exp 1)? and (2) How does new learning affect the performance of intrinsic coordination patterns (Exp 2)? In Exp 1, 12 20–24 yr olds practiced either a 45° or a 135° relative phase pattern for 4 days; in Exp 2, 7 21–24 yr olds practiced a 90° relative phase pattern over 6 days. Retention tests were conducted 4 wks after the last practice session in both experiments. Performance on both the in-phase (0°) and anti-phase (180°) patterns was also measured on each day. Results reveal that reciprocal effects between the intrinsic patterns and the new pattern were only temporary, and did not affect learning in any permanent way. Learning a new pattern was not differentially affected by its relation to an intrinsic pattern. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of similarity and repetition on memory: Registration without learning?

Investigated judgments of the frequency of test items (Y) that were highly similar to studied items (X) to test a prediction made by several memory models: that the judged frequency of Y should be proportional to the judged frequency of X. Whether stimuli were pictures or words, judged frequency of Y was bimodally distributed with 1 mode at zero, suggesting that frequency judgments involve a 2-stage process in which a zero judgment is made if there is a mismatch between retrieved information and the test item. Nonzero judgments, taken by themselves, were consistent with the prediction of proportionality. In 2 experiments, the percentage of zero judgments made to Y increased with repetition of X, but in 2 others the percentage did not change beyond frequency?=?1. The percentage of "new" judgments in recognition memory followed this same pattern. Because the judged frequency of X increased even as X–Y discrimination showed no improvement, the result is characterized as "registration without learning." (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Reduced variability of postural strategy prevents normalization of motor changes induced by back pain: A risk factor for chronic trouble?

Variability is fundamental to biological systems and is important in posturomotor learning and control. Pain induces a protective postural strategy, although variability is normally preserved. If variability is lost, does the normal postural strategy return when pain stops? Sixteen subjects performed arm movements during control trials, when the movement evoked back pain and then when it did not. Variability in the postural strategy of the abdominal muscles and pain-related cognitions were evaluated. Only those subjects for whom pain induced a reduction in variability of the postural strategy failed to return to a normal strategy when pain stopped. They were also characterized by their pain-related cognitions. Ongoing perception of threat to the back may exert tighter evaluative control over variability of the postural strategy. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

倾斜角度对激光选区熔化成形Ti6Al4V合金的影响

利用自主研发的Di Metal-100型激光选区熔化设备制备与基板平面成不同倾斜角的Ti6Al4V非标准拉伸试样,研究熔化成形后合金的显微组织、物理和力学性能。结果表明,Ti6Al4V合金粉末熔化成形后的组织为针状α′马氏体和(α+β)相,随倾斜角度变化,试样中α/α′相与β相的相对含量也发生变化,倾斜角为45°试样中β相含量最高;α′马氏体呈柱状分布于(α+β)相中,并且方向始终平行于成形方向(Z轴方向)。随SLM成形试样的倾斜角从0°增加到90°,其相对密度先减小后增大,并在90°时达到最大值96.1%;试样的硬度和抗拉强度均先升高后降低,在45°时达到最大值,硬度为393 HV,抗拉强度为1 288 MPa;试样表面粗糙度Ra也呈先增大后减小的趋势,在0°时达到最小值8.77μm,在30°时达到最大值19.55μm。     

Aiming error under transformed spatial mappings suggests a structure for visual-motor maps.

Transformed spatial mappings were used to perturb normal visual–motor processes and reveal the structure of internal spatial representations used by the motor control system. In a 2-D discrete aiming task performed under rotated visual–motor mappings, the pattern of spatial movement error was the same for all Ss: peak error between 90° and 135° of rotation and low error for 180° rotation. A two-component spatial representation, based on oriented bidirectional movement axes plus direction of travel along such axes, is hypothesized. Observed reversals of movement direction under rotations greater than 90° are consistent with the hypothesized structure. Aiming error under reflections, unlike rotations, depended on direction of movement relative to the axis of reflection (H. A. Cunningham and M. Pavel, in press). RT and movement time effects were observed, but a speed-accuracy tradeoff was found only for rotations for which the direction-reversal strategy could be used. Finally, adaptation to rotation operates at all target locations equally but does not alter the relative difficulty of different rotations. Structural properties of the representation are invariant under learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Discrete Element Modeling of Strength Properties of Johnson Space Center (JSC-1A) Lunar Regolith Simulant

This paper simulates the three-dimensional axisymmetric triaxial compression of JSC-1A lunar regolith simulant under lunar and terrestrial gravity environments under a wide range of confining pressures and relative densities. To accomplish this, the discrete element method (DEM), using Particle Flow Code In Three-Dimensional (PFC3D) software, was employed. The paper focuses on the peak and the critical state (CS) friction angles, which were predicted in the ranges of 35.4°–82.7° and 31.2°–79.8°, respectively, depending on the specimen density and confining pressure. A significant increase in peak and CS friction angles was predicted at near-zero confining pressure. The DEM results validated an empirical model that relates the peak friction angle with the CS friction angle, relative density, and mean effective stress at the CS. Comparison of DEM results with lunar in situ measurements of friction angle, from Apollo missions and other extraterrestrial laboratory experiments under a microgravity environment, shows a favorable agreement.     

