Expert and Nonexpert String Players’ Movement Durations as They Prepare to Play

Movement execution is not always optimal. Understanding how humans evaluate their own motor decisions can give us insights into their suboptimality. Here, we investigated how humans time the action of synchronizing an arm movement with a predictable visual event and how well they can evaluate the outcome of this action. On each trial, participants had to decide when to start (reaction time) and for how long to move (movement duration) to reach a target on time. After each trial, participants judged the confidence they had that their performance on that trial was better than average. We found that participants mostly varied their reaction time, keeping the average movement duration short and relatively constant across conditions. Interestingly, confidence judgements reflected deviations from the planned reaction time and were not related to planned movement duration. In two other experiments, we replicated these results in conditions where the contribution of sensory uncertainty was reduced. In contrast to confidence judgements, when asked to make an explicit estimation of their temporal error, participants' estimates were related in a similar manner to both reaction time and movement duration. In summary, humans control the timing of their actions primarily by adjusting the delay to initiate the action, and they estimate their confidence in their action from the difference between the planned and executed movement onset. Our results highlight the critical role of the internal model for the self‐evaluation of one's motor performance.

'Blip' analysis, fast wavelet transformations (FWT) and correlation analysis have all been used to actigraphically assess the impact one person is having on another's sleep, yet no review exists as to the differences between, and applicability of, these methods for investigating couples' sleep. Using actigraphy data and audio sleep diaries collected from 18 couples, this paper provides such a review. This paper constructs and assesses two novel, analytical methods: Lotjonen's sleep/wake algorithm, and the partner impact on sleep wake analysis (PISWA). Both 'blip' analysis and correlation suggest that the strongest relationship between bed partners occurs on an epoch-to-epoch basis. However, 'blips' deal strictly with onset of movement and fail to incorporate strength and duration of movement. Conversely, correlation analysis incorporates some elements of strength and duration of movement but makes identification of onset problematic. FWT offer useful 'relativistic' pattern recognition, identifying onset, strength and duration of movement, but are difficult to quantify. Although audio diary data support the potential of Lotjonen's sleep/wake algorithm to identify sleep non-movement, sleep movement, wake non-movement (or quiet wakefulness) and wake movement, the problem remains that this method also relies on visualization. Of most promise, we argue, is the PISWA, which examines 'impact' of bed partners through incorporating elements of 'blip' analysis and the sleep/wake algorithm.

Fast reaction times and the ability to develop a high rate of force development (RFD) are crucial for sports performance. However, little is known regarding the relationship between these parameters. The aim of this study was to investigate the effects of auditory stimuli of different intensities on the performance of a concentric bench-press exercise. Concentric bench-presses were performed by thirteen trained subjects in response to three different conditions: a visual stimulus (VS); a visual stimulus accompanied by a non-startle auditory stimulus (AS); and a visual stimulus accompanied by a startle auditory stimulus (SS). Peak RFD, peak velocity, onset movement, movement duration and electromyography from pectoralis and tricep muscles were recorded. The SS condition induced an increase in the RFD and peak velocity and a reduction in the movement onset and duration, in comparison with the VS and AS condition. The onset activation of the pectoralis and tricep muscles was shorter for the SS than for the VS and AS conditions. These findings point out to specific enhancement effects of loud auditory stimulation on the rate of force development. This is of relevance since startle stimuli could be used to explore neural adaptations to resistance training.

Ability to adjust reach extent in the hemiplegic arm

Our previous study (Hum Mov Sci 25:349-371, 2006) investigated whether and how online vision in the early phase of movement influences the control of reach-to-grasp movements (movement duration: approximately 1000ms). We used liquid-crystal shutter goggles to manipulate the duration of available online vision during the movement and specified that online vision during the early phase influences grasping movements. The current study examined the effect of online early phase vision on the grip configuration according to the movement duration and compared it between two different movement durations (approximately 500 and 1000ms). We found that non-availability of early phase online vision affected the grip configuration (i.e., inducing a larger peak grip aperture) even in the shorter movement duration. The influential period for online vision for grasping control shifts to an earlier time when movement time is shorter (i.e., from approximately 214 to 106ms after movement onset), indicating a flexible mechanism for grip configuration according to the movement duration and the available online vision.

