The Effects of Objectives and Constraints on Motor Control Strategy in Reciprocal Aiming Movements

The goal of this study was to examine how the kinematics of reciprocal aiming movements were affected by both the objective of the movement and the constraints operating on that movement. In Experiment 1, the objective of the movement was indirectly manipulated by capitalizing on the fact that subjects determine their own accuracy and speed limits, despite uniform task instructions to move as quickly and accurately as possible. A Fitts' type reciprocal aiming paradigm was employed, in which 69 subjects were asked to move a stylus repetitively between two spatially separated targets. Four target widths were orthogonally combined with four movement amplitudes, resulting in 16 conditions. Movements were made on an X-Y digitizing tablet. Based on the mean variable error produced on both targets, subjects were differentiated post hoc into three movement objective groups: speed, accuracy, and speed-plus-accuracy. Kinematic analyses revealed that the programming and execution of movements were systematically influenced by both the movement objective and the movement constraints. That is, movement time, peak velocity, dwell time, acceleration and deceleration time, normalized acceleration and normalized deceleration varied systematically as a function of both the speed-accuracy movement objective and the movement constraints of target size and movement distance. Moreover, the consequences of changing the constraints of the movement were affected by an interaction with the objective of the movement. In Experiment 2, the objective of the movement was directly manipulated by varying speed and/or accuracy instructions to subjects. The basic results of Experiment 1 were substantiated. Overall, the results were consistent with the view that motor control is dependent upon sensory consequences.     

Force and Directional Force Modulation Effects on Accuracy and Variability in Low-Level Pinch Force Tracking

The authors investigated how varying the required low-level forces and the direction of force change affect accuracy and variability of force production in a cyclic isometric pinch force tracking task. Eighteen healthy right-handed adult volunteers performed the tracking task over 3 different force ranges. Root mean square error and coefficient of variation were higher at lower force levels and during minimum reversals compared with maximum reversals. Overall, the thumb showed greater root mean square error and coefficient of variation scores than did the index finger during maximum reversals, but not during minimum reversals. The observed impaired performance during minimum reversals might originate from history-dependent mechanisms of force production and highly coupled 2-digit performance.     

On the Relationship Between Peak Force and Peak Force Variability in Isometric Tasks

An experiment is reported documenting the relationship between peak force and peak force variability with a fixed criterion time to peak force for an isometric task requiring activation of the elbow flexors. The results show that maximum peak force increases with increments in time to peak force and that peak force variability increases with increments of peak force in an exponential type function. Furthermore, despite the presence of peak force and time to peak force feedback, subjects systematically shifted time to peak force as a function of the percentage of peak force being produced. This temporal modulation changes the percentage of peak force represented by any given peak force criterion. When peak force is made proportional to the degree of departure from the criterion time to peak force, a linear relationship is found between peak force and peak force variability. These findings suggest that time to peak force and rate of force production are parameters that influence veridical estimates of the force variability function.     

Variability and Noise in Continuous Force Production

In the present 3 experiments, the authors examined the hypothesis, derived from information theory, that increases in the variability of motor responses result from increases in perceptual-motor noise. Three different groups of participants (Ns = 10, 9, and 10, respectively, in Experiments 1, 2, and 3) produced continuous isometric force under either low, intermediate, or high target force levels. When considered together, the results showed that force variability (SD) increased exponentially as a function of force level. However, an index of information transmission (M/SD), as well as measures of noise in both the time (approximate entropy) and the frequency (power spectrum) domains, changed according to an inverted-U-shaped function over the range of force levels. The findings provide further evidence that increased information transmission is related to increases, and not to decreases, in the noisiness of the structure of force output.     

Force and Timing Variability in Rhythmic Unimanual Tapping

In 3 experiments the interdependencies between timing and force production in unimanual paced and self-paced rhythmic tapping tasks were examined as participants (N = 6 in each experiment) tapped (a) to 1 of 3 target periods (333 ms, 500 ms, and 1,000 ms), while they simultaneously produced a constant peak force (PF) over a 50-s trial; (b) to produce 1 of 3 target forces (5, 10, and 15 N) at their preferred frequency, while keeping their rhythm as invariant as possible; and (c) to all combinations of target force and period. The results showed that (a) magnitudes of force and period were largely independent; (b) variability in timing increased proportionally with tapping period, and the variability in force increased with peak force; (c) force variability decreased at faster tapping rates; and (d) timing variability decreased with increasing force levels, (e) Analysis of tap-to-tap variability revealed adjustments over sequences of taps and an acceleration in the tapping rate in unpaced conditions. The interdependencies of force and time are discussed with respect to the challenges they provide for an oscillator-based account.     