Workplace smoking policies in the United States: results from a national survey of more than 100,000 workers

To investigate the activity of cortical regions in the control of movement, we studied event-related desynchronization/synchronization (ERD/ERS), event-related coherence (ERC), and phase coherence in 29-channel EEGs from 9 subjects performing self-paced movements of the right index finger. Movement preparation and execution produced ERD over the sensorimotor areas at 10 Hz and 20 Hz, followed by ERS. ERD corresponded spatiotemporally to an increase in coherence over the frontocentral areas. For both frequency bands, ERD began over the left sensorimotor areas and became bilateral at the time of movement onset. The coherence increase with frontal areas began in the left central areas and became symmetrical after EMG onset. The ERD and coherence increase was longer at 10 Hz than at 20 Hz. Phase coherence at 10 Hz showed a lead of anterior regions to posterior regions throughout the time period, and at 20 Hz showed a tendency toward zero phase delay corresponding with the movement. EEG desynchronization parallels functional coupling over sensorimotor and frontal areas. Event-related coherence and phase coherence findings implicate the frontal lobes in control of movement planning and execution. The involvement of different frequency bands with different timings may represent parallel changes in the cortical network.     

Induced self-motion in central vision.

Previous research on visually induced self-motion found that stimulation of the central visual field (up to 30° in diameter) results in perceived object motion, while self-motion requires peripheral stimulation. The present study examined the importance of area of stimulation in the central field using a radially expanding dot pattern simulating a 3-dimensional structure translating along the line of sight. In Exp I, with 48 undergraduates, perceived self-motion was induced with this radially expanding pattern, with visual angles of 7.5°, 10.6°, 15°, and 21.2°. Speed and texture density were also varied. The duration of reported self-motion (a) decreased with increased speed, (b) failed to increase with increased visual angle, and (c) decreased with visual angle at the highest speed level. In Exp II, 36 Ss rated the perceived depth of the displays. The speed and speed/area interaction effects on judged depth matched those found for induced self-motion. Results suggest an extension of the focal/ambient theory. In addition to a more primitive ambient processing mode that requires peripheral vision, there is a higher level system concerned with ambient processing that functions in the central visual field and uses more complex stimulus information such as internal depth represented in a radially expanding pattern. (33 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Preferred and induced coordination modes during the acquisition of bimanual movements with a 2:1 frequency ratio.

The generalizability of the preferred in-phase and anti-phase coordination modes under isofrequency conditions to bimanual patterns with a 2:1 frequency ratio was studied. Experiment 1 dealt with spontaneously emerging coordination modes and showed that all participants converged to a similar relative phasing pattern, characterized by an alternation between synchronization of the same and opposite relative peak limb positions. This suggests that movement reversals were exploited as intermittent loci of control during multifrequency tasks. Experiment 2 involved the acquisition of a 2:1 ratio with a 90° phase offset and demonstrated the powerful effect of real-time visual relative motion feedback on performance. Removal of this augmented feedback source resulted in a deterioration of the coordination pattern, accompanied by a regression to the aforementioned spontaneous coordination modes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The beat goes on: Rhythmic modulation of cortical potentials by imagined tapping.

A frequency analysis was used to tag cortical activity from imagined rhythmic movements. Participants synchronized overt and imagined taps with brief visual stimuli presented at a constant rate, alternating between left and right index fingers. Brain potentials were recorded from across the scalp and topographic maps made of their power at the alternation frequency between left and right taps. Two prominent power foci occurred in each hemisphere for both overt and imagined taps, one over sensorimotor cortex and the other over posterior parietal cortex, with homologous foci in opposite hemispheres arising from oscillations 180° out of phase. These findings demonstrate temporal isomorphism at a neural level between overt and imagined movements and illustrate a new approach to studying covert actions. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Hand coordination in bimanual circle drawing.