The processes underlying motor decision-making have recently caught considerable amount of scientific attention, focusing on the integration of empirical evidence from sensorimotor control research with psychological theories and computational models on decision-making. Empirical studies on motor decision-making suggest that the kinematics of goal-directed reaching movements are sensitive to the level of target uncertainty during movement planning. However, the source of uncertainty as a relevant factor influencing the process of motor decision-making has not been sufficiently considered, yet. In this study, we test the assumption that the source of target uncertainty has an effect on motor decision-making, which can be proven by analyzing movement variability during the time course of movement execution. Ten healthy young adults performed three blocks with 66 trials of goal-directed reaching movements in each block, across which the source and level of reach target uncertainty at movement onset were manipulated (“no uncertainty”, “extrinsic uncertainty”, and “intrinsic uncertainty”). Fingertip position of the right index finger was recorded using an optical motion tracking system. Standard kinematic measures (i.e., path length and movement duration) as well as variability of fingertip position across the time course of movement execution and at movement end were analyzed. In line with previous studies, we found that a high level of extrinsic target uncertainty leads to increased overall movement duration, which could be attributed to increased path length in this condition, as compared to intrinsic and no target uncertainty (all p < 0.001). Movement duration and path length did not show any differences between the latter two conditions. However, the time course analysis of movement variability revealed significant differences between these two conditions, with increased variability of fingertip position in the presence of intrinsic target uncertainty (Condition × Sampling point: p = 0.01), though considerably less than under high extrinsic target uncertainty (p ≤ 0.001). These findings suggest that both the level and source of uncertainty have a significant effect on the processing of potential action plans during motor decision-making, which can be revealed through the analysis of the time course of movement variability at the end-effector level.

Surgical dexterity depends on economy and precision of movements, and this can be objectively measured using electromagnetic motion analysis. We have assessed the differences in hand movements and task completion times between open, laparoscopic and robotically assisted surgery during an exercise performed in vitro. A standard surgical exercise was performed using open, standard laparoscopic (SL) and robotically assisted laparoscopic (RAL) approaches. The total duration of the exercise was studied along with the number and duration of movements required to complete the exercise in each surgical modality. The time taken to complete the exercise was significantly longer in both the SL and RAL approaches when compared to the open route. However, it was found that RAL had significantly decreased number of movements (mean difference=24 movements, P<0.006) but a longer duration of each movement when compared to SL (mean difference=0.13s, P<0.001). This study shows objectively that the exercise took longer to complete using the RAL approach than the standard open approach. However, RAL had more purposeful movements and required fewer movements to complete the exercise compared to SL.

Omnidirectional pause neurons (OPNs) pause for the duration of a saccade in all directions because they are part of the neural mechanism that controls saccade duration. In the natural situation, however, large saccades are accompanied by head movements to produce rapid gaze shifts. To determine whether OPNs are part of the mechanism that controls the whole gaze shift rather than the eye saccade alone, we monitored the activity of 44 OPNs that paused for rightward and leftward gaze shifts but otherwise discharged at relatively constant average rates. Pause duration was well correlated with the duration of either eye or gaze movement but poorly correlated with the duration of head movement. The time of pause onset was aligned tightly with the onset of either eye or gaze movement but only loosely aligned with the onset of head movement. These data suggest that the OPN pause does not encode the duration of head movement. Further, the end of the OPN pause was often better aligned with the end of the eye movement than with the end of the gaze movement for individual gaze shifts. For most gaze shifts, the eye component ended with an immediate counterrotation owing to the vestibuloocular reflex (VOR), and gaze ended at variable times thereafter. In those gaze shifts where eye counterrotation was delayed, the end of the pause also was delayed. Taken together, these data suggest that the end of the pause influences the onset of eye counterrotation, not the end of the gaze shift. We suggest that OPN neurons act to control only that portion of the gaze movement that is commanded by the eye burst generator. This command is expressed by driving the saccadic eye movement directly and also by suppressing VOR eye counterrotation. Because gaze end is less well correlated with pause end and often occurs well after counterrotation onset, we conclude that elements of the burst generator typically are not active till gaze end, and that gaze end is determined by another mechanism independent of the OPNs.