冠状动脉病变范围与心率变异性的相关性研究

本研究通过对69例CHD患者（完成冠状动脉造影）进行Gensini评分、分组,同时设正常对照组56例。全部进行24h动态心电图监测,并做时域指标和频域指标的HRV分析。结果显示CHD组HRV各项指标均低于对照组（P〈0．05）,不同冠状动脉病变范围和程度其时域指标及频域指标降低程度不同,各组对照具有显著性差异（P〈0．...     

The Impact of Real and Illusory Perturbations on the Early Trajectory Adjustments of Goal-Directed Movements

Examinations of goal-directed movements reveal a process of control that operates to make adjustments on the basis of the expected visual afference associated with the limb's movement. This experiment examined the impact of perturbations to the perceived and actual velocity of aiming movements when each was presented alone or in tandem with the other. Perturbations to perceived velocity were achieved by translating the background over which aiming movements were performed. An aiming stylus that discharged air either in the direction of the movement or in the direction opposite the movement generated the actual velocity perturbations. Kinematic analyses of the aiming movements revealed that only the actual perturbation influenced the control of early movement trajectories. The results are discussed with respect to the influence that visual information has on the control exerted against physical perturbations. Speculations are raised regarding how potential for perturbations influences the strategies adopted for minimizing their impact.     

Force Control Is Greater in the Upper Compared With the Lower Extremity

The authors investigated whether force control is similar between the upper and lower limbs and between contractions that involve 1 or 2 joints. Six volunteers (27.5 ± 11.2 years of age) attempted to produce consistent discrete rapid force responses of 30, 60, and 90 N by using 6 different body postures, 3 with the upper and 3 with the lower limb. One of the postures for each limb involved 2 joints. The standard deviation of peak force and impulse (aggregate of the force-time curve) was significantly greater (?25%) for the lower limb than for the upper limb (p < .01). Contractions that involved 1 or 2 joints within a limb had similar variability. Therefore, the upper limb might have better control of force than the lower limb because of its extensive use in fine motor tasks in daily activities.     

Religious Variability in the Relationship Between Masculinity and Father Involvement

While traditional masculinity and fathering behaviors are seemingly associated, few studies have considered the conditions under which masculine norms may influence fathers’ behavior. Religiosity is an important factor to consider, given its association with both the endorsement of traditional gender attitudes and father involvement. This paper addresses the independent effects of traditional masculine norms and religiosity on fathering behaviors and considers whether religiosity moderates the relationship between masculinity and men's parenting behaviors. Using a national sample of fathers with children aged 2–17 in the United States, the results suggest that masculinity is negatively associated with father involvement, while religiosity is positively associated with father involvement. Yet, both highly masculine and highly religious fathers are more likely to engage in harsh discipline. Moreover, results suggest that religiosity attenuates the negative relationship between masculinity and active father involvement, while exacerbating the positive relationship between masculinity and harsh punishment.     

Notes and Comments the Role of Action Feedback in the Acquisition of Simple Motor Responses

The use of visual action feedback (AIF) in learning a simple motor response can sometimes be as effective as the more conventional terminal feedback (TIF) but sometimes leads to gross overshooting errors when AIF is removed. Both the amplitude of movement and the gain of the AIF have strong and systematic effects on the error in attempted reproductions. Percent overestimation increases linearly with fog. gain and decreases linearly with log. amplitude. This may be due to an intersensory effect in which visual and kinesthetic feedback sum to form a unitary impression of the movement on which subsequent attempts at reproduction are based.     