Two right-handed and 2 left-handed participants drew circles in the horizontal plane with both hands simultaneously in either a symmetrical or an asymmetrical mode, at their preferred rate or as fast as possible. During symmetrical movements, the hands showed frequency and phase synchronization at both rates. During fast asymmetrical movements, the hands showed increased phase difference and phase variability, as well as transitions to symmetrical movements, and cases of frequency decoupling. Large distortions of the hand trajectory were also observed under fast asymmetrical movements. Trajectory distortions and movement direction reversals were confined to the nondominant hand. Under the assumption that circular trajectories are generated by properly timed orthogonal oscillations along the y-axis and the x-axis, these findings are accounted for by the characteristics of coupling between homologous functional oscillators of the 2 body sides. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Measures and models of perceived group variability.

This article examines alternative measures of perceived variability of a group. The pattern of correlations among the measures suggests that variability can be thought of in 2 ways: the perceived dispersion of group members from the group central tendency and the extent to which the group is seen as fitting the group stereotype. Evidence of out-group homogeneity was present for both types of variability judgments, using men and women as the target groups. Judgments of group variability were not predicted by the variance of a retrieved set of group members around their own mean. In the case of the in-group, judgments of variability were predicted by the discrepancy of the retrieved set of group members from the group mean. Likewise, in-group, but not out-group, variability was also predicted by discrepancy of self from the group mean. A 2nd study using talk-aloud protocols revealed that the self and subgroups were more likely to be discussed when one was making variability judgments about the in-group than about the out-group. Instances of the group were almost never discussed for the in-group and were discussed for the out-group. Implications of the results for models of group variability judgments are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visual search for orientation among heterogeneous distractors: Experimental results and implications for signal-detection theory models of search.

Three experiments tested a signal-detection theory (SDT) model of visual search (e.g., as described in J. Palmer, C. T. Ames, & D. T. Lindsey, 1993). In Experiment 1, participants searched for a 0° line among distractors at (a) 30°; (b) ? at 30°, ? at 50°; (c) ? at 30°, 50°, and 70°; and (d) ? at 30°, ? at 70°. The SDT model predicts improved performance in the more heterogeneous conditions, as some distractors are more discriminable from the target. In contrast, in Experiment 1 human performance degraded in the more heterogeneous conditions (c and d). In Experiment 2, sparser displays improved the performance of the SDT model. In Experiment 3, search for θ° among homogeneous θ?+?20° distractors was compared with search for θ° among θ?±?20° distractors. Performance in the latter condition was often worse, relative to performance in the homogeneous condition, than predicted by the SDT model; however, this depended greatly on the identity of the target. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

50 t转炉四孔变角氧枪射流融合距离的数值模拟

采用Fluent软件模拟了50 t转炉四孔变角和非变角氧枪气体射流,研究了喷孔倾角对氧气射流流场和流股融合距离的影响。结果表明,在距喷头出口距离较近时,各流股独立为自由射流,随着距喷头出口距离的增加,各流股不断扩张,并在一定距离时融合成单股射流;非变角喷头A的流股融合距离为1.3 m,与冷态水模实验得出枪位1.3 m时炉口溅出量最大是一致的;变角氧枪B至I的对角喷孔倾角不同,射流流股融合了两次,大大降低了炉口溅出量;变角氧枪对角喷孔倾角相差0.5°较对角喷孔倾角相差1°时更有利于射流融合距离的增加;在研究喷孔倾角10.5°~11.5°/12.5°的9个喷头中,倾角11°/11.5°的喷头H射流融合距离最长,其理论炉口喷溅量最少。     

La manipulation d'indices kinesthésiques et tactiles lors d'une tache de reproduction de mouvement.

Reexamined the effect of several variables on the performance of the kinesthetic system. A classical movement duplication task was used in which each of the 48 18-38 yr old Ss was required to duplicate a passive criterion movement of one arm by positioning the same arm. Six factors were manipulated in a randomized design with fixed effects: mode of duplication (passive, active), tactile sensation (limb uncovered, limb covered, limb covered with forced air currents), kinesthetic cues for reproduction (either final arm position or distance moved), the sector of presentation of the criterion movement (43-76°, 87-217°, 128-264° in a horizontal arm adduction movement), information load (1, 2, or 4 criterion demonstrations of the movement), and the starting position of duplication. Constant and variable errors were used as dependent variables. Results confirm that active duplication was superior to passive, concerning variable, but not constant error. Duplication of final arm position was better than duplication of distance moved, also concerning only variable error. Two significant interactions (mode of duplication by kinesthetic cues, and kinesthetic cues by starting position of duplication) were found. Results indicate that final location cue and starting position of duplication are important markers in accurate reproduction. It is suggested that joint afference is transformed into a motor plan compatible with active duplication. (English summary) (25 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)