&lt;p&gt;變向 (change of direction, COD) 是運動員執行多方向移動的必要能力，變向能力可以透過專項訓練、敏捷性訓練、和技術發展提升，俾使競技運動比賽時的戰略成功達到攻防合一。過去發展許多關於變向、敏捷性的測驗，如：折返跑、505敏捷測驗或專業敏捷測驗等，這些田野方法通常用動作時間測量敏捷性，而變向動作則有採用生物力學研究方法的量化分析探討其動作特徵。但是，這些動作時程較長的單一測驗結果，卻也夾雜了衝刺能力、無氧代謝能力等因素。方向變換逆差 (change of direction deficit, CODD) 參數的發展，乃是通過數學的扣除方法，結合了純粹衝刺與變向衝刺等二項測驗的結果，能夠更精準地獲得敏捷能力的指標。本文整合了敏捷測驗、變向技能個別差異與生物力學特徵的過去相關文獻，提供教練員、肌力與體能訓練專家、運動員、體育教師在運動現場監控敏捷表現的資訊，也提醒方向變換逆差的參數是國際正發展評估敏捷能力具高靈敏度及準確度的指標，其信度與效度議題則有發展及探索的價值。&lt;/p&gt; &lt;p&gt;&amp;nbsp;&lt;/p&gt;&lt;p&gt;Change of direction (COD) is an essential ability for athletes to perform multi-directional locomotion. COD can be enhanced through specific training, agility training, and technique development in order to successfully achieve the tactics of defense and offense within sport activities. Previous studies have developed many COD and agility tests, such as shuttle runs, 505 agility tests, and pro-agility tests. These field tests are used to assess agility by measuring movement time. There has been quantitative analysis of COD movements through a biomechanical approach to identify movement characteristics. However, using single outcome measures with long movement duration can blend the factors of sprint ability and anaerobic capacity. The development of the parameter of change-of-direction deficit (CODD) is a subtractive method in mathematics that combines two measurements to evaluate the index of agility precisely. This article summarizes previously published material on individual differences and biomechanical characteristics of COD skills to provide sport instructors, strength and conditioning specialists, athletes, or physical educators with information to monitor agility performance in the field. CODD is a sensitive and precise indicator for assessing agility. It is worth developing and exploring the issues of reliability and validity.&lt;/p&gt; &lt;p&gt;&amp;nbsp;&lt;/p&gt;

This study examined the relationship between movement duration and movement stiffness in speech. Stiffness was measured as the interval from movement onset to peak velocity. The speech material consisted of long and short Japanese consonants produced by native speakers. A magnetometer was used to track articulatory movements. For the lower lip, the velocity of vertical closing movement for bilabial consonants was measured, while the speed of the tongue tip was measured for dental stops and fricatives. Results from six subjects show that the lower lip movement duration was longer for the long consonants, which also had a lower stiffness than their short cognates. The results also show higher correlations between duration and stiffness for the short consonants. The results for the tongue tip showed more variability across and within subjects, although the overall trend was similar to the one found for the lower lip. In addition, all correlations between tongue tip movement duration and stiffness were high. These results extend earlier work on the same relationship, where it has mostly been studied across variations in speaking rate. They also suggest potential differences between articulators and between stops and fricatives. [Work supported by NIH.]

In rapid interceptive actions such as hitting a baseball, cricket ball or tennis ball, ball speed varies between trials, and players have to compensate the time lag by controlling the moment of movement onset and movement duration. Previous studies have found that these two variables can flexibly co-vary and are robustly influenced by target speed (i.e. velocity-coupling effect: faster movement for faster target). However, some studies reported an interpersonal variability in the timing control strategy and the relationship between the strategy and temporal accuracy in rapid interception is unclear. We used a baseball-simulated rapid interceptive task to assess this issue. Under relatively easy time constraints, there was a large interpersonal variability, and participants were distinctively divided into two groups: those who mainly modulated their movement duration and those who mainly controlled their movement onset. When the time constraint became severe, the second strategy shifted to the first strategy in most of the second group participants. In the both cases, being able to mainly control movement onset resulted in higher temporal accuracy. These results suggest that minimising the velocity-coupling effect is an important factor to achieve high temporal accuracy in rapid interception.