Directional Variability of the Isometric Force Vector Produced by the Human Hand in Multijoint Planar Tasks

Numerous studies have examined control of force magnitude, but relatively little research has considered force direction control. The subjects applied isometric forces to a handle and the authors compared within-trial variability when force is produced in different directions. The standard deviation of the force parallel to the prescribed direction of force production increased linearly with the targeted force level, as did the standard deviation of the force perpendicular to the instructed direction. In contrast, the standard deviation of the angle of force production decreased with increased force level. In the 4 (of 8) instructed force directions where the endpoint force was generated due to a joint torque in only 1 joint (either the shoulder or elbow) the principal component axes in force space were well aligned with the prescribed direction of force production. In the other directions, the variance was approximately equal along the 2 force axes. The variance explained by the first principal component was significantly larger in torque space compared to the force space, and mostly corresponded to positive correlation between the joint torques. Such coordinated changes suggest that the torque variability was mainly due to the variability of the common drive to the muscles serving 2 joints, although this statement needs to be supported by direct studies of muscle activation in the future.     

The Dynamic Relationship Between Accuracy and Bias in Social Perception Research

How do perceivers make accurate social judgments? A substantial amount of evidence suggests that perceivers' judgments are often quite accurate even when they do not have direct access to the truth, in part because they make judgments through biased processes. In the present article, we examine the dynamic relationship between bias and accuracy in social perception research. We outline how bias and accuracy are theoretically and empirically distinct processes and describe the importance (and difficulty) of defining and measuring both truth variables and bias variables in order to make empirical conclusions in accuracy research. Additionally, we examine how both bias variables (e.g., stereotypes, perceivers' own beliefs) and truth variables exert an influence on how perceivers make social judgments, as well as the extent to which judgments are accurate. Lastly, we provide steps that researchers can take in order to examine the relationship between bias and accuracy in their own research.     

The Influence of Contraction Types on the Relationship Between the Intended Force and the Actual Force

Abstract

It has been demonstrated that the intended force (subjective estimation of force) does not always match to actual force without external feedback. The purpose of this study was to compare the influence of ballistic and tonic contractions on the relationship between the intended and actual force. Subjects produced isometric force at requested percentages of their MVC (20, 40, 60 and 80%) based on subjective estimation of force under two conditions (tonic and ballistic conditions). The tonic condition was to maintain force production, whereas the ballistic condition was to produce force as fast as possible. As a result, the actual force amplitude, the coefficient of variance and EMG amplitude were larger under the ballistic contraction compared with the tonic condition, even the same intended force levels. These results suggest that different motor unit activity and control systems in the ballistic and tonic contractions could alter the relationship between the intended force and the actual force.     

变异性心绞痛患者心率变异性与冠状动脉病变关系的研究

研究变异性心绞痛患者 ST 段抬高对心率变异性的影响。回顾性分析122例变异性心绞痛患者 ST 段抬高幅度及持续时间对心率变异性的影响;心率变异性与冠状动脉病变及病变支数、狭窄程度有相关性。结果心率变异性在 ST 段抬高≥0．4mv 患者中较 ST 段抬高＜0．4mv 患者中明显降低（P＜0．05）;其在 ST 段抬高持续时间≥3min 患者中较 ST 段抬高持续时间＜3min 患者中明显降低（P＜0．05）;其在冠状动脉狭窄≥50％患者中较冠状动脉狭窄＜50％患者中明显降低（P＜0．05）;心率变异性在多支较单支病变明显降低（P ＜0．05）,单支病变狭窄程度≥75％较50％～75％者明显降低（P＜0．05）。提示变异性心绞痛患者自主神经系统受损程度与冠状动脉缺血严重程度,缺血持续时间密切相关,心率变异性能一定程度反映变异性心绞痛患者冠状动脉病变严重程度。     

心率变异性与人格的神经质之间关系研究

本研究探讨心率变异性（HRV）特征在高水平应激条件下对神经质水平的区分力。研究选取200名被试以大五人格量表测量情绪稳定性,实施了应激诱发实验,利用光体积扫描传感器采集被试者HRV指标;利用LASSO回归分析筛选参数构建对神经质的预测模型。结果显示：模型的预测数据与神经质得分高低显著正相关;不同阶段内预测数据与神经质得分显著正相关;两两比较中实验条件阶段与其他阶段预测值差异显著。研究表明,在高应激条件下,HRV是人格神经质较好的预测指标。     

Quadriceps Torque,Peak Variability and Strength Endurance in Patients after Anterior Cruciate Ligament Reconstruction: Impact of Local Muscle Fatigue