Sport and Physical Activity Following Primary Total Knee Arthroplasty: A Systematic Review and Meta-Analysis

Debate exists as to whether humans use prospective or predictive control to intercept an object falling under gravity (Baurès et al. in Vis Res 47:2982-2991, 2007; Zago et al. in Vis Res 48:1532-1538, 2008). Prospective control involves using continuous information to regulate action. τ, the ratio of the size of the gap to the rate of gap closure, has been proposed as the information used in guiding interceptive actions prospectively (Lee in Ecol Psychol 10:221-250, 1998). This form of control is expected to generate movement modulation, where variability decreases over the course of an action based upon more accurate timing information. In contrast, predictive control assumes that a pre-programmed movement is triggered at an appropriate criterion timing variable. For a falling object it is commonly argued that an internal model of gravitational acceleration is used to predict the motion of the object and determine movement initiation. This form of control predicts fixed duration movements initiated at consistent time-to-contact (TTC), either across conditions (constant criterion operational timing) or within conditions (variable criterion operational timing). The current study sought to test predictive and prospective control hypotheses by disrupting continuous visual information of a falling ball and examining consistency in movement initiation and duration, and evidence for movement modulation. Participants (n=12) batted a ball dropped from three different heights (1, 1.3 and 1.5m), under both full-vision and partial occlusion conditions. In the occlusion condition, only the initial ball drop and the final 200ms of ball flight to the interception point could be observed. The initiation of the swing did not occur at a consistent TTC, τ, or any other timing variable across drop heights, in contrast with previous research. However, movement onset was not impacted by occluding the ball flight for 280-380ms. This finding indicates that humans did not need to be continuously coupled to vision of the ball to initiate the swing accurately, but instead could use predictive control based on acceleration timing information (TTC2). However, other results provide evidence for movement modulation, a characteristic of prospective control. Strong correlations between movement initiation and duration and reduced timing variability from swing onset to arrival at the interception point, both support compensatory variability. An analysis of modulation within the swing revealed that early in the swing, the movement acceleration was strongly correlated to the required mean velocity at swing onset and that later in the swing, the movement acceleration was again strongly correlated with the current required mean velocity. Rather than a consistent movement initiated at the same time, these findings show that the swing was variable but modulated for meeting the demands of each trial. A prospective model of coupling τ (bat-ball) with τ (ball-target) was found to provide a very strong linear fit for an average of 69% of the movement duration. These findings provide evidence for predictive control based on TTC2 information in initiating the swing and prospective control based on τ in guiding the bat to intercept the ball.

Displacement thresholds for various types of movement: Effect of spatial and temporal reference proximity

To investigate how the sensorimotor systems of eye and hand use position, velocity, and timing information of moving targets, we conducted a series of three experiments. Subjects performed combined eye-hand catch-up movements toward visual targets that moved with step-ramp-like velocity profiles. Visual feedback of the hand was prevented by blanking the target at the onset of the hand movement. A multiple regression was used to determine the effects of position, velocity, and timing accessed before each movement on the movement amplitudes of eye and hand. The following results were obtained: 1. The predictive strategy of eye movements could be modeled by a linear regression on the basis of the position error and the target velocity. This was not the case for hand movements, for which there was a significant partial correlation between the movement amplitude and the product of target velocity and movement duration. This correlation was not observed for eye movements suggesting that the predictive strategy of hand movements takes movement duration into account, in contrast to the strategy used in eye movements. 2. To determine whether the movement amplitudes of eye and hand depend on a categorical classification between a discrete number of movement types, we compared an experiment in which target position and velocity were distributed continuously with an experiment using only four different combinations of target position and velocity. No systematic differences between these experiments were observed. This shows that the system output is a function of continuous, interval-scaled variables rather than a function of discrete categorical variables. 3. We also analyzed the component of the movement amplitudes not explained by the regression, i.e., the residual error. The residual errors between subsequent trials were correlated more strongly for eye than for hand movements, suggesting that short-term temporal fluctuations of the predictive strategy were stronger for the eye than for the hand.