Abstract

We tested if ACL-reconstructed participants show a decreased quadriceps torque, a lower muscle endurance capacity and a higher peak torque variability compared to unimpaired control participants prior to and following local muscle fatigue. Participants (n?=?19, 10 women; 25?±?5yrs.) with unilateral hamstrings autograft ACL-reconstruction and a matched unimpaired control group were recruited. Participants performed two maximal isometric voluntary force (MIVF) contractions of the knee extensors. In between, standardized local muscle fatigue was induced. ACL-reconstructed knees display a lower peak torque of the knee extensors in comparison to the contralateral limb (3.2?±?.3Nm/kg vs. 3.5?±?.3 Nm/kg). Peak torque variability and fatigue resistance were not affected by local muscle fatigue (p > .05). Participants with ACL-reconstructed knees show a persistent quadriceps muscle dysfunction. This dysfunction and lower limb side asymmetries might be risk factors for ACL re-ruptures.     

Movement Speed and Accuracy in Space and Time: The Complementarity of Error Distributions

Movement speed-accuracy trade-off is a function of the space-time constraints of the task. We investigated the space-time account of Hancock and Newell (1985) and the hypothesis of complementarity between the four moments of the error distribution in space and time. Twelve participants performed 15 conditions in a line drawing task composed of different spatial (10, 20, and 30 cm) and temporal (250 to 2,500 ms) criteria. The results showed that all moments of distributions changed systematically between conditions but there were some departures from the Hancock and Newell predictions. In contrast, individual analysis revealed the complementarity of the spatial and temporal error including a trade-off between the four moments of error. These findings support a complementary space-time account of movement speed and accuracy.     

No Relationship Between Joint Position Sense and Force Sense at the Shoulder

In practice, a single test is used to quantify an individual's proprioception. Previous studies have not found a correlation between joint position sense (JPS) and force sense (FS), which are submodalities of proprioception. The purpose of the present study is to determine if root mean square (RMS) error in JPS and FS are related at the shoulder, controlling for external load and elevation angle. Active shoulder angle and force reproduction protocols were performed. No correlation was found between JPS and FS (r = –.019, p = .941) nor were any individual angle and load combinations significant. The main effect for angle in JPS was significant (p < .001). Follow-up contrast demonstrated a significant (p < .001) decrease in RMS error with increased elevation. A significant load by angle interaction was found for FS (p = .014). Follow-up simple effects tests by angle demonstrated RMS error decreased with load at 50° and 70° but not at 90°. By load, RMS error only decreased for 120% between 50° and 90°. JPS and FS demonstrate different behavior with load and angle. This differing behavior is more likely responsible for the lack of correlation than angle and load differences in JPS and FS protocols.     

多重样例变异性与先前知识对样例学习效果的影响述评

样例学习研究表明多重样例的学习效果好于单个样例。然而研究者关于如何有效设计多重样例得出了不同的发现。通过综述已有关于多重样例学习的实证研究,总结出两个尚未得到解决的问题：（1）多重样例之间的相似或相异程度应该如何;（2）学生的先前知识在多重样例学习中的作用如何。针对已有研究的局限性,本文指出,具有不同先前知识的学生学习时感受到不同的关键属性,多重样例应该基于学生学习时的关键属性设计特定的变易范式以帮助学生学习。     

Blocking in Rapid Finger Tapping: The Role of Variability in Proximodistal Coordination

In rapid finger tapping, occasional intertap intervals of about twice the normal length or even longer, called blockings, can be observed. Skilled rapid tapping requires that flexor and extensor activity be timed so that they coincide with certain phases of the finger movement. In the present study, the hypothesis examined was that blockings are associated with a deviation from the proper timing relations between the more proximal signals (electromyographic [EMG] bursts) and the more distal signal (position-time curve of the finger). Participants (N = 8) performed up-and-down tapping. Blockings were compared with the preceding normal tapping cycles; a temporal forward shift of the flexor burst in the time interval between two kinematic landmarks—the lifting of the finger and the reversal of the movement—was found consistently in the blockings The phase shift of the flexor burst relative to the kinematic landmarks did not develop gradually in the course of the tapping cycles that preceded the blocking but was an abrupt deviation, which suggests that blockings occur with an increased likelihood as the extremes of the normal variability of the phase relation are approached.